INTERNATIONAL COURT OF JUSTICE
DISPUTE OVER THE STATUS AND USE OF THE
WATERS OF THE SILALA
(CHILE v. BOLIVIA)
REJOINDER OF THE
PLURINATIONAL STATE OF BOLIVIA
ANNEX 23.5
VOLUME 4 OF 6
15 MAY 2019
LIST OF ANNEXES TO THE REJOINDER OF THE PLURINATIONAL STATE OF BOLIVIA VOLUME 4 OF 6 ANNEX N° TITLE PAGE N° TECHNICAL DOCUMENTS (ANNEX 23.5) Annex 23.5 Appendix b SERGEOMIN, “Structural Geological Mapping of the Area Surrounding the Silala Springs”, September 2017 (English Translation) 5 Annex 23.5 Appendix c Tomás Frías Autonomous University (TFAU), “Hydrogeological Characterization of the Silala Springs”, 2018 (English Translation) 137
Annex 23.5
Appendix b
SERGEOMIN, “Structural Geological Mapping of the Area Surrounding the Silala Springs”, September 2017
(English Translation)
7
FINAL REPORT
INTERINSTITUTIONAL AGREEMENT
GEOLOGICAL-STRUCTURAL MAPPING PROJECT
OF THE SURROUNDING AREA TO THE SILALA SPRINGS
DEPARTMENT OF POTOSI
La Paz, September 2017
8
Prepared by:
GEOLOGICAL MINING SERVICE “SERGEOMIN”
Federico Zuazo Street N° 1673
P.O. Box N° 2729
Phone: (591-2) 2330981 – 2331236 – 2330895
Fax: (591-2) 2391725
E-mail www.sergeomin.gob.bo
La Paz – Bolivia
Management:
Eng. Roberto Perez M. EXECUTIVE DIRECTOR
Eng. Fernando Caceres J.
TECHNICAL DIRECTOR OF PROSPECTION AND EXPLORATION
Eng. Javier Rodriguez G.
HEAD OF THE EXPLORATION UNIT
For DIREMAR: Strategic Office of Strategic Office of Maritime Vindication
Management:
Lic. Emerson Calderon Guzman
SECRETARY GENERAL – SILALA AND INTERNATIONAL WATER RESOURCES
Lic. Omar Rocha
PROJECT SUPERVISOR
Eng. Phd. Fernando Urquidi Barrau, PROJECT SUPERVISOR
Technical Personnel:
Eng. Jorge Vega Enrriquez
Eng. Nielsen Morillas Vidangos
Eng. Efrain Apaza Poma
Eng. Limber Carlo Garcia
Grad. Maribel Urquiete Quenallata
Grad. Diego Gonzalez Herrera
Support Personnel: (Drivers)
Mr. Bernardo Medrano Uturuncu
Mr. Vicente Coro Loayza
Mr. Hector Cusi Quispe
Mr. Juan Roque Lobaton
Eng. Adolfo Orsolini Campana
Eng. Mario Barragan Espinoza
Eng. Jorge Bejarano Delgado
Eng. Andres Casas Saavedra
Eng. Hernan Condori Ticona
Eng. Laura Cahuana Flores
9
Index
CHAPTER 1
1. BACKGROUND
CHAPTER 2
2. OBJECTIVES
2.1. General objective
2.2. Specific objective
2.3. Methodology
2.3.1 Desk work
2.3.2 Field work
CHAPTER 3
3. GENERALINFORMATION
3.1 Earlier works
CHAPTER 4
4. GENERALITIES
4.1 Location of the area studied
4.2 Accessibility
4.3 Relief Climate
4.4 Vegetation and fauna
4.5 Resources and infrastructure
CHAPTER 5
5. SATELLITE IMAGE INTERPRETATION
5.1. Landsat 7 ETM + RGB 742 images
5.1.1 Methodology to process satellite images
5.1.2 Results
5.1. Bing Maps
5.2.1 Methodology to process satellite images
5.2. Combination of LANSAT 7 ETM and Y Radar Alos-Palsar images
5.3.1 Methodology to process satellite images
5.3.2 Data processing
5.3.2.1 LANDSAT 7 ETM + (Enhanced Thematic Mapper Plus)
5.3.2.2 Alos-Palsar (Phased Array Type L-Band Synthetic Aperture Radar)
5.3.2.3 Conclusions from image processing
CHAPTER 6
6. GEOLOGICAL MAPPING
6.1 Geomorphology
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6.2. Regional Geology
6.3 Volcanic products and morphology
6.4 Local geology
6.5 Stratigraphy
6.5.1 Stratigraphic column for Silala
6.5.2 Cross-sections of the Silala springs area
6.5.3 Data Base
6.6 Generalized Geological Section of the Silala springs area
6.7 Conclusions
6.8 Recommendations
CHAPTER 7
7. STRUCTURAL GEOLOGY
7.1 Introduction
7.2 Objectives
7.3 Work performed
7.3.1 Clerical work
7.3.2 Field work
7.4 Regional structural setting
7.5 Structural geology of the area
7.5.1 Fracturing characteristics
7.5.2 Principal Structures
7.5.2.1 Inacaliri Graben
7.5.2.2 Lipez Lineaments
7.5.2.3 Silala-Lincor Lineament
7.5.2.4 Runtu Jarita Lineament
7.6 Work methodology
7.6.1 Data processing
7.6.2 Population analysis of fractures by sector
7.7 Fracture and discontinuity analysis
7.7.1 Nmse Sector – El Meson hill
7.7.1.1 Structures identified in Meson hill
7.7.1.1.1 Nmse Faults – El Meson hill
7.7.1.1.2 Meson hill joints
7.7.2 Silala ignimbrite sector (Nslt)
7.7.2.1 Structures identified in the Silala ignimbrite sector
7.7.2.1.1 Faults of the Silala Ignimbrite sector
7.7.2.1.2 Silala ignimbrite joints
7.7.3 Silala Chico hill sector (NsII)
7.7.3.1 Structures identified in Silala Chico hill
7.7.3.1.1 Silala Chico hill faults and joints
7.7.4 Negro Hill sector (Ncnd)
7.7.4.1 Structures identified in Negro Hill
7.7.4.1.1 Faults and Joints of Negro Hill
11
7.7.5 Inacaliri Lavas sector (Ninl)
7.7.5.1 Structures identified in the Inacaliri lavas
7.7.5.1.1 Faults and joints of the Inacaliri lavas
7.7.6 Torito Lava Volcano (Ntol)
7.7.6.1 Structures identified in the Torito hill lavas
7.7.6.1.1 Faults of the Torito hill lava
7.7.6.1.2 Torito hill joints
7.7.7 North and South Pastos Grandes Tuffs
7.7.7.1 Structures identified in the Pastos Grandes Tuff
7.7.7.1.1 North and South Pastos Grandes Tuff
7.7.7.1.2 Joints of the North and South Pastos Grandes
Tuff
7.7.8 Cahuana hill sector (Qlie)
7.7.8.1 Structures identified in Cahuana hill
7.7.8.1.1 Cahuana hill faults
7.7.8.1.2 Cahuana hill joints
7.7.9 Silala Grande sector (Qlie)
7.7.9.1 Structures identified in Silala Grande hill
7.7.9.1.1 Faults of the Silala Grande hill
7.7.9.1.2 Joints of the Silala Grande Lavas
7.7.10 Inacaliri hill sector (Qlie)
7.7.10.1 Structures identified
7.7.10.1.1 Inacaliri hill faults (Qlie)
7.7.10.1.2 Western Inacaliri hill joints (Qlie)
7.8 Microstructural analysis of the fault population
7.9 Relation between faulting and volcanism
7.10 Relation between the fracturing and the water regime
7.11 Conclusions
CHAPTER 8
8. BIBLIOGRAPHY
12
List of figures
Figure No. 1. Location of the area of the Silala springs
Figure No. 2. Access map of the area of the Silala springs
Figure No. 3. Histogram of average monthly rainfall, Laguna Colorada
meteorological station
Figure No. 4. Temperature historiography, Laguna Colorada meteorological
station
Figure No. 5. Landsat Satellite Image 7 ETM + 742 RGB bands used for
lithological discrimination
Figure No. 6. Bing Map Image used to interpret structural lineaments and to
discriminate the lithological units in the Silala area
Figure No. 7. Landsat 7 ETM + 742 RGB Bands combined with the Alos Palsar
L Band radar image used for the preliminary interpretation of the structural
lineaments
Figure No. 8. Stratigraphic column for the Silala springs
Figure: 9 Localitation of the cross sections made in the Silala ravine
Figure No. 10. Map of the coverage of the structural data survey
Figure 11. Rose diagram of lineaments and faults (n = 5) Silala area
Figure No. 12. Major tectonic structures of the area surveyed
Figure No. 13. Scheme for the sectors used to process structural data
Figure No. 14. a) Rose diagram for normal fault fracturing. Meson hill. b) rose
diagram for the fracturing of inverse faults
Figure No. 15. a) Rose diagram for the joints of Meson hill. b) pole diagram
and preferred plane for the fractures of Meson hill
Figure No. 16. a) Rose diagram for normal fault fracturing, Silala ignimbrite;
b) rose diagram representing inverse fault fractures, Silala ignimbrite
Figure No. 17. a) Rose diagram for contours; b) rose diagram for jointing
planes in the Silala ignimbrite sector (n = 637)
Figure No. 18. a) Rose diagram of the fractures of Silala Chico; b) pole diagram
for the Silala Chico fractures
Figure No. 19. a) Rose diagram for the fractures of Negro hill; b) Pole diagram
of the fractures of negro hill
Figure No. 20. a) Rose diagram for the fractures of Inacaliri lavas; b) rose
diagram of the joints of Inacaliri lava
Figure No. 21. a) Rose diagram representing the fractures of normal faults
of Torito hill; b) Rose diagram representing inverse faults, lateral faults and
unclassified faults
Figure No. 22. a) Rose diagram representing the Torito hill joints; b) rose
diagram of poles, preferred planes and joints of Torito hill
13
Figure No. 23. a) Rose diagram representing the normal faults of North Pastos
Grandes; b) rose diagram representing the inverse faults of North Pastos
Grandes
Figure No. 24. a) Rose diagram representing the normal faults of South Pastos
Grandes; b) rose diagram representing the inverse faults of South Pastos
Grandes
Figure No. 25. a) Rose diagram for the North Pastos Grandes joints; b) rose
diagram for the jointing of South Pastos Grandes
Figure No. 26. a) Rose diagram for the fracturing of Cahuana hill; b) rose
diagram for the jointing of Cahuana hill
Figure No. 27. a) Rose diagram of normal fracturing faults; b) rose diagram of
reverse fault fracturing, Silala Grande
Figure No. 28. a) Rose diagram of jointing in the Silala Grande hill; b) Pole
frequency diagram presenting the joints of the Silala Grande hill
Figure No. 29. a) Rose diagram of the fractures of Eastern Inacaliri hill; b) rose
diagram of the jointing of Eastern Inacaliri hill
Figure No. 30. a) Rose diagram of normal fault fractures of western Inacaliri
hill; b) rose diagram of inverse, unclassified and strike-slip faults of the Western
Inacaliri hill
Figure No. 31. Rose diagram for the jointing of Western Inacaliri hill
Figure No. 32. Microstructural analysis of stresses in the east flank and south
sector of the Silala springs
Figure No. 33. Structural scheme of the Silala-Llancor Lineament
Figure No. 34. 3D Structural scheme of the Silala-Llancor Lineament
Picture List
Picture No. 1. Ignimbrite of the Silala springs area
Picture No. 2. Lava flow, presenting pseudo-stratification
Picture No. 3. View of Inacaliri stratovolcano
Picture No. 4. a) Debris flow 1 in sub-horizontal contact with the Silala
ignimbrite 1 (Nis 1). b) Debris flow 1 with sub-rounded clasts of igneous rocks
of up to the 30 cm.
Picture No. 5. a) Silala ravine, where the Silala ignimbrite 1 (Nis 1) can be
observed with vertical fractures. b) the Silala ignimbrite 1 (Ns1), presenting a
brownish-reddish color on the surface.
14
Picture No. 6. a) Marker horizon corresponding to a crystal-vitreous tuff, 20 cm
thick, that delimits the Silala Ignimbrite 1 (Nis 1) and Silala Ignimbrite 2 (Nis
2); b) Hand sample of the tuff level where a banded structure can be observed.
Picture No. 7. Silala Ignimbrite 2 (Nis 2) which underlies the tuff horizon and
Silala Ignimbrite 1 (Nis 1); b) The Silala ignimbrite 2 (Nis 2) with pumice
content, presenting a massive structure
Picture No. 8. a) brownish-reddish debris flow 2 (NFd2), sub-rounded clasts of
igneous rocks can be observed; b) chaotic structure that does not present any
clast structuring
Picture No. 9. Reddish Silala Ignimbrite 3 (Nis 3), presenting a splintered
structure; b) Silala ignimbrite 3 (Nis 3), presenting a porphiric texture, with
plagioclase, potassium feldspar and quartz
Picture No. 10. a) Silala Chico hill, Inacaliri stratovolcano in the back; b) Silala
Chico lava (Nlsc), of a dacite composition, presenting a splintered structure
Picture No. 11. a) Cerro Negro with a dome-like morphology. b) Lava flow of
Cerro Negro (Nlcn), it presents a reddish-brown coloration with a splintered
structure
Picture No.12. Volcanic dome of Torito hill (Nlct), rock outcrops and handdrawn
samples
Picture No. 13 a) Inacaliri lava flows (Nlin1), b) basal breccia of the
aforementioned flows
Picture No. 14. Pseudo-stratified lava flows (Nlsg)
Picture No. 15. Stratovolcanic lava flows (Nlin 2)
Picture No. 16. Pastos Grandes Tuff (Ntpg)
Picture No. 17. Panoramic view of the Runtujaritas dome-lava
Picture No. 18. Lava flows of Cerro Chico hill (Nlcc)
Picture No. 19. High-angle normal conjugated faulting, affecting the Silala
Grande lavas
Picture No. 20. Sub-horizontal, conjugate faults, affecting the joints of the
Silala ignimbrite
Picture No. 21. Fractured massif outcrop of dacite lava, Meson hill
Picture No. 22. Silala ignimbrite mantles, presenting fractures that cut the
outcropping levels. South side of the Silala ravine
15
Picture No. 23. a) Lower angle inverse fault; b) Block sunken between normal
faults; 15 cm displacement; c) Block found between a normal fault and an
inverse fault; d) Fractured block with a regular centimetric displacement
Picture No. 24. Inacaliri lava outcrops, presenting sectioned by normal
transversal faults. Southern flank of the Inacaliri hill
Picture No. 25. Joints that cut the pseudo-stratification planes of the Torito hill
lavas
Picture No. 26. a) Tuff outcrops in South Pastos Grandes; b) joint planes that
form fractured structures and contain thrust planes
Picture No. 27. a) Flow front of outcropping lava in blocks; b) morphology of
the factures in dacitic lava; c) banding folds caused by lava flow; d) porphiric
tails, a kinematic indicator of dextral shear stress
Picture No. 28. Normal fault cutting the pseudo-stratification planes of the
lavas. Northern flank of Silala Grande hill
Picture No. 29. a) Sheared outcrops of Eastern Inacaliri hill (Qlie); b) Joint
planes that form fractured columns in the Eastern Inacaliri hill (Qlie)
Picture No. 30. Dextral shearing in the Silala Grande hill
Picture No. 31. Joint plain infilled with calcite in the fractures of the Inacaliri
lava
LIST OF TABLES
Table No. 1. Statistical Table of structural trends in the Silala area
Table No. 2. Sectors of each of the structural data processing, presenting the
ages and codes used for the structural processing
Table No. 3. Fracture parameters recorded
ANNEXES
Annex A: Geological – Structural Plans
Annex B: Geological profiles
Annex C: Results from the Laboratory analysis
a) Petrographical analyses results
b) Mineralogical analyzes results
Annex D: Data base
a) Geological data base
b) Structural data base
16
GLOSSARY OF GEOLOGICAL-STRUCTURAL TERMS
Alluvial Fan: Detrital material deposited in the form of a fan, by an aqueous
current, at the change of slope of a torrent, or close to its base level. Synonym:
alluvial cone.
Alluvial: Term used to refer to all type of process or material related to the
fluvial processes. Example: alluvial deposit, alluvial terrace, alluvial cone, etc.
Andesite: Volcanic igneous rock (intermediate) of aphanitic or porphyritic
texture, generally of green color, being able to vary to reddish, violet and other
colors, acquired by the alteration of the ferromagnesian minerals that it contains.
Spectral band: Each of the ranges of wavelengths that a sensor is capable of
detecting.
Bofedal: In arid environments, lowlands, waterlogged or well watered and very
fertile, where it is common the existence of springs and whose abundance of
vegetation is due to mineralized and clayey soils, which store water all year
round.
Pitch: Angle of intersection between the alignments and a horizontal plane.
Volcanic caldera: It is a large depression of volcanic origin, elliptical or circular
in shape, which can reach tens of kilometers in diameter.
Cirque: Deep circular or sub-circular valley formed by erosion and glacial
eruption, snow accumulation and formation of glaciers.
Colluvial: Materials weathered and transported by the action of gravity; for
example, slope debris, etc.
Colluvial-Fluvial: They are materials transported and deposited by water. Its
size varies from clay to thick gravel, cobbles and blocks.
Geometric correction: Correction of the distortions that occur during the process
of acquiring an image due to the rotation and curvature of the Earth, the angle
of vision or variations in the position of the satellite.
Radiometric correction: Any modification that alters the original values recorded
by the sensor, in order to correct the possible effects produced in the image by
the atmosphere, the observation geometry or the physical characteristics of the
sensor itself.
Volcanic crater: Circular or elliptical depression limited by an abrupt edge.
Dacite: Igneous, volcanic, acid rock, equivalent to granodiorite, has an aphanitic
texture.
Joint: Fracture without displacement.
17
Rose diagram: Graphic representation of fractures in two dimensions.
Dome: Emission duct characterized by a structure similar to a volcanic cone
but lacking a crater. Their lava flows are usually acidic and very thick, so they
do not usually get too far from the emitting center.
Radiometric age: Method of measuring the disintegration of unstable elements.
Since each radioactive element has a defined half-life period.
Eluvial: Deposit of detrital material, resulting from the alteration or
decomposition of parent rocks that remain in-situ.
Stress: Strength per unit area.
Stratovolcano: The stratovolcanoes are large conical buildings in which lavas
and pyroclasts accumulate. For its formation a long period of eruptive activity
or the repetition of numerous eruptions in a restricted area is required.
Structure: Geological or structural feature referring to the way in which rocks
or fractures are related.
Reverse fault: Fracture with displacement or rise of the roof or lower block.
Right side fault: Fracture with horizontal displacement to the right.
Left side fault: Fracture with horizontal displacement to the left.
Normal fault: Fracture with displacement or fall of the roof or upper block.
Fault: Fracture with relative displacement of blocks.
Faulting: Fracking zone.
Spectral signature: Curve that represents the variation of the reflectance of an
object as a function of wavelength.
Debris flow: Debris flows or so-called debris flows occur when rainwater begins
to erode the material of a slope or when a landmass is saturated with water, aided
by slope and gravity. Fluvial-Glacial: Abandoned after the retreat of glaciers and
ice sheets.
Fracture: Any opening or fissure with or without displacement.
Geophysics: Surveying technique inside the subsoil.
18
Graben: Normal faulting zone with collapse of blocks.
Ignimbrite: Rock or deposit formed from a pumice pyroclastic flow, regardless
of whether it is welded or not.
Merged image (Pan-Sharpened): Image product of the fusion of a panchromatic
image and its multispectral equivalent by means of a series of mathematical
algorithms. The resulting image has the spatial resolution of the panchromatic
and the spectral bands
Multispectral image: Image captured by a sensor that measures the energy
simultaneously in two or more spectral bands
Immersion or plunge: Angle that forms the line with its projection in the
horizontal plane, measured in the vertical plane.
Lava: Fluid rocky material that comes out of a volcano or a crack in the Earth’s
crust and that flows or slides on the surface. The lava in natural fusion is in a
liquid-viscous state product of the volcanic eruption.
Lineament: Structural or morphological feature that has a direction.
Spring: Continuous natural flow to the Earth’s surface, from groundwater, is
formed around an upwelling by physical and chemical accumulation.
Microstructure: Small-scale structure or feature.
Morphology: Natural form of rocky outcrops.
Moraines: A moraine is a mountain range or mantle of till deposited near a
glacier. There are several types of moraines, which depend on their relationship
with the glacier: moraine in the bottom: it is located under the ice, in contact
with the bed.
Secondary permeability: The ability of a fractured material to allow the flow
of liquids.
Pixel: Each of the elements that make up an image, arranged in a matrix and
columns
Fault plane: Fracture plane through which the blocks move.
Porosity: System of empty spaces through which fluids can move.
Stereographic projection: Graphic representation of structural data in three
dimensions.
Reflectance: Relationship between the amount of radiation reflected by a
surface and the one that falls on it. It is usually expressed in % or with values
between 0 and 1.
Trend or orientation: Geometric layout of the structures according to a direction.
19
Stress Tensioner: Vector force of compression or distension.
Tuff: Volcanic igneous rock, product of the consolidation of pyroclastic
materials, pumps, lapilli, ash, with sedimentary material that favors its
cementation.
20
EXECUTIVE SUMMARY
Within the framework of the consultancy contract between the Strategic Office
for the Maritime Claim, Silala and International Water Resources (DIREMAR)
and the Geological Mining Service (SERGEOMIN), the geological and structural
survey of the areas surrounding the Silala springs was carried out, generating
geological-structural information exposed in the following paragraphs.
The Silala Springs area is characterized by a relatively flat to undulating
topography, with a slight inclination to the west, with wide depressions flanked by
various volcanic structures such as domes, cones, calderas and stratovolcanoes.
The morphology of the place was modeled by both endogenous and exogenous
processes and has an average height of 4,000 meters above sea level, varying
from 4,278 meters above sea level (Silala Ravine) to 5,701 meters above sea
level (Stratovolcano of Silala Grande Hill).
The development of the study contemplates diverse phases (office and field), in
the first one was collected and analyzed all the existing technical information,
proceeding with the interpretation and analysis of satellite images, for example;
Images Landsat 7 ETM + Bands RGB 742, Bing Maps and Fusion of images
Landsat 7ETM + Y Radar Alospalsar, in order to discriminate geological
features, such as lithological contacts and regional lineaments, structuring the
base maps that were later corroborated with the field work, using the method of
station point, transects and GPS points.
Within the geological part we must mention that, the study area is within the
morpho-structural domain of the Western Mountain Range or Volcanic Belt in
its southern block, it develops in the Central Volcanic Zone of the Andes and
is part of the Altiplano-Puna Volcanic Complex (APVC). The volcanic activity
develops from the Upper Miocene to the Lower Pleistocene, generating igneous
rocks intermediate to calc-alkalic intermediates rich in potassium, related to the
subduction of the Nazca plate during the Andean tectonic phase.
The intense magmatic activity of the region begins with an explosive volcanism
of the Plinian type, building large volcanic calderas and chains (Guacha, Pastos
Grandes, Agua de Perdiz) and extensive ignimbrite shields to which the Silala
Ignimbrites of dacitic composition would correspond, (defining in this study
three members). Later a gradual reduction in the volatile content of the magma
causes the volcanism to change to an effusive type, placing volcanic domes
such as Silala Chico and Torito hills and emitting lava flows of andesitic-dacitic
composition forming Stratovolcanoes such as Inacaliri and Silala Grande.
As for the tectonic framework, the structural survey of fractures and faults was
carried out, with a subsequent analysis, management and interpretation of these
data and results through the use of the Dips 5.1 program, generating maps of
main structures with kinematic components and field of associated stresses,
fused with the existing regional lineaments.
The system of general fracturing is defined by three dominant
structural trends: the first and main system is of general trend NESW
(40° - 70°), the Uyuni-Khenayani fault system is included. The
second system has longitudinal direction NW-SE (100° - 140°);
ii
21
the main volcanic centers of the area coincide with this system. A third structural
system with general trend N-S (340° - 10°), some volcanic cones are aligned
in this direction.
In the volcanic rocks of the area the deformation is of fragile type, it is clear
that by its tectonic and volcanic activity (cooling) the fracturing is potentially
suitable for the transport and circulation of fluids. The most intense fracturing
is located along the Silala springs, where the ignimbrites are better exposed.
It is important to point out that, in an aquifer composed of volcanic rocks,
the secondary porosity is more relevant than the primary one and derives
from the network of fractures and discontinuities depending on their opening,
continuity, persistence and infilling, these characteristics define the Silala
Ignimbrites (Members 1 and 2) as the lithology with the greatest potential to
become aquicludes due to the acquired secondary porosity.
ii
22
STRUCTURAL GEOLOGICAL MAPPING OF THE AREA
SURROUNDING THE SILALA SPRINGS
1. BACKGROUND
In accordance with Supreme Decree No. 3131, the Strategic Office for the
Maritime Claim, Silala and International Water Resources (DIREMAR for
its Spanish acronyms) procured the product-based counselling services of
the Geological Mining Service of Bolivia (SERGEOMIN for its Spanish
acronyms) under a contract dated 05/05/2017 for the performance of a
geological and structural mapping of the area surrounding the Silala springs.
The study is intended to acquire data on the geology and structural features of
the area—which is characterized by lineaments, faults and joints—and their
influence and control on the Silala springs. The study will constitute a basis
to be complemented with geophysical, hydrological, hydrogeological and
geomorphological studies of the area and is strategic for the State’s interests.
2. OBJECTIVES
2.1. General objective
- Geological data is essential to define the textural features of volcanic rocks
and their influence on the accumulation of water in the aquifers that conform
the outcrops of the Silala springs.
- The structural survey is fundamental to identify the structural features
of the lineaments, faults and joints present in the sectors that comprise the
area as a whole. Defining the behavior of the native and non-native geological
structures is essential to determine their influence on the accumulation of water
in the aquifers and the emergence of water in the Silala springs.
- The geological-structural survey will be the basis for additional geophysical,
hydrological, hydrogeological and geomorphological studies.
2.2. Specific objective
To perform a geological survey at scales of 1:10.000; 1:20.000 and
1:50.000 in three specific Areas in order to:
-Delimit and define the local formations and units present in the area
(stratigraphy), particularly in regard to the ignimbrite found in the
vicinities of the Silala springs (1st Area), their thickness and position
(inclination for their reconstruction and to try identify their sources).
-Take rock samples for the performance of petrographic surveys to
define their texture and composition related features.
1
23
Prepare maps, lithological columns, geological sections and a report containing
a geological interpretation of the area.
To perform a semi-detailed structural survey and collect data at the scales of
1:10.000; 1:20.000 and 1:50.000 for three specific areas in order to:
- Collect data on the regional faults, joints and local fractures to
prepare rose diagrams intended to better comprehend the behavior and
stresses that acted in the area.
- Collect structural data on the fractures and joints of the potential
recharge areas (ignimbrite) in order to determine the recharge ratio of the
aquifers (density map).
- Perform a structural interpretation of the faults, joints and fractures
of the geological units in order to acquire knowledge on their effect as a
potential water recharge source in the aquifer that discharges waters into
the Silala springs.
2.3. Methodology
2.3.1 Desk work
- Preparation of an activity time table
- Compilation and analysis of existing data
- Preparation of base maps of the three areas to be studied
- Satellite image processing and interpretation
- Preparation of spreadsheets for the data; geological and structural
data collection
2.3.2 Field work
- Geological and structural mapping at different scales
- Rock sampling for petrographic analysis
- Preparation of maps at different scales
- Preparation of stratigraphic columns
- Data collection to generate structural data tables
3. GENERAL INFORMATION
3.1 Earlier works
“Chrono-stratigraphy of Ar40/Ar39 of the ignimbrite of the
Altiplano-Puna Volcanic Complex Reveals the Development of an
Important Magmatic Province”
This study comprised the mapping and laser dating of the sanidine and
biotite of 56 points, together with the collection of magnetic data and a
comparison of the ages established in earlier works to define the specific
volumes and time in which the ignimbrite emplacement occurred in
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Bolivia and the north of Chile so as to unveil that monotonous volcanism
of intermediate composition was prodigious and episodic in the whole
complex. These new results present the eruptive history of the Pastos
Grandes and Guacha calderas, two big complexes of multi-cyclical lava
flows located in Bolivia. These two calderas, together with the complexes
of Vilama and La Pacana calderas and the small ignimbrite shields, were
the main sources of ignimbrite-producing eruptions during the Miocene
in the history of the Altiplano-Puna volcanic complex.
“Geological technical survey on the Silala”
This was a technical-geological survey carried out in 2016 by senior
students of the Faculty and was presented by the Tomas Frias Autonomous
University to the Governorate of the Potosi Department. The survey
reaffirms that the waters of the Silala constitute springs located in Bolivian
soil—the university, however, demanded more resources and technology
to pursue the survey further.
“Study on the Geology, Hydrology and Environment of the Silala
Springs area”
The Regional Integration Project (PIR, for its Spanish acronyms) of the
national Geology and Mining Service (SERGEOMIN) was carried out
at the instruction of the Ministry of Economic Development and the
Ministry of Foreign Affairs and Worship.
The objective of this survey, completed within the PIR’s scope, was to
attain data on the geological, hydrological and hydrogeological evolution
of the area of the Silala Springs, the approximate extent of which is
of 150 km2, with details on the formation and evolution of the Silala
ravines—where the Silala springs, which comprise an extent of 79 km2,
are located—together with a characterization of its waters.
“Study on the hydrographical basins of Pastos Grandes, Cuenca 16
and the North and South Lipez Provinces of the Potosi Department”
This survey was intended to identify and characterize the hydrological units
that have the potential to discharge groundwater, relating the emergence
of water springs, wetlands, and others, with the relative permeability of
the igneous and/or sedimentary rocks. The units delimited correspond
to three categories linked with the emergence of groundwater in porous,
unconsolidated soils.
“Structural evolution of the Miocene-Quaternary of the Uyuni-
Atacama region, Chilean–Bolivian Andes”
This survey was intended to describe the Miocene-Quaternary geologicalstructural
evolution of the Uyuni Salt Flat and Atacama regions, found in
the Chilean–Bolivian Andes.
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Four main tectonic events were recognized on basis of the geometry and
the kinetics of the faults and stratigraphic data.
“Geological Map for the Inca hill/Khara Lagoon Sheet No. 5928-
6028”
The survey was performed by taking samples of the lithology of Inacaliri
volcano, the volcanic domes of Torito, Negro and Chascon hills. The
extent of the Silala ignimbrite and the Pastos Grandes caldera ignimbrite
were also surveyed, concluding that those of Silala are younger in age.
“Geological Map for the Sanabria Sheet No. 5927-6027”
This geological sheet records the volcanic units of the area and defines a
series of volcanic formations lined up with a NNW and NNE direction that
present andesite-dacite related features—believed to have given origin to
the Meson Negro, Linzor and Pabellon stratovolcanoes. The survey also
defined the Silala tuffs (6.6. mya.) and the Silala lava, together with the
tectonic framework and petrology of the area.
“Geological Map of the Silala Sheet No. 5927”
This survey presents an initial outline of the units that conform the Silala
springs. The area was mapped at a scale of 1:50.000.
“Volcanoes and supervolcanoes of the Lipez region of Potosi
Department”
This geological survey summarizes the volcanic structures identified in
Bolivian soil and that form part of the Altiplano-Puna Volcanic Complex,
with an emphasis on the significant ignimbrite eruptions of the area
studied and a detail on the volumes, ages and types of eruptions.
4. GENERALITIES
4.1 Location of the area studied
The Silala springs are located in Canton Quetena Chico of the San Pablo
de Lipez Municipality, of South Lipez Province, in Potosi Department
(Figure No. 1).
The central coordinate of the area, in the UTM-WGS 84 system, Zone
No. 19, of the South Hemisphere is: East: 601004, North: 7566389. The
site is found at 4,378 MASL.
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Figure No. 1. Location of the area of the Silala springs
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4.2 Accessibility
The area surveyed can be accessed through the 1st order La Paz-Oruro-
Challapata-Uyuni road, which is found at 560 km. Two 2nd and 3rd order
routes can also be used from Uyuni to the area, i.e. the Uyuni-Culpina
K-Cruce Avaroa-Silala road, found at 350 km, and the Uyuni-Villa Alota-
Villa Mar-Laguna Colorada-Silala, at 290 km. (Figure No. 2).
Figure No. 2. Access map of the area of the Silala springs
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4.3 Relief
The relief of the Silala springs are is characterized by an undulated
topography, with wide depressions and a slight inclination to the west. The
area is flanked by different volcanic structures, such as domes, volcanic
cones and stratovolcanoes. The average altitude of the area is of 4,000
MASL, and raises from 4,278 (at the Silala ravine) to 5,701 MASL (at
the Silala Grande stratovolcano). The area also presents ample plains with
wide valleys, forming a characteristic U-shaped profile, which then evolve
to fluvio-glacial valleys, favoring the formation of lagoons in topographic
depressions.
4.4 Climate
According to Koppen’s climatic classification, adapted for the Bolivian
territory by Montes de Oca (1997), “the main types of climates in Bolivia
are: tropical rainy climates, dry climates, mesothermic climates and cold
climates”. The area is characterized by the following climates: Cold
climates (E), Tundra climates (ET) in the lower flanks of the mountain
ranges and part of the high plateau, associated with minor morpho-structural
units (mountain ranges and intra-mountainous valleys), and high mountain
climates (EB) which correspond to the high summits of the mountain ranges
that are covered with snow or ice most of the year.
The climatic conditions of Bolivia’s western region are essentially determined
by its altitude above the sea level and local factors such as sunlight, the
valleys’ orientation and atmospheric currents (Montes de Oca, 1997). The
major morpho-structural units of the region exert a decisive influence as a
climate moderating factor, but do not reduce latitudinal dependence. The
climate of the Altiplano is a direct function of its altitude above sea level.
This altitude, which reaches an average of 3,800 meters above sea level,
has an influence on the atmospheric conditions, making ample insolation
and irradiation possible due to the rarefied and diaphanous air, and the little
humidity and absence of heat diffusion, causing temperature to be high
under sunlight and cold in the shadow. The maximum temperature of the
Altiplano reaches the 31.1˚C and the minimum 35˚C below zero, both of
which were recorded in Laguna Colorada (in February, 1996 and September,
1992 respectively).
According to Koppen’s classification, the climate of Bolivia’s South
Altiplano (Lipez region) is characterized by a polar high mountain climate
(EB), which corresponds to the high summits of the region, and a Tundra
climate (ET), which would correspond to the mountain ranges and much of
the Altiplano (Potosi, Oruro and part of La Paz). The hydrological parameters
that are described below correspond to the meteorological station of Laguna
Colorada (considered the most representative of the basin), which recorded
hydrological data for 18 years and allow having an idea of the hydrological
behavior of the area.
The National Service of Hydrology and Meteorology divides the country
into three categories, i.e. highlands, valleys and plains.
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The Altiplano, with elevations between 3,500 to 6,000 m or more and cold lands
that include the entire Andean region, and the high plateau, which comprises the
departments of Potosi, Oruro and part of La Paz are both characterized by tundra
(ET) and high mountain polar (EB) climates.
The period of fluvial precipitation begins in December and extends until March,
reaching a maximum of 21.8 mm in January. The drought period extends from
April to November.
The maximum temperatures are recorded from December to March, reaching
the 14 ºC. From April to August, on the other hand, the minimum temperatures
fluctuate between 0 to -20 ºC, with a minimum annual average of -15 ºC. The total
annual precipitation is very low and presents an annual average of 59 mm, which
decreases to 0.0 mm in July.
Below, historical data obtained from the Laguna Colorada weather station is
presented:
Precipitation. –The monthly distribution of average rainfall is unimodal. The
period of highest precipitation extends from December to March, which represents
90% of the general precipitation, with a maximum of 21.8 mm in January. The dry
season extends from April to November, with a minimum precipitation of 0.0 mm.,
recorded in July. The average annual precipitation for the period of 1983 to 2001
is 72.1 mm/year.
Figure No. 3. Histogram of average monthly rainfall, Laguna Colorada
meteorological station
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Temperature. –The distribution of average monthly temperature is also
unimodal. The highest temperatures are recorded from December to
March, with maximum of 7.2 °C recorded in the former. The minimum
temperatures are observed from April to August, with average temperatures
that fluctuate between 4.3 °C to -8.9 °C. The average annual maximum
temperature is 12.9 °C and the minimum -8.7 °C, with a variation range
of approximately 21 °C.
Figure No. 4. Temperature historiography, Laguna Colorada meteorological
station
4.5 Vegetation and fauna
The plant life and fauna is very limited and characteristic of the western
mountain range and the Bolivian Altiplano. The Silala wetlands present a
flora and fauna that is characteristic of high-altitude wetlands. The flora
comprises paja brava, yareta and thola and the fauna, llamas and wild
animals as vizcachas, flamingoes, vicunas and foxes.
4.6 Resources and infrastructure
The most relevant infrastructures are found in Laguna Colorada, 38 km
to the south of the springs. These comprise an overnight and feeding
installation for tourists crossing from Uyuni to Laguna Verde (border
with Chile) and vice versa, and the installations of the National Electricity
Company and National Protected Areas Service. The closest towns are
found in Villa Mar, Quetena Grande.
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The main road network constitutes the road that connects Uyuni with
Laguna Colorada. There are also several parallel (third order) alternative
routes, which are used by tourism companies. Currently, the road to the
Silala military post is unobstructed and in good conditions.
The San Cristobal and Uyuni towns are the main sources of fuel and food
provisions. Authorization is required to purchase fuel in drums for long
trips.
Most of the towns lack a potable water supply system. Water is supplied
by wells, springs and/or rivers. The Silala springs are the only place
where there is good quality water for human consumption.
Electricity in Silala is supplied by solar panels and by diesel electric
generators in Laguna Colorada. The military post counts on an Entel
satellite antenna that provides cell-phone signal.
Health centers and other services are not available in the area, since the
region is quite uninhabited.
5. SATELLITE IMAGE INTERPRETATION
The desk work stage comprehended the processing and interpretation of
different satellite images, using SERGEOMIN’s image processing. The
images were processed on basis of the needs for the geological mapping
(lithological contact) and structural mapping (preliminary lineament
interpretation).
Three image types were used for the interpretation:
- Landsat 7 ETM + RGB 742 images
- Bing Maps
- Combination of Landsat 7ETM + Y Radar Alospalsar images
5.1. Landsat 7 ETM + RGB 742 images
The data collected by the LANDSAT 7 satellite was consulted for this part
of the survey, together with the data collected by The Enhanced Thematic
Mapper Plus (ETM+) sensors. The multispectral processing and analysis
was made with 7 ETM + bands, which allow for a study that comprises
specter ranges from visible (0.45 μ) to far infrared (12.5 μ).
The spatial resolution is of 30 x 30, comprising seven bands that
correspond to thermal infrared, with the exception of the sixth band,
which is of 120 x 120 m. The spatial resolution of ETM+ images in the
panchromatic is of 15 x 15 m.
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The image was obtained from the United States Geological Survey’s
servers (http://earthexplorer.usgs.gov/). The scene used for the area was
LE72330752003067COA01, acquired on 8 March 2003.
5.1.1 Methodology to process satellite images
The methodology was based on the integrated analysis of the data
obtained from multispectral optical images. Visual interpretation and
digital analysis were completed to obtain the needed data.
The data obtained allowed a lithological identification/classification
for the area of the Silala springs. The methodology needed and digital
processing used were the following:
- Geometrical corrections
- A visual improvement of the images
- Band combination
Geometrical correction. Owing to its experience, LANDSAT provides a
proper correction based on the processing level of the image—which was
nevertheless not completed for this part of the survey, inasmuch as the
correction was performed with a geometrical adjustment only.
Visual analysis and improvement. The images’ visual analysis was
performed using three RGB sensor bands. Contrasts, highlights and
filters were used for visual improvement.
Composition of Images. Band combination allowed for highlighting
color, texture, tone variations, and identifying the different types of
lithology present on the surface.
5.1.2 Results
Combination of spectral bands
- 1st, 2nd and 3rd Band (RGB): This is a natural color image, which
reflects the area as seen by the human eye in a color aerial photograph.
- 4th, 5th and 7th Bands (RGB): The 4th band corresponds to the
infrared for the near field; the 5th Band highlights the altered rocks and
humid areas related to fracturing zones; the 7th Band is useful to highlight
lithological contrasts.
- The 7th, 4th and 2nd (RGB): This combination of bands is widely
used in geology. It uses the three less correlated bands; the 7th Band,
presented in red, covers the segment of the electromagnetic spectrum in
which the clay minerals absorb the energy, instead of reflecting it. The
4th Band, in green, covers the segment in which the vegetation strongly
reflects [SIC, the energy]. The 1st Band, in blue, covers the segment in
which minerals with iron oxides absorb the energy (Chuvieco E. Emilio
2002).
Of all the color compositions generated, the 742nd composition was the
one that presents a better lithological discrimination and the one used most
for the preliminary interpretation of lithology necessary for the geological
mapping. (Figure No. 5).
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Figure No. 5. Landsat Satellite Image 7 ETM + 742 RGB bands used for
lithological discrimination
5.2. Bing Maps
Bing Maps is a versatile tool that provides a determined precision and
allows to position, in an almost exact manner, a specific point. The tool can
be applied in Geology for geological mapping by means of a visual analysis
of satellite images, due to its high spatial resolution, which is of up to 0.30
m, in some cases. In addition, with a spectral treatment of the image, it
is possible to highlight the lithology on basis of the characteristic spectral
patterns, which in this case is in the range of the visible spectrum, covered
by the BING server.
5.2.1 Methodology to process satellite images
There are many tools that can be employed to perform spectral processing
and improve the data.
Contrast improvement: One the most important quality-related factors
of satellite images is contrast. Contrast is created by the difference of
brightness reflected from two adjacent surfaces. If an image’s contrast is
concentrated in a specific range, the information might be lost in areas
that are excessive and uniformly concentrated. The idea behind contrast
stretching is augmenting the dynamic range of the gray levels in which
the image is processed. Contrast stretching entails an alteration of the
distribution and value range of the Digital Number (Arezo Marcos, 2013).
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Intensity-Hue-Saturation (HIS): Intensity is the total brightness or
opacity of a specific color. Hue is related to what is perceived as the
predominant color or wavelength of light. Saturation refers to color purity.
In general, the transformation uses an image composed of three colors
taken from the original satellite data. Original spatial data is separated in
the intensity component, while spectral data is separated in the tone and
saturation of the components (Arezo Marcos, 2013).
Figure No. 6. Bing Map Image used to interpret structural
lineaments and to discriminate the lithological units in the Silala
area
The above image was used to differentiate the lithological units,
discriminate the ignimbrite, lava, and alluvial and colluvial deposits, and
identify the structural lineaments.
5.3. Combination of LANSAT 7 ETM and Y Radar Alos-Palsar images
A lineament is a linear, rectilinear or slightly curvilinear physical feature on
the earth’s surface (O’ Leary et. al. 1976). Lineaments can be either simple
or composite as a function of the expression of their complexity on the soil,
and thus constitute “natural structural discontinuities” of the earth’s surface
and generally reflect structural phenomena of the subsoil (Ohara & Flores
B., 1998). A structural system categorized as a “fault” can present different
dimensions, millimetric dislocations and even continental dimensions
(Flores Naranjo G., 2000).
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This technique demonstrates the usefulness of mapping lineaments on
shaded relief maps (hill shades) for analysis of satellite images based on a
combination of radar images and optical images.
5.3.1 Methodology to process satellite images
Two image types were used to perform the combination: i.e. Landsat
7 images–ETM + (optical) and ALOS-PALSAR (radar). These images
were selected due to the accessibility of the data, the spatial resolution
of the images (appropriate for the regional scale of the study) and the
wavelengths that cover the 7 Landsat bands between 0.45 and 2.35
μm—ranging from the visible region of the electromagnetic spectrum to
mid-infrared, which offers the possibility of analyzing the physical and
chemical characteristics of the coverages—and the L band of the ALOS
PALSAR radar image with a wavelength of 23.62 cm, which provides
information on the geometry of the coverages. These wavelengths
complement each other and allow analyzing the earth’s surface taking
into consideration its different characteristics. Rodriguez-Esparragon
Dionisio et.al., 2015.
• Optics (ETM + 233/075 (08-03-2003)).
• Radar (HH - 1.5 FBS (12-31-2010)).
5.3.2 Data processing
5.3.2.1 LANDSAT 7 ETM + (Enhanced Thematic Mapper Plus)
The data comprises satellite images for which each pixel is assigned a
digital level (DL) after the radiance data captured by the sensor for the
different wavelengths is adjusted, which is why it does not present the
direct physical dimension of the objects observed (Chuvieco, 2002).
The original DL from the satellite images were converted into the
actual physical dimension of the objects, resulting in corrected images
represented in reflectance values (Conesa, et.al., 2004).
5.3.2.2 Alos-Palsar (Phased Array Type L-Band Synthetic Aperture
Radar)
These comprise georeferenced images, with a uniform pixel size,
calibrated radiometrically with the backscattering coefficient sigma (s)
scaled to decibels [dB] and filtered to reduce the errors introduced by the
speckle effect. (Palomino-Angel et.al. 2014).
Since each scene covers only an area of 50 x 70 km, a mosaic of radar
images was generated to cover the entirety of the area of concern.
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The processing was performed with the ENVI 5.3 (Pan Sharpering)
software to then integrate the data to the ArcGis 10.4.1 software. These
shaded and merged relief images were used for the visual interpretation
of regional lineaments.
Figure No. 7. Landsat 7 ETM + 742 RGB Bands combined with the Alos
Palsar L Band radar image used for the preliminary interpretation of the
structural lineaments
5.3.2.3 Conclusions from image processing
There are certain advantages in the use of radar images for mapping lineaments.
It allows controlling the angle of incidence of light and its azimuth (hill shade)
and changing the image scale at any time, for instance. Further, as opposed to
aerial photographs, radar images are not flawed by any type of deformation and
the vegetation does not interfere in the interpretation.
It should be noted, however, that the lineaments obtained must be contrasted
with the structural information obtained in the field. The combination of the
742 Landsat satellite images (RGB) was the one that best highlighted the lithological
units, and was thus used for the geological mapping described below.
The desk work carried out in regard to the different images allowed the geological
mapping to determine lithological contacts that were subsequently corroborated
with the field work stage.
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6. GEOLOGICAL MAPPING
6.1 Geomorphology
The relief of the study area is characterized by a relatively flat to
undulating topography, with a slight inclination to the west and wide
depressions flanked by various structures such as domes, volcanic cones
and stratovolcanoes.
The average altitude of the area is 4,000 MASL which increases from
4,278 MASL (at Silala ravine) to 5,701 MASL (Cerro Silala Grande
Stratovolcano).
The morphology of the area was modeled by endogenous and exogenous
processes; among the former, the most significant comprised volcanism
followed by tectonism, which formed the predominant geoforms of the
area, i.e. domes, volcanic cones, stratovolcanoes, calderas, ignimbrite
shields, collapse escarpments, circular fractures and plateaus, which
were then were degraded by erosion and weathering.
Among the later, the most significant for the area are glacial, eolian and
gravitational processes, together with—through to a lesser degree—
fluvial and physical weathering processes, particularly erosion, giving
place to geoforms of accumulation and erosion such as glacial cirques,
moraines, U-profile valleys, dunes, pillars or stone trees, colluvial cones,
fans, plains and abrupt ravines.
The area studied does not present drainage designs of any kind, since no
surface or permanent water flows were identified.
The glacial activity, together with volcanic activity and weathering,
modeled the current geomorphological forms of the region, which are
represented by constructional and destructive geoforms, evidenced
above all in the vicinity of the Inacaliri stratovolcano. The area presents
a glacial cirque, and its pre-existing valleys have deepened, lengthened
and widened.
The most representative accumulation geoforms are lateral and terminal
moraines and fluvioglacial deposits (at the Inacaliri hill). These products
were formed during the isotope stage 4 (85,000 to 65,000 years BP) and
isotope stage 3 (65,000/36,000 years BP), which had an influence on the
Andes (the mountain ranges and high plateau) (Argollo et. al., 1987).
In general, the area is characterized by moraines encased in glacial
valleys, the most distal of which are at an approximate altitude of 4,500
MASL and correspond to the Last Glacial Maximum, which took place
in the Central Andes 14,500 years BP (Argollo, J., 1991).
Other fluvio-glacial geoforms are present as accumulations of a semiheterogeneous
granulometric composition that extend as far as the
endpoints of the glacial valleys, which are surrounded by stratovolcanoes,
and Silala ravines.
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The colluvial deposits are found in different parts of the area studied and
cover gentle slopes. These deposits have a quite incipient sedimentary
structure, and are heterogeneous and often polygenic.
Alluvial activity is represented by the runoff of fluvioglacial waters, which
gave rise to forms of erosion and accumulation that date back to 10,000
years BP, which are in turn represented by older and extensive fans, and
plains characterized by reddish paleosols developed on the ignimbrite and
lavas.
Where spring waters well up, wetlands are formed by the influence of the
stagnant waters on the fine to medium sandy-loamy material, particularly
in the upper part of the topographic depressions, where the slope is much
softer, or inexistent—these are characteristic high-altitude wetlands (known
also as Bofedales).
6.1 Regional Geology
The area of the Silala springs, the present object of the study, is found within
the morpho-structural domain of the Western Mountain Range or Volcanic
Belt, in its southern block, which is in turn formed in the Central Volcanic
Zone of the Andes and is part of the Altiplano-Puna Volcanic Complex.
The volcanic activity developed from the Upper Miocene to the Lower
Pleistocene and its products were placed and deposited on a substrate of
Paleozoic and Paleogenic rocks exposed in neighboring areas. Regionally,
the outcropping volcanic rocks constitute large structures that form the
Pastos Grandes and Capina calderas and smaller ones such as the Capina,
Kheñawal and Agua de Perdiz centers and volcanic chains. The magmatic
activity in the area is interconnected with the subduction of the Nazca plate,
an event that occurred during the Andean tectonic phase.
The intense magmatic activity of the region began with an explosive
volcanism of the Plinian type, forming large calderas (Chuhuilla, Guacha,
Pastos Grandes) and extensive ignimbrite shields that correspond to
extra-caldera facies (the Silala Ignimbrite). These ignimbrite deposits are
monotonous, and contain dacite and calc-alkaline rhyolites rich in potassium.
Thereafter, a gradual reduction in the volatile magma content caused
volcanism to change to an effusive type, forming volcanic domes, such as
Cerro Silala Chico and Torito hills, discharging lava flows of andesiticdacitic
composition and creating stravolcanoes, as the Inacaliri and Silala
Grande.
The most representative structural feature of the area is the transcurrent fault
of Pastos Grandes-Cojina, to the east and southeast of the Khenayani-Uyuni
fault system, characterized by a minor vergence. The tectonics of the zone is
linked to the subduction of the Nazca plate under the South American plate
and the uplift of the Cordillera, which occurred during the Andean Cycle.
Two preferred fault and fracture directions are defined in the area: NW-SE
and NE-SW, the former is more evident, although both control the region’s
magmatism and combine in a series of dextral course faults in a transpressive
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tectonic environment. They also develop transtensional areas that facilitate
the emission or effusion of volcanic products, such as the circular collapse
structures of large calderas, which in turn is an indication of their resurgence
stage.
6.3 Volcanic products and morphology
Ignimbrite
Ignimbrite is a term that is difficult to define due to its special characteristics;
occasionally, the term has been used in a lithological sense, to refer to welded
tuffs, in others it has been used in a generic sense, referring to pyroclastic
flow deposits.
The first concept—welded tuffs—is inherently confusing, since the
ignimbrites can present non-welded zones. Thus, the definition presented by
Cas and Wright (1992), which provides that ignimbrite is a rock or deposit
formed from a pumice pyroclastic flow, independently of whether it is
welded or not, is used in this report. The fragments can vary in size, with
pumice and xenolith rocks floating in a matrix composed of ash.
Picture No. 1. Ignimbrite of the Silala springs area
The regional basement is made up of partially welded tuff mantles called
Silala Ignimbrite, of colors that range from light pink to violet, and of dacitic
composition constituted by plagioclase, quartz, biotite and hornblende.
Their matrix is composed of reddish-brownish iron oxides of the limonite
type, volcanic glass and microliths of plagioclase. They correspond to the
calc-alkaline series rich in K2O and their SiO2 content varies between 63
and 66%.
The ignimbrite layers, based on extrapolated radiometric data obtained from
geology maps published by SERGEOMIN and/or SERGEOTECMIN, have
an age of 7.8 (Myr) and correspond to the Upper Miocene (Choque, 1996,
Lema & Ramos, 1996, Richter, et al., 1992).
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Throughout the area studied, ignimbrite outcrops of a reddish brown color
have been identified; the degree to which these are welded, as well as the
matrix and lithic components that differentiate one from the others, varies.
Lava flows
These comprise lava flows that are likely to have been emitted from a
volcano’s upper, or secondary crater, or from a crack in its crust or flanks.
Driven by gravity, these flows are distributed on the surface in proportion to
the topography. In general terms, they occur in low or intermediate eruptions.
Picture No. 2. Lava flow, presenting pseudo-stratification
The different temperatures and compositions of the magma can give place
to different types of lava flows. Another type of lava flow, which is very
common in volcanoes that present more acidic and viscous products, are lava
blocks, which appear when the flow surface solidifies and gets fragmented.
Extensive areas of lava flows have been identified in the area studied.
These are characterized by forming thin pseudo-stratification layers. Their
mineralogical composition indicates the presence of intermediate composition
andesitic and dacitic lava, which are commonly superposed on one another.
Scoriaceous lava flows have also been observed. These present very rough
surfaces that are formed by a thick layer of scoriaceous fragments and that
develop autoplastically by breaking and welding the external layer that
solidified during movement.
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Debris flow
These debris include mud and rock particles. Debris flow occurs when
rainwater, or snow that melts during eruption, erodes a slope’s materials,
or when a landmass is sub-saturated with water, facilitated by the gradient
and gravity. This movement is faster on steep slopes and collects debris in
its way. In the valley of concern for the study, loose soil and rolling rocks
that have slid off the slope and moved by water have been dragged by debris
flow.
When the water drags on more mud and rocks, it starts acquiring the
appearance of a fast-flowing river. This debris mass can move so fast that it
can drag large-size rocks and leave them on their way along the flow path.
The speed and vastness of the particles dragged cause a dangerous debris
circulation, wherein rocks are likely to be mixed into a viscous mass.
Stratovolcanoes or Composite Volcanoes
These constitute steep conical shapes, the top of which is truncated by a
crater. These are complex structures formed by the alternating accumulation
of lava flows and pyroclastic material discharged through the same outlet,
which present an apparent stratification—reason why they are called
stratovolcanoes.
Picture No. 3. View of Inacaliri stratovolcano
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Dykes, sills, volcanic plugs, inter alia, can be observed in these areas. There
are also smaller cones on the slopes—known as adventitious cones—that
result from the presence of secondary emission conduits (Cepeda 1982).
These structures result from volcanic emissions characterized by alternating
stages of significant explosive activities and calmer periods evidenced by
different lava traces, which are the result of different eruption types, e.g.
Pelean, Strombolian or Vulcanian eruptions (Vargas 1992).
In the area studied, it is possible to observe this kind of structures characterized
by prominent elevations, such as the Inacaliri stratovolcano and the Silala
Grande.
Domes
These are volcanic structures characterized by an accumulation of dense
lava around their outlet, which, owing to its high viscosity, was unable to
flow during eruption and formed steep slopes of a dome-like shape—reason
why they are called volcanic domes, bulbous domes and cluster toroidal
domes (Baily, 1968).
The lava that forms these domes are generally rhyolitic or andesitic and
can form in the crater of an older volcano. Domes are mostly wide, and not
too high, and present needle-like forms on the top and protruding vertical,
abrupt walls.
In the area studied, the common domes of the sector are represented by the
rock outcrops of Runtu Jaritas, Chascon (which are lined up following a NESW
orientation) and Silala Chico (of a N-S orientation).
6.4 Local geology
The Silala springs are located in the southern block of the Western Mountain
Range and are part of the Andes Central Volcanic Zone.
The weathering, erosion and deposition processes are represented by
unconsolidated Quaternary and Recent sediments that cover large parts
of this area. The materials deposited form glacial, fluvio-glacial, colluvial
and alluvial deposits constituted by blocks, or polygenic boulders, clasts of
different rocks and sizes, and fine sediments such as sand and silt.
Tectonism, manifested as the faulting and jointing of the effusive and
explosive rocks in the area, had a significant influence on the location of the
Silala springs.
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Upper Miocene volcanic activities are of importance for the area. Several
craters, volcanic centers and domes were formed during this cycle. These
are manifested by the eruption and deposition of a regionally extensive
ignimbrite cover—known as the Silala ignimbrite—, which is exposed
on the surface of the area and is partially covered by lava flows from the
stratovolcanoes of the sector.
The basal unit is constituted by ignimbrite of dacitic-andesitic composition
that dates back to 6.6 and 7.8 Myr. Andesitic-dacitic lava of a porphyritic
texture overlay this unit, forming the Silala Chico volcanic dome—the age
of which dates back to 6.04 Ma. (Source: Andean Multinational Project–
AMP).
An observation made in the springs’ ignimbrite (Spring No.1) confirmed
the presence of malachite (copper carbonate-supergene) on the ignimbrite
surface, which is possibly an indicator of the existence of copper sulphide
(hypogenic mineral) in the depth.
Sample No.7814 was taken from the rock that hosts the malachite, which,
based on a petrographic analysis, corresponds to andesitic ignimbrite that
contains hornblende crystals (Annex C). On the other hand, a mineralogical
analysis evidenced the absence of malachite as the main rock constituent,
indicating that this mineral constitutes only an impregnation on the rock.
Copper forms oxidized mineral that remains in the oxidized zone, but can
also be precipitated below the groundwater level by hypogenic sulphide and
form sulphide that is richer in copper—this process is efficient for copper
(secondary enrichment).
A siliceous layer (opal) overlays the ignimbrite, as a nodular-shaped crust.
Its formation is attributed to diagenetic processes that resulted from the
chemical precipitation of continental thermal waters formed by the fast
cooling of silica-containing waters.
Patches of silica crust are found surrounding the spring, corroborating the
silica’s origin by thermal waters. Chert was also found in the immediacies
of Laguna Blanca.
6.5 Stratigraphy
Based on the geological information generated in the field through detailed
geological mapping of exposed outcrops, as well as the gathering of data
found in technical reports, geological and geophysical maps, inter alia, the
elaboration and interpretation of a stratigraphic sequence has been achieved,
allowing the elaboration of lithological profiles for the area studied. These
profiles present, in a schematic and representative way, the lithological units,
from base to top, that outcrop in the region.
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6.5.1 Stratigraphic column for Silala
The work carried out resulted in the preparation of a stratigraphic column
(Figure No. 8) for the three areas mapped in the Silala (Geological Map
for Areas 1-2-3, Annex A) The dating established for the different units
is presented below. The base of ignimbrite 1 (Nis1) does not appear in
the Silala ravine. Geophysical studies have concluded that there is a deep
lithological continuation. The description of the column will begin with
the description of Debris Flow 1 (Nfd1).
Debris Flow 1 (Nfd1)
This horizon appears on both banks of the Silala ravine and has a reddishbrownish
color, on altered surfaces, and reddish-salmon on fresh surfaces.
It is composed of clasts of igneous rocks with a sub-angular to sub
rounded morphology, and diameters that range from a few centimeters to
25 centimeters, dispersed in a rather earthy clay-sandy matrix with a low
degree of compaction.
The thickness of this level fluctuates between 60 to 140 centimeters. This
variation in thickness is caused by the paleorelief present at the time of
deposit and the amount of material dragged by the flow. The deposits do
not present any type of defined structure, resulting in a chaotic mass.
However, in the middle of this unit, fragments of rock up to 40 centimeters
in diameter (monomictic blocks) were observed, stacked in a more or less
continuous horizon, reflecting a high transport energy, facilitated by the
slope.
Picture No. 4. a) Debris flow 1 in sub-horizontal contact with the Silala
ignimbrite 1 (Nis 1). b) Debris flow 1 with sub-rounded clasts of igneous
rocks of up to the 30 cm.
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Figure No. 8. Stratigraphic column for the Silala springs
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46
Based on the petrographic analysis carried out by SERGEOMIN’s laboratory,
in samples collected from this horizon, the rock clasts would correspond to
pyroxene andesite and present an agglomerated structure and a mid-grain
porphiric texture (> 2 mm), with abundant ferruginous paste of limonitegoethite.
A very small amount of volcanic glass and pumice fragments has
also been found.
Silala Ignimbrite 1 (Nis1)
The ignimbrite deposits of the Silala springs are pyroclastic flows of the
Neogene. They outcrop in both Silala canals and date back to 7.8 Myr.,
(Upper Miocene). Their root does not outcrop, but overlays debris flow
(Nfd1) in discordant contact in some parts.
The unit is composed of ignimbrite of a moderately welded flow and a
pinkish-brown color, on altered surfaces, and whitish-gray to rosacea on
fresh surfaces. It presents light to brown banding, with vertical parallel to
subparallel fractures It has a porphyritic texture with feldspar phenocrysts,
quartz, biotite and limited pyroxene (35%), lithic igneous rocks (2%),
limited pumice (5%) (in fiamme sectors), and a matrix (58%) composed of
microcrystals, vitreous fragments and ferruginous paste.
The exposed thickness varies from 3 to 8 meters, has a sub-horizontal
arrangement with a slight inclination toward the center of the ravine. This
unit is of importance because of its lithology and higher fracture index. This
is the rock that hosts the Silala springs. This theory is confirmed by the
amount of springs mapped along the ravine.
Picture No. 5. a) Silala ravine, where the Silala ignimbrite 1 (Nis 1) can be
observed with vertical fractures. b) the Silala ignimbrite 1 (Ns1), presenting
a brownish-reddish color on the surface.
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A petrographic analysis carried out for a rock sample taken from the
North Canal established a dacitic composition, with plagioclase crystals
(oligoclase variety), smoky quartz, oxidized biotite, volcanic glass and iron
oxides, agglutinated in a limonitic paste (ferruginous), volcanic glass and
some microliths of plagioclase [SIC].
Microscopically, the rock has a banded, or fluidal structure and a mediumgrain
porphyritic texture (> 1 mm), the matrix does not present a specific
structure; it is of the massive type characterized by a propagation of scattered
iron oxides and pumice.
Cristal-vitreous tuff (Ntcv)
This unit overlaps the Silala ignimbrite 1 in almost all of the main ravine. It
is constituted by very thin and compact tuffs, with an average thickness of
15 centimeters, an intermediate texture, and a phaneritic grain texture that
ranges from fine to medium grains. In some sectors, it presents a vesicular
texture. It also presents an alternation of lenticular bands of a reddish-brown
color and dark gray bands—giving the rock a laminar aspect.
Due to the small size of the crystals, it is difficult to recognize them
macroscopically; however, it was possible to establish the presence
of feldspars, biotite, hematite and magnetite surrounded by a vitreous
ferruginous matrix. To provide a better description, samples were taken
(Nos. 7702 and 7706) and their results are detailed infra.
This is an intermediate composition pyroclastic rock (glassy vitreous tuff),
which corresponds to andesitic ignimbrite, characterized by a fluidal to
banded structure, medium-grain porphyritic texture (> 1 mm), tabular—and
slightly oriented—prismatic plagioclase crystals (oligoclase), and quartz in
the form of anhedral crystals, clinopyroxene (Augite) with a prismatic and
tabular habit for brown tones, pumice and scattered iron oxides.
Picture No. 6. a) Marker horizon corresponding to a crystal-vitreous tuff, 20
cm thick, that delimits the Silala Ignimbrite 1 (Nis 1) and Silala Ignimbrite
2 (Nis 2); b) Hand sample of the tuff level where a banded structure can be
observed.
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The matrix is mainly a massive texture and is composed of reddishbrown
iron oxides of the limonite (ferruginous) type, volcanic glass and
microliths of plagioclase.
This tuff level is very important and constitutes a marker horizon. Due
to its lithostratigraphic position, areal extension and its sub-horizontal
arrangement, it allowed subdividing the Silala Ignimbrite in two
members (Nis1 and Nis2) and it is also an indicator of possible vertical
displacements produced by the faulting or sliding of the rock massif.
Silala Ignimbrite 2 (Nis2)
The ignimbrite deposits that correspond to this horizon (Nis2) outcrop
along the Silala ravine. They concordantly overlap the level of the vitreous
crystal tuff (Ntcv) at the base and are topped by Debris Flow 2 (Nfd2).
The unit is composed of welded ignimbrite (flow tuffs) of a reddish to
pinkish color on altered surfaces and whitish gray, with pinkish tones, in
fresh surfaces, somewhat rusty, massive structure in some sectors banded
[SIC]. It has a porphyritic texture with lithic plagioclase phenocrysts,
quartz, pyroxene and amphibole, with very variable diameters; it
corresponds to andesite, pumice of up to 10 cm length, and are crushed,
or deformed, showing the welding degree. The matrix occupies 65% of
the rock and is composed of microcrystals of plagioclase and volcanic
glass.
Its thickness can reach 10 meters. It is different from the underlying
ignimbrite in that their lithic components have a fining or inverse gradation
and a lower fracturing degree. They are more competent, or more welded
and therefore are less permeable—although, due to supergene alteration,
they present thin crusts of malachite in some sectors.
Picture No. 7. Silala Ignimbrite 2 (Nis 2) which underlies the tuff horizon and
Silala Ignimbrite 1 (Nis 1); b) The Silala ignimbrite 2 (Nis 2) with pumice
content, presenting a massive structure
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Sample No. 7814 (Annex C) analyzed petrographically, belongs to this
unit. It presents an acid-intermediate composition and corresponds to a
biotite-hornblende dacite, with plagioclase crystals of the Oligoclase-
Andesine variety, quartz with fractures and embayment, prismatic to tabular
clinopyroxene (augite), in addition to altered hornblende; the pumice also
contains splinters of volcanic glass and plagioclase microcrystals.
The matrix is the main component of the rock; it is composed of microliths
of plagioclase and does not present a preferred orientation. To a lesser
percentage, it has volcanic glass and very fine grain iron oxides. The whole
set presents a massive structure.
Debris Flow 2 (Nfd2)
This unit outcrops in both sides of the Main Ravine, in the form of windows
surrounding the south end of the Inacaliri lava. It has a brownish-reddish color
on altered surfaces and grayish-brownish in fresh surfaces. It is composed
of clasts of igneous rocks with a sub-angled to surrounded morphology and
a chaotic distribution. It can reach diameters of up to 40 centimeters and is
dispersed in a sandy-clayey, ferruginous and slightly earthy matrix, with a
fair degree of compaction.
Picture No. 8. a) brownish-reddish debris flow 2 (NFd2), sub-rounded clasts
of igneous rocks can be observed; b) chaotic structure that does not present
any clast structuring
The thickness of Debris Flow 2 (NfD2) varies between 50 to 180 centimeters.
This thickness variation is a function of the slope and instability of its base
when the flow was deposited. The deposits do not present any defined
structure—e.g. clast interweaving. It comprises an agglomerated mass that
presents no geometrical structure. It presents a vesicular texture in some
sectors.
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The thickness of Debris Flow 2 (NfD2) varies between 50 to 180 centimeters.
This thickness variation is a function of the slope and instability of its base
when the flow was deposited. The deposits do not present any defined
structure—e.g. clast interweaving. It comprises an agglomerated mass that
presents no geometrical structure. It presents a vesicular texture in some
sectors.
The petrographic analysis performed for this horizon presents an
agglomerated structure and a porphiric structure of mid to thick grains (>2
mm), with an abundant ferruginous matrix and pumice fragments. The rock
clasts correspond to dark andesite and dacite.
This flow is more widely distributed in the area than the Nfd1 flow and is
thicker and more compacted. Its surface has been more polished by glacial
processes, giving it a desert varnish brightness, with faceted sides and stretch
marks.
Silala Ignimbrite 3 (Nis3)
The rocks of this unit constitute the major ignimbrite outcropping in the area
and are found in the north-east sector of the ravines. This unit has the shape
of a fan, with the apex pointing in the direction of the Silala South Ravine.
This unit’s base does not outcrop, but it is assumed that its basal part is
similar to that of units Nfd2 and Nis2. Its contact with the unit found above
it creates an angular discordance.
The Nis3 unit is constituted by moderately welded tuffs of a reddish-pinkish
color in altered surfaces and whitish-pinkish in fresh surfaces. It has a
splintered structure that is similar to pseudo-stratification. It is massive in
some sectors, with a saccharide to porphiric texture. The rock is slightly
oxidized. (Picture No. 9).
Picture No. 9. Reddish Silala Ignimbrite 3 (Nis 3), presenting a splintered
structure; b) Silala ignimbrite 3 (Nis 3), presenting a porphiric texture, with
plagioclase, potassium feldspar and quartz
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It presents quartz phenocrysts (some are smoked), plagioclase, potassium
feldspar and biotite (40-45%), andesite, dacite and tuffs (2-3 %) and pumice
(5%). In some sectors, it presents fiammes that reflect the unit’s welding
degree. All these components are connected by a 45-47% matrix, which
is constituted of glass, iron oxides and microcrystals. This unit has an
approximate thickness of 12 meters. It has been differentiated from the Silala
ignimbrite because of its composition, higher content and development of
crystals, structure, position and ample areal distribution.
The analysis of samples Nos. 7716, 7721 and 7802 has established that this
rock corresponds to welded crystalline glass, or acid-composition ignimbrite,
which corresponds to biotite dacite, with fractured quartz crystals and
oligoclase-andesite plagioclase, presenting a preferred direction and crystal
twinning. There is a reduced proportion of potassium feldspar and biotite,
forming oriented tabular crystals.
The paste or matrix is abundant. It is formed mainly by glass, limonite,
hematite, and presents a massive structure. Sporadically, it presents
spherulites. The pumice has inclusions of biotite and plagioclase. The lithic
rocks are volcanic (andesite and dacite).
Silala Chico Lava (Nlsc)
The Nlsc unit outcrops mostly in the southern part of the ravines. Half of the
rock mass is found in Chilean territory (Cerro Silala Chico), although there
are also relicts in the northern sector. In both cases, the ravines flank the
Silala Ignimbrite 1 and 2 in the Silala Main Ravine.
Picture No. 10. a) Silala Chico hill, Inacaliri stratovolcano in the back; b)
Silala Chico lava (Nlsc), of a dacite composition, presenting a splintered
structure
These rocks correspond to a volcanic dome, with a N-S orientation,
approximately (it lines up with other similar bodies in Chile). The dome is
constituted by brown dacite on altered surfaces and whitish gray on fresh
surfaces. It has a porphiric texture, with developed quartz, feldspar, pyroxene
and biotite. The crystals are rounded, and present a fine paste. They have
a fluidal structure, with dark and brown bands. They form centrimetrical
to decimetrical banks and present a mild-to-strong oxidation and calcite
impregnations.
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Samples Nos. 7712 and 7713—taken from the west of the volcanic dome—
present the following petrographic features (see Annex C): acid-composition
lava, corresponding to biotite dacite to quartz biotite andesite, with fractured
and embayed quartz anhedral crystals, oligoclase-andesite plagioclase, as
tabular and prismatic crystal twinning. Biotite is represented as subhedral
tabular crystals, as clinopyroxene, hornblende and iron oxides accessories.
The lava paste, or matrix is abundant and composed of volcanic glass
of a massive texture, and plagioclase microliths to a lesser degree, as
well as limonite and hematite disseminations. Its microscopic structure
is holocrystalline and its texture is medium-grain porphiric (> 2mm). It
presents a microlitic matrix of an altered aspect.
Cerro Negro Lava (Nlcn)
This unit outcrops to the northeast of the Inacaliri stratovolcano, as a body
of an isolated dome shape that intrudes the surrounding ignimbrite, since
it has an age of 6.04 Myr (Regional Integration Project, 2001-2003). This
volcanic body has a basal diameter of 2 km; and an approximate altitude of
5,200 MASL.
The Nlcn unit corresponds to a volcanic dome composed of violet gray
lava flows on altered surfaces and dark gray on fresh surfaces. It has a
massive laminar structure that shows pseudo-stratification. The porphyritic
texture presents phenocrysts of plagioclase, quartz, biotite and hornblende,
agglomerated in a very fine ferruginous matrix and with microcrystals of
plagioclase. The rock has a high degree of hardness and conchoidal fractures.
Picture No. 11. a) Cerro Negro with a dome-like morphology. b) Lava
flow of Cerro Negro (Nlcn), it presents a reddish-brown coloration with a
splintered structure
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The petrographic analysis of samples No. 7822, 7822 and 7727 (Annex C)
established that these are intermediate composition lavas, that correspond to
biotite to hornblende andesite, with a holocrystalline structure, a medium grain
porphiric texture (> 2 mm), composed of plagioclase crystals (oligoclase)
with tabular to prismatic forms, with reaction edges and crystal twinning,
anhedral quartz, tabular biotite, with inclusions of plagioclase, hornblende as
phenocrysts, euhedral and subhedral, asides from disseminated iron oxides.
The matrix is in a percentage of 55 to 60% and is constituted mainly by
microliths of plagioclase without orientation, and a smaller amount of brown
volcanic glass. The paste has a massive texture in felty sectors.
Cerro Torito lava (Nlct)
The rocks that make up this unit emerge northeast of Silala, in two contiguous
sectors; the first is presented as a volcanic dome with an approximate height
of 4,900 MASL in its highest part, and a basal diameter of approximately
1.6 km. The second is presented as a lava dome of an ellipsoidal shape with
a length of up to the 10 km and a maximum height of 5,024 m. Because of
their chronostratigraphic position, they both intrude the Silala Ignimbrite.
The Nlct unit is formed by lavas of a greenish-gray color on altered surfaces
and dark gray to whitish on fresh surfaces, with well-developed crystals of
plagioclase, biotite, pyroxenes and sparse quartz; it is surrounded by a very
fine paste and presents a porphiric saccharide texture, with fractures of the
hexagonal type; in some places, it presents pseudo-stratification and in other
sectors, it becomes massive, quite competent rock; due to the weathering,
some outcrops are quite crumbly.
Picture No.12. Volcanic dome of Torito hill (Nlct), rock outcrops and handdrawn
samples
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Microscopically, the volcanic rocks of Torito hill correspond to lavas of acid
to intermediate composition. They are biotite and hornblende dacite and
andesite; the former mostly appear at the base. These rocks are constituted by
abundant fractured plagioclase crystals (Oligoclase-Andesite) that present
crystal twinning. Moderate to sparse quartz, anhedral and subhedral, they
present embayment, clinopyroxene (Augite) of a prismatic to polygonal
habit, biotite and hornblende as main accessories of tabular and rhombic
forms, somewhat altered and with inclusions of iron oxides.
Abundant matrix, formed by microliths of plagioclase without an orientation
and with a felty texture, asides from volcanic glass, hematite and limonite.
All these characteristics were evidenced in the field samples Nos. 7726,
7729 and 7805, (See Annex C).
Inacaliri Lava 1 (Nlin1)
The rocks of this unit form the Inacaliri stratovolcano and emerge on its
eastern flank. They correspond to the first pulses that formed this volcanic
structure. They date back to 5.94 Myr (PIR Regional Integration Project,
2001-2003).
The Inacaliri Lavas 1 are constituted by lava flows of a grayish brown color
on altered surfaces and dark gray on fresh surfaces. They present lamination,
forming a pseudo-stratification and are massive in some sectors; they have
a porphyritic to aphanitic texture, with plagioclase phenocrysts, pyroxenes,
biotite and quartz, surrounded by a very fine grain paste. In some places, a
fluid structure can be observed. The rock is quite hard and compact.
In various sectors, these lava flows develop basal breccia constituted by
the same rock that is cooling and solidifying as it flows downhill dragging
and assimilating clasts from the underlying rocks. The morphology of the
clasts varies from sub-angular to sub-rounded with very variable diameters,
reaching even one meter in diameter.
Picture No. 13 a) Inacaliri lava flows (Nlin1), b) basal breccia of the
aforementioned flows
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The analysis of samples Nos. 7813 and 7833 (Annex C) has established
that these are lavas of intermediate composition, which correspond to a
hornblende andesite, weakly oxidized, with a holocrystalline structure, constituted
by plagioclase crystals of the oligoclase variety with a preferred
orientation, anhedral and subhedral quartz, brown prismatic hornblende,
suboptimal prismatic clinopyroxene and polygonal euhedral and tabular
biotite. The matrix is constituted by plagioclase microliths.
Silala Grande Lava (Nlsg)
This unit is one of the largest in the area. Its rocks outcrop to the north and
northeast of Silala, forming a Quaternary Stratovolcano (1.9 Myr, Regional
Integration Project). It has a diameter of 14 km and a height of 5,700 MASL;
its slope varies, from the base to the peak, from 12% to more than 40%.
The Nlsg unit is constituted of several andesitic-to-quartz andesitic lava and
basal breccia. It has a brownish reddish to gray color on altered surfaces and
dark gray on fresh surfaces. Its structure is very variable, ranging from massive
to splintered and fluidal. It presents a porphyritic, aphanitic, trachytic
and even vesicular texture, composed of phenocrysts of plagioclase, pyroxene,
amphibole, biotite and quartz.
The basal breccia of the andesitic lava flows has the same composition and
presents a ferruginous matrix and polymictic lithoclasts of volcanic rocks,
with sub-angular to sub-rounded morphology and diameters that range from
the few centimeters to the 100 centimeters in diameter. The breccia and the
lava flows both have a high degree of hardness and compaction, and present
bread-like or hexagonal crust fractures. Pseudo-stratification has also been
established in disturbed sectors, and pseudo-folding in others.
Picture No. 14. Pseudo-stratified lava flows (Nlsg)
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The petrographic analyzes of these flows (samples Nos. 7816, 7820, 7818,
7830 among others, see Map No. 4) have indicated that these are lavas of
intermediate exclusion, that correspond to pyroxene and hornblendic andesite
with a holocrystalline structure, porphyritic rock texture, with abundant
plagioclase crystals of the Oligoclase-Andesite variety, hornblende, augite
and biotite in anhedral, subhedral and euhedral crystals. Texture of the
trachytic and felty matrix, composed mainly of microliths of plagioclase
and, to a lesser extent, volcanic glass and iron oxides [SIC].
Inacaliri Lava 2 (Nlin2)
The rocks that make up this unit were emitted in a second pulse dated back
to 1.9 Myr (Lema & Ramos, 1996), covering the volcanic cone formed in
the first event. A well preserved crater can be observed in the upper part
of the volcano. The deposits of the Nlin 1 and Nlin2 units cover the Silala
Ignimbrite.
The Inacaliri Lava 2 consists of lava flows of an andesitic composition with a
basic tendency. They also develop basal breccia in several sectors; the rocks
show a brown to reddish gray coloration in altered surfaces and dark gray
in fresh surfaces, and develop lamination that forms a pseudo-stratification
and centimetric to decimetric splinters and are massive in certain sectors. [It
presents a] Porphyritic to aphanitic texture, with plagioclase phenocrysts,
pyroxenes, biotite and quartz, surrounded by a very fine grain paste. Fluidal
structure is observed, and the rock is quite hard and compact.
Picture No. 15. Stratovolcanic lava flows (Nlin 2)
The analyses of samples Nos. 7720, 7743, 7810 and 7811 have established
that the lavas are of intermediate composition, rather basic, and correspond
to pyroxene-hornblende andesite with fluidal
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to vesicular microstructure. The texture of the porphyritic rock with tabular
to prismatic plagioclase (oligoclase-andesite) crystals that present crystal
twinning and zoning [SIC]; clinopyroxene (augite) as anhedral and subhedral
phenocrysts, some of which are twinned; brown prismatic and polygonal
hornblende, iron oxides as inclusions and disseminated in the paste, with a
minor proportion of quartz. The matrix presents a eutaxitic to felty texture
composed of microliths of plagioclase and volcanic glass, limonite and
hematite.
Pastos Grandes Tuffs (Ntpg)
This unit consists of fall and flow tuffs, with a brown to pinkish coloration
on altered surfaces and whitish pinkish on fresh surfaces, [; it presents] a
massive structure and is formed in blocks, porphyritic texture with feldspar
phenocrysts, some smoky quartz and biotite, volcanic stone lithic materials
ranging from millimeters to up to 50 centimeters in diameter and pumice
with quartz and biotite crystals as inclusions in sectors form fiammes,
agglutinated in a tuff-vitreous matrix. The rocks vary in their hardness or
welding degree.
The outcrops that correspond to this unit are located northeast and southeast
of the Silala springs, these tuff deposits are part of the Caldera of Pastos
Grandes and date back to 3.4 Myr in their southern distribution (Lema &
Ramos, 1996) and to 2.9 Myr in their northern proportion (Salisbury et al.,
2010).
The analysis of samples Nos. 7722 and 7723 (Annex C) has indicated that
these are vitro-crystalline tuffs of acidic composition, biotite dacite, with
a hypo-crystalline structure and medium grain texture (> 1 mm), with a
vitreous matrix of a massive texture.
Runtujaritas hill lava (Nlcrj)
These domes outcrop in the easternmost part of the area and present a NW
direction connected with the faults. It has a horizontal elongated lobular
shape, with a length of approximately 6 kilometers and an average height of
4,900 MASL.
Macroscopically, the rocks that constitute this unit are presented as lavas
formed in scoriaceous blocks, of a grayish brown color on altered surfaces
and whitish gray on fresh surfaces. [They present a] massive vesicular
structure, a porphyritic texture with feldspar phenocrysts, biotite, pyroxenes
and rare quartz, surrounded by a fine matrix apparently composed of volcanic
glass. The rock presents a medium hardness and is mildly oxidized.
The microscopic analysis of sample No. 7737 has indicated that this is
lava of acid-intermediate composition that corresponds to pyroxene dacite,
with a holocrystalline structure and medium-grain porphyritic texture (> 2
mm), with twinned plagioclase crystals, oxidized tabular biotite, prismatic
hornblende partially replaced by limonite, [and] clinopyroxene of the augite
variety in clusters. The matrix is vitreous and presents a perthitic texture.
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Picture No. 16. Pastos Grandes Tuff (Ntpg)
Cerro Chico hill lava (Nlcc)
This volcanic formation is located southeast of Silala Grande stratovolcano,
adjacently to the Runtujaritas domes. It has an irregular lobed shape,
regularly sub-horizontal—which is why it is called El Meson Negro hill.
The lavas of this unit have a brown coloration on altered surfaces and whitish
gray to dark gray on fresh surfaces. The unit presents a massive structure
formed in blocks, in laminated sectors, porphyritic texture with feldspar
phenocrysts, biotite, pyroxenes, quartz and iron oxides, inside a fine-grained
matrix. The rock displays a high hardness and compaction.
Picture No. 17. Panoramic view of the Runtujaritas dome-lava
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The analysis of sample No. 7827 (see Annex C) has indicated that the lava is
of acidic composition and corresponds to weakly oxidized pyroxene dacite,
with a holocrystalline structure and a medium grain porphiric texture (> 2
mm), with subhedral and anhedral quartz crystals, plagioclase with crystal
twining of the albite type, dark brown tabular biotite, prismatic augite and
greenish polygons. The matrix is composed of microliths of plagioclase and
iron oxides, showing a microlitic texture.
Picture No. 18. Lava flows of Cerro Chico hill (Nlcc)
Quaternary deposits
Glacial Deposit-Moraines (Qgm)
Glacial activity is represented by erosion and accumulation geoforms located
in the vicinity of the stratovolcanoes and in the Silala Main Ravine. Within
the former, glacial cirques developed in the Inacaliri and Silala Grande
stratovolcanoes can be observed. Another effect of glacial erosion is the
deepening, lengthening and widening of pre-existing valleys, giving them
the typical U-profile.
The main accumulation geoforms are the lateral, frontal and terminal
moraines. The formation of these glacial products can generally be
associated to the Isotopic Stage 4 (85,000 to 65,000 BP) and Isotopic Stage
3 (65,000/36,000 BP), which occurred in Los Andes (the Mountain Ranges
and Altiplano) (Argollo et al., 1987 and Argollo and Iriondo, 1991).
There are three groups of moraines encased in glacial valleys. The outermost,
or most distal one is located at an approximate elevation of 4,500 MASL and
corresponds to the Last Glacial Maximum, which occurred in the Central
Andes 14,500 years ago BP (Argollo, J., 1991)—according to earlier studies
carried out by radio-carbon methods, mainly in tuffs and shells, for both
the Western and Eastern Cordillera. The second moraine is found at 4,670
MASL and the last one at 4,800 MASL, and corresponds to a tardiglacial.
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Glaciation events that date back to 14,500 BP caused strong alterations in the
landscape owing to the movement and thawing of ice masses, which resulted
in the formation of lakes, lagoons and deep valleys.
Thawing activity was essential for the formation of the Silala ravine, which
is a typical example of a ravine that was carved by meltwater, facilitated
by areas of weakness (faults and fractures); the current design of the Main
Ravine, however, presents a U-shaped cross section, with vertical side walls
and a flat base. The water produced by the melting of the glacier mass is an
important source for the current groundwater stored in the Silala ignimbrite.
Fluvioglacial deposit (Qfg)
The fluvioglacial sediments are represented by the accumulation of volcanic
and pyroclastic rock fragments, of an almost heterogeneous granulometric
size. They are deposited at the ends of the glacial valleys that surround the
stratovolcanoes and in the Silala ravine.
These deposits are made up of sand and some silt, with clasts, boulders and
cobblestones of volcanic rocks of different diameters. The larger blocks present
glacial striations that reflect the movement of ice masses, while the
material of a smaller granulometry reflects a fluvio-glacial transport and erosion.
Colluvial-Fluvial deposit (Qcf)
This is a deposit formed on a gentle slope, where the sediment accumulated
as a result of the transport of rocky material caused by gravity, combined
with the action of intermittent runoff water. They are the product of melting
and snowfall.
Colluvial-Deposit (Qc)
Colluvial sediments are found in different parts of the area, forming on
smooth and steep slopes as colluvial cones. These accumulations present
incipient sedimentary deposits, are heterometric and frequently polygenic
and are constituted of blocks, boulders, pebbles and gravel of volcanic rocks
that outcrop from the Silala Chico, Silala Grande and Inacaliri, inter alia,
inactive volcanoes.
Alluvial Fan Deposit (Qaa)
Alluvial activity is represented by the runoff of fluvioglacial waters that gave
rise to forms of erosion and accumulation 10,000 years BP. Large alluvial
fans can be observed, reflecting somewhat more temperate climatic conditions,
causing ice masses to melt and, in consequence, amounts of runoff
water that were completely different from the current ones. These deposits
were formed by varied materials of medium to fine granulometry, (gravel,
sand, silt and clays), arranged in a decreasing grain shape from top to bottom,
with the apex exposed in the highest part.
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Alluvial Deposits (Qa)
These deposits are located in the springs, where water deposits are found,
but do not circulate and remain stagnant, forming high Andean wetlands.
Fine sediments, mostly organic matter, can be observed here. Other forms
of alluvial accumulation in the area studied comprise alluvial plains with
red paleosols developed on ignimbrite (which dates back to 7.8 Myr) and
andesite-dacite lava (which dates back to the Quaternary).
6.5.2 Cross-sections of the Silala springs area
Seven cross-sections (Figure No. 9), approximately every two hundred
meters, were produced on basis of the field work with the aim of correlating
the different ignimbrite and debris flow horizons of the area (Annex B).
According to the cross-sections obtained, it can be assumed that the debris
flow horizons are distributed at different levels, have an irregular base
and reflect the instability of the valley. These horizons are syngenetic to
explosive volcanic activities.
The Silala ignimbrite units are differentiated by their degree of welding,
fracturing and vertical jointing, which allows the water to infiltrate through
the fractures. Other parameters to differentiate the ignimbrite units comprise
the content of pumice (fiammes), lithic materials and crystals.
The geological sections were produced on basis of the topographic map
prepared by the Military Geographical Institute (IGM, for its Spanish
acronyms), which provides more precise data, since it was elaborated with
total station equipment.
6.5.3 Data Base
The field data, sampling points, and dating collected from different reports
and petrographic analyzes are presented in Annex D to this report.
6.6 Generalized Geological Section of the Silala springs area
Radiometric data obtained within the framework of the Regional Integration
Project (2001-2003) has indicated that the Silala ignimbrite (Nis 1) dates
back to 7.8 Myr BP. This ignimbrite corresponds to explosive products
and extra-caldera facies of the Chuhuilla event. This unit is widespread at
the regional level and is the oldest unit of the area. At a first stage, it was
subsequently intruded by the domes of Silala Chico, Cerro Negro and Cerro
Torito. These intrusions date back to 5.94-6.04 Myr BP and have andesitic
to dacitic compositions.
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Figure: 9 Location of the cuts made in the quarry of Silala
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Another explosive pulse was then recorded, which resulted in the deposition
of wide ignimbrite mantles between 3.4 and 2.9 (Salisbury et al., 2010); these
are assigned as the Pastos Grandes event, although they are not represented
in this section due to their location in respect to the cross-section.
Following the largest intrusions, and with ages that range between (1.6-1.9)
Myr, the Inacaliri stratovolcanoes (second pulse) and the Silala Grande were
formed. These were events of the effusive type. These lavas that currently
constitute the topography of the Silala area have andesitic and dacitic
compositions.
6.7 Conclusions
The detailed geological survey works carried out for the area of the Silala
springs allowed defining that the base of the area is constituted by the Silala
Ignimbrite 1 (Nis 1). The salient feature of this unit is its high degree of
fracturing. Debris flows were also identified in the exposed lower area.
Considering the genesis of these volcanic-clastic products, however, it has
been concluded that they are local. The Silala Ignimbrite 1 dates back to 7.8
Myr BP, the Upper Miocene. From the hydrogeological perspective, this
unit is the most important one inasmuch as it contributes to the formation of
water springs.
A crystallovitreous tuff level of 15 centimeters of power has been identified.
It has an andesitic composition that forms a marker horizon and separates
the first two Silala ignimbrite units (Nis1 and Nis2).
Overlaying this horizon, there is a level of flow tuffs that are semi-welded
and denominated as Silala Ignimbrite 2 (Nis 2). This level presents a higher
degree of welding and inverse grain-growth or gradation of lithic [materials],
and is of a dacitic composition. In the area, this level culminates with quite
compact debris flows (Nfd2).
A final ignimbrite level, denominated the Silala Ignimbrite 3 (Nis 3), of a
greater areal exposure and exposed to the east of the Silala springs area,
presents a pink coloration. Its distinctive feature is a larger development of
crystals. This set of ignimbrite units are the product an event that preceded
the formation of the Pastos Grandes Caldera and can be attributed as extracaldera
facies of the event known as the Chuhuilla Caldera.
Lava flows from the Silala Chico volcanic dome (Nlsc), dating back to 6.04
Myr, ejected from the first pulses (5.94 Ma) of the Inacaliri volcano (Nlin1)
cover the Silala ignimbrites Nis1 and Nis2, as well as debris flow Nfd1 and
Nfd2. Thereafter, the ejection of lava and dome-lava from Torito hill (Nlct),
Negro hill (Nlcn) and Silala Grande stratovolcano, of a dacitic to andesitic
composition, display a continuity in the volcanic activity in the sector. This
set of effusive products dates back to the Late Miocene to Lower Pliocene.
The volcanic activity of the sector ends with effusive products of the Pliocene
in the second pulse of the Inacaliri stratovolcanoes (Nlin2), as well as the
lavas of the Runtujaritas and Chascon.
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During the Pliocene, the Pastos Grandes Caldera developed with the formation
of explosive products of extra-caldera facies constituted by crystalline vitro
tuffs that date back to 3.5 Myr and the subsequent development of their
intra-caldera facies (outside the area), dating back to 2.9 Myr (Salisbury et
al., 2010).
Products of the Pleistocene to Holocene constitute Glacial deposits conformed
by lateral, frontal and terminal moraines, developed in the Inacaliri and
Grande hills, the remains of the formation of which constitute the glacial
cirques currently visible in the area. These were once of importance as
recharge products for the aquifer of the Silala springs.
It is important to underline that, at that time, meltwater was the main product
that gave place to the origin and recharge of the Silala springs. It has been
found that the Silala Ignimbrite (Nis1), due to their degree of fracturing,
permeability and secondary porosity, constitutes the host rock of the aquifers
that gave rise to the Silala springs. Lava, on the other hand, behaves as
semipermeable layers, allowing water to infiltrate and circulate very slowly
through fractures and joints; therefore, they did not have an influence in the
formation of aquifers.
Finally, it should be emphasized there are no drainage designs in the area.
Further, no surface or permanent water flows were identified. This aspect
is determinant to define the formation of the Silala springs and ravine that
surrounds them as a product of erosion and deposition of glacial processes,
which acted in areas of tectonic weakness where fluvio-glacial processes
subsequently formed the current topography of the Silala.
6.8 Recommendations
• So as to determine the physical properties of the rocks of the area,
particularly the Silala ignimbrite, it is recommended that permeability
tests be carried out for the core samples that will be obtained from the
ongoing drilling program.
• The petrological survey and geochemical analysis of whole rock
samples and trace elements is also of importance, particularly in regard
to ignimbrite and tuff. This analysis will allow defining, from a chemical
perspective, the rock type and magma that formed the different units of
volcanic rocks, differentiating their varieties and the level from which the
magma emerged.
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7. STRUCTURAL GEOLOGY
7.1 Introduction
A robust description and interpretation of structural data based on the
cartography of the distinct deformation phases connected with the volcanic
deposits are not available. Characterizing the fracture systems on basis of
stress and structural control is important for the process of water movement.
A geological-structural interpretation will allow establishing the variation
degree of permeability as a function of the geology.
It is clear that due to the tectonic and volcanic activities, fracturing is
potentially suitable for the generation and circulation of water, linked with
secondary permeability.
The results and observations presented in this survey will help understand
the zones that are likely to contribute with and distribute formation water.
7.2 Objectives
To analyze the fracturing and faulting of rocks at different scales, an analysis
of the structural geology of the area was carried out on basis of two objectives:
- To identify the geological structures related with the fractures of the area,
mainly in regard to secondary-type fractures, which are a major concern for
secondary permeability. To this end, structural data on the joints, foliation
and fault striation has been obtained in the field so as to conduct an analysis
of weak deformation on basis of microstructural data.
- From the analysis and interpretation of structural data, maps containing
the main structural features of the area were prepared and complemented
with rose diagrams for the fractures, with a kinematic stereographical
projection and stresses linked with the fractures, to present a view of the
existing relation between fracturing and zones that are likely to contain and
discharge waters. The work carried out is detailed below in the subheading
entitled “Work methodology”.
7.3 Work performed
7.3.1 Clerical work
The work started with a review of existing data on the tectonics, structural
geology, geophysics and volcanology of the area. It was complemented with
an analysis and interpretation of Landsat 7 - ETM + optical satellite images
(RGB: 3 2 1, 5 4 3, 7 4 2) and images taken from the Google Earth, Bing and
Esri servers; digital elevation models (DEM SRTM V3) and radar images
Alos Palsar (L band) were also analyzed.
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The result of the structural interpretation was recorded in a base map and
integrated into geographic information systems (ArcGis). The study was
continually enriched with new structural data after each field campaign.
7.3.2 Field work
The field survey was carried out with the idea that the fracturing presents a
fractal behavior, therefore, that map prepared at a metric scale (mesostructure)
contains a clear representation in the whole area.
The absence of microstructural data regarding the area studied constituted
the main disadvantage to perform a structural analysis of a further
approximation.
The structural survey comprised 32 workdays, completed in 3 field
campaigns. The places to perform the field surveys were chosen on basis of
an initial discussion with the working group. The selection and routes for the
survey were based on the importance of the fracturing and main structures.
See Figure No. 10.
7.4 Regional structural setting
The area studied is part of Bolivia’s western volcanic chain, where the
tectonic setting is the result of the convergence of the Nazca and south
American plates and the volcanism that occurred throughout the mountain
ranges. This plate interaction is responsible for the different structural forms
present in the region. The tectonic framework of the zone that comprises the
area studied indicates that the latter is dominated by a set of synthetic and
antithetical conjugated structures that respond to the regional stress tensor,
with a σ1 in a W-E general direction.
The volcanism of the area is characteristic of a geodynamic arc environment,
regionally dominated by compressive tectonics that forms regional faults
that serve as feeding channels of volcanic foci. The tectonic environment
also favors the development of fractures that serve as channels for the
circulation of fluids.
In their “Structural evolution of the Quaternary Miocene of the Uyuni-
Atacama regions, Chilean-Bolivian Andes”, Tibaldi, Corazzato and Rovida
(2008), members of the Department of Geological and Geotectonic Sciences
of the University and National Institute of Geophysics and Volcanology of
Milan, Italy, note that the Mio-Pliocene compression is directly related with
a fast convergence and apparently significant coupling of the continental
and oceanic plates. The EW to WNW-ESE shortening direction of the
Miocene structures and the σ1 NW-SE of the Pliocene structures seem to
be more related with an inter-Andean reorientation of structures, following
an absolute WNW movement of the South American plate. The extensional
deformations can be interpreted as being related with the forces of gravity
that affect the highest parts of the volcanic belt, causing a somewhat
asymmetrical collapse of the latter.
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Figure No. 10. Map of the coverage of the structural data survey
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Herail et. al. (1990), researchers of the ORSTOM-France and Bolivian Fiscal
Oil Fields elaborated a cross-cutting relationship of the South of Bolivia and
note that the geological and geophysical data of the Lipez basin evidence
that Andean deformation began during the Late Oligocene by a sinistral
wrenching, followed by landslides on its edges (Khenayani fault system in
the west, San Vicente fault in the east). The shortening produced by these
thrust faults is of 50 km approximately.
The Uyuni-Khenayani fault is a regional structure whose trace is found few
kilometers to the south of the area studied. Mention is made of this fault by
Aranibar and Martinez (1990) in their paper on the Structural Interpretation
of the Bolivian Altiplano, wherein it is noted that the fault has a northeast
trend and separates two provinces: i.e., the Uyuni Salt Flat province—which
presents right-lateral faults and comprises flower structures and step-overs—
to the west and the Lipez province—which is dominated by thin-skinned
landslides—to the east.
7.5 Structural geology of the area
The structural setting of the area has been initiated on basis of the interpretation
of satellite images that were addressed in the chapters above. These images
present a variety of tones and hues, which highlight the rectilinear elements
of the landscape and the limits of tone variations.
The rose diagram prepared on basis of the lineament and fault maps of the
studied area (cf. Structural Map of Liniments and Faults, Annex) indicates
that the general fracturing system presents three predominant structural
trends (Figure No. 11).
The fist and main system presents a general NE-SW trend (40°-70°) and
discontinuous, shorter features that are well-represented in the south and
north of the area—this includes the Uyuni-Khenayani fault.
Figure 11. Rose diagram of lineaments and faults (n = 5) Silala area
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The second system has a NW-SE longitudinal direction (100°-140°); the
main volcanic centers in the area coincide with this system, which is more
frequent and continuous in the northwest and northeast of the area.
The third structural system presents a general N-S trend (340°-360°) and
is mainly found in the south. Some volcanic cones are lined up in this
direction. An E-W to E-NE structural system, less frequent and transversal
to the others, is found in the central part of the area. These cones cut and
dephase some lineaments that present a N-S longitudinal trend. The table
below presents a statistical table of the main structural trends of the area.
Table 1. Statistical Table of structural trends in the Silala area
The aeromagnetic data obtained by SERGEOMIN for the western mountain
range and the Altiplano (BGM Airborne Survey, 1991) evidences that there
is concordance between the structural design of the surface and the magnetic
properties of the area. In the area surveyed, some magnetic anomalies reduced
to the local pole and the first derivative (Map No. 6) present lineal features
connected with the magnetic gradients that follow an EW to NNE-SSW
direction. These lineaments are projected from the eastern limit of Pastos
Grandes Caldera (4,500 MASL) transversally towards the western slope of
this caldera until they reach the lower topographical end of the Silala springs
(4,300 MASL). Similarly, a magnetic high in the Pastos Grandes Caldera is
adjusted to the Silala-Llancor lineament (which has an ENE-WSW (70°)
trend). The latter presents major anomalies in the influence sector of the
Silala springs. On the other hand, it is also possible to observe gradients
that separate magnetic lows and highs that coincide with the position of the
volcanoes of the area. It is also possible to see that certain NW lineaments
that concur with the surface of monogenetic volcanic cones have blurred
out, allowing to infer their surface source.
The structural control of magnetic anomalies is evidenced by the fact that
these anomalies predominantly follow an ENE to WSW direction the
secondary structural trend of the area.
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7.5.1 Fracturing characteristics
Most of the faults are less visible in the field, though with some
morphological indications; these are characterized by almost vertical
fault planes. Some of the fault planes, however, present inclinations that
border the 45°. Most of the faults, owing to their cartography, are minor
and shallow.
Picture No. 19. High-angle normal conjugated faulting, affecting the Silala
Grande lavas
Fracturing and faulting of the dacite, andesite and ignimbrite units. These
generally present a semi-vertical geometry and are represented as follows:
- In the dacite and andesite lava of the area, the fracturing commonly
presents inclined and sub-horizontal planes, which are not representative
for the area. The faulting caused by the current deformation is mainly
semi-vertical (80°-90°) (Picture 20). Some normal faults that have NWSE
to NNW-SSE and NE-SW orientations have been identified in the
ignimbrite of the Silala springs. These generally present high dips (70°-
80°) and become vertical as they go deeper. These faults normally present
a high angle and a slight displacement, with rebounds that do not surpass
the thirty centimeters.
- Fracturing of the ignimbrite is greater, concurring with the
frequencies obtained, where fracturing presents semi-vertical planes, that
respond to thermal concentration processes caused by cooling; the limited
sub-horizontal planes obey to a lateral faulting of slight displacement,
caused more by relaxation than by lithostatic pressure. Hence, the
intersection of fracture planes in the ignimbrite must be considered as
a significant planar element for the movement of water, mainly as far as
aquifer recharge is concerned.
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Since the lithological units present a joint conjunction and faults to a lesser
degree, it is possible to mention that the fracturing of the zone is conjugated,
i.e. that fracturing also affects the jointing system (Picture No. 20).
Picture No. 20. Sub-horizontal, conjugate faults, affecting the joints of the
Silala ignimbrite
7.5.2 Principal Structures
The Silala springs sector is dominated by NEE-SWW lineaments (60°-80°)
that are transversal to those that constitute the general NW-SE trend and
parallel to the Silala-Llancor lineament. To the east, the lineaments reach the
limits of the western end of the Pastos Grandes Caldera.
To the north of the springs, a series of normal NW-SE orientation faults reach
the limits of the Cerro Negro dome. The faults are truncated and laterally
dephased to the right by the NE-SW faults of the same system as that of the
Silala. To the south of the spring, the main fracturing maintains NEE-SWW
trends, with some N-S to NNW-SSE variations.
7.5.2.1 Inacaliri Graben
A major normal fault system of a NW direction is present from Aguilucho
hill (Chile) to Inacaliri hill (Chile-Bolivia). In this sector, two major
faults present converging dips and escarpments of 150 m height, forming
a symmetric graben (Tibaldi, et. al., 2008). The graben affects a series of
stratovolcanoes of the Pliocene, lined up in NW-SE direction. The main
fault related to the graben, to the NE, is truncated to the NE by a lava dome
that dates back to 80-130 ka BP, 40Ar/39Ar (Renzulli et. al., 2006, quoted
in Tibaldi et. al., 2008). Since the dome is found right on the main faults
trace, its displacement was guided by the fault. A minor fault, parallel to the
escarpment of the main fault, compensates the graben’s base and also affects
the dome with a normal predominant movement.
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The structure of the graben has a NW-SE direction (300°) and a width of 3.5
km; the fault’s traces that limit the structure, towards the southeast, prolong
into Bolivian territory beyond the Cerro Negro hill (2 km to the north
of the Silala wetlands), and are clearly visible in the satellite image that
combines Landsat 7 and Alos Palsar radar images (Figure No. 9). Slightly to
the northwest of Cerro Negro hill, the faults of the structure are apparently
dephased dextrally by other faulting systems of a NE-SW direction (50°).
The aeromagnetic data of BGM Airborne Survey (1991), reduced to the
pole and the main derivative, coincide with an anomalous low magnetic area
until it reaches Negro Hill, demonstrating the deep nature of the structure.
To the NW, there is a loss in the definition of the anomaly.
The distension related nature of the structures, the traces of which involve
the Silala ignimbrite to the north, allow fluids to mover and circulate.
7.5.2.2 Lipez Lineaments
Figure No. 12. Major tectonic structures of the area surveyed
Regionally and within this graben structure, the western trace of the “Lipez
Lineament” is delineated (Figure No. 12). According to Kaiser’s work on the
evolution of the Pastos Grandes Caldera, this structure is a sinistral movement
fault with a NW-SE
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orientation. This lineament prolongs as far as the northern area of the Silala
wetlands (Figure No. 12) and is parallel to a fault that presents a similar
movement and that is marked a few kilometers to the northeast of the area.
These two faults of leftward lateral movement are slightly analogous to the
Khenayani fault (south of the area), although in opposed directions.
7.5.2.3 Silala-Lincor Lineament
This is an ENE-WSW (70°) lineament that crosses the central part of the area.
It coincides pro parte with the Silala springs canal (cf. Map of Lineaments
and Faults). This lineament is formed in between the Silala ignimbrite and
the Silala Grande hill lavas. On the level of Silala Grande hill, the lavas
present a somewhat lined-up morphology, in an E-W direction, with a slight
inclination to the north. This lineament’s trace towards the east is dephased
dextrally by other transversal lineament that presents a NW-SE direction
(300°) near the Cerro Torito hill lava. Further to the east, in the vicinities
of the edge of the Pastos Grandes Caldera, the lineament crosses over the
Runtu Jarita tuffs, ignimbrite and domes, where apparently the lineament
seems to sinisterly displace the northern segment of the domes.
The aeromagnetic anomalies that are reduced to the local pole and the first
derivative of the BGM Airborne Survey (Map 6) underscore a magnetic
high from the Silala springs to the Pastos Grandes Caldera, with a loss in
the anomaly’s definition in the central part, close to Torito hill. In the area
where the Silala springs bear a certain influence, the lineament reaches
higher magnetic anomalies.
7.5.2.4 Runtu Jarita Lineament
This lineament crosses the eastern edge of the area surveyed, with a NW-SE
orientation (335°) adjusting to the general “trend” of the area. In turn, the
lineament adjusts to the occurrence of the Runtu Jarita dome, which is linedup
further to the north with the Chascon dome; apparently the lineament cuts
the southern part of Chascon dome. In the map of total magnetic intensity
(Map No. 6) high anomalies are observed; these coincide pro-parte with the
lineament until they reach the limits of the Chascon hill dome, where they
are truncated—according to the aeromantic data—with a negative anomaly.
7.6 Work methodology
The objective of this part of the survey is to identify the geological structures
related with the fractures of the area. Structural data on the joints, foliation
and faulting planes was obtained in the field to perform an analysis of fragile
deformation on basis of microstructural data. For this analysis, faulting
planes that present striations and are abundant in the area were preferably
surveyed. The limited data on striations was processed to deduce the force
fields that caused them, or the tension of paleo-stress linked with faulting,
as well as the kinematics of the structures produced during deformation. To
determine the displacing direction of the faults, kinematic indicators, such
as Riedel-type structures, striated surfaces and echelons, were used.
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As a result of the preliminary analysis and interpretation of structural data,
and on basis of the major kinematic features maps were prepared to visualize
the relation between fracturing and the presence of water sources identified
in the area surveyed.
7.6.1 Data processing
The data obtained in the field was processed using a database prepared in
an Excel sheet, recording the most relevant structural characteristics of
the faults and joints. The processed data was thereafter further processed
with the Rocscience DIPS 5.0 software (free version), which is a useful
program to analyze the orientation of spatial data through rose diagrams and
a stenographic network.
The input and storage data required by this program are: the dipping direction,
dipping, plunge direction (azimuth) and plunge for the fault striation. The
value for the dipping direction ranges from 0 to 359°, considering the
correction of magnetic inclination, which is currently of 6° to the W. The
dipping angle and plunge range between 0° and 89°, from the horizontal
plane. Where it was possible, the relative direction of displacement (normal,
inverse, dextral, sinistral) was also recorded for the faults. Additionally,
data on the frequency, form, thickness, openness, continuity, infilling and
presence of water was also recorded.
The ArcGis v.10.1 software was used to integrate the data on faults and
fractures and correlate them with the lineaments interpreted on basis of
satellite images.
To estimate the structural domains, or perform force analysis, the structural
elements are discriminated taking into account similar geological events and
are treated separately, projecting poles, planes and pitch directions.
7.6.2 Population analysis of fractures by sector
In order to simplify the correlation, analysis and interpretation of the
fracturing systems that form the database for the structural geological survey,
the area surveyed was divided into 11 sectors so that each sector groups the
outcroppings that present a similar lithology and approximate origin age.
In some of these sectors, the lithological features, fracturing intensity
and morphological characteristics of fractures that are similar were also
correlated.
The sectors that cover the areas surveyed are presented in Table No. 2 and
Figure No. 13
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Figure No. 13. Scheme for the sectors used to process structural data
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7.7 Fracture and discontinuity analysis
The relation between the fracture type and the lithological unit type defines
a fissure system that also determines the secondary permeability of the
sector. The morphology of the fractures presents additions factors that affect
porosity and, thus, the permeability of the lithological unit. In the structural
sector-based mapping, the fracture or discontinuity type were identified
collecting structural data and the morphological parameters of the fractures
(Table 3).
Table No. 3. Fracture parameters recorded
7.7.1 Nmse Sector – El Meson hill
This sector is located to the southern end of the third area. It comprises three
hills that extend from south to north, the Meson, Apacheta and Cerro Chico.
These are composed of dacitic, andesitic and trachyandesitic lava, of a dark
gray to brown color, a thick texture and tuffaceous enclaves of up to 5 cm.
The outcropping massifs present few fault planes that get confused between
joint and pseudo-stratification planes and fractures caused by weathering.
These massifs are intertwined and intersected and take the appearance of
disturbed blocks (Picture No. 21.).
Picture No. 21. Fractured massif outcrop of dacite lava, Meson hill
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7.7.1.1 Structures identified in Meson hill
To perform the structural analysis of this sector, 105 data grouped into three
subgroups was reproduced in fault and joint rose diagrams. To prevent a
limited number of fault populations, 15 inverse faults, 1 thrust fault and
1unidentified movement fault were grouped into a second subgroup; 38
normal faults and 50 joints were identified in the area.
7.7.1.1.1 Nmse Faults – El Meson hill
Most of the faults of this geological unit present a planar to undulated form,
with a continuity that exceeds the 10 m, with openings of 1 to 5 cm and a
rugose surface. The density for every 10 m is of 1.
Figure No. 14. a) Rose diagram for normal fault fracturing. Meson hill. b)
rose diagram for the fracturing of inverse faults
Figure No. 14 (a) presents the normal faults of the sector, which have a
NNE-SSW preferred direction. This trend is close to the N-S domain, which
is observed in the units located north of the area. The sector’s inverse faults
are represented in Figure (b). Given that this subgroup includes a thrust fault
and an unidentified movement fault, it can be concluded that the number
of normal structures is higher in a relation of 2 to 1 with respect to inverse
faults.
7.7.1.1.2 Meson hill joints
The features of the joint planes in the outcroppings of this sector are mostly
of a high-angle, discontinuous and planar to escalated. Rugosity is high
owing to their crystalline texture. The joints present openings, are unfilled
and do not contain humidity. Their frequency reached 1 to 2 fractures for
every meter.
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Figure No. 15. a) Rose diagram for the joints of Meson hill. b) pole diagram
and preferred plane for the fractures of Meson hill
The above Figure presents three preferred directions, i.e. NW-SE (120°-300°),
N-S and E-W, that coincide with the macrostructures of the region, suggesting
that there is a kinematic relation at the microstructural scale similar to that of
the macrostructural scale.
7.7.2 Silala ignimbrite sector (Nslt)
This sector is located in the ravine that is formed between the base of Inacaliri
and Silala Chico hills. It extends towards the NE, in an elongated and narrow
fashion, through the ravine upstream as far as the wetlands, from where it
further broadens forming a regular surface with a positive slope towards
the east. The rock outcroppings that are present in this sector correspond to
pyroclastic deposits formed in a sub-horizontal form. Most of these outcrops
present sub-vertical fractures that shape columnar forms with heights that reach
the 5 m (Picture No. 20) and conjugate with minor discontinuous fracture sets
that have greater inclinations.
To the east, these outcrops are highly weathered and present a foliation in the
form of highly fractured splints. The outcroppings where data was recorded
are dispersed mainly in the northern end of the sector. The ignimbrite presents
a massive structure, mild hardness and fracturing. Joints and faults in varied
directions can be observed in the thickness (Picture No. 22).
The fracturing density is determined by the amount of cooling joints,
rearrangement fractures and limited minor faults, which extend continuously
and intertwined. Generally, the fractures are closed and occasionally opened,
displaying a water flow. They are rugged, their continuity is variable and their
fracturing frequency ranges from 2 to 4 for every 10 m, on the side of the station
cell, which is why this rock massif is characterized as moderately fractured.
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Picture No. 22. Silala ignimbrite mantles, presenting fractures that cut the
outcropping levels. South side of the Silala ravine
7.7.2.1 Structures identified in the Silala ignimbrite sector
7.7.2.1.1 Faults of the Silala Ignimbrite sector
The faults identified in the Silala Ignimbrite sector, recorded in station
points, reached a total amount of 185, comprising 85 normal faults, 26
inverse faults, 11 lateral faults and 63 faults that don’t present kinematic
displacement. The relative movement of these faults present displacements
of a few centimeters that are mostly caused by gravity-triggered landslides.
It is not possible to identify the direction of these striations in the fault planes
to differentiate the events that occurred in the sector.
A structural analysis was carried out with additional data to process and
produce a rose diagram for the fractures, ensuring that the data represents
the structural domains of the unit to correlate them at a macrostructural level
with faults and lineaments defined on basis of the satellite image analysis.
Figure No. 16 a) presents the rose diagram for the fracturing of normal
faults (n = 85) that compose the first subgroup of fractures measured in the
Silala ignimbrite sector, which have NW-SE (125°-305°), N-S (175°-355°),
NE-SW (35°-215°) orientations. Figure No. 16 b) presents a stenographic
projection of inverse faults (n = 26) that conform the second subgroup of
fractures measured in this sector, which have NE-SW (55°-235°) and NW
(325°-145°) orientations. The number recorded for this trend is to the number
of normal faults, which leads to the tentative conclusion that distension
forces are predominant in the area.
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Figure No. 16. a) Rose diagram for normal fault fracturing, Silala ignimbrite;
b) rose diagram representing inverse fault fractures, Silala ignimbrite
Picture No. 23. a) Lower angle inverse fault; b) Block sunken between normal
faults; 15 cm displacement; c) Block found between a normal fault and an
inverse fault; d) Fractured block with a regular centimetric displacement
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The frequency of the normal faults of the first trend (NW-SE, 125°-305°)
presents an immediate directional relation with the Inacaliri graben traces
(NW-SE, 300°), which is found to the north of the area. Another trend (N-S)
represented in the normal fault rose diagram is less frequent and presents a
relation with the N-S lineaments that are parallel to Linzor stratovolcanoes
and to others that have a shorter length to the south and center of the area.
7.7.2.1.2 Silala ignimbrite joints
These joints present the characteristics of planar forms, are continuous
and surpass the 5 m, displaying a frequency of 10 to 15 joints every 10 m.
They prevail in the whole ravine (Picture No. 23). The openings range from
millimetric to centimetric (occasionally reaching the 20 cm).
Most of these joints do not present any type of infilling. The joints that
present clay infilling millimetric separations are of a reduced percentage.
Wall thickness is two-type, i.e. walls formed by cooling are smooth and those
that are formed by stress present moderate rugosity. Water and humidity are
only present to the north of the ravine, from the latter’s forking onwards.
Figure No. 17. a) Rose diagram for contours; b) rose diagram for jointing
planes in the Silala ignimbrite sector (n = 637)
Figure No. 17 a) represents the contour diagram produced on basis of the
jointing population. A joint family of a lesser frequency, a NW-SE (125°-
305°) and prevailing sub-vertical dipping have also been identified. Based
on 637 planes measured in fixed points, the rose diagram for the joints
of the Silala ignimbrite sector also contain joints formed by cooling and
weathering, which causes the direction frequency to be chaotic.
Most of the joints formed by cooling present a predominant direction that is
similar to that of normal faults (NW-SE, 305°), which was directly related
with the Inacaliri Graben’s structure (Tibaldi et.al. op. cit) and the regional
lineaments that present similar direction.
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7.7.3 Silala Chico hill sector (NsII)
This mapped sector is located on the top of Silala Chico hill and extends
longitudinally towards that hill, with fixed data collection points distributed
as a function of the outcroppings found. Silala Chico hill is composed of
dacitic, porphiric and pseudo-stratified lava, formed in dark-gray to light
brown blocks.
7.7.3.1 Structures identified in Silala Chico hill
The structures mostly observed correspond to jointing caused by cooling.
These are transversal to the flow direction.
7.7.3.1.1 Silala Chico hill faults and joints
The faults found and identified for their classification are reduced in number
and, thus, comprise a small percentage of the massif’s total fractures; these
bear little incidence on the global direction of the fracturing observed in the
pole projection and contour diagram (Figure No. 18 a) and b)) constituted
by: normal faults (2), inverse faults (2), lateral faults (1) and joints (79).
The distribution of fixed points and amount of data collected within the area
are precarious. For the analysis of structural domain, faults and joints are
assumed as representing a single group of the unit’s global fractures.
Figure No. 18. a) Rose diagram of the fractures of Silala Chico; b) pole
diagram for the Silala Chico fractures
Figure No. 18 a) and b) presents the dispersion of the fault’s plane poles
projected in a rose diagram for the fractures, representing the varied frequency
and trends without defining a clear domain. The diagram of percentage
contours presents the domain planes for the fractures of the Silala Chico.
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The three direction trends are:
- NE-SW (45°-225°)
- NWN-SES (160°-240°)
- NW-SE (130°-310°)
The joints generally present planar shapes. Most of them have a continuity
that surpasses the 5 meters, and persist between 2 to 6 fractures every 10
meters. The opening of these fractures ranges from millimetric to centimetric
(20 cm).
Most of the joints do not present infilling. The rugosity observed in the
fractures’ plane differs relatively between JRC from 8 to 10 (Hoek, 2007),
corresponding to a moderate rugosity. Water or humidity are not present in
the fractures measured. All these fractures correspond to andesite lava rock,
with hardness of R4-R5 (hard to very hard rock).
7.7.4 Negro Hill sector (Ncnd)
This sector corresponds to the areas that surround Negro hill, north of the
third area. It comprises lava domes to the NE of its base. Its composition is
dacitic, porphiric, pseudo-stratified formed on dark gray light brown blocks.
7.7.4.1 Structures identified in Negro Hill
The majority of the structures correspond to joints formed by thermal
contraction during the cooling phase and generally present a bedding that
is transversal to block foliation. The tectonic joints are hard to differentiate
from the fractures produced by weathering and can be recognized by the
continuity in the massif.
7.7.4.1.1 Faults and Joints of Negro Hill
The faults found and identified for their classification are reduced in number
and thus represent a small percentage of total fractures of the massif. They
have a reduced incidence on the global fracturing direction that can be
observed in the pole projection and contour diagram (Figure No. 19a and
19b). These are constituted by normal faults (9), inverse faults (0), lateral
faults (1), joints (191) and unclassified faults (10).
The distribution of fixed points and amount of data collected from the area
are precarious; as a result, faults and joints were assumed as a single group
for the global fractures to complete the analysis of structural domains.
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Figure No. 19. a) Rose diagram for the fractures of Negro hill; b) Pole
diagram of the fractures of negro hill
The above figure represents the pole dispersion of the fault planes projected
in the rose diagram of fractures, placing in evidence a high frequency of
fractures that have a NE-SW trend. The diagram of percentage contours
presents, in a particular way, the general direction preference in the fracture
planes of Negro Hill, the domain of which is NE-SW (50°-230°).
The joints generally present planar to stepped forms. Most of them have a
continuity that surpasses the 5 meters and persists between 1 and 2 fractures
every 10 meters. The opening of these fractures ranges from millimetric to
centimetric, reaching the 40 cm.
Most of these joints do not present infilling. The rugosity that can be
observed in the fracture planes differs relatively between JRC from 4 to 8
(Hoek, 2007), which corresponds to moderate rugosity. There is no water
or humidity in the fractures measured. All these fractures correspond to the
dacitic lava rock-type, with a hardness that ranges between R4 to R5 (hard
rock to very hard rock).
7.7.5 Inacaliri Lavas sector (Ninl)
The Inacaliri Lavas display small outcrops as lithological windows that
date back to 5.84 Myr on the southern flank of the Inacaliri hill; these are
composed of crystalline coarse-grain dacitic lavas, which form foliate blocks
that have the appearance of small boards and present a brownish-grayish
coloration.
7.7.5.1 Structures identified in the Inacaliri lavas
This sector is characteristic of pseudo-stratification planes that can be
observed throughout the outcropping massif. The faults and joints are
presented transversally, with a high angle and present a continuity that
surpasses the 20 m. The morphometric features of the fault planes are similar
in all structures.
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Picture No. 24. Inacaliri lava outcrops, presenting sectioned by normal
transversal faults. Southern flank of the Inacaliri hill
7.7.5.1.1 Faults and joints of the Inacaliri lavas
Owing to the reduced amount of structures in this sector, it was deemed
convenient to make the global analysis of the structures (faults) without a
prior classification, preparing a rose diagram for the fractures to determine
the major trends of the sector. Another subgroup is composed by joint planes,
which configure a field of approximate stresses.
Figure No. 20. a) Rose diagram for the fractures of Inacaliri lavas; b) rose
diagram of the joints of Inacaliri lava
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The faults found in this sector are continuous, and have a planar to bended
form, with openings of a few centimeters. Their rugosity is high and are
present every 1 to 2 meters. They present no infilling and do not contain
water.
Figure No. 20 a) presents the rose diagram for total fracturing, with a
representation of undifferentiated faults. These fractures present a NE-SW
trend (40°-70°), which has a connection with the NEE-SWW lineaments—
determined in the macrostructural lineament and fault map. A second
preferred direction is NWW-SEE and presents a fewer amount of relevant
faults.
The joint sets (Figure No. 20 b) of this sector define a similar trend,
approximating to an E-W (125°-305°) preferred direction. A second joint set
with a NW-SE (125°-305°) can also be identified, reaffirming the directional
control in the fault set.
7.7.6 Torito Lava Volcano (Ntol)
The Torito lava sector comprises the Meson Bayo Lomas, Torito, Colorado,
Pabelloncito, Pajonal, Chanca Loma and Bayo hills, which are dispersed
and lined up with the western edge of Pastos Grandes Caldera; to the north,
it is found between Chascon and Negro hill. The south end, begins 1.4 km to
the east of the entry to the Silala springs.
The volcanic body exposed is apparently related with the lava domes, which
have a dacitic composition, with plagioclase crystals, feldspars, quartz and
biotite in a dark greenish gray matrix. It forms in pseudo-stratified lavas of
a massive appearance piled up by blocks.
The lava outcrops of the Torito hills present structures formed by the cooling
of volcanic material, joints and some faults, which are an indication of a
fragile regime. The holocrystalline-crystalline textures form continuous
fractures of an undulated-to-stepped shape that present centrimetrical
openings with rugose surfaces. These are occasionally infilled by coarse
sands, but are generally not infilled and do not present humidity. The 10 m
lineal frequency reaches 2 fractures. The pseudo-stratification planes present
closed, continuous and apparently shallow junctions, the frequency of which
reaches the 8 junctions per lineal meter.
Another structural element of relevance for the frequency are pseudostratification
planes that are displaced in a localized fashion in the area.
They present laminar structures that are intersected by joints (Picture No.
25). These laminations represent the lava flow direction. They present
continuous and discontinuous planar forms and pronounced openings on
the weathering surface, which close up a few millimeters towards the massif
body and repeat 7 times per meter transversally to their planes and do not
present humidity. This structural data is related with the massif’s fracturing
level and secondary porosity. Thus, this data cannot be used for an analysis
of the structures or stresses of the area.
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Picture No. 25. Joints that cut the pseudo-stratification planes of the Torito
hill lavas
7.7.6.1 Structures identified in the Torito hill lavas
Two-hundred eighty-three structural data pieces on the lava were recorded
in this area; these include 234 joints, 18 normal faults, 32 faults. Structural
data of the pseudo-stratification planes was also recorded.
7.7.6.1.1 Faults of the Torito hill lava
The fractures are dry and present average 4-cm openings. This sector
contains both open fractures that are not infilled and fractures infilled with
coarse sand. Most structures present direction trends analyzed in the rose
diagrams. The reduced number of the faults found in the outcrops of the
area require that the structures be analyzed taking into account three fracture
subgroups composed by:
1. Normal faults
2. Inverse faults, right-lateral faults, left-lateral faults and faults in
which movement types were not identified
3. Joints
Due to the scarce amount of fault data collected for the area, the normal
fault planes, inverse faults and unclassified faults are regarded sufficient for
the analysis of domains, or forces, which is why the projection of poles and
planes is presented in concert so the directions and dips can be better appreciated.
The preferred direction of these faults, among which those that
are unclassified predominate, are presented in the rose diagram prepared
for the fractures (Figure No. 21).
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Figure No. 21. a) Rose diagram representing the fractures of normal faults
of Torito hill; b) Rose diagram representing inverse faults, lateral faults and
unclassified faults
7.7.6.1.2 Torito hill joints
The rock type of the sector differentiates the joints found in other sectors
and present stepped and undulated, discontinuous and continuous, rugose to
very rugose forms. Their openings are centimetric and are infilled by coarse
sands. Their persistence is changeable. Many of these forms are caused by
physical weathering, while a great number of the others correspond to joints
formed by transversal cooling of lava blocks.
Figure No. 22. a) Rose diagram representing the Torito hill joints; b) rose
diagram of poles, preferred planes and joints of Torito hill
The joints of Torito hill present a major NWW-SEE trend and a secondary
NE-SW fracture trend. A great number of the joints correspond to fractures
formed by the cooling of lava.
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7.7.7 North and South Pastos Grandes Tuffs
This sector corresponds to an extensive area that covers the Altiplano and
surrounds the edge of Pastos Grandes Caldera, from the southern limit of
the 3rd area to the northern and western limit of the major area. The rock
outcrops are dispersed towards the edges of this unit and the interior of the
ravines. They generally present tuff columns that reach the 8m of height.
These have a whitish-gray coloration (Picture No. 26 a), with brownish
tones, and are formed on mantles that have sub-horizontal contact [bedding]
planes. Their structure presents lithic fragments that correspond to dacite.
Pumice of up to 12 cm in diameter can be observed gradually ascending
towards the top.
Picture No. 26. a) Tuff outcrops in South Pastos Grandes; b) joint planes that
form fractured structures and contain thrust planes
The orientation and inclination dataset obtained in these stations is reduced
(n=31) owing to the repetition of planes in the cooling joints. However,
normal and inverse faults, together with jointing caused by stress, have also
been identified and are relevant for the interpretation carried out.
These inverse faults present a displacement of up to 10 cm and form a low
angle with the horizontal, which evidences thrusting of tuff mantles at a
low scale and demarcates local kinetics related with the regional structure
(Picture No. 26 b).
7.7.7.1 Structures identified in the Pastos Grandes Tuff
For the analysis of fault and joint data collected at great scale, two sectors
were divided, i.e. South and North, and normal and inverse faults, along
with joints, are represented in rose diagrams. The data that is reduced in
number is not significantly representative for the population of fractures
in area, nevertheless, it is sufficient to observe the preferred directions in
relation to major scale lineaments.
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7.7.7.1.1 North and South Pastos Grandes Tuff
Figure No. 23. a) Rose diagram representing the normal faults of North
Pastos Grandes; b) rose diagram representing the inverse faults of North
Pastos Grandes
The trends of this sector are different. The normal faults present a WWNEES
preferred direction (100°-280°). The inverse faults present variable
directions. A general trend for the sector has not been defined, which is why
the preferred direction considered will be that obtained as a result of the
normal fault plotting.
Figure No. 24. a) Rose diagram representing the normal faults of South
Pastos Grandes; b) rose diagram representing the inverse faults of South
Pastos Grandes
The above figure presents clear trends. The normal faults have a preferred
N-S direction and the inverse faults, which are reduced in number, have a
W-E preferred direction.
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7.7.7.1.2 Joints of the North and South Pastos Grandes Tuff
Fracturing caused by joints in these tuffs is predominant. The joints are flat,
almost smooth, continuous, contain no water and have openings that are
smaller than 1 cm. They do not present any infilling, and some of the joints
are even closed.
Figure No. 25. a) Rose diagram for the North Pastos Grandes joints; b) rose
diagram for the jointing of South Pastos Grandes
The major trend in the south sector follows a W-E direction, while the
secondary one presents a N-S to NE-SW direction. These domains are
similar in the north sector, the only difference being that they have an hourly
rotation of up to the 20°. The general fracture direction is, nevertheless,
E-W.
7.7.8 Cahuana hill sector (Qlie)
The structural data collected in Cahuana hill also correspond to the body of
the stratovolcano that conforms the hill, which is located in the prolongation
of the volcanic chain to the south of Silala hill, as part of the Linzor
stratovolcanoes, with a composition that is similar to that of the Silala Grande
hill. It presents dacitic, andesitic and trachyandesite lavas, with massive and
banded textures. They present a NE lava flow direction.
7.7.8.1 Structures identified in Cahuana hill
The structural dataset measured in Cahuana hill reaches a total of 76
particulars, i.e. 14 normal faults, 10 inverse faults, 10 unclassified faults, 1
lateral fault and 41 joints.
The reduced amount of structures requires that the structures be treated in
two subgroups, the first one of which is formed by normal, inverse, strikeslip
and unclassified fault planes, inasmuch as these are produced by tectonic
stress. The second subgroup corresponds to joints that generally include
cooling surfaces and occasionally weathering surfaces.
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7.7.8.1.1 Cahuana hill faults
The faults that were generally identified present displacement of a few
centimeters, without exceeding the 10 cm on flat surfaces of nearly vertical
to moderate angles. Most of these faults are represented in undulated and
stepped forms, with a limited continuity and centimetric openings. They
do not present any infilling. The dacite and andesite present hardness that
ranges from high to very high. The rugosity of the fault planes is high. Just
like in other places, the fault planes do not show traces of striation directions
that might help differentiate the events that took place in this sector.
Figure No. 26. a) Rose diagram for the fracturing of Cahuana hill; b) rose
diagram for the jointing of Cahuana hill
The major macrostructural trend found in this sector reaffirms the E-W
direction structural domain that can be observed in other sectors. The
secondary trend approximates the N-S direction, and is lined up with the
occurrence of volcanic bodies.
7.7.8.1.2 Cahuana hill joints
The composition of the rock outcrops of Cahuana hill has led to the conclusion
that the joints present characteristics that are similar to those of the Silala
Grande hill lava, with undulated, stepped, continuous and rugose planes,
mainly arranged transversally to the flow fronts, with centimetric openings
that do not present infilling or humidity. These planes can be observed with
a certain frequency in weathered outcrops.
The preferred jointing direction is NW-SE (155°-335°) and coincides with
the second fracture trend measured in this hill. Likewise, the dip faults range
from high to moderate. Fractures formed by cooling can be distinguished in
a sub-vertical position transversally to the pseudo-stratified blocks.
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7.7.9 Silala Grande sector (Qlie)
The structural data collected in Silala Grande hill correspond to the inactive
stratovolcano found on a base of 41 km2 and composed of massive and
banded dacitic and andesitic lava, brecciated on the base. These flowed to
the NW-N-NE and reached a distance of up to 5.5 km.
These lavas present sub-horizontal banding, of a light gray to dark gray
coloration, indicating the flow direction. These form rock outcrops composed
of massive flows that conform a structure in blocks and are dispersed,
occasionally presenting flow folding (Picture No. 27 b) in elongated and
convex forms, corresponding to the flow front. In most of the surface, these
flows are covered with colluvial deposits.
These fronts formed in blocks are mildly weathered and form fractured
scarplets that reach 3 m in height. They frequently present a vertical form
transversally to the block, owing to cooling effects. It is also possible to
observe pseudo-stratification planes that form open discontinuities. The
density of the joints is higher in relation to pseudo-stratification planes and
the faults identified.
Picture No. 27. a) Flow front of outcropping lava in blocks; b) morphology
of the factures in dacitic lava; c) banding folds caused by lava flow; d)
porphiric tails, a kinematic indicator of dextral shear stress
Elongated tails are observable in the brownish-reddish porphyroclast. This
indicator of block movement evidences that the simple sheer stress of a
right-lateral direction and high deformation had an effect on the rock massif,
causing rotation and dragging the porphyroclast’s re-crystalized tails.
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7.7.9.1 Structures identified in Silala Grande hill
7.7.9.1.1 Faults of the Silala Grande hill
Fifty-nine faults were observed in this sector, comprising 30 normal faults,
6 inverse faults, and 23 displacement faults that do not present kinematics.
The normal faults identified present displacements of a few centimeters
only—not exceeding the 10 cm—and have flat and discontinuous forms,
with centimetric openings. They do not present infilling. The dacite and andesite
have a rock hardness that ranges from high to very high. The fault
planes do not show evidence of an striation direction that might help differentiate
the events that took place in this sector.
Figure No. 27. a) Rose diagram of normal fracturing faults; b) rose diagram
of reverse fault fracturing, Silala Grande
The above representation of normal faults presents two preferred directions,
i.e. NEE-SWW (70°-250°) and N-S. The first trend presents a slight hourly
rotation (20°) with respect to the trends determined in the Silala ignimbrite
sector, given that fault frequency is smaller in number. The second trend
concurs with the direction determined in the Silala ignimbrite sector and the
macrostructural lineaments.
The above figure presents the pole density diagram and establishes the preferential
plane of faults with a predominant direction of NE-SW (40°-220°).
The poles and planes plotted belong to inverse faults (6) and faults that do
not present any identified movement type (26), which are grouped together
owing to the absence of frequency of reverse faults.
Other discontinuities present in this unit are pseudo-stratification planes
formed by the foliation of lava (Picture No. 28).
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Picture No. 28. Normal fault cutting the pseudo-stratification planes of the
lavas. Northern flank of Silala Grande hill
7.7.9.1.2 Joints of the Silala Grande Lavas
These joints present mostly discontinuous planar surfaces. They persist between
3 to 5 fractures every 10 meters. The openings that can be observed
range from millimetric to centimetric (25 cm).
The majority of these joints don’t present any type of infilling. The rugosity
observed in the fracture plane differs relatively between JRC from 8 to 12
(Hoek, 2007), corresponding to moderate rugosity. It was not possible to
observe water in the fractures, nevertheless, there were fractures where humidity
and certain contents of water were observed, possibly owing to the
presence of snow and to the fact that thawing creates an apparent humidity
in the fractures.
Figure No. 28. a) Rose diagram of jointing in the Silala Grande hill; b) Pole
frequency diagram presenting the joints of the Silala Grande hill
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Based on the 257 planes measured in each fixed station, it has been established
that the joints have a N-S and NE-SW (55°-235°) predominant direction,
with a general mean dip of 70°. The poles that are less frequent and
present disarranged dips correspond to joints that are transversal to the lava
flow direction, which are arranged in the form of blocks and have a variable
direction that is a function of the slope of the stratovolcano.
7.7.10 Inacaliri hill sector (Qlie)
So as to differentiate the data collection in accordance with the lithological
differences that pertain to this stratovolcano, this sector was divided into two
subsectors:
• Eastern Inacaliri hill (Qlie). This sector corresponds to the lenticular lava
flow body and has a NW-SE flow direction, covering a great proportion of
the Silala ignimbrite towards the bottom of the valley. Its composition corresponds
to porphiric dacite of vitreous texture and andesite of a trachytic
texture, with dark gray vesiculated coloration and a presence of plagioclase,
forming flow front structures in blocks (Picture No. 29 a).
• Western Inacaliri hill (Qlie). This sector corresponds to the highest past of
Inacaliri hill. It is composed of dacite and andesite of a vitreous aphanitic
texture and dark gray coloration. These are arranged on lava flow mantles
and superposed volcanic breccia and extend as far as the volcano’s crater
(Picture No. 29 b).
Picture No. 29. a) Sheared outcrops of Eastern Inacaliri hill (Qlie); b) Joint
planes that form fractured columns in the Eastern Inacaliri hill (Qlie)
The structural dataset prepared as a result of the tectonic forces that were
recorded in these stations is reduced in number. Owing to the nature of the
lithological unit, the fault planes are confused with the thermic jointing
planes, which are arranged in a chaotic manner—a common feature of flow
front blocks.
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7.7.10.1 Structures identified
• Eastern Inacaliri hill (Qlie)
The structures registered in the flow front correspond almost in their entirety
to flow front blocks, where the fracturing density is the result of jointing
transversal to the massif, displaying high angles. These merge with pseudostratification
planes, forming a chaotic fracturing.
• Western Inacaliri hill (Qlie)
The few rock outcrops found in the higher part of the stratovolcano are hard
to access inasmuch as they are surrounded by rocky ground [sallerios] that
present a steep slope. These are also displayed as rocky peaks that can reach
several meters of height. The data was collected from the face of the outcrops.
7.7.10.1.1 Inacaliri hill faults (Qlie)
Figure No. 29. a) Rose diagram of the fractures of Eastern Inacaliri hill; b)
rose diagram of the jointing of Eastern Inacaliri hill
The whole set of faults are too few to carry out a trend analysis. The joints,
on the other hand, present a significant amount of fractures, though a preferential
direction cannot be distinguished clearly given that their chaotic
arrangement.
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Figure No. 30. a) Rose diagram of normal fault fractures of western Inacaliri
hill; b) rose diagram of inverse, unclassified and strike-slip faults of the
Western Inacaliri hill
The preferential trends of this sector are different, inasmuch as the normal
faults present a WWN-EES (100°-280°) preferred direction. The inverse
faults in this sector display variable directions and do not define a general
trend; thus, the preferred direction taken into account will be that obtained
from the plotting of normal faults.
7.7.10.1.2 Western Inacaliri hill joints (Qlie)
Unlike the direction of the Eastern Inacaliri joints (Qlie), where a chaotic
arrangement was observed, the joints measured in this sector display a
significant proximity in its preferred direction (Figure No. 32).
Figure No. 31. Rose diagram for the jointing of Western Inacaliri hill
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The Western Inacaliri sector (Qlie C) displays a NNE-SSW (20°-200°)
major trend direction. The secondary trend displays a W-E direction, which
coincides with the trends defined in other sectors.
7.8 Microstructural analysis of the fault population
As a result of an assessment of the results obtained from the field and clerical
works performed for the sectors covered in the project, a representative area
was selected to perform a microstructural analysis that contains the data
necessary for a process of stress calculation. That the sector had to contain
data on the fractures of the same lithological unit and bear a close relation
with the trace of specific microstructural faults was deemed important for
the analysis. It was within these criteria that the area found in the southern
flank of the south ravine of the Silala wetlands was selected, inasmuch as it
is in this area that the ravine shifts its direction from SW to NW, following
the ravine’s slope (Figure No. 33). A microstructural survey at a scale of
1:250 was completed in the area chosen, using a 10 x 10 grid in orthogonal
directions that coincide to the north and east of the sector. The starting point
corresponds to the 601501 E and 7566222 N coordinates.
The area comprises 81 structural data, which contain:
• Six normal faults (2 striations)
• Three inverse faults (2 striations)
• Two unclassified faults
• Seventy joints
The methodology employed for this analysis was the Right Dihedral
Method, which is broadly accepted and adjusts to kinematic models for fault
population analyses. The area selected does not present a significant number
of faults to pinpoint a pitch direction, however, owing to the pyroclastic
deposits medium, this area is the one that contains the largest number
of faults with kinetics that can be reconciled in relation with the surface
analyzed, as compared to other sectors found within the 3 areas studied.
The paleostress tensor was derived from the abovementioned Right Dihedral
Method, which bears a certain similarity with the calculation of the focal
mechanisms of earthquakes; with a supplementary plane perpendicularly to
the displacement striation, the region is divided into four right dihedrals
around a fault. The major stress (σ1) is contained in the compression
dihedrals, while the minor one (σ3) is contained in the extension dihedrals.
The superposition of compression and extension dihedrals of all the faults
of a specific population defines the most probable direction of σ1 and σ3,
respectively. The application calculates, for each of the direction spaces,
the percentage of faults included in the dihedral of extension; the maximum
value corresponds to the optimal position of the extension axis and the
minimal to that of the compression axis. According to “The Analysis Methods
of Paleostress based on Fault Population: Systematics and Application
Techniques” (Casa et. al., 1990), the rationale to use this method is that it
enables a fast observation of the approximate orientation of the stress axes
likely to explain the set of analyzed faults.
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Figure No. 32. Microstructural analysis of stresses in the east flank and south
sector of the Silala springs
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The major problem connected with this method has to do with the impossibility
of separating compatible faults from tensors of different stresses (Casa
et. al. op. cit.).
The analysis of right dihedrals resulted in the finding of stress dihedral
D1 (Figure 32), which marks the direction of the main stresses σ1 NW-SE
(295°), σ3 NE-SE (35°); to this, the data of the area mapped, where the largest
number of normal faults was found, is added, allowing the deduction of
a field of distension stresses, which is coherent with the extension directions
of the faults mapped. This field also lines up with the direction shift of the ravine,
suggesting that there is a normal fault that extends with the depth. This
distension forms vertical structures that shape the sector’s relief.
Regarding the structural geological history, it is essential to state that the
distention stress σ3 was activated after the compressive efforts, configuring
the ground with normal small-scale faults.
7.9 Relation between faulting and volcanism
The Central Volcanic Belt is characterized by eruptive centers that are mainly
lined up throughout a NW-SE corridor, which is crosswise to the major N-S
orientation of this part of the Andean Volcanic Arc. Most of the stratovolcanoes
from the Late Miocene are clearly lined up with a NW-SE orientation.
These fractures of a NW-SE direction are likely to have exerted tectonic control
over the distribution of volcanic centers, which are crosswise to the general
pattern of volcanism in this part of the Andes (de Silva et. al. 1994). The
region is, thus, important to understand the structure of the Central Andean
Chain, as well as the relation between tectonics and volcanism, which is in
turn important inasmuch as they concern volcanoes that have a strong explosive
activity. The structures that have a NW direction were created when the
volcanic arc was formed. Many of the volcanoes of the Pliocene are spread
throughout the area; in the central and southern parts of the area, they display
a clear lined-up NW-SE direction. The stratovolcanoes of the Late Pliocene-
Pleistocene concentrate in the south of the area, where they are lined up in a
NE-SE direction in the north and in a N-S direction in the south.
7.10 Relation between the fracturing and the water regime
It is clear that, owing to their tectonic and volcanic activities, fracturing is
potentially adequate for water-flow transport and circulation. This relation
leads to the postulate that the Silala-Llancor lineament—which has an ENEWSW
(70°) orientation—behaves as a left-lateral fault, which crosses the
central part of the area, coinciding pro-parte with the Silala springs’ canal,
passing between the Silala ignimbrite and the Silala Grande hill lavas. An
analysis of the Silala hill level indicates that the lavas present a somewhat
abrupt morphology, lined up with a general E-W orientation and an inclination
to the north (45°). In the absence of kinematic field evidence, but bearing
in mind the secondary fracturing that develops in the sectors that are
adjacent to the structure, it is possible to assume that the structure presents a
transtensional character (Figures Nos. 33 and 34).
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The fracturing measured in the Torito hill lava has a NE-SW (15° to 35°)
orientation and behaves as tension fractures arranged crosswise to a fault
that has an angle inferior to 35°. The fracturing corresponds to the general
jointing of the sector and the sporadic faults that present reduced displacement.
In the Silala Grande hill, tension fractures are represented by short
lineal segments that follow the same direction, which is clearly visible in
the satellite image below and is demarcated by the rectilinear limits of tone
variations that can be observed. At the level of the outcrops, the apparently
dextral shears affect the lavas, sustaining the sinistral character of the structure
(Picture No. 30).
Figure No. 33. Structural scheme of the Silala-Llancor Lineament
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Figure No. 34. 3D Structural scheme of the Silala-Llancor Lineament
Picture No. 30. Dextral shearing in the Silala Grande hill
In general, the field observations and interpretation of structural data have
led to the following considerations:
The sporadic presence of a thin film of calcite in some fractures (Picture
No. 31) and the occurrence of banded chalcedony elements, with a globular
habit and little transport, accumulated surrounding the Silala-Llancor fault
trace, seem to indicate that an intense circulation of fluids occurs throughout
deep fractures. These flows are mainly produced by a combination of deep
peri-volcanic hydro-thermal fluids, which could be an indication of a recent
tectonic activity.
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The deep fluids move to the surface through fractured zones, mixing up on
their way with weathered waters until they reach the fault, which is fit for
lateral flow and serves as the preferred path for the migration of deep fluids.
To the east of the area, the Silala-Llancor fault coincides with the wetlands
and springs of the Pastos Grandes Caldera; the mean altitude of these springs
is 4,500 MASL. To the west, the fault reaches the limits of the Silala (4,300
MASL). The unevenness of the terrain seems to contribute to the lateral
migration of fluids towards the area that is topographically lower.
Finally, the interrelation between the kinematics of the reduced number of
faults under the current stress field apparently causes a displacement that
also affects the jointing, creating, in given sectors of the area, openings in
some corners and closures in others, namely, producing compressional and
dilatational syntaxes. The water sources well up in the intersection of open
joints, throughout certain NW-SE transversal faults and in their intersection
with semi-vertical joints.
Picture No. 31. Joint plain infilled with calcite in the fractures of the Inacaliri
lava
7.11 Conclusions
The fracturing system displays predominant structural trends, i.e. the first
and major system presents a NE-SW
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general trend (40°-70°) and displays discontinuous and shorter features that
are well represented in the south and north sector of the area—this is where
the Uyuni-Khenayani fault system is included. The second system has a
NW-SE longitudinal direction (100°-400°); the main volcanic centers of the
area coincide with this system, which is more frequent and continuous in
the northwest and northeast sector of the area. A third structural system,
presenting a N-S general trend (340°-360°) is found to the south of the area;
some volcanic cones are lined up in this direction.
The most intense fracturing is found throughout the Silala springs, where
ignimbrites are more exposed (up to 2 fractures per meter). It must be noted
that in a complex aquifer of fractured rocks, the permeability and porosity
of a lithological unit are composed of a network of fractures, discontinuities,
block matrixes, open continuities and fracture infilling. These characteristics
define the Silala ignimbrite as the component that generates the most
secondary porosity, owing to the continuity, opening and flat-smooth form
of their fractures.
The fracturing and faulting observed in the dacitic and andesitic lava of the area
are not representative of the area, because they are considered discontinuous.
The fracturing directions measured at the level of microstructures clearly
respond to the regional fracturing, inasmuch as the same NE-SW, NW-SE
and N-S trend structures, which coincide with the main reduced fault and
fracture systems of the area, can be observed.
Though it is possible to observe some morphological evidence characterized
by almost vertical planes and inclinations approximate to the 45°, the
faults are not really visible in the field. Many of the faults, owing to their
cartography, are minor and shallow. The fractures generally present a semivertical
geometry in all their lithological units, ranging from the 70° to 90°.
The Silala-Llancor lineament—which has an ENE-WSW (75°) orientation
that coincides pro-parte with the South Canal of the Silala springs—is
modeled in the middle of the Silala ignimbrite and the Silala Grande hill
lava. Its E-direction trace is arranged dextrally by a transversal NW-direction
(300°) trace, at the level of the Torito hill lavas.
If the lineament is regarded as a lateral sinistral (strike-slip) fault, the trace
of which would be located in the vicinity of the Silala springs, the fracture
variation or orientation shift from NW-SE (Silala ignimbrite) to NE-SW
(Silala Grande hill lavas) might be related with that structure; in theory, the
former orientation would present sinistral kinematics and the latter dextral
kinematics. This variation in the kinematics, which is unexplainable for
the time being owing to the absence of evidence of subsequent successive
tectonic events, might have some influence on the origin of the canals formed
by the Silala waters.
The NW-SE (3.5 km of width) orientation graben structure would apparently
prolong to 2 km to the north of the Silala wetlands; a priori, the distensive
nature of the structures the traces of which involve the jointed ignimbrite
of Silala with an agglomerate on its basal part, constitute a favorable
environment for the transport and circulation of fluids.
A WSW-ENE distension direction stress field was determined in the field
for the ignimbrite and lava. This is assumed to be related with a deformation
event subsequent to the Pliocene—the Pleistocene perhaps—that is older
than the Inacaliri lava.
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Finally, a table-summary presenting the first and second order trends,
together with rose diagrams for the fractures of the different sectors, are
presented:
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109
8. BIBLIOGRAPHY
Aranibar O. and Martinez E., 1990, Structural Interpretation of the Altiplano,
Bolivia. Final work: Structure and Evolution of the Atlas Mountain System
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Chile, Southern Bolivia and Northwestern Argentina. Abstract Volume,
Berlin, p. 47
Arezo Marcos, 2013, (SATELLITE REMOTE SENSORS IN THE
MEASUREMENT OF ENVIRONMENTAL IMPACT IN MINING, Master
in Spatial Applications of Early Warning and Response to Emergencies).
Argollo J. and Iriondo, 1991, The Quaternary of Bolivia and Neighboring
Regions.
Argollo J. et al., 1987, Plio-quaternary Geology of Bolivia. Unpublished.
Argollo J. and Mourguiart P., 1995, Quaternary Climates in South America,
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Baby P., Sempere T., Oller J., Barrios L., Herail G., 1990, The Southern
Altiplano of Bolivia: An Oligo-Miocene Intermontane Foreland Basin. Final
work: Structure and Evolution of the Atlas Mountain System in Morocco and
Structure and Evolution of the Central Andes in Northern Chile, Southern
Bolivia and Northwestern Argentina. Abstract Volume, Berlin, p. 69
Cas R. A. F. and Wright J. V., 1992, Volcanic Successions. Modern and
Ancient. Ed. Chapman & Hall, p. 528
Casa, A. M., Gil, I., and Simon, J. 1990, Analysis Methods of Paleo-Efforts
based on Fault Populations: Systematics and Application Techniques.
Geological studies, p. 385-398.
Cepeda, H., Acevedo A. P. 1982, The Sotara volcano: geology and
geochemistry of major elements, p. 19-30.
Chuvieco E. Emilio, 2002, Fundamentals of Space Remote Sensing, Second
Edition RIALP Editions. S.A. Madrid (p. 449).
Conesa, Alvarez, Martinez, 2004, Environment, Resources and Natural
Risks—Analysis by Sig technologies and remote sensing Vol. II—University
of Murcia, (p. 473).
Flores Naranjo Gonzalo, 2000, (Interpretation of Structural Lineaments
based on Mosaic-Image Landsat/Tm and Data obtained from the Shuttle
Radar Topography Mission for the Definition of Critical or Sensitive Areas—
Scientific Research Journal of the Institute de Petroleum Studies (p. 218).
Jorge Davila Burga, 2011, Geological Dictionary, INGEMMET.
Jose Lugo Hubp, 2011, Geomorphological Dictionary, Institute of Geography
of the UNAM.
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Herail G., Baby P., Sempere T., Oller J., Barrios L., Montemurro G., Salinas
R., 1990, Structural Cross Section in Southern Bolivia. Final work: Structure
and Evolution of the Atlas Mountain System in Morocco and Structure and
Evolution of the Central Andes in Northern Chile, Southern Bolivia and
Northwestern Argentina. Abstract Volume, Berlin, p. 53
Kaiser J. F., 2014, Understanding Large Resurgent Boilers and Associated
Magma Systems: The Large Pastures Caldera Complex, Southwest Bolivia.
Thesis degree of Doctor of Philosophy, 192 p.
Montes de Oca Ismael, 1997, Geography and Natural Resources of Bolivia.
O’Leary, D. W., Friedman, J. D., and Pohn, H. A., 1976. Lineament, linear,
lineation, Some proposed new standards for old terms: Geological Society
of America, v. 87, p. 1463-1469
Palomino-Angel Sebastian, - Anaya-Acevedo Jesus A., 2014, Synergy
between optical and radar data to determine soil cover: preliminary results
for the Uraba region, Colombia – Faculty of Engineering, University of
Medellín. XVI INTERNATIONAL SYMPOSIUM SELPER (p. 21).
Peter L. Nester, Eugenia Gayo, Claudio Torre, Teresa Jordan, Nicolas
Blanco, 2007, Perennial stream discharge in the hyper-arid Atacama Desert
of northern Chile during the last Pleistocene. PNAS, vol. 104 No.50.
Rodriguez-Esparragon Dionisio, Garcia-Pedrero Angel, Gonzalo-Martin
Consuelo, Marcello-Ruiz Javier and Eugenio-Gonzalez Francisco, 2015,
Measurement of the spectral quality of images fused using the CIEDE2000
algorithm. Remote Sensing: Wetlands and Protected Areas. XVI Congress
of the Spanish Association of Remote Sensing (p. 4).
Salisbury M.J., Jicha B. R., De Silva S.L., Singer B.S., Jimenez N.C., Ort M.
H., 2010, Ar/Ar Chrono-stratigraphy of Altiplano-Puna volcanic complex
ignimbrites reveals the development of a major magmatic province.
Geological Service of Bolivia, Report on Regional Geology of the
Southwestern part of Bolivia, GEOBOL-CONAMAR, 1977 vol. 1 and vol.
2.
National Geology and Mining Service, 1996, Bolivia Geological Charter
Sheet 5927-6027 Silala-Sanabria, Scale 1: 100 000.
National Geology and Mining Service, 2003, Bolivia Geological Charter
Sheet 5928-6028 Cerro del Inca-Laguna Khara, Scale 1: 100 000.
National Service of Geology and Mining, 2003, Study of Pastos Grandes
basin—Basin 16.
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National Service of Geology and Mining, 2003, Study of the geology,
hydrogeology and environment of the area of the springs of Silala (Project
of Integration PIR) Study of the hydrographical basin-basin of the Silala
springs–basin 20. June 2000-2001.
Tibaldi A., Corazzato C., Rovida A., 2008, Miocene-Quaternary structural
evolution of the Uyuni-Atacama region, Andes of Chile and Bolivia.
Tectonophysics. Ed. Elsevier, p.114-135.
Vargas E., 1992, Aerial photography and its application to geological and
geomorphological studies: principles of remote perception, 436 p. 90.
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Geological and Structural Maps Annex A
113
114
115
116
117
East North Elevation Sample
Code
Lithology Rock Name
118
119
120
121
122
123
124
Geological Profiles Annex B
125
126
127
128
129
130
131
132
133
Results of laboratory analysis Annex C
134
STRATEGIC OFFICE FOR THE MARITIME CLAIM, SILALA AND INTERNATIONAL WATER
RESOURCES
GEOLOGICAL MAPPING OF THE AREA SURROUNDING THE SILALA SPRINGS
SUMMARY LABORATORY TABLE
East North
Elevation
(m.a.s.l.)
Elevation
(m.a.s.l.)
Sent to
laboratory Rock Name Petrographic Result
Mineralogical Result
(Mineral Associations)
135
Lava intermedia = Intermediate lava
Toba vitro cristalina = Vitro crystal tuff
Lava ácida = Acidic lava
Toba cristalo vítrea = Glass crystal tuff
Lava básica = Basic lava
volcano sedimentaria = sedimentary volcano
Toba = Tuff
Andesítica Biotítica = Biotic Andesitic
Dacita Biotítica = Biotic Dacite
Andesita Piroxénica = Pyroxene Andesite
Andesítica Biotítica = Biotitic Andesitic
Ignimbrita Andesítica = Andesite Ignimbrite
Basalto Piroxénico = Pyroxene Basalt
Andesita hornbléndica = hornblende andesite
Arcillita = Arcillite
Andesita Biotítica Cuarzosa = Quartzite Biotitic Andesite
Dacita Piroxénica = Pyroxene Dacite
Dacita Biotítica y Hornblénda = Biotic and Hornblende Dacite
Andesita Biotítica Oxidada = Oxidized Biotitic Andesite
Andesita hornbléndica = hornblende andesite
Magnetita – Hematita – Limonita = Magnetite – Hematite – Limonite
Hematita – Magnetita – Calcopirita – Limonita = Hematite – Magnetite – Chalcopyrite – Limonite
Annex 23.5
Appendix c
Tomás Frías Autonomous University (TFAU), “Hydrogeological Characterization of the Silala Springs”, 2018
(English Translation)
139
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[Front cover]
[Logos of the Tomas Frias Autonomous University and the Faculty of Geological Engineering]
“TOMAS FRIAS” AUTONOMOUS UNIVERSITY
OFFICE OF THE VICE-PRINCIPAL
FACULTY OF GEOLOGICAL ENGINEERING
INSTITUTE OF GEOLOGICAL – ENVIRONMENTAL RESEARCH
“HYDROGEOLOGICAL
CHARACTERIZATION OF THE
SILALA SPRINGS”
FINAL REPORT
(2018)
DIRECTION AND SUPERVISION BY:
Dr. Eng. Pedro Guido Lopez Cortes
VICE-PRINCIPAL
TOMAS FRIAS AUTONOMOUS UNIVERSITY
POTOSI – BOLIVIA
140
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
PRESENTATION OF THE RESEARCH WORK ENTITLED “HYDROGEOLOGICAL
CHARACTERIZATION OF THE SILALA SPRINGS”
In my capacities as the chief Academic Authority of the Tomas Frias
Autonomous University, I am pleased to present the research work
carried out by the Faculty of Geological Engineering, with the
Institute of Geological–Environmental Research and a group of
professors committed to regional development.
With this perspective in mind, over this last period, the university
has strengthened the Research Institutes of different Faculties, with
the purpose of carrying out researches that have a social impact,
reciprocating with the diligence that society demands from this
House of Higher Studies and allowing their students to complete
their theses to obtain their academic degree, as is the case of the
Geological Engineering and Environmental Engineering careers.
One of the research works carried out by the aforementioned institute is the
“HYDROGEOLOGICAL CHARACTERIZATION OF THE SILALA SPRINGS,” as
technical input for the existing issue related to these springs, the sovereignty of which, despite being
found within the territory of the Potosi province, is now facing an unjustified claim filed by the
Republic of Chile.
The results reported in said technical survey show that the springs are found within Bolivian
territory, specifically in the Potosi Department and, in light of everything that is specified in the
project, there should be absolute certainty that the technical aspects are settled by the adequate
argumentation and substantiation presented in the final report, which is put to the consideration of
the readers. It is up to the relevant institutions to take on the defense of this significant groundwater
resource from a Historical–Legal perspective and as a State Policy.
The University hopes that the present technical study will constitute a fundamental contribution for
the team of professionals that are dealing with the defense of the Silala springs as a principle of
respect for the territory of our Homeland, preserving the rights of future generations.
Dr. Eng. Pedro Guido Lopez Cortes
VICE-PRINCIPAL OF THE TOMAS FRIAS AUTONOMOUS UNIVERSITY
141
3
English translation prepared by DIREMAR. The original language text remains the authoritative one.
TEAM OF TECHNICIANS
Dr. Eng. Pedro Guido Lopez Cortes Vice-Principal of the Tomas Frias Autonomous
University
M.Sc. Eng. Juan Carlos Erquicia Landeau Director of the Geological – Environmental
Research Institute
M. Sc. Eng. Jorge Diaz Zelada Professor of the Geological Engineering Faculty
Eng. Yerko Wilber Lopez Velasquez Professor of the Geological Engineering Faculty
LOGISTICS SUPPORT
INSTITUTE OF GEOLOGICAL – ENVIRONMENTAL RESEARCH
University Student Issabo Miranda Zamudio Researcher of the Geological Engineering
Faculty
University Student Gabriela Isabel Mealla Barrera Researcher of the Geological Engineering
Faculty
University Student Erice Loma Andia Researcher of the Geological Engineering
Faculty
University Student Salomon Medinaceli Terrazas Researcher of the Geological Engineering
Faculty
LOGISTICS SUPPORT IN THE FIELD
Field Geology students – GLG 831 S
Geophysics students 11- GLG 625
Hydrogeology students – GLG 834
Candidates to the Bachelor Degree
DIRECTION AND SUPERVISION
Dr. Eng. Pedro Guido Lopez Cortes
VICE-PRINCIPAL OF THE TOMAS FRIAS
AUTONOMOUS UNIVERSITY
142
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
INDEX
1.1. Description of the area
1.1.1. Location
1.1.2. Flora
1.1.3. Wildlife
1.1.4. Climate
1.2. GEOLOGY
1.2.1. Regional geology
1.2.2. Local geology
1.3. Structural geology
1.3.1. Local structural geology
1.4. Lithology
1.4.1. Inacaliri volcano
1.4.2. Silala volcano
1.4.3. Quaternary and recent deposits
1.4.3.1. Colluvial processes
1.4.3.2. Alluvial activity
1.5. Petrographic description
1.5.1.1. Silala ignimbrite
1.5.1.2. Hypo-crystalline dacitic ignimbrite, > Plag
1.5.1.3. Dacitic ignimbrite with andesitic clasts
1.5.1.4. Light pink Silala dacitic ignimbrite
1.5.1.5. Tuff
1.5.1.6. Trachyandesite
1.5.1.7. Andesitic lava
Conclusions
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FIGURES
Figure 1.1. Location of the Silala Springs
Figure 1.2. Silala Volcanic Domes
Figure 1.3. Lithological column of the Silala Springs
PHOTOGRAPHS
Photograph 1.1. Hypo-crystalline dacitic ignimbrite, > Plag
Photograph 1.2. Dacitic ignimbrite with andesitic clasts
Photograph 1.3. Light pink Silala dacitic ignimbrite
Photograph 1.4. Tuff
Photograph 1.5. Trachyandesite
Photograph 1.6. Andesitic lava
ANNEXES
ANNEX A. GEOLOGY
ANNEX A. 1. STRUCTURAL INTERPRETATION
ANNEX A. 2. MAPS; STRUCTURAL GEOLOGY
ANNEX A. 3. GEOLOGICAL CUTTINGS
ANNEX A. 4. PHOTOGRAPHS
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HYDROLOGICAL CHARACTERIZATION OF THE SILALA SPRINGS
ABSTRACT
We are honored to present the research work completed by the TOMAS FRIAS AUTONOMOUS
UNIVERSITY, with the help of the Geological Engineering Faculty, as a response to the mandate
of society as a whole in the face of the issue that arose in relation to the utilization of the waters of
Silala Springs.
Said problem arose in 2004, when the Government of Chile proposed our nation a financial
compensation of the 50% derived from its use of the spring waters of this groundwater resource, for
a five-year term, in order to—meanwhile—carry out technical surveys that would demonstrate that
the right [Chile claims over this resource] is based on the fact that this is a shared aquifer, and that
natural and permanent waterbodies within Chilean territory recharge said aquifer. By 2006, earlier
diagnosis surveys began to be carried out to address the issue.
In face of the above, and given that there are dissimilar opinions concerning the origin of the waters
of the Silala Springs, it was decided that a scientific research ought to be performed regarding the
following research topic: “CHARACTERIZATION OF THE SILALA SPRINGS,” in the
understanding that characterization means “de ning, analyzing and determining rieolnast,” in order
to DEFINE in clear terms the meaning of Aquifer, High Andean Wetland [hereinafter Bofedal],
Springs, Fossil waters and international course river; ANALYZE, quantitatively, the surface waters
by means of a water balance; MODEL the possible water scenarios derived from climate change
and guarantee the availability of water for future generations; and DETERMINE the RELATION
between surface water and groundwater resources, quantitatively and qualitatively.
In order to achieve this goal, a detailed structural geological mapping was prepared for the area
where the springs well up, de ning the area’s rock types and the in uence of primary and
secondary porosity of colluvial-alluvial material and ignimbrite rocks.
Fifteen Vertical Electrical Soundings (VES) were preformed to define the thickness of the different
formations of the area, up to a depth of 90 meters. In the areas close to where these profiles were
carried out, permeability tests—with the falling head method—and infiltration speed tests—with the
Kostiakov-equation double ring method—were also completed and yielded real values for these
variables.
The surveys described above are contained in this report and, by having completed them, we
believe we have complied with the bearing that the people deserve from the University. Thank you.
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[Logo of the Tomas Frias Autonomous University]
CHAPTER I
GEOLOGY
[Logo of the Faculty of Geological Engineering]
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
[Letterhead on all pages: “Tomas Frias Auton omous University, Faculty of Geological
Engineering”
“Hydrogeological characterization of the Silala Springs” ]
CHAPTER I. GEOLOGICAL DESCRIPTION OF THE SILALA SPRINGS
1.1. DESCRIPTION OF THE AREA
1.1.1. Location
The surveyed area of the Silala Springs is located in Canton Quetena Grande, South Lipez Province,
of Potosi Department. It is geographically located in the Western Cordillera of the Andes, at
reference coordinates 7566000 North and 602000 East, UTM WGS84 ZONE 19 SUD. The area
borders the international border with the Republic of Chile to the west, passing through boundary
landmarks LXXIII, LXXIV and LXXV; the North Lipez province to the north; the San Antonio de
Lipez and San Antonio de Esmoruco Cantons to the east; and the International border with the
Republic of Argentina to the south (See Annex A.2, Map 1/8).
Figure 1.1. Location of the Silala Springs
The main access route to the area surveyed is the First Order Potosi – Uyuni paved road, with a
distance of 220 Km; the second section comprises the Uyuni – San Cristobal second order road,
with a distance of 90 km; and, finally, the third section—the third order San Cristobal – Alota –
Silala road, with a distance of 160 km. The total length comprises 470 Km, from Potosi city to the
area where the Silala Springs well up.
[Letterhead on all pages: “Tomas Frias Autonomous University, Faculty of Geological Engineering”
“Hydrogeological characterization of the Silala Springs”]
CHAPTER I. GEOLOGICAL DESCRIPTION OF THE SILALA
SPRINGS
1.1. DESCRIPTION OF THE AREA
1.1.1. Location
The surveyed area of the Silala Springs is located in Canton Quetena Grande,
South Lipez Province, of Potosi Department. It is geographically located in the
Western Cordillera of the Andes, at reference coordinates 7566000 North and
602000 East, UTM WGS84 ZONE 19 SUD. The area borders the international
border with the Republic of Chile to the west, passing through boundary landmarks
LXXIII, LXXIV and LXXV; the North Lipez province to the north; the
San Antonio de Lipez and San Antonio de Esmoruco Cantons to the east; and
the International border with the Republic of Argentina to the south (See Annex
A.2, Map 1/8).
The main access route to the area surveyed is the First Order Potosi – Uyuni
paved road, with a distance of 220 Km; the second section comprises the Uyuni
– San Cristobal second order road, with a distance of 90 km; and, finally, the
third section
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the third order San Cristobal – Alota – Silala road, with a distance of 160 km.
The total length comprises 470 Km, from Potosi city to the area where the Silala
Springs well up.
1.1.2. Flora
The flora or vegetation cover present in the Silala region is poor, typical of the
region’s ecosystem and is represented by high altitude bofedals and a community
of Puna desert thickets. The typical flora of the Mountain Range includes
several types of thola (Parastrephia, Adesmia and Baccharis spp.) and
yareta (Azorella compacta) plants, the latter of which grows sporadically on
the slopes of the Inacaliri and Silala volcanoes. The yareta presents features of
having been over-exploited and is considered an endangered species.
1.1.3. Wildlife
The wildlife of the area surveyed comprises varieties of species that are characteristic
of the Bolivian High Plateau and Western Mountain Range habitats,
with no endangered species having been recorded. The following can be mentioned:
Vicuna (Vicugna vicugna) – Huari – Sawalla
Viscacha, or Andean chinchillon (Lagidum viscaccia cuvieri)
Among the bird species, the following have been observed:
Cordillerano Ostrich (Pterocnemia pennata) – Suri
Andean partridge (Nothoprocta ornata) – Pisaka
Andean seagull (Larus serranus)
Blue billed Puna teal (Ana puna) – Chirokankana
Andean swallow (Petrochelin andecola)
1.1.4. Climate
The Silala area presents a climate characteristic of high mountain desert areas,
with extreme temperature variations. The mean monthly temperatures are also
unimodal. The maximum temperatures are recorded from December to March,
with the highest mean temperature recorded in December—3.9° C. The lowest
temperatures are observed from April to August,
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with mean temperatures that fluctuate between 0° to -4.0° C. The highest mean
annual temperature is of 14.2° C and the lowest mean annual temperature is of
-15° C. These two extremes provide an approximate variation range of 29° C.
1.2. GEOLOGY
1.2.1. Regional geology
The area of the Silala Springs is located in the southern block of the Western
Mountain Range and forms part of the Andes’ Central Volcanic Zone. Its regional
geology is dominated by the outcropping of materials formed from volcanic
activity dating back from the Miocene to the Recent ages. This landscape
was modelled by glacial Pleistocene–Holocene processes. The weathering, erosion
and deposition processes are represented by unconsolidated Quaternary
and Recent sediments that cover large parts of the area. The deposited materials
form glacial, fluvioglacial, colluvial and alluvial deposits that comprise polygenic
blocks or boulders, clasts of different rocks and sizes, and fine sediments
as sand and lime.
By the late Pleistocene, other volcanic centers, as the Cerro Negro Volcano
began to form and their effusive volcanism gave rise to andesitic lava deposits,
which have covered the preexisting reliefs (Urquidi Barrau, F. Coordinator of
the Study on the Geology, Hydrology, Hydrogeology and Environment of the
Silala Springs, Final Edition, La Paz - Bolivia. June, 2003, pp. 9-10).
In the Silala ignimbrites, the regional basement is formed by layers of consolidated
tuffs that bear the same name. These ignimbrites have a light pink to violet
color, a dacitic composition and are made up of plagioclase, quartz, biotite
and hornblende. They correspond to the calcalkaline series and are rich in K2O.
Their SiO2 content varies between 63 to 66%. The volcanic glass matrix includes
lithic fragments of different rock types—mainly pumice rock fragments
of up to 10 cm in size—and its flattening index varies from 3 to 1. Data on their
total thickness in the area is unavailable, given that their basal contact cannot
be observed and that the rock type on which they rest is unknown. These are
partially welded tuffs and are strongly fractured and jointed.
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These ignimbrite mantles have an inclination to the west. According to radiometric
data extrapolated from surrounding areas, these ignimbrites have an age
of 7.8 +/- 0.3 million years (Mys), namely, they date back to the Upper Miocene
(Choque, 1996; Lema & Ramos, 1996; Richter, et. al., 1992).
The Silala Chico hill Volcanic Dome. This volcanic body of reduced dimensions
emerges to the northeast of the Silala volcano, intruding the Silala ignimbrites.
It has an approximate basal diameter of 3 km and reaches an altitude of
4849 m.a.s.l. It is covered by dark gray porphyric andesitic-dacitic lavas, comprising
88 to 90% of plagioclase (andesite-labradorite) and 4 to 10% of Pyroxene.
The dating completed with samples collected by the Regional Integration
Project (RIP, hereinafter) show an age of 6.04 +/- 0.07 Myr for the Silala Chico
hill volcanic dome (RIP, in preparation).
The Cerro Negro Volcanic Dome. This volcanic body is found on the margins
of the surveyed area, in the northeast. It has a basal diameter of 2 km and an
approximate 5200 m.a.s.l. and is composed of light gray andesitic rocks.
The Torito volcanic Dome. This volcanic dome is located in the western sector
of the area surveyed. It has a dacitic and andesitic composition and an approximate
altitude of 4900 m.a.s.l. Its basal diameter is of 1.6 Km, approximately
(see Figure 1.2., p. 5).
1.2.2. Local geology
Locally, the area surveyed has developed in an effusive volcanic environment.
The materials, formed as a result of volcanic activity, rest on the ―Silala Ignimbrites‖
and have an age of 7.8 +/- 0.3 million years, i.e. from the Upper
Miocene (Choeque, 1996; Lema & Ramos, 1996; Richter, et. al., 1992). The
―Silala Ignimbrites‖ are divided in three horizons; the oldest ones correspond
to ignimbrites that have a higher content of violet to whitish plagioclase, over
which dacite composition ignimbrites, with consolidated Andesite fragments,
rest. Ignimbrites rich in plagioclase–Na rest on top of the latter (See Figure 1.3,
p. 11).
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Figure 1.2. Silala Volcanic Domes
The ignimbrites rich in plagioclase outcrop in lower areas, clearly exposed on the flanks of the
structural canyon [ravine] where the canals were installed (see Annex A. 4, photograph 3). The
presence of the dacite composition ignimbrite, by contrast, is restricted to a guiding horizon of an
approximate thickness of 20 cm and is clearly identifiable on the northeast flank of the main canal.
In higher parts, the ignimbrites that have a higher content of plagioclase-Na are much more exposed
in the central part of the area surveyed. Reduced tuff outcrops of a whitish color and a massive
texture can be observed to the east, between the Andesite lava and the Silala ignimbrite. In the
central northeastern part, it is possible to observe a horizon that is clearly delimited by its coloration
and composition, which corresponds to gray–blackish Andesite Lava. Silala Chico dome
outcrops to the southwest, presenting a composition that corresponds to light gray trachyandesite of
a medium granulometry and intermediate composition. This sequence of exposed materials
prolongs with the presence of glacial sediments to the northwest of the area surveyed, on the south
flank of Inacaliri Volcano. Colluvial sediments cover 30 to 40% of the area, mainly due to the
extreme action of temperature changes, the low gradient and the absence of hydric activities as
material transport agents. Alluvial sediments are restricted to water runoff from the springs, in the
canalized areas or in their vicinities (see Annex A.2. Map 2/8).
The ignimbrites rich in plagioclase outcrop in lower areas, clearly exposed on
the flanks of the structural canyon [ravine] where the canals were installed (see
Annex A. 4, photograph 3). The presence of the dacite composition ignimbrite,
by contrast, is restricted to a guiding horizon of an approximate thickness of 20
cm and is clearly identifiable on the northeast flank of the main canal. In higher
parts, the ignimbrites that have a higher content of plagioclase-Na are much
more exposed in the central part of the area surveyed. Reduced tuff outcrops
of a whitish color and a massive texture can be observed to the east, between
the Andesite lava and the Silala ignimbrite. In the central northeastern part, it
is possible to observe a horizon that is clearly delimited by its coloration and
composition, and which corresponds to gray–blackish Andesite Lava. Silala
Chico dome outcrops to the southwest, presenting a composition that corresponds
to light gray trachyandesite of a medium granulometry and intermediate
composition. This sequence of exposed materials prolongs with the presence of
glacial sediments to the northwest of the area surveyed, on the south flank of
Inacaliri Volcano.
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Colluvial sediments cover 30 to 40% of the area, mainly due to the extreme
action of temperature changes, the low gradient and the absence of hydric activities
as material transport agents. Alluvial sediments are restricted to water
runoff from the springs, in the canalized areas or in their vicinities (see Annex
A.2. Map 2/8).
1.3. STRUCTURAL GEOLOGY
The tectonism of the area surveyed is influenced by the uplift and faulting of
the Lipez regional block, known as the Cuña Occidental [Western Wedge].
The major representation of this tectonism in the area are the Khenayani fault
system, which crosses the area with a regional ENE direction, adjustment faults
that follow the same course, and transversal adjustment faults with EW and
WNW directions. The latter have a limited but deep extent, and facilitated volcano
effusion—with the resulting deposition of igneous and effusive pyroclastic
rocks—and the fracturing of basal ignimbrite rocks.
1.3.1. Local Structural Geology
Using the structural mapping and data processing as a basis, 4 domains were
identified. These represent the structural zones that govern the geological behavior,
which in turn determined the upwelling of the Silala Springs (see Annex
A. 1 – Structural Interpretation).
Joints: 1,500 fractures were mapped throughout the study area. Following
their interpretation, it was concluded that the maximum stress axis has a preferred
EW direction, which gave rise to four structural domains (see Annex A.
2, Map 3/8), each with particular characteristics. For example, fault mirrors
were mapped in the 4th domain. These determined the current position of the
structural canyon, as well as the secondary porosity of the whole ignimbrite
complex that allows the springs to well up (see Annex A. 4, Photographs 4 and
5).
Faults: The position of the fault mirrors (striae) shows that the fractures of the
4th domain were activated by the action of shear stresses, which formed the
current geomorphology of the canyon (tectonic pit/structural gully).
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The fault mirrors mapped have an average dipping direction of 140/48°
(azimuth of the dipping direction), a trend with an azimuth of 225, and a plunge
(subsidence) of 110; with a raque of 110 SW, conditioning a structural control
for the upwelling of the springs of the NWW sector.
1st Domain
From the structural interpretation, it can be perceived that fractures “b” and “c”
respond to shear fractures with respect to the main stress axis of a NE trend of
81°; fractures “a” and “d” respond to shears of a second order in relation to the
shear stresses.
There are fractures of angle strike extension, which fluctuate from 81° N – 85°
E and concur with the direction of the topographic depression of the area in
which the springs flow, with a preferential Rb [no explanation on what the
acronym means is provided in the source text, but Direction is inferred as the
possible meaning] of N 81° E.
From an interpretation of the Rose diagram, it can be perceived that the ruling
fracture direction is 80° N – 85° W. The latter is the reason why the flow of the
SEE sector springs has a higher rate, inasmuch as water always flows to areas
where there is less resistance. These extension fractures are open fractures that
enable the upwelling of the springs because of their high secondary permeability
rate (See Annexes A.1, p. 1-4).
2nd Domain
The 2nd domain is characterized for having a 1st δ (maximum effort axis) of an
85° NE direction and a Plunge of 12° NE, a 2nd δ of an 85° NE direction and a
Plunge of 78° SW, and a 3rd δ of an 5° NW direction and a Horizontal Plunge.
These caused fractures “b” and “e” to be shear fractures, fractures “a” to be
compression fractures, and “c” to be second order shear fractures.
From an interpretation of the Rose diagram (see Rose Diagram, Annex A. l.,
p. 29), it is possible to perceive a predominant Rb [Direction] in a range of 0°
N – 10° W, which matches the compression fractures, and a fracture frequency
in a range of 60° - N 68 ° W matching the shear fractures.
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The above provides an explanation as to why the 2nd domain section does not
comprise any springs, i.e. this domain presents closed fractures, unlike the 1st
Domain. (see Annex A. 1, pp. 5-9).
3rd Domain
The 3rd domain is characterized for presenting a 1st δ of a 75° NE direction
and a Plunge of 10° SW, a2nd δofa75°NEdirectionandaPlungeof80°NE,anda3
rd δofa15°NWdirectionanda Horizontal Plunge. These caused fractures “a” and
“d” to be first order shear fractures, fractures “b” and “c” to be second order
shear fractures, and fracture “e” to be compression fractures.
From an interpretation of the Rose diagram, it can be perceived that there is
a predominant NS fracture Rb [direction], which corresponds to compression
fractures, and NW fractures that correspond to shear fractures, to a lesser degree.
This is why springs do not well up in this domain (see Annex A. 1, pp. 10-14).
4th Domain
Fractures “a”, “b” and “c” are first order shear fractures, with respect to the
1st δ. Fractures “e” and “d” are second order shear fractures activated by shear
stresses. These have activated the predominant faults in the 4th Domain, as a
result of the action of shear stresses, where a fault mirror was mapped with
a dipping direction of 140°/148°, a 225° trend, a 11° plunge, and a SW 11°
raque. This structural control predetermines the emergence of the NWW sector
springs (see Annex A. 1, pp. 15-19; see Annex A. 4, photograph 5).
1.4. LITHOLOGY
1.4.1. Inacaliri Volcano
Inacaliri volcano has an approximate diameter of 10 Km, in its basal part, and
culminates in a crater of a diameter of 380 m, at an altitude of 5570 m.a.s.l. Two
effusive events can be observed in this volcano.
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The first volcanic event is represented by the effusion and deposition of dark
gray andesitic lava, similar, or subsequent to, the rocks of the Silala Chico hill
dome, but falling within the same volcanic event.
The second effusive event superposes new material over the volcanic cone of
the first event. This last volcanic activity discharged a flow of andesitic lava
that is more basic than that of the Silala Volcano, which covers the preexisting
reliefs.
1.4.2. Silala volcano
The Silala volcano is located in the southeast margin of the area surveyed. It
has an approximate basal diameter of 4 Km and an altitude of 5700 m.a.s.l. The
rocks that this volcano presents comprise dark-gray to gray-light-blue porphyric
andesitic-dacitic lavas, with 70 % of plagioclase (andesite-labradorite) and
28 % of pyroxene, which rest on the Silala pyroclastic flows.
1.4.3. Quaternary and Recent Deposits
The unconsolidated deposits, or Quaternary and recent soils cover approximately
30 to 40 % of the area’s surface. These are the result of weathering and
erosion events that conditioned the colluvial- alluvial material present in the
area.
1.4.3.1. Colluvial processes
The colluvial sediments or deposits are found in different parts of the area
surveyed, covering soft slopes. These deposits present a primary sedimentary
structure.
1.4.3.2. Alluvial activity
The alluvial activity is represented by the runoff of fluvio-glacial waters that
gave rise to forms of erosion and material accumulation dating back to 10.000
BP, approximately. The area comprises large alluvial fans that reflect the climatic
conditions, and amounts of water runoff that are different from the current
ones. Other forms of alluvial accumulation in the area surveyed are alluvial
plains, with red paleosols developed on the ignimbrites that date back to 7.8
Myr and
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andesitic-dacitic lavas from 1.7 Myr ago. In cases where springs or pooling
waters well up, they condition the presence of bofedals developed by the influence
of a superficial piezometric level on fine to medium sandy-clayey material,
particularly in the upper part of the topographical depressions, where the
slope is softer, or inexistent. These are bofedals characteristic of high altitudes.
1.5. PETROGRAPHIC DESCRIPTION
Petrographically, the area surveyed formed as a result of a volcanic activity
that began during the Andean Cycle of the Upper Miocene. During this cycle,
several calderas, and volcanic centers and domes were formed, including Agua
de Perdiz (found outside the area surveyed), which manifests as the eruption
and deposition of a regionally large ignimbrite mantle, known as the Silala Ignimbrite.
The latter are clearly visible in the area and partially covered by lava
flows from stratovolcanoes, intruding the latter. This is the first effusive stage
that characterizes the area. The most visible volcanic structures that surround
the area are the Silala Chico and Torito volcanic domes and the Inacaliri and
Silala stratovolcanoes (see Figure No. 1.2, p. 5), which formed as a result of the
accumulation of products derived from extrusive and effusive phases. The first,
extrusive, phase is represented by the formation of volcanic domes, while the
second, effusive, is represented by andesite and andesitic-dacitic lava.
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Figure 1.3. Lithological column of the Silala springs
By the end of the Pleistocene, the formation of other volcanic centers, as the Cerro Negro, began.
The effusive volcanism of Cerro Negro developed andesite lava deposits that covered preexisting
reliefs.
Six lithological units have been identified through the petrographic description of the Silala. The
latter’s lower part comprises dacite ignimbrite of an unidenti ed basement and a higher content of
plagioclase; the second unit comprises a thin layer of dacite-ignimbrite, with andesite clasts derived
from the first [volcanic] event of the Inacaliri; the third unit comprises dacite ignimbrites with a
higher content of plagioclase-Na; the fourth unit contains tuffs; the fifth one trachyandesite; and the
sixth andesite lava.
1.5.1.1. Silala Ignimbrite
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By the end of the Pleistocene, the formation of other volcanic centers, as the
Cerro Negro, began. The effusive volcanism of Cerro Negro developed andesite
lava deposits that covered preexisting reliefs.
Six lithological units have been identified through the petrographic description
of the Silala. The latter’s lower part comprises dacite ignimbrite of an unidentified
basement and a higher content of plagioclase; the second unit comprises a
thin layer of dacite-ignimbrite, with andesite clasts derived from the first [volcanic]
event of the Inacaliri; the third unit comprises dacite ignimbrites with
a higher content of plagioclase-Na; the fourth unit contains tuffs; the fifth one
trachyandesite; and the sixth andesite lava.
1.5.1.1. Silala Ignimbrite
The inferior layer that outcrops in the area is composed of the Silala ignimbrites,
which in turn comprises three units:
1.5.1.2. Dacitic-Hypocrystalline Ignimbrites, > Plag
These are characterized for their whitish color and are mainly composed of
plagioclase (> Plagioclase). They are of dacitic composition, and also comprise
quartz and biotite. They correspond to the calcalkaline series, rich in K2O, and
their SiO2 content varies between 63% and 66%. Their matrix is vitreous and
includes lithic fragments of different rock types, mainly pumice stone fragments.
Their thickness is uncertain, given that their basal contact and the rock
on which they rest are unknown also. These are partially welded ignimbrite and
are strongly fractured and jointed (see Photograph 1.1., p. 13). According to the
surveys performed in the area, and on basis of radiometric data extrapolated
from surrounding areas, these ignimbrites have an age of 7.8 +/- 0.3 millions
of years, i.e. from the Upper Miocene (Choque, 1996; Lema & Ramos, 1996;
Richter, et. al., 1992).
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1.5.1.2. Dacitic-Hypocrystalline Ignimbrites, > Plag
These are characterized for their whitish color and are mainly composed of plagioclase (>
Plagioclase). They are of dacitic composition, and also comprise quartz and biotite. They
correspond to the calcalkaline series, rich in K2O, and their SiO2 content varies between 63% and
66%. Their matrix is vitreous and includes lithic fragments of different rock types, mainly pumice
stone fragments. Their thickness is uncertain, given that their basal contact and the rock on which
they rest are unknown also. These are partially welded ignimbrite and are strongly fractured and
jointed (see Photograph 1.1., p. 13). According to the surveys performed in the area, and on basis of
radiometric data extrapolated from surrounding areas, these ignimbrites have an age of 7.8 +/- 0.3
millions of years, i.e. from the Upper Miocene (Choque, 1996; Lema & Ramos, 1996; Richter, et.
al., 1992).
1.5.1.3. Dacitic ignimbrite with andesitic clasts
These have a pinkish color and are composed of dacite, with a predominance of feldspar. This unit
is more compacted and has less power. To the west of the area surveyed, these ignimbrites have a
thickness of, approximately, 15 cm and are restricted in the eastern part. Their grain size is
aphanitic, with phaneritic phenocrysts of andesite composition, which pertain to the first Inacaliri
volcanic event. Their color index is lower than the 10% (holo-felsic), they have a quartz content that
is higher than the 10% (acid), a silica percentage that surpasses the 66%, and contain quartz,
feldspar and plagioclase crystals to a lesser extent (see photograph 1.2., p. 14). The crystal faces do
not present defined shapes (granular allotriomorphic) and have a banded massive texture (they do
present a preferred flow direction).
Photograph 1.1. Dacitic-Hypocrystalline Ignimbrites, > Plag - Na
1.5.1.3. Dacitic ignimbrite with andesitic clasts
These have a pinkish color and are composed of dacite, with a predominance
of feldspar. This unit is more compacted and has less power. To the west of the
area surveyed, these ignimbrites have a thickness of, approximately, 15 cm and
are restricted in the eastern part. Their grain size is aphanitic, with phaneritic
phenocrysts of andesite composition, which pertain to the first Inacaliri volcanic
event. Their color index is lower than the 10% (holo-felsic), they have a
quartz content that is higher than the 10% (acid), a silica percentage that surpasses
the 66%, and contain quartz, feldspar and plagioclase crystals to a lesser
extent (see photograph 1.2., p. 14). The crystal faces do not present defined
shapes (granular allotriomorphic) and have a banded massive texture (they do
present a preferred flow direction).
1.5.1.4. Dacitic ignimbrite > Plag-Na. Light pinkish color Silala
These ignimbrites present Plagioclase – Na, hence their pinkish coloration, as
well as feldspar, plagioclase—in a lesser amount—silica, in a 55 to 60 % size of
aphanitic grain, with andesitic composition phenocrystals, a color index lower
than the 10 % (holofelsic), a quartz content higher than the 10% (acid), and
a silica percentage higher than the 66%, presenting quartz, feldspar and plagioclase
in minor quantities (see Photograph 1.3. p. 14). The crystals do not
present
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1.5.1.4. Dacitic ignimbrite > Plag-Na. Light pinkish color Silala
These ignimbrites present Plagioclase – Na, hence their pinkish coloration, as well as feldspar,
plagioclase—in a lesser amount—silica, in a 55 to 60 % size of aphanitic grain, with andesitic
composition phenocrystals, a color index lower than the 10 % (holofelsic), a quartz content higher
than the 10% (acid), and a silica percentage higher than the 66%, presenting quartz, feldspar and
plagioclase in minor quantities (see Photograph 1.3. p. 14). The crystals do not present defined
forms (granular allotrimorphic) and have a banded massive texture (they do not show a preferential
flow direction).
Photograph 1.2. Dacitic-ignimbrite with andesitic clasts
Photograph 1.3. Dacitic ignimbrite > Plag - Na
defined forms (granular allotrimorphic) and have a banded massive texture
(they do not show a preferential flow direction).
1.5.1.5. Tuff
These tuffs are visible only in the northeast of the area surveyed. They have a
gray-whitish color, and a dacitic composition. They present feldspar, plagioclase,
quartz and biotite minerals. Their grain size is aphanitic. They have a
color index lower than the 10% (holofelsic), a quartz content that surpasses the
10% (acid), and a silica content
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1.5.1.5. Tuff
These tuffs are visible only in the northeast of the area surveyed. They have a gray-whitish color,
and a dacitic composition. They present feldspar, plagioclase, quartz and biotite minerals. Their
grain size is aphanitic. They have a color index lower than the 10% (holofelsic), a quartz content
that surpasses the 10% (acid), and a silica content higher than the 66% (see photograph 1.4. p. 15).
The crystal faces do not present defined shapes (granular allotriomorphic) and have a banded
massive texture (they do present a preferred flow direction).
Photograph 1.4. Tuff
1.5.1.6. Trachyandesite
A trachyandesite (intermediate) volcanic dome is found southwest of the area surveyed. This rock
has a light gray color and medium grain sizes. Its mineral composition comprises quartz, feldspar,
biotite and plagioclase (< amount). Its color index is lower than the 10% (holofelsic), its quarts
content is higher than 10% (acid), and its silica content is higher than 66% (see photograph 1.5. p.
16). The crystal faces do not present defined shapes (granular allotriomorphic), have an aphanitic
grain size, and present a subophitic texture.
1.5.1.7. Andesitic lavas
These lavas form a layer that overlaps, north of the area surveyed, the Silala Ignimbrites and, to the
northeast, the tuffs. They are andesitic in composition, and comprise quartz, feldspar, pyroxene and
plagioclase crystals (< amounts). They do not present a fluidal structure, their grain size is
aphanitic, their color index lower than the 10-40% (intermediate), and their silica percentage higher
than the 52-66% (see photograph No. 8). The crystal faces do not present defined shapes (granular
allotriomorphic) and present a massive texture.
higher than the 66% (see photograph 1.4. p. 15). The crystal faces do not present
defined shapes (granular allotriomorphic) and have a banded massive texture
(they do present a preferred flow direction).
1.5.1.6. Trachyandesite
A trachyandesite (intermediate) volcanic dome is found southwest of the area
surveyed. This rock has a light gray color and medium grain sizes. Its mineral
composition comprises quartz, feldspar, biotite and plagioclase (< amount). Its
color index is lower than the 10% (holofelsic), its quarts content is higher than
10% (acid), and its silica content is higher than 66% (see photograph 1.5. p.
16). The crystal faces do not present defined shapes (granular allotriomorphic),
have an aphanitic grain size, and present a subophitic texture.
1.5.1.7. Andesitic lavas
These lavas form a layer that overlaps, north of the area surveyed, the Silala
Ignimbrites and, to the northeast, the tuffs. They are andesitic in composition,
and comprise quartz, feldspar, pyroxene and plagioclase crystals (< amounts).
They do not present a fluidal structure, their grain size is aphanitic, their color
index lower than the 10-40% (intermediate), and their silica percentage higher
than the 52-66% (see photograph No. 8).
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Photograph 1.5. Trachyandesite
Photograph 1.6. Andesite
The crystal faces do not present defined shapes (granular allotriomorphic) and
present a massive texture.
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CHAPTER I (GEOLOGY) – CONCLUSIONS
Locally, the area surveyed has developed in an effusive volcanic environment.
The basement of the materials formed as a result of volcanic activity is found
on the ―Silala Ignimbrite‖, with an age of 7.8 +/- Myr, namely, the Upper Miocene
(Choque, 1996; Lema & Ramos, 1996; Richter, et. al., 1992). The ―Silala
Ignimbrites‖ are divided in three horizons; the oldest ones correspond to ignimbrites
that have a higher content of whitish plagioclase, over which the dacitic
ignimbrites – with consolidated andesitic fragments – rest. The ignimbrites rich
in Plagioclase – Na are found in the latter sequence.
The structural mapping and data processing led to the identification of 4 domains
that represent the structural zones that predominate the geological behavior,
which in turn defines the occurrence of the Silala springs (see Annex A.
2, Map 3/8).
1st Domain: based on the structural interpretation, it can be perceived that fractures
“b” and “c” respond to shear fractures in relation to the main axis of a NE
81° trend; fractures “a” and “b” respond to second order sheers in relation to
shear stress.
There are fractures of angle strike extension, which fluctuate from 81° N – 85°
E and concur with the direction of the topographic depression of the area in
which the springs flow, with a preferential Rb [direction] of N 81° E.
From an interpretation of the Rose diagram, it can be perceived that the ruling
fracture direction is 80° N – 85° W. The latter is the reason why the flow of the
SEE sector springs has a higher rate, inasmuch as water always flows to areas
where there is less resistance. These extension fractures are open fractures that
enable the upwelling of the springs because of their high secondary permeability
rate (See Annexes A.1, p. 1-4).
2nd Domain: it is characterized for having a 1st δ (maximum effort axis) of an
85° NE direction and a Plungeof12°NE,a2nd δofan85°NEdirectionandaPlunge
of78°SW,anda3rd δofan5°NW direction and a Horizontal Plunge. These caused
fractures “b” and “e” to be shear fractures, fractures “a” to be compression
(closed) fractures, and “e” to be second order shear fractures.
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From an interpretation of the Rose diagram (see, Annex A. l., p. 29), it is possible
to perceive a predominant Rb [Direction] in a range of 0° N – 10° W, which
matches the compression fractures, and a fracture frequency in a range of 60°
N – 68 ° W—matching the shear fractures.
The above provides an explanation as to why the 2nd domain section does not
comprise any springs, i.e. this domain presents closed fractures, unlike the 1st
Domain. (see Annex A. 1, pp. 5-9).
3rd domain: it is characterized for presenting a 1st δ of a 75° NE direction and
a Plunge of 10° SW, a 2nd δofa75°NEdirectionandaPlungeof80°NE,anda3rd
δofa15°NWdirectionanda Horizontal Plunge. These caused fractures “a” and
“d” to be first order shear fractures, fractures “b” and “c” to be second order
shear fractures, and fracture “e” to be compression fractures.
From an interpretation of the Rose diagram, it can be perceived that there is
a predominant NS fracture Rb [direction], which corresponds to compression
fractures, and NW fractures that correspond to shear fractures, to a lesser degree.
This is why springs do not well up in this domain (see Annex A. 1, pp.
10-14).
4th Domain: Fractures “a”, “b” and “c” are first order shear fractures, with
respect to the 1st δ. Fractures “e” and ―d” are second order shear fractures
activated by shear stresses. These have activated the predominant faults in the
4th Domain, as a result of the action of shear stresses, where a fault mirror was
mapped with a dipping direction of 140°/148°, a 225° trend, a 11° plunge, and
a SW 11° raque. This structural control predetermines the emergence of the
NWW sector springs (see Annex A. 1, pp. 15-19; see Annex A. 4, photograph
5).
Faults have also been identified in the area. The position of the fault mirrors
(striae) shows that the fractures of the 4th domain were activated by the action
of shear stresses, which formed the current geomorphology of the canyon (tectonic
pit/structural gully).
The mapped data of the fault mirrors have an average Dip/Dir of 140/48° (azimuth
of the dipping direction); a trend with an azimuth of 225 and a plunge of
110 (sinking); with a raque of 110 W (see Annex A.4, photograph 5), conditioning
a structural control for the emergence of the springs of the NWW sector.
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Glossary
Crushing:
The action and effect of crushing [something]. To crush (to deform something
by exerting pressure, flattening, or reducing its thickness).
Real Academia Española © All rights reserved.
BP:
(Commonly abbreviated as AP, and occasionally as BP, from the English ―Before
Present‖. It is a time scale used in archeology, geology and other scientific
disciplines as a standard to specify when some event occurred in the past.
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165
Bibliography
SERGEOMIN Report, ―Study of the Geology, Hydrology, Hydrogeology and
Environment of the Silala Springs‖, 2015
Suárez, R. (2000), Compendium of Bolivia’s Geology. Technical Magazine of
the Bolivian Fiscal Oil Fields (YPFB). Vol. 18. Cochabamba-Bolivia.
Cabre, R. and Vega, A. 1989. Seismicity of Bolivia. San Calixto Laboratory,
Publication 40, La Paz.
Clapperton, C.M. 1979. Glaciation in Bolivia before 3.27 Myr. Nature, 277
(5695): 375-377.
Lavenu, A. 1995. Plio-Quaternary Geodynamics in the Central Andes: the
Northern Altiplano of Bolivia. In Suarez R. (ed.) Fossils and Facies of Bolivia:
III YPFB Technical Review, 16 (2): 76-96, Cochabamba.
Sebrier, M., Lavenu, A., Fornari, M. and Soulas, J.P. 1988. Tectonics and elevation
in the Andes of southern Peru and central Bolivia from the Oligocene to the
present. Géodynamique 3 (1-2): 85- 106.
Normal and reverse faulting and the state of stress in the southern central Andes
of south Peru. Tectonics 4: 739-780.
Sanchez Otazo, J., ―Notes on Igneous and Metamorphic Petrography‖ p. 30-
53, Edit 2001, Potosi-Bolivia
Calcina, l. ―Notes on Igneous and Metamorphic Petrography‖ p. 2-10
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[Logo of the Tomas Frias Autonomous University]
CHAPTER II
GEOPHYSICS
[Logo of the Faculty of Geological Engineering]
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INDEX
2.1. Introduction
2.2. Specific Objectives
2.3. Theoretical fundamentals of the geophysical methods
2.3.1. Application of electrical methods
2.3.2. Characteristics of the SAS 4000/1000 TERRAMETER measurement equipment
2.4. Geoelectrical survey methodology
2.4.1. Field Activities
2.4.2. Desk work
2.4.2.1. Data processing
2.5. Profile – Geoelectrical Cross Section
2.5.1. Resistivity profiles
2.5.2. Geoelectrical Cross-Sections
Conclusions
Recommendations
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PHOTOGRAPHS
Photograph 2.1. SAS 4000/1000 TERRAMETER Equipment
Photograph 2.2. Location of the transversal line with respect to the springs
Photograph 2.3. Location of the longitudinal line with respect to the springs
FIGURES
Figure 2.1. Schlumberger configuration for the VES
Figure 2.2. Geoelectrical Resistivity Cutting 1
Figure 2.3. Geoelectrical Resistivity Cutting 2
Figure 2.4. Geoelectrical Resistivity Cutting 3
Figure 2.5. Geoelectrical Resistivity Cutting 4
Figure 2.6. Geoelectrical Resistivity Cutting 5
Figure 2.7. Geoelectrical Resistivity Cutting 6
GRAPHICS
Graph 2.1. Apparent Resistivity Values
Graph 2.2. Interpretation of the Resistivity Model – Layers
Graph 2.3. Apparent resistivity values vs. AB/2
Graph. 2.4. Interpretation of the Resistivity Model – Layers
IMAGES
Image 2.1. Location of the VES in the S-E sector
Image 2.2. Location of the VES in the N-E sector
Image 2.3. Resistivity profile 1
Image 2.4. Resistivity profile 2
Image 2.5. Resistivity profile 3
Image 2.6. Resistivity profile 4
Image 2.7. Resistivity profile 5
Image 2.8. Resistivity profile 6
Image 2.9. Geoelectrical section 1
171
Image 2.10. Geoelectrical section 2
Image 2.11. Geoelectrical section 3
Image 2.12. Geoelectrical section 4
Image 2.13. Geoelectrical section 5
Image 2.14. Geoelectrical section 6
Annex B (Geophysics)
Annex B. 1. Geophysical sounding for the SEE sector – Silala Springs
Annex B. 2. Geophysical sounding for the NWW sector – Silala springs
Annex B. 3. Resistivity profiles – Silala springs
Annex B. 4. Geoelectrical sections – Silala springs
Annex B. 5. NWW – SEE Longitudinal and Transversal cuttings
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IMAGES
Image 2.1. Location of the VES in the S-E sector
Image 2.2. Location of the VES in the N-E sector
Image 2.3. Resistivity profile 1
Image 2.4. Resistivity profile 2
Image 2.5. Resistivity profile 3
Image 2.6. Resistivity profile 4
Image 2.7. Resistivity profile 5
Image 2.8. Resistivity profile 6
Image 2.9. Geoelectrical section 1
172
CHAPTER II. GEOPHYSICAL SURVEY IN THE SILALA SPRINGS
2.1. Introduction
One of the specific objectives of importance for the Hydrogeological characterization
of the Silala springs project has been the application of detailed geophysical
surveys to attain knowledge on the electrical properties of the subsoil
in order to correlate the lithological units and determine the thickness of each
of the geological units present in area.
Said surveys comprised field works completed to elaborate a geophysical modeling
based on the extraction of geoelectrical profiles in the areas of interest,
which have been defined with the application and use of a SAS 4000/1000 Terrameter
resistivity meter.
2.2. Specific objectives
The specific objectives set for the present report are the following:
Identification of the different geological units in the subsoil, alluvial material
layers and ignimbrite by interpreting the different resistivities of the data taken
in the field with the Vertical Electrical Sounding technique.
Determination of the petrophysical properties of the different layers to complement
the surface mapping data and correlate it with the information obtained
from the subsoil.
Production of supplementary base information of the subsoil for the geological
survey for the purpose of completing the hydrogeological characterization
of the Silala springs.
2.3. Theoretical fundamentals of the geophysical method
2.3.1. Application of electrical methods
These methods use the electrical properties variations, and resistivity particularly,
of rocks and minerals. They generally use an artificial electric field created
on the surface through the passing of a current in the subsoil.
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One of the techniques that are most widely used in hydrogeological surveys are
electric methods.
The resistivity method allows not surveying sub-horizontal formations, but
also determining sub-vertical formations (faults, seams, contact zones, etc.). It
further helps define the latter’s characteristics to correlate surface formations
with those of the subsoil.
2.3.2. Characteristics of the ABEM 4000/1000 TERRAMETER measurement
equipment
The SAS 4000/1000 Terrameter is able to complete measurements in four channels,
implying that both the resistivity and IP measurements can be performed
at a pace four time faster. It can operate in three ways: the resistivity mode comprises
power supply from a battery, deep penetration resistivity measurer, with
sufficient output for a separation of 2000-m electrodes in proper survey conditions.
Circuiterium, namely, electric discrimination and programming network,
of separated continuous current tensions, spontaneous powers and noise from
the input signal. The relation between tension and intensity (V/I) is calculated
automatically and presented digitally in kiloohms, ohms, microohms, or microohms.
It provides geometric data on distribution; it can show apparent resistivity.
The total range is thus extended from 0.5 milliohms to 1999 kiloohms (see
photograph 2.1).
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Photograph 2.1. SAS 4000/1000 TERRAMETER Equipment
The most important of all methods that use continuous current produced by artificial generators
is the Vertical Electrical Sounding (VES). It is mainly applied in regions where the geological
structure is formed by horizontal strata.
The purpose of the VES is to determine the depths of the subsoil layers and their electrical
resistivities or conductivities through measurements carried out from the surface.
The graph shown in Figure 2.1. presents an outline of the electrode deposition with the
Schlumberger configuration applied in the present report.
Figure 2.1. Schlumberger configuration for the VES
Where:
A and B are current electrodes (through which electric current is injected)
M and N are power electrodes (through which the potential difference – created by the
injection of electric current of electrodes A and B – between these points is measured).
O is the point in which the VES is performed.
2.4. Geoelectrical survey methodology
The methodology used for the present report was the application of the indirect Vertical
Electrical Sounding (VES) geoelectric method based on the collection of surface geological data.
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2.4.1. Field activities
In order to determine the subsoil characteristics, 15 vertical electrical soundings (VES) have
been performed with their respective locations in UTM WGs 1984 coordinates and at average
distances of 250 m, with an estimated depth between 70 to 90 m and a southeast – northeast
direction (see Annexes B. 1 and B. 2).
The satellite images show the completion of nine vertical electrical soundings in the NWW area
and six in the SEE area, reflecting their respective location (see Image 2.1 and 2.2).
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M and N are power electrodes (through which the potential difference – created by the
injection of electric current of electrodes A and B – between these points is measured).
O is the point in which the VES is performed.
2.4. Geoelectrical survey methodology
The methodology used for the present report was the application of the indirect Vertical
Electrical Sounding (VES) geoelectric method based on the collection of surface geological data.
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Image 2.1. Location of the VES in the SEE sector (see Annex B. 5)
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Image 2.2. Location of the VES in the NWW sector (see Annex B. 5)
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2.4.2. Desk work
It consisted in processing, analyzing and interpreting all the data generated in the field and desk,
with the support of programs that served to integrate the present report.
2.4.2.1. Data processing
The results obtained in the field comprise 6 VES with a SEE direction and 9 VES with a NWW
direction, aligned longitudinal and transversally to the springs, with the following
characteristics:
VES-01SE Geophysical line
Location
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Photograph 2.2. Location of the transversal line with respect to the springs
Graph 2.1. Apparent Resistivity Values vs. AB/2
Graph 2.2. Interpretation of the Resistivity Model – Layers
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VES-01SE Analysis
The first layer has a depth of 3.6 meters, with a resistivity of 640.2 Ohm-m, and is an indication
of the presence of alluvial material saturated with weathered ignimbrite. The second layer, with
6.43 meters of depth, a thickness of 3.66 m and a resistivity of 88.74 Ohm-m, corresponds to
welded material.
The third layer has a depth of 14.08 meters; the resistance increases at more than 1000 Ohm-m;
this high resistivity corresponds to medium to highly welded ignimbrite, which is an indication
of the rock’s fracturing. The last layer, with a depth of 31.09 m, thickness of 17.01 m, and a
resistivity of 16.5 Ohm-m, corresponds to fractured ignimbrite material.
Note: Prolongation of the following VES in SEE direction (see Annex B. 1).
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Graph 2.1. Apparent Resistivity Values vs. AB/2
Graph 2.2. Interpretation of the Resistivity Model – Layers
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VES-01SE Analysis:
The first layer has a depth of 3.6 meters, with a resistivity of 640.2 Ohm-m, and
is an indication of the presence of alluvial material saturated with weathered
ignimbrite. The second layer, with 6.43 meters of depth, a thickness of 3.66 m
and a resistivity of 88.74 Ohm-m, corresponds to welded material.
The third layer has a depth of 14.08 meters; the resistance increases at more
than 1000 Ohm-m; this high resistivity corresponds to medium to highly welded
ignimbrite, which is an indication of the rock’s fracturing. The last layer,
with a depth of 31.09 m, thickness of 17.01 m, and a resistivity of 16.5 Ohm-m,
corresponds to fractured ignimbrite material.
Note: Prolongation of the following VES in SEE direction (see Annex B. 1).
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VES-01 NE Geophysical line
Location:
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Photograph 2.3. Location of the longitudinal line with respect to the springs
Graph 2.3. Apparent resistivity values vs. AB/2
Graph. 2.4. Interpretation of the Resistivity Model – Layers
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VES-01 NE Analysis:
The 1st layer with resistivity of 866.9 Ohm-m and a depth of 16.28 meters, indicating the presence
of alluvial material saturated with clay sediments and weathered Ignimbrite.
The last layer with 32.32 meters of depth and resistivity of 44.42 Ohm-m corresponds to fractured
Ignimbrite.
NOTE: Continuation of the Vertical Electrical Sounding (VES) in a northwest-west direction (see
Annex B.2).
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LITHOLOGICAL COLUMN OF RESISTIVITIES
2.5. Interpretation of Profiles – Geo-electric Sections
The methodology for the interpretation of the Vertical Electrical Sounding (VES), mentioned in this
chapter, involved the generation of six profiles of resistivity, shown in Annex 8.3, and six geoelectric
sections applying the one-dimensional model of interpretation shown in Annex 8.4.
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2.5.1. Resistivity Profiles
Six resistivity profiles were integrated with an average research depth of 70 to 90 meters; which are
shown below.
Resistivity Profile 1
Integrated by three Vertical Electrical Sounding (VES) (VES-01SE, VES-02SE and VES-03SE)
carried out in the Silala springs with an AB length of 300 meters, with preferential southeast-east
direction and a depth of investigation of up to 70 meters (see Image 2.3). Resistivity values from 30
to more than 1,000 Ohm-m are identified.
Image 2.3: Resistivity Profile 1 (see Annex B.3)
The values between 60 to 180 Ohm-m are located in the superficial part of the north flank up to a
variable depth of 0 to 18 meters. The values of 200 to 600 Ohm-m are located at depth below 20
meters up to a distance of 180 meters. A body of resistivity higher than 800 Ohm-m is located in the
sounding VES-02SE and VES-01SE at a depth of 70 meters, registering volcanic rock. In the VES-
01SE sounding at the depth of 6 meters there is a resistivity of 300 to 600 Ohm-m identified by the
light green color.
2.5. Interpretation of Profiles – Geo-electric Sections
The methodology for the interpretation of the Vertical Electrical Sounding
(VES), mentioned in this chapter, involved the generation of six profiles of
resistivity, shown in Annex 8.3, and six geo- electric sections applying the onedimensional
model of interpretation shown in Annex 8.4.
2.5.1. Resistivity Profiles
Six resistivity profiles were integrated with an average research depth of 70 to
90 meters; which are shown below.
Resistivity Profile 1
Integrated by three Vertical Electrical Sounding (VES) (VES-01SE, VES-02SE
and VES-03SE) carried out in the Silala springs with an AB length of 300 meters,
with preferential southeast-east direction and a depth of investigation of
up to 70 meters (see Image 2.3). Resistivity values from 30 to more than 1,000
Ohm-m are identified.
The values between 60 to 180 Ohm-m are located in the superficial part of the
north flank up to a variable depth of 0 to 18 meters. The values of 200 to 600
Ohm-m
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Resistivity Profile 2
Integrated by three VES (VES-04SE, VES-05SE and VES-06SE) carried out in the Silala springs
with an AB length of 200 meters, with preferential southeast-east direction and a depth of
investigation of up to 70 meters (see Image 2.4).
Figure 2.4: Resistivity Profile 2 (see Annex B.3).
Resistivity values from 40 to more than 500 Ohm-m are identified. The values between 150 to 250
Ohm-m are located in the VES-06SE and VES-05SE up to a variable depth of 1 to 5 meters and 30
meters. The values of 100 to 200 Ohm-m are located at depth, below 10 meters. A body of
resistivity lower than 80 Ohm-m is located in the VES-04SE sounding at a depth of 3 to 5 meters,
recording the presence of groundwater.
Resistivity Profile 3
Integrated by three VES (VES-01NE, VES-02NE - VES-03NE), carried out with an AB length of
300 meters, with preferential northwest-west direction and a depth of investigation of up to 70
meters (see Image 2.5).
are located at depth below 20 meters up to a distance of 180 meters. A body of
resistivity higher than 800 Ohm-m is located in the sounding VES-02SE and
VES-01SE at a depth of 70 meters, registering volcanic rock. In the VES- 01SE
sounding at the depth of 6 meters there is a resistivity of 300 to 600 Ohm-m
identified by the light green color.
Resistivity Profile 2
Integrated by three VES (VES-04SE, VES-05SE and VES-06SE) carried out in
the Silala springs with an AB length of 200 meters, with preferential southeasteast
direction and a depth of investigation of up to 70 meters (see Image 2.4).
Resistivity values from 40 to more than 500 Ohm-m are identified. The values
between 150 to 250 Ohm-m are located in the VES-06SE and VES-05SE up
to a variable depth of 1 to 5 meters and 30 meters. The values of 100 to 200
Ohm-m are located at depth, below 10 meters. A body of resistivity lower than
80 Ohm-m is located in the VES-04SE sounding at a depth of 3 to 5 meters,
recording the presence of groundwater.
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Image 2.5: Resistivity Profile 3 (see Annex B.3).
Resistivity values from 20 to more than 1,000 Ohm-m are identified. Values above 1,000 Ohm-m
are located in the VES-03NE and VES-01NE, up to a variable depth of 3 to 25 meters. The values
of 200 to 500 Ohm-m are located at depth below 20 meters. A body of resistivity lower than 40
Ohm-m is located in the VES-03NE sounding at a depth of 30 meters from 5 meters away,
recording the presence of groundwater due to the low resistivity.
Resistivity Profile 4
Integrated by three VES (VES-01NE, VES-04NE, VES-05NE), with an AB/2 length of 300 meters,
with preferential northwest-west direction and a depth of investigation of 70 meters (see Image
2.6).
Resistivity Profile 3
Integrated by three VES (VES-01NE, VES-02NE - VES-03NE), carried out
with an AB length of 300 meters, with preferential northwest-west direction
and a depth of investigation of up to 70 meters (see Image 2.5).
Resistivity values from 20 to more than 1,000 Ohm-m are identified. Values
above 1,000 Ohm-m are located in the VES-03NE and VES-01NE, up to a variable
depth of 3 to 25 meters. The values of 200 to 500 Ohm-m are located at
depth below 20 meters. A body of resistivity lower than 40 Ohm-m is located in
the VES-03NE sounding at a depth of 30 meters from 5 meters away, recording
the presence of groundwater due to the low resistivity.
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Figure 2.6: Resistivity Profile 4 (see Annex B.3).
Resistivity values from 50 to more than 1,000 Ohm-m are identified. Values between 500 to 1000
Ohm-m are located in VES-01NE - VES-04NE to a variable depth of 0 to 20 meters. The values of
100 to 200 Ohm-m are located in VES-01NE at a depth below 25 meters. A body of resistivity
higher than 200 Ohm-m is located in sounding VES-04NE and VES-05NE at a depth of 8 to 30
meters, respectively, recording the presence of confined groundwater; this is due to the low
resistivity value verified in the profiles.
Resistivity Profile 5
Integrated by three VES (VES-05NE, VES-06NE and VES-07NE), with an AB/2 length of 300
meters, with preferential northwest-west direction and a depth of investigation of up to 70 meters
(see Image 2.7).
Resistivity Profile 4
Integrated by three VES (VES-01NE, VES-04NE, VES-05NE), with an AB/2
length of 300 meters, with preferential northwest-west direction and a depth of
investigation of 70 meters (see Image 2.6).
Resistivity values from 50 to more than 1,000 Ohm-m are identified. Values
between 500 to 1000 Ohm-m are located in VES-01NE - VES-04NE to a variable
depth of 0 to 20 meters. The values of 100 to 200 Ohm-m are located in
VES-01NE at a depth below 25 meters. A body of resistivity higher than 200
Ohm-m is located in sounding VES-04NE and VES-05NE at a depth of 8 to 30
meters, respectively, recording the presence of confined groundwater; this is
due to the low resistivity value verified in the profiles.
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Figure 2.7: Resistivity Profile 5 (see Annex B.3).
Resistivity values from 150 to more than 650 Ohm-m are identified. Values higher than 450 Ohm-m
are located in VES-05NE up to a variable depth of 30 meters and values of 200 to 250 Ohm-m, with
a depth of 30 meters at a distance of 5 meters, registering the presence of underground water.
Values of 300 to 400 Ohm-m are located at a depth below 8 meters, and comprise a distance of 40
meters. A body of resistivity lower than 300 Ohm-m is located in the VES-07NE sounding at a
depth of 5 meters.
Resistivity Profile 6
Integrated by two VES (VES-08NE - VES-09NE), with an AB/2 length of 250 meters, with
preferential northwest-west direction and a depth of investigation of up to 70 meters (see Image
2.8).
Resistivity Profile 5
Integrated by three VES (VES-05NE, VES-06NE and VES-07NE), with an
AB/2 length of 300 meters, with preferential northwest-west direction and a
depth of investigation of up to 70 meters (see Image 2.7).
Resistivity values from 150 to more than 650 Ohm-m are identified. Values
higher than 450 Ohm-m are located in VES-05NE up to a variable depth of 30
meters and values of 200 to 250 Ohm-m, with a depth of 30 meters at a distance
of 5 meters, registering the presence of underground water. Values of 300 to
400 Ohm-m are located at a depth below 8 meters, and comprise a distance of
40 meters. A body of resistivity lower than 300 Ohm-m is located in the VES-
07NE sounding at a depth of 5 meters.
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Distance (m)
Figure 2.8: Resistivity Profile 6 (see Annex B.3).
Resistivity values from 20 to more than 1,000 Ohm-m are identified. The values between 200 to
500 Ohm-m are located in both VES of the survey (VES-08NE and VES-09NE) up to a depth of 70
meters, recording the presence of groundwater in fractured ignimbrites, and this is due to low
resistivity.
2.5.2. Geo-electric Sections
In order to identify the geo-electric units present in the sub-soil and correlate them with the
geological units, six geo-electric sections were elaborated, taking as a basis the resistivity profiles
and the results of the one-dimensional models of each VES.
Geo-electric Section 1. Figure 2.2.
This section identified the last contact at a depth of 70 meters. It has a north-south preferred
direction and is integrated by three VES (VES-01SE, VES-02SE and VES-03SE) with a total AB
length of approximately 300 meters. The analysis indicates the presence of four geo-electric units
with variable thicknesses (see Image 2.9).
Resistivity Profile 6
Integrated by two VES (VES-08NE - VES-09NE), with an AB/2 length of 250
meters, with preferential northwest-west direction and a depth of investigation
of up to 70 meters (see Image 2.8).
Resistivity values from 20 to more than 1,000 Ohm-m are identified. The values
between 200 to 500 Ohm-m are located in both VES of the survey (VES-
08NE and VES-09NE) up to a depth of 70 meters, recording the presence of
groundwater in fractured ignimbrites, and this is due to low resistivity.
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The resistivity values presented in this section range from 50 to more than 1,000 Ohm-m. Unit A is
the first geo-electric unit that is presented; it has resistivity values of 130 to 600 Ohm-m with a
thickness of 1 to 6 meters. Then Unit B is presented, with resistivity values of 70 to 90 Ohm-m with
a thickness of 3 to 5 meters. Unit C has resistivity values from 100 to greater than 1,000 Ohm-m
with a thickness of 7.5 to 20.5 meters. Unit D corresponds to the last geo-electric layer; it has
resistivity values of 20 to 400 Ohm-m with a thickness of 20 to 200 meters. The characteristics of
each geo-electric unit are described in the tables of each respective VES.
Image 2.9: Geo-electric Section 1
GEO-ELECTRIC SECTION N – 1
2.5.2. Geo-electric Sections
In order to identify the geo-electric units present in the sub-soil and correlate
them with the geological units, six geo-electric sections were elaborated, taking
as a basis the resistivity profiles and the results of the one-dimensional models
of each VES.
Geo-electric Section 1. Figure 2.2.
This section identified the last contact at a depth of 70 meters. It has a northsouth
preferred direction and is integrated by three VES (VES-01SE, VES-
02SE and VES-03SE) with a total AB length of approximately 300 meters. The
analysis indicates the presence of four geo-electric units with variable thicknesses
(see Image 2.9).
The resistivity values presented in this section range from 50 to more than 1,000
Ohm-m. Unit A is the first geo-electric unit that is presented; it has resistivity
values of 130 to 600 Ohm-m with a thickness of 1 to 6 meters. Then Unit B is
presented, with resistivity values of 70 to 90 Ohm-m with a thickness of 3 to
5 meters. Unit C has resistivity values from 100 to greater than 1,000 Ohmm
with a thickness of 7.5 to 20.5 meters. Unit D corresponds to the last geoelectric
layer; it has resistivity values of 20 to 400 Ohm-m with a thickness of 20
to 200 meters. The characteristics of each geo-electric unit are described in the
tables of each respective VES.
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Image 2.9: Geo-electric Section 1
GEO-ELECTRIC SECTION N – 1
Figure 2.2: Geo-electric Section of Resistivities 1 (see Annex B.4).
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Geo-electric Section 2. Figure 2.3.
The last contact was identified at a depth between 35 and 50 meters, depending on the location of
the soundings, the largest depth is located in the central part of the profile. It has a preferential eastwest
direction and is composed of three soundings, VES-04SE, VES-05SE and VES-06SE, with a
total AB length of approximately 200 meters. The analysis identifies three geo-electric units with
variable thicknesses (see Image 2.10).
The resistivity values presented in this section vary from 10 to more than 600 Ohm-m. Unit A has
resistivity values of 150 to 207 Ohm-m with a thickness of 1.5 to 3.5 meters. Unit B presents the
values of resistivity from 13 to 98 Ohm-m with a thickness of 1.6 to 5.9 meters. Unit C with
resistivity values greater than 600 Ohm-m is presented as the last layer with a thickness greater than
45 meters. The characteristics of each geo-electric unit are described in the tables of each respective
VES.
Image 2.10: Geo-electric Section 2
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GEO-ELECTRIC SECTION N – 2
Figure 2.3: Geo-electric Section of Resistivities 2 (see Annex B.4).
Geo-electric Section 3. Figure 2.4.
The last contact was identified at a depth of 70 meters. It has a north-south preferred direction and
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Image 2.11: Geo-electric Section 3
GEO-ELECTRIC SECTION N – 3
Geo-electric Section 3. Figure 2.4.
The last contact was identified at a depth of 70 meters. It has a north-south
preferred direction and is integrated by three VES (VES-01NE, VES-02NE
and VES-03NE) with a total AB length of approximately 300 meters. The
analysis indicates the presence of two geo-electric units with variable thicknesses
(see Image 2.11).
The resistivity values presented in this section range from 31 to more than
1,000 Ohm-m. Unit A is the first geo-electric unit that is presented; it has resistivity
values of 200 to 1,167 Ohm-m with thicknesses of 7.7 to 15.6 meters.
Unit B is the last geo-electric unit that is presented, with values of resistivity
from 31 to more than 900 Ohm-m with a thickness of 16 to 30.5 meters. The
characteristics of each geo-electric unit are described in the tables of each
respective VES.
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Image 2.11: Geo-electric Section 3
GEO-ELECTRIC SECTION N – 3
Figure 2.4: Geo-electric Section of Resistivities 3 (see Annex B.4).
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Geo-electric Section 4. Figure [2].5.
The last contact was identified at a depth of 70 meters. It has a north-south preferred direction and
is composed of three VES (VES-01NE, VES-04NE and VES-05NE) with a total AB length of
approximately 300 meters. The analysis indicates the presence of three geo-electric units with
variable thicknesses (see Image 2.12).
The resistivity values presented in this section range from 40 to more than 800 Ohm-m. Unit A is
the first geo-electric unit that is presented only in VES-04NE and VES-05NE; it has resistivity
values of 200 to 300 Ohm-m with a thickness of 4 to 11.5 meters. Unit B has the largest depth that
is located in the central part of the profile, with resistivity values of 430 to 867 Ohm-m with a
thickness of 7 to 41.6 meters. Unit C has resistivity values from 44 to greater than 200 Ohm-m with
a thickness of 16 to 123.5 meters. The characteristics of each geo-electric unit are described in the
tables of each respective VES.
Image 2.12: Geo-electric Section 4
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GEO-ELECTRIC SECTION N – 4
Figure 2.5: Geo-electric Section of Resistivities 4 (see Annex B.4).
Geo-electric Section 5. Figure 2.6.
The geo-electric section 5 identified the last contact at a depth of 70 meters. It has a preferential
east-west direction and is integrated by three VES (VES-05NE, VES-06NE and VES-07NE) with a
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Image 2.13: Geo-electric Section 5
GEO-ELECTRIC SECTION N – 5
Geo-electric Section 5. Figure 2.6.
The geo-electric section 5 identified the last contact at a depth of 70 meters.
It has a preferential east-west direction and is integrated by three VES (VES-
05NE, VES-06NE and VES-07NE) with a total AB length of approximately
300 meters. The analysis indicates the presence of three geo- electric units
with variable thicknesses (see Image 2.13).
The resistivity values presented in this section range from 141 to more than
1,000 Ohm-m. Unit A is the first geo-electric unit that is presented; it has
resistivity values of 230 to 393 Ohm-m with a thickness of 3.6 to 11.5 meters.
Unit B has resistivity values from 342 to more than 1,000 Ohm-m with
a thickness of 7.3 to 59.6 meters. Unit C has the largest depth located on the
right side of the profile, with resistivity values from 141 to greater than 700
Ohm-m with a thickness of 25.3 to 40 meters. The characteristics of each geoelectric
unit are described in the tables of each respective VES.
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Image 2.13: Geo-electric Section 5
GEO-ELECTRIC SECTION N – 5
Figure 2.6: Geo-electric Section of Resistivities 5 (see Annex B.4).
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Geo-electric Section 6. Figure 2.7.
The last contact was identified at a depth of 70 meters. It has a preferential east-west direction and
is integrated by two VES (VES-08NE and VES-09NE), with a total AB length of approximately
250 meters. The analysis indicates the presence of two geo-electric units with variable thicknesses
(see Image 2.14).
The resistivity values presented in this section range from 161 to more than 600 Ohm-m. Unit A is
the first geo-electric unit that is presented; it has resistivity values of 161 to 695 Ohm-m with a
thickness of 1.8 to 2.4 meters. Unit B is presented in greater depth with respect to Unit A as shown
in the profile, with resistivity values of 223.6 to 330 Ohm-m and with a thickness of 60 to 65.8
meters. The characteristics of each geo-electric unit are described in the tables of each respective
VES.
Image 2.14: Geo-electric Section 6
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GEO-ELECTRIC SECTION N – 6
Figure 2.7: Geo-electric Section of Resistivities 6 (see Annex B.4).
Conclusions CHAPTER 11 (GEOPHYSICS)
In the study area, 15 Vertical Electrical Soundings (VES) were made; in southeast-east and northwest
direction, where the following aspects are concluded:
VES-01SE Analysis:
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Conclusions CHAPTER 11 (GEOPHYSICS)
In the study area, 15 Vertical Electrical Soundings (VES) were made; in southeast-
east and north- west direction, where the following aspects are concluded:
VES-01SE Analysis:
The 1st layer has a depth of 3.6 meters, with a resistivity of 640.2 Ohm-m; it
indicates the presence of alluvial material saturated with weathered Ignimbrite.
The 2nd layer with 6.43 meters of depth, has a thickness of 3.66 meters and a
resistivity of 88.74 Ohm-m, corresponding to welded ignimbrite material.
The 3rd layer is 14.08 meters deep and the resistance increases to more than
1000 Ohm-m. This high resistivity corresponds to a medium-high saturated
ignimbrite, which indicates the fracturing of the rock. The last layer has a depth
of 31.09 meters, a thickness of 17.01 meters and a resistivity of 16.5 Ohm-m; it
corresponds to fractured ignimbrite material. The presence of the water table is
found from 0.28 meters, being a level considered as almost emerging.
VES-02SE Analysis:
The 1st layer has a depth of 5,255 meters, a resistivity of 137.8 Ohm-m, which
indicates the presence of alluvial material saturated with weathered ignimbrite.
The 2nd layer has 9.92 meters of depth, a thickness of 4,664 meters and a resistivity
of 75.83 Ohm-m, corresponding to welded ignimbrite.
The 3rd layer has a depth of 30.71 meters and a resistivity of 158.4 Ohm-m.
This resistivity corresponds to medium-high saturated ignimbrite, which indicates
the fracturing of the rock.
Finally, the last layer has a resistivity of 249.4 Ohm-m with a depth of 70.92
meters, indicating the presence of fractured ignimbrite.
VES-03SE Analysis:
The 1st layer has a depth of 5,255 meters, has a resistivity of 135.8 Ohm-m,
which indicates the presence of alluvial material saturated with weathered ignimbrite.
The 2nd layer has a depth of 16.44 meters, a thickness of 1,962 meters
and a resistivity of 75.27 Ohm-m, corresponding to welded ignimbrite.
The 3rd layer has a depth of 34.35 meters and a resistivity of 145.2 Ohm-m.
This resistivity corresponds to medium-high saturated ignimbrite, which indicates
the fracturing of the rock.
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The last layer has a depth of 71.78 meters, a thickness of 17.91 meters and a
resistivity of 368.6 Ohm-m, indicating the presence of fractured ignimbrite.
VES-04SE Analysis:
The 1st layer has a depth of 2,697 meters, a resistivity of 202.2 Ohm-m, which
indicates the presence of alluvial material saturated with mixture of mediumhigh
fractured ignimbrite. The 2nd layer has a depth of 4,324 meters and a
thickness of 1,628 meters, a resistivity of 37.88 Ohm-m and corresponds to
welded material.
The 3rd layer has a depth of 43.88 meters, a thickness of 39.55 meters, a resistivity
of 206.1 Ohm-m, resistivity that responds to fractured ignimbrite, which
indicates the fracturing of the rock.
VES-05SE Analysis:
The 1st layer has a depth of 1.5 meters with a resistivity of 155.3 Ohm-m; it
indicates the presence of alluvial material saturated with fractured mediumhigh
ignimbrite mixture. The 2nd layer has a depth of 4,324 meters, a thickness
of 1,628 meters, with a resistivity of 37.88 Ohm-m, corresponding to welded
ignimbrite.
The 3rd layer has a depth of 43.88 meters, a thickness of 45.55 meters and a
resistivity of 206.1 Ohm-m; it responds to fractured ignimbrite, which indicates
the fracturing of the rock.
VES-06SE Analysis:
The 1st layer has a depth of 3,174 meters with a resistivity of 207.3 Ohm-m;
it indicates the presence of alluvial material saturated with fractured mediumhigh
ignimbrite mixture. The 2nd layer has a depth of 3.31 meters, a thickness
of 3.301 meters, with a resistivity of 13.22 Ohm-m, corresponding to welded
material.
The last layer has a depth of 35.43 meters and a resistivity of 604.2 Ohm-m; it
belongs to fractured ignimbrite, which indicates the fracturing of the rock.
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VES-01NE Analysis:
The 1st layer has a resistivity of 866.9 Ohm-m and a depth of 16.28 meters. It
indicates the presence of alluvial material saturated with clay sediments and
weathered ignimbrite.
The last layer has a depth of 32.32 meters and a resistivity of 44.42 Ohm-m,
corresponding to fractured ignimbrite. The presence of the water table is found
from 0.40 meters.
VES-02NE Analysis:
The 1st layer has a resistivity of 200.4 Ohm-m and a depth of 20.76 meters. It
indicates the presence of alluvial material with clay sediments and weathered
ignimbrite.
The last layer has a depth of 62.55 meters and a resistivity of 901 Ohm-m, corresponding
to fractured ignimbrite.
VES-03NE Analysis:
The 1st layer has a resistivity of 1167 Ohm-m and a depth of 22.7 meters. It
indicates the presence of alluvial material saturated with clay sediments and
weathered ignimbrite.
The last layer has a depth of 46.59 meters and a resistivity of 31.23 Ohm-m,
corresponding to fractured ignimbrite.
VES-04NE Analysis:
The 1st layer has a depth of 4,044 meters and a resistivity of 257.4 Ohm-m. It
indicates the presence of alluvial material saturated with sandy sediments. The
2nd layer has a depth of 45.69 meters, a thickness of 41.65 meters and a resistivity
of 429.6 Ohm-m, corresponding to sandy-clayey sediments.
The 3rd layer has a depth of 69.3 meters and a resistivity of 200.8 Ohm-m,
corresponding to fractured ignimbrite that indicates the fracturing of the rock.
VES-05NE Analysis:
The 1st layer has a depth of 11.45 meters and a resistivity of 295.6 Ohm-m,
indicating the presence of alluvial material saturated with sandy sediments. The
2nd layer has a depth of 26.96 meters, a thickness of 15.5 meters and a resistivity
of 600.9 Ohm-m, corresponding to sandy-clayey sediments.
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The last layer has a depth of 54.27 meters and a resistivity of 141.9 Ohm-m,
corresponding to fractured ignimbrite that indicates the fracturing of the rock.
VES-06NE Analysis:
The 1st layer has a depth of 3.622 meters and a resistivity of 239 Ohm-m, indicating
the presence of alluvial material saturated with sandy sediments. The
2nd layer has a depth of 63.25 meters, a thickness of 59.63 meters and a resistivity
of 342.4 Ohm-m, corresponding to sandy-clayey sediments.
The 3rd layer has a depth of 59.52 meters and a resistivity of 780.1 Ohm-m,
corresponding to fractured ignimbrite that indicates the fracturing of the rock.
VES-07NE Analysis:
The 1st layer has a depth of 10.12 meters and a resistivity of 392.9 Ohm-m, indicating
the presence of alluvial material with sandy sediments. The 2nd layer
has a depth of 17.48 meters, a thickness of 7.363 meters and a resistivity of
1,112 Ohm-m, corresponding to sandy-clayey sediments.
The last layer has a depth of 42.81 meters and a resistivity of 154.4 Ohm-m,
corresponding to fractured ignimbrite that indicates the fracturing of the rock.
VES-08NE Analysis:
The 1st layer has a depth of 2.368 meters and a resistivity of 694.9 Ohm-m,
indicating the presence of alluvial material with sandy-clayey sediments. The
2nd layer has a depth of 58.47 meters, a thickness of 60.36 meters and a resistivity
of 223.6 Ohm-m, corresponding to fractured ignimbrite.
VES-09NE Analysis:
The 1st layer has a depth of 1.831 meters and a resistivity of 161.3 Ohm-m,
indicating the presence of alluvial material with sandy-clayey sediments. The
2nd layer has a depth of 67.65 meters, a thickness of 65.82 meters and a resistivity
of 330.4 Ohm-m, corresponding to fractured ignimbrite material.
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Recommendations
It is recommended to take into account the VES geophysical tests carried out
in the south- east and north-east directions in the springs, which show lithological
correlation of alluvial sediments and fractured ignimbrite volcanic material.
Seismic refraction methods must be designed at a great depth in order to pass
the ignimbrite packages and detect the underground water storage package.
Drilling is recommended in the southeast - northeast sectors, in the head and
at the end of the spring system, where the capacity of groundwater flow can be
defined through hydraulic tests (Lefrang Method).
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CHAPTER 3
MODELLING
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TABLE OF CONTENTS
3.1. Background
3.2. Justification
3.3. Objective
3.4. Meteorological Information
3.5. Water Balance Calculation Methodology
3.6. Simulation of the percentage of runoff from precipitation
3.6.1. Geology of the Silala zone
3.6.2. Description of the vegetation map
3.6.3. Description of the infiltration map
3.6.4. Percent Slope Map
3.6.5. Map of Surface Runoff, Infiltration and Storage
3.7. Potential Evapotranspiration
3.7.1. Temperature Adjustment with Digital Terrain Elevation Model
3.7.2. Heat index (I)
3.7.3. Hours of brightness (d)
3.7.4. Modification factor (a)
3.7.5. Calculation of Potential Evapotranspiration (Combination of T, I, d, a)
3.8. Soil Water Retention Capacity
3.9. Soil texture map
3.10. Map of stoniness and gravel in percentage (%)
3.11. Potential retention capacity
3.12. Real moisture retention in the soil
3.13. Real Evapotranspiration
3.14. Water deficit
3.15Water surplus
3.16. Water supply
Conclusions
Recommendations
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FIGURES
Figure 3.1. Location of simulated stations
Figure 3.2. Monthly precipitation graph for simulated stations
Figure 3.3. Monthly average temperature graph for simulated stations
Figure 3.4. Flowchart of the numerical simulation of water supply
Figure 3.5. Potential annual evapotranspiration in the zone of the Silala springs
Figure 3.6. Actual annual evapotranspiration in the zone of the Silala springs
Figure 3.7. Percentage of stoniness. Silala Springs
Figure 3.8. Calculation point and statistical analysis
TABLES
Table 3.1. Stations taken into account for numerical simulation (Source LOCCLIM)
Table 3.2. Total monthly precipitation data of stations simulated from the LOCCLIM satellite
Table 3.3. Average monthly temperature data for simulated stations from the LOCCLIM satellite
Table 3.4. Geological units of the Silala springs
Table 3.5. Vegetation units of the Silala springs
Table 3.6. Infiltration units of the Silala springs
Table 3.7. Factors for the estimation of the SCS USA Surface Runoff
Table 3.8. Possible duration of hours of brightness Thornthwaite (1948)
Table 3.9. Silala Basin Soil Texture Units
Table 3.10. Percentage of stoniness. Silala Springs
Table 3.11. Retention capacity of soil moisture. (Drainage Analisis and Extraction of hidrologic
Propertis from a Digital Elevation Model (1996)
Table 3.12. Table of attributes of the map of the geological units of the area of the springs of Silala
Table 3.13. Statistical analysis of the area of the Silala springs (in hm³ and in l/sec)
MAPS
Map 3.1. Geological map of the Silala springs
Map 3.2. Vegetation units of the Silala springs
Map 3.3. Infiltration units of the Silala springs
Map 3.4. Silala Springs digital terrain elevation model
Map 3.5. Percentage map of runoff from Silala springs
Map 3.6. Soil texture map of the Silala springs
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CHAPTER III. SIMULATION OF THE WATER SUPPLY OF THE SILALA
SPRINGS
3.1. Background
According to Hydraulic Dams and Desertification in Bolivia (1995), to determine
the relationships between water supply, captured water, water dedicated
to consumptive use of crops, and water which returns, and requires a series of
hydrological analysis data.
In the study area, the hydrological regime is variable during the seasons of the
year, with very little contribution of rain, according to historical precipitation
data is 80 mm; therefore, the problem of establishing a water balance becomes
more complicated.
According to water balance calculation methods, knowledge of the structure of
the water balance of lagoons, surface basins and subterranean basins is fundamental
for to achieve a more rational use of water resources in space and time,
as well as to improve their control and redistribution.
On the other hand, the effects of climate change are becoming increasingly
evident in the world and therefore in Bolivia. In the highlands of our country,
the surface water regime has emerged from the historically known hydrological
regimes. Periods of drought and intense precipitation are less and less predictable.
It is therefore necessary to clarify the relationship between soil-waterplant-
air.
The present research consists of carrying out a water balance to establish the
movement of water and the water supply or runoff. In the study area, the numerical
simulation value of the water balance is intended to quantify the contribution
of rainwater to the volume of water anthropically channeled to the
neighboring country of Chile.
In the study area there is no meteorological information or hydrological studies,
the station closest to 40 km is Laguna Colorada, whose data are very consistent,
the same that served to calibrate the modeling. For this reason, a classical
water balance was not undertaken, which is why it was decided to carry out a
“numerical simulation” of the water supply from the Silala springs.
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3.2. Justification
During the last few decades, there has been a lack of information on the origin
of the water resources drained by the aforementioned artificial channels; therefore
it is necessary to quantify the origin of these water resources and determine
whether the source is surface water, groundwater or a percentage of both.
3.3. Objective
Numerically simulate the surface water supply of the Silala zone, which will
make it possible to quantify the amount of rainwater that reaches the drainage
channels.
3.4. Meteorological Information
In spite of having a very significant advance in the application of remote sensors
with multi- resolution and multi-temporal images, the greatest difficulty
consists in obtaining meteorological data. This occurs in Bolivian territory as
in most of the countries of the region; however through specialized software it
is possible to access data, including timetables, from automatic stations located
in various parts of our planet and our country.
In this respect, in 2002, the LOCLIM software was developed to provide an
estimate of the climatic conditions around the globe, and to obtain a database
of more than 30000 stations located all over the world. This software has incorporated
several methods of interpolation of specific data and it was considered
that, for the purposes of estimating the water supply of the study area, this information
is appropriate because it was validated with historical data from the
weather station of Colorada Lagoon.
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
In this respect, in 2002, the LOCLIM software was developed to provide an estimate of the climatic
conditions around the globe, and to obtain a database of more than 30000 stations located all over
the world. This software has incorporated several methods of interpolation of specific data and it
was considered that, for the purposes of estimating the water supply of the study area, this
information is appropriate because it was validated with historical data from the weather station of
Colorada Lagoon.
Figure 3.1. Location of simulated stations
N° NAME COUNTRY Longitude Latitude Elevation
(m.a.s.l.)
1 Alto D Comete Argentina -65,26 -24,21 1.253,0
2 Jujuy Argentina -65,28 -24,16 1.303,0
3 La Quiaca Argentina -65,60 -22,10 3.459,0
4 S. Salvador D Argentina -65,30 -24,18 1.303,0
5 Salta-Aereo Argentina -65,48 -24,85 1.221,0
6 Challapata Bolivia -66,76 -18,86 3.720,0
7 Chuquina Bolivia -67,40 -17,83 3.824,0
8 Oploca Bolivia -65,76 -21,31 3.120,0
9 Oruro Bolivia -67,06 -18,05 3.702,0
10 Pazña Bolivia -66,90 -18,60 3.710,0
11 Pocoata Bolivia -66,16 -18,65 3.423,0
12 Potosi Bolivia -65,71 -19,53 3.934,0
13 Puna Bolivia -65,46 -19,75 3.420,0
14 Salinas de G Bolivia -67,70 -19,60 3.630,0
15 Sucre Bolivia -65,26 -19,01 2.903,0
16 Tacagua Bolivia -66,76 -18,88 3.720,0
17 Tarija Bolivia -64,71 -21,53 1.875,0
18 Calama Chile -68,90 -22,50 2.312,0
19 Parincota Chile -69,26 -18,16 4.420,0
20 Refresco Chile -69,86 -25,31 1.850,0
Table 3.1. Stations taken into account for numerical simulation (Source LOCCLIM)
The LocClim software, based on information from a point expressed in latitude, longitude and
elevation, provides data on the monthly total precipitation average and monthly average
temperature for a year (January to December). The consistency of the simulated information
through ten points located in the study area was verified with data from the Laguna Colorada
station.
Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
EstSim1 82,7 69,0 24,8 0,0 0,0 1,3 1,3 0,5 0,0 0,0 0,0 7,3
EstSim2 23,5 0,0 0,0 0,4 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim3 9,8 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
12 Potosi Bolivia -65,71 -19,53 3.934,0
13 Puna Bolivia -65,46 -19,75 3.420,0
14 Salinas de G Bolivia -67,70 -19,60 3.630,0
15 Sucre Bolivia -65,26 -19,01 2.903,0
16 Tacagua Bolivia -66,76 -18,88 3.720,0
17 Tarija Bolivia -64,71 -21,53 1.875,0
18 Calama Chile -68,90 -22,50 2.312,0
19 Parincota Chile -69,26 -18,16 4.420,0
20 Refresco Chile -69,86 -25,31 1.850,0
Table 3.1. Stations taken into account for numerical simulation (Source LOCCLIM)
The LocClim software, based on information from a point expressed in latitude, longitude and
elevation, provides data on the monthly total precipitation average and monthly average
temperature for a year (January to December). The consistency of the simulated information
through ten points located in the study area was verified with data from the Laguna Colorada
station.
Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
EstSim1 82,7 69,0 24,8 0,0 0,0 1,3 1,3 0,5 0,0 0,0 0,0 7,3
EstSim2 23,5 0,0 0,0 0,4 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim3 9,8 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim4 29,2 12,2 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim5 41,7 26,0 1,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim6 32,6 15,3 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim7 25,1 8,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim8 18,4 1,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim9 39,1 23,1 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
EstSim10 48,4 32,9 4,9 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0 0,0
Table 3.2. Total monthly precipitation data of stations simulated from the LOCCLIM satellite
The LocClim software, based on information from a point expressed in latitude,
longitude and elevation, provides data on the monthly total precipitation
average and monthly average temperature for a year (January to December).
The consistency of the simulated information through ten points located in the
study area was verified with data from the Laguna Colorada station.
Figure 3.1 shows the location of the simulated stations (points), with precipitation
and temperature data. The simulation of the water supply or surface runoff
was carried out with information from the stations shown in Table 3. 1. 20 stations
were taken into account, of which 5 are from Argentina, 12 from Bolivia
and 3 from Chile Table 3.1.
Figure 3.2. Monthly precipitation graph for simulated stations
Figure 3.1 shows the location of the simulated stations (points), with precipitation and temperature
data. The simulation of the water supply or surface runoff was carried out with information from the
stations shown in Table 3. 1. 20 stations were taken into account, of which 5 are from Argentina, 12
from Bolivia and 3 from Chile Table 3.
1.
Station Jan Feb Mar Ap
r
May Jun Jul Aug Sep Oct Nov Dec Elevation
EstSim1 9,50 9,34 9,24 7,5
5
4,60 1,19 1,52 2,36 5,33 6,92 8,19 9,21 4281,00
EstSim2 5,27 5,44 5,68 4,4
3
1,37 -2,16 -1,76 -1,22 1,67 3,18 4,30 5,08 5345,00
EstSim3 5,42 5,59 5,86 4,4
6
1,48 -1,97 -1,51 -1,08 1,84 3,27 4,36 5,17 5636,00
EstSim4 7,09 7,11 7,22 5,8
1
2,77 -0,76 -0,40 0,31 3,26 4,84 6,03 6,89 4897,00
EstSim5 10,0
5
10,0
6
10,3
0
6,9
7
1,33 -4,89 -4,03 -3,14 2,00 4,58 6,74 9,97 4591,00
EstSim6 7,20 7,21 7,31 5,9
0
2,86 -0,68 -0,32 0,40 3,36 4,94 6,13 7,00 4876,00
EstSim7 7,90 7,92 8,26 6,7
3,70 0,19 0,68 1,33 4,42 5,98 7,07 7,79 4978,00
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
Figure 3.2. Monthly precipitation graph for simulated stations
Figure 3.1 shows the location of the simulated stations (points), with precipitation and temperature
data. The simulation of the water supply or surface runoff was carried out with information from the
stations shown in Table 3. 1. 20 stations were taken into account, of which 5 are from Argentina, 12
from Bolivia and 3 from Chile Table 3.
1.
Station Jan Feb Mar Ap
r
May Jun Jul Aug Sep Oct Nov Dec Elevation
EstSim1 9,50 9,34 9,24 7,5
5
4,60 1,19 1,52 2,36 5,33 6,92 8,19 9,21 4281,00
EstSim2 5,27 5,44 5,68 4,4
3
1,37 -2,16 -1,76 -1,22 1,67 3,18 4,30 5,08 5345,00
EstSim3 5,42 5,59 5,86 4,4
6
1,48 -1,97 -1,51 -1,08 1,84 3,27 4,36 5,17 5636,00
EstSim4 7,09 7,11 7,22 5,8
1
2,77 -0,76 -0,40 0,31 3,26 4,84 6,03 6,89 4897,00
EstSim5 10,0
5
10,0
6
10,3
0
6,9
7
1,33 -4,89 -4,03 -3,14 2,00 4,58 6,74 9,97 4591,00
EstSim6 7,20 7,21 7,31 5,9
0
2,86 -0,68 -0,32 0,40 3,36 4,94 6,13 7,00 4876,00
EstSim7 7,90 7,92 8,26 6,7
8
3,70 0,19 0,68 1,33 4,42 5,98 7,07 7,79 4978,00
EstSim8 7,60 7,65 8,07 6,6
2
3,49 -0,06 0,45 1,11 4,22 5,80 6,88 7,51 5117,00
EstSim9 9,13 9,05 9,27 7,6
9
4,61 1,10 1,54 2,33 5,44 7,05 8,21 8,99 4650,00
EstSim10 8,85 8,75 8,71 7,0
7
4,11 0,68 1,03 1,81 4,78 6,35 7,59 8,57 4455,00
Table 3.3. Average monthly temperature data for simulated stations from the LOCCLIM satellite
Figure 3.3. Monthly average temperature graph for simulated stations
Table 3.2 shows the average monthly precipitation of the ten simulated stations. Figure 3.2 details
the relationship of precipitation vs. months of the ten stations simulated in the Silala.
On the other hand, Table 3.3 shows the information on the average monthly temperature of the ten
simulated stations, and Figure 3.3 shows the graph representing the average monthly temperature of
the ten simulated stations.
From these data, interpolated and rasterized precipitation maps are obtained for the twelve months.
For temperature, the Thornthwaite-Mather formula uses the average temperature per month. In flat
terrain it is correct to interpolate the linear temperature between the seasons of the climate. In
regions where there is a large difference in altitude, this method will not work. With the empirical
knowledge that temperature decreases by 0.46 C for every 100 meters of altitude increase it is
possible to optimize the interpolation method (Agricultural Compendium, 1981). If the actual
altitude is greater than the theoretical altitude, the temperature correction is subtracted (the
temperature decreases as the altitude increases). If the actual altitude is lower than the theoretical
altitude, the temperature correction is added (the temperature increases as the altitude decreases).
Table 3.2 shows the average monthly precipitation of the ten simulated stations.
Figure 3.2 details the relationship of precipitation vs. months of the ten
stations simulated in the Silala.
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On the other hand, Table 3.3 shows the information on the average monthly
temperature of the ten simulated stations, and Figure 3.3 shows the graph representing
the average monthly temperature of the ten simulated stations.
From these data, interpolated and rasterized precipitation maps are obtained
for the twelve months.
For temperature, the Thornthwaite-Mather formula uses the average temperature
per month. In flat terrain it is correct to interpolate the linear temperature
between the seasons of the climate. In regions where there is a large difference
in altitude, this method will not work. With the empirical knowledge that
temperature decreases by 0.46 C for every 100 meters of altitude increase it
is possible to optimize the interpolation method (Agricultural Compendium,
1981). If the actual altitude is greater than the theoretical altitude, the temperature
correction is subtracted (the temperature decreases as the altitude
increases). If the actual altitude is lower than the theoretical altitude, the
temperature correction is added (the temperature increases as the altitude
decreases). This form of interpolation was used by Orstom/Unesco/II 11I/Scnamhi
(1990).
Under this principle, the interpolated temperatures were corrected, obtaining
corrected temperature maps for the months January to December.
3.5. Water Balance Calculation Methodology
The water balance model is based on equilibrium calculations by C.W. Thorntwaite
and J.R. Mather Thorntwaite and Mather, 1995. The model calculates
the water balance for a point. With the use of GIS, the water balance is modeled
taking into account the spatial distribution of precipitation, evapotranspiration,
temperature and characteristics of geology, soil, vegetation, etc.
The general formula of the water balance can be expressed by the following
equation:
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Where:
P= Precipitation
ETR= Real Evapotranspiration
D= Surface Runoff (Supply)
R= Deep Infiltration or Percolation
S= variation in retention of water storage in the soil
These are the main elements that have to be estimated to calculate the moisture
content in the soil, deficit and supply or runoff of water for the area of the Silala
springs.
It is then possible to visualize how the deficit and supply act, in spatial and
temporal variation, during the hydrological year, to estimate how much of the
water flow, coming from rain, feeds the flow of the artificial channels, without
taking into account the great contribution of the underground aquifers of the
Silala springs.
In a simple way, the work methodology is exemplified in the flow chart represented
in Figure 3. 4. This flow diagram conceptualizes the GIS platform with
the relationships and links of the elements considered in the calculation of the
water supply, as they are presented below where each of the formulas used is
specified.
One of the great advantages of the Geographic Information System is that it
allows the introduction and execution of mathematical and statistical formulas
that even facilitate the elaboration of a model for the calculations as if they
were matrices in raster format for spatial-temporal analysis. All the formulas
used are described in this report according to their application.
In the flow diagram it can be observed that the initial maps are the GEOLOGICAL,
the TOPOGRAPHIC, the HISTORICAL MONTHLY ACCUMULATED
PRECIPITATION information and the HISTORICAL MONTHLY MEDIUM
TEMPERATURE of the ten points strategically chosen according to their
geographical location and elevation (see Figure 3.1).
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
Figure 3.4. Flowchart of the numerical simulation of water supply
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3.6. Simulation of the percentage of runoff from precipitation
The biophysical maps required for the calculation of the "monthly supply" of water in the Silala study area by
the Thornthwaite & Mather method are (see Figure 3.4):
Geological
Vegetation
Infiltration
Digital Elevation Model
3.6.1. Geology of the Silala zone
The interpretation of the geology of the study area was carried out using the interpretation of remote sensors and
based on geological reports from institutions such as SERGEOMIN, corroborated by the survey of geological
information from field to detail carried out by the brigade of the Tomas Frias Autonomous University.
The unit that occupies the largest area are the Mio-Pliocenic volcanic lava, occupying 105, 16 km2, representing
42.2% of the study area. This unit is preferably located on the southern and northern flanks with small outcrops
to the east and west of the study area (see Table 3. 4 and Map 3. 1).
The second most important geological unit are the Rhyolitic Ignimbrites (Welded tu ’s) with a total of 87 km2,
representing 34.9% of the total area. This unit is preferably located to the north and east; however, there are also
smaller outcrops to the west and south of the study area (see Table 3.4 and Map 3.1).
On the other hand, with an area of 57.2 km2 and 22.9% of the study area, there are the Pleistocene Non-
Consolidated Deposits, which are located in the central part of the study area (see Table 3. 4 and Map 3. 1).
GEOLOGICAL UNIT Area (m2) Area (km2) % Area
Mio-pliocenic volcanic lavas 105162500 105,2 42,2
Rhyolite Ignimbrites (Welded Tu ’s) 86996875 87,0 34,9
Pleistocenic non-consolidated deposits 57160000 57,2 22,9
SUM 249319375 249,3 100,0
Table 3.4. Geological units of the Silala springs
3.6. Simulation of the percentage of runoff from precipitation
The biophysical maps required for the calculation of the “monthly supply” of
water in the Silala study area by the Thornthwaite & Mather method are (see
Figure 3.4):
Geological
Vegetation
Infiltration
Digital Elevation Model
3.6.1. Geology of the Silala zone
The interpretation of the geology of the study area was carried out using the
interpretation of remote sensors and based on geological reports from institutions
such as SERGEOMIN, corroborated by the survey of geological
information from field to detail carried out by the brigade of the Tomas Frias
Autonomous University.
The unit that occupies the largest area are the Mio-Pliocenic volcanic lava,
occupying 105, 16 km2, representing 42.2% of the study area. This unit is
preferably located on the southern and northern flanks with small outcrops to
the east and west of the study area (see Table 3. 4 and Map 3. 1).
The second most important geological unit are the Rhyolitic Ignimbrites
(Welded tuff’s) with a total of 87 km2, representing 34.9% of the total area.
This unit is preferably located to the north and east; however, there are also
smaller outcrops to the west and south of the study area (see Table 3.4 and
Map 3.1).
On the other hand, with an area of 57.2 km2 and 22.9% of the study area,
there are the Pleistocene Non- Consolidated Deposits, which are located in
the central part of the study area (see Table 3. 4 and Map 3. 1).
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
GEOLOGICAL MAP SPRINGS
OF SILALA
Volcanic lavas
Ignimbrites
Non-consolidated deposits
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186
English translation prepared by DIREMAR. The original language text remains the authoritative one.
3.6.2. Description of the vegetation map
The vegetation has a very important influence on the amount of surface runoff. Dense and high vegetation can
intercept rainfall, while incipient vegetation can favor soil erosion and the amount of supply water in the study
area. The vegetation also protects the soil against the direct impact of raindrops on soil aggregates (Margan,
1981). According to the Soil Conservation Service (1964), five classes are defined:
No vegetation
Crops (permanent and temporary)
Grass, open vegetation
Shrubs and
Forest, dense vegetation
Due to the characteristics of the area of the Silala springs, only two units were identified: ''Grass, open
vegetation'' and 'no vegetation' (see Table 3.5).
VEGETATION UNITS Area (m2) Area (Km2) % Area
No vegetation 192159375 192,2 77,1
Grass and open vegetation 57160000 57,2 22,9
SUM 249319375 249,3 100,0
Table 3.5. Vegetation units of the Silala springs
The predominant unit is "No vegetation", with an area of 192.2 km2, occupying 77.1% of the total area of the
study area. This unit is found throughout the entire study area (see Table 3.5 and Map 3.2).
A second unit is "Grass and open vegetation", whose area is 57.2 km2, which represents 22.9% of the total area.
Like the previous unit, it is found along the whole basin, with intercalations of the unit of Pasture and Open
Vegetation (see Table 3. 5 and Map 3. 2).
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
MAP OF VEGETATION
SPRINGS OF SILALA
Grass and open vegetation
No vegetation
Map 3.2. Vegetation units of the Silala springs
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3.6.3. Description of the infiltration map
Infiltration is the passage of water through the surface of the soil to the interior of the earth; percolation is the
movement of water within the ground and both phenomena are closely linked, because the first cannot continue
until the second takes place.
The water that infiltrates in excess of the subsurface runoff may become part of the groundwater, which may
eventually reach the watercourses.
Therefore, infiltration is the process by which water penetrates the soil, through the surface of the land, and is
retained by it or reaches an aquifer level increasing the previously accumulated volume. Surpassed by the field
capacity of the soil, the water descends by the combined action of capillary forces and gravity. This part of the
process is called infiltration - storage.
In the present research work, this parameter is fundamental to define the degree of infiltration, which in turn is
defined as the volume of water infiltrated by a horizontal unit of the surface soil area at any given moment (Hess
& Lovelace, 1994). In the US Soil Conservation classification, 3 classes are assigned to infiltration velocity: low,
moderate and high.
For this purpose, several infiltration tests were carried out in the area of the Silala springs (see photographs 5, 6
and 7 in Annex C.1). After evaluating the infiltration tests, the geology map was reclassified according to these
three levels of infiltration; however, in the study zone only Moderate and Low infiltration are presented (see
Table 3. 6). This information is used for its application in the crossing of two-dimensional maps and tables for
the estimation of runoff.
INFILTRATION UNITS Area (m2) Area (Km2) % Area
Moderate 162322500 162,3 65,1
Low 86996875 87,0 34,9
SUM 249319375 249,3 100,0
Table 3.6. Infiltration units of the Silala springs
The moderate infiltration coincides with the outcrops of quaternary rock, whose porosity is high. The geological
formations of this group are characterized by the fact that they are made up of loose material from nonconsolidated
materials. Moderate porosity formations occupy 162.3 km2, representing 65.1% of the study area
and are located throughout the study area (Table 3. 6 and Map 3. 3).
The low permeability formations occupy 87.0 km2, representing 34.9% of the total area of the study zone. Their
location is adjacent to the least permeable geological formations of the area, such as outcrops of volcanic
igneous rock (Table 3. 6 and Map 3. 3).
3.6.4. Percent Slope Map
For the calculation of the slope, it is required the digital elevation model of the terrain that was obtained from the
delimitation of the study area. The highest elevation of the study basin is 5689 and the minimum elevation is
4301 meters above sea level. (see Map 3. 4)
3.6.3. Description of the infiltration map
Infiltration is the passage of water through the surface of the soil to the interior
of the earth; percolation is the movement of water within the ground and both
phenomena are closely linked, because the first cannot continue until the second
takes place.
The water that infiltrates in excess of the subsurface runoff may become part of
the groundwater, which may eventually reach the watercourses.
Therefore, infiltration is the process by which water penetrates the soil, through
the surface of the land, and is retained by it or reaches an aquifer level increasing
the previously accumulated volume. Surpassed by the field capacity of the
soil, the water descends by the combined action of capillary forces and gravity.
This part of the process is called infiltration - storage.
In the present research work, this parameter is fundamental to define the degree
of infiltration, which in turn is defined as the volume of water infiltrated by a
horizontal unit of the surface soil area at any given moment (Hess & Lovelace,
1994). In the US Soil Conservation classification, 3 classes are assigned to infiltration
velocity: low, moderate and high.
For this purpose, several infiltration tests were carried out in the area of the
Silala springs (see photographs 5, 6 and 7 in Annex C.1). After evaluating the
infiltration tests, the geology map was reclassified according to these three levels
of infiltration; however, in the study zone only Moderate and Low infiltration
are presented (see Table 3. 6). This information is used for its application
in the crossing of two-dimensional maps and tables for the estimation of runoff.
The moderate infiltration coincides with the outcrops of quaternary rock, whose
porosity is high. The geological formations of this group are
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From the digital elevation model, gradients in the "x" and "y" directions were extracted. From the gradient maps
dfdx and dfdy and applying the following equation, the percentage slope map is obtained in raster format.
Slope:= (((HYP(dfdx, dfdy)/20)*100))
However, this map of percentage slopes must still be reclassified in the ranges that allow the application of the
runoff classification method. The ranks are as follows:
0-1%
1-5%
5-20%
20-50%
>50
This reclassified map is intended to perform a multi-criteria analysis in combination with vegetation and
infiltration maps.
From the digital elevation model, gradients in the "x" and "y" directions were extracted. From the gradient maps
dfdx and dfdy and applying the following equation, the percentage slope map is obtained in raster format.
Slope:= (((HYP(dfdx, dfdy)/20)*100))
However, this map of percentage slopes must still be reclassified in the ranges that allow the application of the
runoff classification method. The ranks are as follows:
0-1%
1-5%
5-20%
20-50%
>50
This reclassified map is intended to perform a multi-criteria analysis in combination with vegetation and
infiltration maps.
characterized by the fact that they are made up of loose material from nonconsolidated
materials. Moderate porosity formations occupy 162.3 km2,
representing 65.1% of the study area and are located throughout the study
area (Table 3. 6 and Map 3. 3).
The low permeability formations occupy 87.0 km2, representing 34.9% of the
total area of the study zone. Their location is adjacent to the least permeable
geological formations of the area, such as outcrops of volcanic igneous rock
(Table 3. 6 and Map 3. 3).
3.6.4. Percent Slope Map
For the calculation of the slope, it is required the digital elevation model of
the terrain that was obtained from the delimitation of the study area. The highest
elevation of the study basin is 5689 and the minimum elevation is 4301
meters above sea level. (see Map 3. 4)
From the digital elevation model, gradients in the “x” and “y” directions were
extracted. From the gradient maps dfdx and dfdy and applying the following
equation, the percentage slope map is obtained in raster format.
However, this map of percentage slopes must still be reclassified in the ranges
that allow the application of the runoff classification method. The ranks are as
follows:
This reclassified map is intended to perform a multi-criteria analysis in combination
with vegetation and infiltration maps.
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
MAPA DE
VEGETACION
MANANTIALES DEL
SILALA
Low
Moderate
Map 3.3. Infiltration units of the Silala springs
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191
English translation prepared by DIREMAR. The original language text remains the authoritative one.
DIGITAL ELEVATION MODEL
MAP OF SILALA SPRINGS
5688.446
5411.124
5133.802
4856.481
4579.159
4301.837
Map 3.4. Silala Springs digital terrain elevation model
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
3.6.5. Map of Surface Runoff, Infiltration and Storage
From the maps of VEGETATION (Map 3. 2), INFILTRATION VELOCITY (Map 3. 3) and SLOPE (Classified
in ranges), the reclassification is carried out according to Table 3. 7. Thus, for each vegetation unit, it was
reclassified with the values of infiltration speed and slope range. From the crossing and algebra of maps, we
obtain the map of the percentage of rainwater that will become runoff from the Silala springs (see Map 3.5).
VEGETATION INFLITRATION
VELOCITY
SLOPE
>50% 50-20% 20-5% 5-1% < 1%
No vegetation Low 0.80 0.75 0.70 0.65 0.60
Moderate 0.70 0.65 0.60 0.55 0.50
High 0.50 0.45 0.40 0.35 0.30
Crops Low 0.70 0.65 0.60 0.55 0.50
Moderate 0.60 0.55 0.50 0.45 0.40
High 0.40 0.35 0.30 0.30 0.25
Grass, open
vegetation
Low 0.65 0.60 0.55 0.50 0.45
Moderate 0.55 0.50 0.45 0.40 0.35
High 0.35 0.30 0.25 0.20 0.15
Shrubs Low 0.60 0.55 0.50 0.45 0.40
Moderate 0.50 0.45 0.40 0.35 0.30
High 0.30 0.25 0.20 0.15 0.10
Forest, dense
vegetation
Low 0.55 0.50 0.45 0.40 0.35
Moderate 0.45 0.40 0.35 0.30 0.25
High 0.25 0.20 0.15 0.10 0.05
Table 3.7. Factors for the estimation of the SCS USA Surface Runoff
On the map of the percentage of runoff from the Silala springs (see Map 3.5), it can be seen that the more runoff,
the more impermeable formations are present, and conversely, the more permeable formations, the less runoff.
Map 3.5, therefore, reflects the percentage of precipitation, which will become surface runoff, and then become
part of the volume of water drained by artificial channels. Map 3.5, multiplied by the monthly precipitation
maps, provides maps of monthly surface runoff in mm (see Annex C.2).
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193
English translation prepared by DIREMAR. The original language text remains the authoritative one.
MAP OF THE PERCENTAGE OF
RUNOFF FROM THE SILALA
SPRINGS
80%
70%
60%
50%
40%
% of total precipitation volume
Map 3.5. Percentage map of runoff from Silala springs
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231 194
English translation prepared by DIREMAR. The original language text remains the authoritative one.
On the other hand, the concept taken from "Infiltration and storage": in this calculation method, it is
the water infiltrated into the soil up to one meter deep in direct relation between precipitation and
surface runoff. As seen in the formula below.
Infiltration and storage = precipitation – runoff
To obtain the "Infiltration and Storage" maps, each runoff map (mm/month) is subtracted from the
precipitation map of the same month (mm/month) from which twelve new "Infiltration and Storage"
maps were obtained.
3.7. Potential Evapotranspiration
The simulation of Potential Evapotranspiration was carried out using the Thorntwaite equation,
which in 1948 developed an empirical method to estimate potential evapotranspiration. It is mainly
based on the average monthly temperature. The method was optimized with Mather in 1957 adding
the factor "hours of sun".
The Thorntwaite-Mather formula is as follows:
ETp = 16.0 (10T/I)ª * d
Where:
ETp = Potential Evapotranspiration
T = average monthly temperature
I= heat index in a year (12 months = i monthly)
a = change factor
d = hours of brightness (in units of 30 days with 12 hours of sun each)
The temperatures of ten strategically chosen points were simulated taking into account the Colorada
lagoon station as an index station (see Table 3. 3).
3.7.1. Temperature Adjustment with Digital Terrain Elevation Model
The Thorntwaite-Mather formula uses the average temperature per month. In flat terrain it is correct
to interpolate the linear temperature between the seasons of the climate. Since there is a great
difference of altitude in the zone of the springs of the Silala, with elevations that oscillate between
4301 and 5689 m.a.s.l., this method is not correct reason why it is required to include a factor of
correction to the maps of monthly temperatures. With the theoretical knowledge that temperature
decreases by 0.46 degrees for every 100 m of altitude increase it is possible to optimize the
interpolation method (Agricultural Compendium, 1981). Thus, the interpolated temperature maps
were adjusted with the digital elevation model to obtain a better adjustment for the temperature
maps from January to December.
On the other hand, the concept taken from “Infiltration and storage”: in this calculation
method, it is the water infiltrated into the soil up to one meter deep in
direct relation between precipitation and surface runoff. As seen in the formula
below.
Infiltration and storage = precipitation – runoff
To obtain the “Infiltration and Storage” maps, each runoff map (mm/month)
is subtracted from the precipitation map of the same month (mm/month) from
which twelve new “Infiltration and Storage” maps were obtained.
3.7. Potential Evapotranspiration
The simulation of Potential Evapotranspiration was carried out using the
Thorntwaite equation, which in 1948 developed an empirical method to estimate
potential evapotranspiration. It is mainly based on the average monthly
temperature. The method was optimized with Mather in 1957 adding the factor
“hours of sun”.
The Thorntwaite-Mather formula is as follows:
Where:
ETp = Potential Evapotranspiration
T = average monthly temperature
I= heat index in a year (12 months = Ʃi monthly)
a = change factor
d = hours of brightness (in units of 30 days with 12 hours of sun each)
The temperatures of ten strategically chosen points were simulated taking into
account the Colorada lagoon station as an index station (see Table 3. 3).
3.7.1. Temperature Adjustment with Digital Terrain Elevation Model
The Thorntwaite-Mather formula uses the average temperature per month. In
flat terrain it is correct to interpolate the linear temperature between the seasons
of the climate. Since there is a great
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232
difference of altitude in the zone of the springs of the Silala, with elevations
that oscillate between 4301 and 5689 m.a.s.l., this method is not correct reason
why it is required to include a factor of correction to the maps of monthly
temperatures. With the theoretical knowledge that temperature decreases by
0.46 degrees for every 100 m of altitude increase it is possible to optimize the
interpolation method (Agricultural Compendium, 1981). Thus, the interpolated
temperature maps were adjusted with the digital elevation model to obtain
a better adjustment for the temperature maps from January to December.
3. 7.2. Heat index (I)
To obtain this annual parameter, we start by calculating the monthly heat
indexes applying the relationship:
Where:
i = Monthly heat index
T = Average monthly temperature
The annual heat index (1) is the sum of the heat indexes per month (i) (Thorntwaite
and Mather, 1957). In the geographic information system, an “i” factor
map was created for each month. The sum of these twelve maps generated the
annual heat index map.
I = Annual heat index or correction factor based on latitude
3.7.3. Hours of brightness (d)
The average number of hours of brightness depends on the latitude of the
basin and the month of the year. Thornwaite and Mather created a table to express
the average duration of hours of brightness (d) in units of 30 days with
12 hours of sun each. The Silala springs are found at 22 degrees latitude in
the southern hemisphere. For each month, a map was created with a value for
the whole basin. The values were extracted by interpolation for the required
latitude of 22o, from the table created by Thorntwaite and Mather (1957),
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233
3.7.4. Modification factor (a)
The modification factor "a" is directly related to the temperature by means of the annual heat index
(1) and is calculated according to the following formula:
a = 6.75 * 10-7 * I3 – 7.71 * 10-5 * I2 + 1.792 * 10-2 * I + 0.49239
Where:
a = Modification factor
I = Annual heat index
3.7.5. Calculation of Potential Evapotranspiration (Combination of T, I, d, a)
Twelve maps were created, from January to December, to visualize the ETp distribution.
Combining all factors "T", "I", "d" and "a" using the equation of Thorntwaite and Mather. The ETp
is calculated in each pixel per month with a pixel size of (25*25) m2 (See Annex C3).
The Etp, annual total, is equal to the sum of the monthly Etp. Figure 3. 5 shows the potential annual
evapotranspiration of the study area ranging from 430 to 530 mm per year.
On the other hand, taking into account the ETp, and the real availability of water, twelve maps of
the real evapotranspiration ETr were obtained. In turn, the sum of these 12 maps resulted in the
annual ETr map shown in Figure 3. 6. Due to the low levels of precipitation in the study area, the
annual ETr ranges from O to 91 mm
EVAPOTRANSPIRACIO
N
POTENCIAL
(mm)
195
English translation prepared by DIREMAR. The original language text remains the authoritative one.
The annual heat index (1) is the sum of the heat indexes per month (i) (Thorntwaite and Mather,
1957). In the geographic information system, an "i" factor map was created for each month. The
sum of these twelve maps generated the annual heat index map.
I = (i)
I = Annual heat index or correction factor based on latitude
3.7.3. Hours of brightness (d)
The average number of hours of brightness depends on the latitude of the basin and the month of the
year. Thornwaite and Mather created a table to express the average duration of hours of brightness
(d) in units of 30 days with 12 hours of sun each. The Silala springs are found at 22 degrees latitude
in the southern hemisphere. For each month, a map was created with a value for the whole basin.
The values were extracted by interpolation for the required latitude of 22º, from the table created by
Thorntwaite and Mather (1957), in which the relationship between latitude and hours of brightness
is expressed (see Table 3. 8).
LAT
SUR
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DIC
5 1.04 0.95 1.04 1.00 1.02 0.99 1.02 1.03 1.00 1.05 1.03 1.06
10 1.08 0.97 1.05 0.99 1.01 0.96 1.00 1.01 1.00 1.06 1.05 1.10
15 1.12 0.98 1.05 0.98 0.98 0.94 0.97 1.00 1.00 1.07 1.07 1.12
20 1.14 1.00 1.05 0.97 0.96 0.91 0.95 0.99 1.00 1.08 1.09 1.15
25 1.17 1.01 1.05 0.96 0.94 0.88 0.93 0.98 1.00 1.10 1.11 1.18
30 1.20 1.03 1.06 0.95 0.92 0.85 0.90 0.96 1.00 1.12 1.14 1.21
35 1.23 1.04 1.06 0.94 0.89 0.82 0.87 0.94 1.00 1.13 1.17 1.25
40 1.27 1.06 1.07 0.93 0.86 0.78 0.84 0.92 1.00 1.15 1.20 1.29
45 1.31 1.10 1.07 0.91 0.81 0.71 0.78 0.90 0.99 1.17 1.26 1.36
50 1.37 1.12 1.08 0.89 0.77 0.67 0.74 0.88 0.99 1.19 1.29 1.41
Table 3.8. Possible duration of hours of brightness Thornthwaite (1948)
in which the relationship between latitude and hours of brightness is expressed
(see Table 3. 8).
3.7.4. Modification factor (a)
The modification factor “a” is directly related to the temperature by means of
the annual heat index (1) and is calculated according to the following formula:
Where:
a = Modification factor
I = Annual heat index
3.7.5. Calculation of Potential Evapotranspiration (Combination of T, I,
d, a)
Twelve maps were created, from January to December, to visualize the ETp
distribution. Combining all factors “T”, “I”, “d” and “a” using the equation of
Thorntwaite and Mather. The ETp is calculated in each pixel per month with a
pixel size of (25*25) m2 (See Annex C3).
The Etp, annual total, is equal to the sum of the monthly Etp. Figure 3. 5
shows the potential annual evapotranspiration of the study area ranging from
430 to 530 mm per year.
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234
REAL ANNUAL
EVAPOTRANSPIRATION
in mm. SILALA SPRINGS
Figure 3.6. Actual annual evapotranspiration in the zone of the Silala springs
3.8. Soil Water Retention Capacity
Soil retains water in two ways: as free moisture in the pores in interstices between solid clay
particles and organic particles (Agricultural compendium, 1981). The second type of moisture is not
available for plants and is called Hygroscopic Moisture.
The amount of water retained in the soil, available to the plants, is a factor in the water balance. If
effective precipitation and the actual amount of water stopped are not sufficient to comply with
evapotranspiration requirements, a deficit will occur. This means that the vegetation will not be able
to absorb moisture from the soil and will fall under stress. On the other hand, when the retention
capacity of the soil is saturated and there is effective precipitation, the water will percolate to the
subsoil. In this case it is a surplus of water.
It is important to calculate the maximum amount of water that can be retained in the soil. This is
called potential retention capacity. Booker in 1984 expressed the potential retention capacity as a
196
English translation prepared by DIREMAR. The original language text remains the authoritative one.
3.7.5. Calculation of Potential Evapotranspiration (Combination of T, I, d, a)
Twelve maps were created, from January to December, to visualize the ETp distribution.
Combining all factors "T", "I", "d" and "a" using the equation of Thorntwaite and Mather. The ETp
is calculated in each pixel per month with a pixel size of (25*25) m2 (See Annex C3).
The Etp, annual total, is equal to the sum of the monthly Etp. Figure 3. 5 shows the potential annual
evapotranspiration of the study area ranging from 430 to 530 mm per year.
On the other hand, taking into account the ETp, and the real availability of water, twelve maps of
the real evapotranspiration ETr were obtained. In turn, the sum of these 12 maps resulted in the
annual ETr map shown in Figure 3. 6. Due to the low levels of precipitation in the study area, the
annual ETr ranges from O to 91 mm
EVAPOTRANSPIRACIO
N
POTENCIAL
(mm)
Figure 3.5. Potential annual evapotranspiration in the zone of the Silala springs
On the other hand, taking into account the ETp, and the real availability of water,
twelve maps of the real evapotranspiration ETr were obtained. In turn, the sum of
these 12 maps resulted in the annual ETr map shown in Figure 3. 6. Due to the low
levels of precipitation in the study area, the annual ETr ranges from O to 91 mm.
3.8. Soil Water Retention Capacity
Soil retains water in two ways: as free moisture in the pores in interstices between
solid clay particles and organic particles (Agricultural compendium, 1981).
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235
The second type of moisture is not available for plants and is called Hygroscopic
Moisture.
The amount of water retained in the soil, available to the plants, is a factor in
the water balance. If effective precipitation and the actual amount of water
stopped are not sufficient to comply with evapotranspiration requirements, a
deficit will occur. This means that the vegetation will not be able to absorb
moisture from the soil and will fall under stress. On the other hand, when the
retention capacity of the soil is saturated and there is effective precipitation,
the water will percolate to the subsoil. In this case it is a surplus of water.
It is important to calculate the maximum amount of water that can be retained
in the soil. This is called potential retention capacity. Booker in 1984
expressed the potential retention capacity as a relationship between soil texture
and stoniness by means of a table from which we extracted only the data
that were applied in this balance and which is shown in Table 3.11.
3.9. Soil texture map
The soil textural classification was carried out in the Soil Laboratory of the
Agronomy Major from samples that were obtained in the surveyed area.
This classification is based on the system applied by the USDA according to
the size of the particles, in which the following classification is used:
Silt, all particles whose size varies from 0.002 to 0.05 mm;
Clay, all particles less than 0.002 mm.
In the description of the texture map, we have that the unit that occupies the
largest area of the basin is the ―Rocky Outcrop‖: with 192.2 km2, which
represent 77.1% of the area of the basin. This unit is characterized by being
formed by outcrops of volcanic rock and is located along the entire basin
(see Table 3. 9 and Map 3.6).
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
The second soil textural unit is the silty-loam, which occupies an area of 57.2 km2, which represents
22.9% of the total area of the basin, which is located in the central part of the surveyed area (see
Table 3. 9 and Map 3. 6).
Soil Texture Area (m2) Area (km2) % Area
Rocky outcrop 192159375 192,2 77,1
Loamy Silty 57160000 57,2 22,9
TOTAL 249319375 249,3 100,0
Table 3. 9: Units of soil texture of the Silala basin
3.10. Map of stoniness and gravel in percentage (%)
The stoniness map refers to the area occupied by rocks between boulders and angles. This value is
important, because the higher this percentage is, the lower the possibility of impact of raindrops.
In Figure 3.7 and Table 3.10. Percentage of stoniness. Silala Springs – Table 3.10, it can be
observed that the predominant unit is the unit with a content of 80 to 100% of stoniness. This unit
occupies an area of 105.2 km2, which represents 42.2% of the surveyed area; while the unit with 0
to 5% of stoniness occupies 22.9% of the total area with 57.2 km2.
Figure 3.7: Percentage of stoniness – Silala Springs.
Stoniness Percentage Area (m2) Area (km2) % Area
80 – 100 105162500 105,2 42,2
100 86996875 87,0 34,9
0 – 5 57160000 57,2 22,9
TOTAL 249319375 249,3 100,0
Table 3.10: Percentage of stoniness – Silala Springs.
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Stoniness Percentage Area (m2) Area (km2) % Area
80 – 100 105162500 105,2 42,2
100 86996875 87,0 34,9
0 – 5 57160000 57,2 22,9
TOTAL 249319375 249,3 100,0
Table 3.10: Percentage of stoniness – Silala Springs.
Map 3.6: Map of soil texture of the Silala Springs.
TEXTURE WATER RETENTION CAPACITY IN THE SOIL (mm/m).
STONYNESS AND GRAVEL IN%
0% 0-5% 5-15% 15-40% 40-80% 80%
Clay 140 130 120 90 50 10
Loam 170 160 140 110 40 20
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3.11. Potential retention capacity
The potential retention capacity is calculated by multiplying the effective soil depth and the water
retention capacity. It is assumed that there are no variations in stoniness and texture in a unit of
land, so all the pixels located in a unit of land are classified with a value of texture and stoniness
(see table 3.11). The potential retention capacity is used in the first month as a maximum of retained
water to start the water balance. The water balance begins in December as this is the first month
with storage that also uses the rain of the previous month (first month with rains). The maps used
for Texture (see Map 3.6) and percentage of stoniness (see Figure 3.7) were constituted in important
elements and were derived from the geological map with the change of attribute according to the
parameters of Table 3.12.
GEOLOGICAL
UNITS
Infiltration Soil Texture Vegetation (SCS) Stoniness
(&)
Effective
Depth (cm)
Unconsolidated
deposits
Moderate Loamy-Silty Grass and open
vegetation
0 – 5 0.20
Ignimbrites Low Rocky outcrop Without vegetation 100 0.09
Volcanic lavas Moderate Rocky outcrop Without vegetation 80 – 100 0.09
Table 3. 12: Table of attributes of the map of the geological units of the Silala springs area.
3.12. Actual retention of moisture in the soil
Water retention will vary over time as evapotranspiration reduces water and effective precipitation
adds water. The effective precipitation is added to the maximum retention capacity and the potential
evapotranspiration is subtracted. For the next month the rest of the water retained is added again to
the effective precipitation and the potential evapotranspiration is subtracted. The actual retention
can be calculated with the following equation:
Where:
S(a) = Potential storage
P(ef) = Potential evapotranspiration
S(a)mes-1 = Actual storage of the previous month
ETp = Effective precipitation
199
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Map 3.6: Map of soil texture of the Silala Springs.
TEXTURE WATER RETENTION CAPACITY IN THE SOIL (mm/m).
STONYNESS AND GRAVEL IN%
0% 0-5% 5-15% 15-40% 40-80% 80%
Clay 140 130 120 90 50 10
Loam 170 160 140 110 40 20
Sand 90 80 70 60 30 10
Sandy-Loamy 110 100 90 70 40 10
Clay-Sandy 110 100 90 70 40 10
Clay-Loamy 150 140 130 100 55 10
Sandy
Loamy-Sandy 150 130 120 100 55 10
Clay-Silty 160 140 130 110 55 10
Clay-Loamy 170 150 140 110 65 20
Silty
Loamy-Silty 190 170 150 130 70 20
Loamy-Clay 150 130 120 100 55 10
Table 3. 11: Retention capacity of soil moisture. (Drainage Analysis and Extraction of Hydrologic
Properties from a Digital Elevation Model, 1996).
3.11. Potential retention capacity
The potential retention capacity is calculated by multiplying the effective soil
depth and the water retention capacity. It is assumed that there are no variations
in stoniness and texture in a unit of land, so all the pixels located in a unit of
land are classified with a value of texture and stoniness (see table 3.11). The
potential retention capacity is used in the first month as a maximum of retained
water to start the water balance. The water balance begins in December as this
is the first month with storage that also uses the rain of the previous month (first
month with rains). The maps used for Texture (see Map 3.6) and percentage
of stoniness (see Figure 3.7) were constituted in important elements and were
derived from the geological map with the change of attribute according to the
parameters of Table 3.12.
3.12. Actual retention of moisture in the soil
Water retention will vary over time as evapotranspiration reduces water and
effective precipitation adds water. The effective precipitation is added to the
maximum retention capacity and the potential evapotranspiration is subtracted.
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239
For the next month the rest of the water retained is added again to the effective
precipitation and the potential evapotranspiration is subtracted. The actual
retention can be calculated with the following equation:
Where:
S(a) = Potential storage
P(ef) = Potential evapotranspiration
S(a)mes-1 = Actual storage of the previous month
ETp = Effective precipitation
S(p) = Actual storage
The water balance calculations begin after the dry season, when P > Etr. In our
case, it started in December and showed the maximum humidity retention in
the months of February to March, with insignificant volumes for the volume
of water drained to the drainage canals. In the rest of the months, there is no
moisture retention, showing still much less significant values.
3.13. Actual Evapotranspiration
Potential evapotranspiration is the amount of water that evaporates when there
is enough available water retained in the soil and subsoil and that month’s precipitation.
The actual evapotranspiration depends on the effective precipitation, the potential
evapotranspiration and the water storage of the previous month. When the
effective precipitation and storage of the previous month is equal to or greater
than the potential evapotranspiration, the actual evapotranspiration is equal to
the potential evapotranspiration. If the effective precipitation and storage of the
previous month is less than the potential evapotranspiration, the actual evapotranspiration
is equal to the effective precipitation plus the storage of the previous
month’s humidity. The following equation expresses the aforementioned:
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201
English translation prepared by DIREMAR. The original language text remains the authoritative one.
The actual evapotranspiration depends on the effective precipitation, the potential
evapotranspiration and the water storage of the previous month. When the effective precipitation
and storage of the previous month is equal to or greater than the potential evapotranspiration, the
actual evapotranspiration is equal to the potential evapotranspiration. If the effective precipitation
and storage of the previous month is less than the potential evapotranspiration, the actual
evapotranspiration is equal to the effective precipitation plus the storage of the previous month’s
humidity. The following equation expresses the aforementioned:
If:
Therefore, the actual evapotranspiration is the amount of water that really evaporates from the
plants and the bare soil. In case there is enough water to evaporate (or in situations of excess), the
potential evapotranspiration is equal to the actual evapotranspiration (ETp = ETr). If there is not
enough water available then ETr < ETp. Due to the high water deficit of the survey area, the actual
evapotranspiration is much lower than the potential evapotranspiration.
The calculations begin in December (generally the first month with precipitation). The actual
retention for November is then used for the following calculations that begin in December.
3.14. Water deficit
The amount of soil moisture will be reduced when the effective precipitation is less than the
potential evapotranspiration. At a certain moment the amount of water retained is zero and the
vegetation still requires evaporation. Then there is a deficit. The deficit in this survey does not refer
to the stress situation of the plants or to the point of permanent wilting, but to a moment of water
stress suffered by the plants. This can also be expressed in an equation:
The deficit only occurs when positive values are calculated. When negative values are calculated
for the water deficit in this equation (ó: P(ef) + S(a)mes-1 > ETp and Eta = ETp) then these values
are reclassified as zero (for calculation purposes).
It should be understood as the water deficit the amount of water that the plants in the survey area
require, according to their spatial and temporal presence, for their normal development. However,
deficit levels do not mean that plants reach the point of permanent wilting, but that they suffer water
stress, which is reflected in plant development and production.
Month Superficial
runoff
(hm3)
Inf_Alm
(hm3)
ETP (hm3) Deficit
(hm3)
Supply
(hm3)
Supply
(l/sec)
January 5,81 3,14 16,74 11,57 7,86 2,93
February 3,22 1,75 14,56 12,81 1,55 0,64
March 0,46 0,25 15,93 15,68 0,21 0,08
April 0,00 0,00 12,19 12,19 0,00 0,00
May 0,00 0,00 1,39 7,39 0,00 0,00
June 0,02 0,01 0,78 0,78 0,01 0,00
201
English translation prepared by DIREMAR. The original language text remains the authoritative one.
The actual evapotranspiration depends on the effective precipitation, the potential
evapotranspiration and the water storage of the previous month. When the effective precipitation
and storage of the previous month is equal to or greater than the potential evapotranspiration, the
actual evapotranspiration is equal to the potential evapotranspiration. If the effective precipitation
and storage of the previous month is less than the potential evapotranspiration, the actual
evapotranspiration is equal to the effective precipitation plus the storage of the previous month’s
humidity. The following equation expresses the aforementioned:
If:
Therefore, the actual evapotranspiration is the amount of water that really evaporates from the
plants and the bare soil. In case there is enough water to evaporate (or in situations of excess), the
potential evapotranspiration is equal to the actual evapotranspiration (ETp = ETr). If there is not
enough water available then ETr < ETp. Due to the high water deficit of the survey area, the actual
evapotranspiration is much lower than the potential evapotranspiration.
The calculations begin in December (generally the first month with precipitation). The actual
retention for November is then used for the following calculations that begin in December.
3.14. Water deficit
The amount of soil moisture will be reduced when the effective precipitation is less than the
potential evapotranspiration. At a certain moment the amount of water retained is zero and the
vegetation still requires evaporation. Then there is a deficit. The deficit in this survey does not refer
to the stress situation of the plants or to the point of permanent wilting, but to a moment of water
stress suffered by the plants. This can also be expressed in an equation:
The deficit only occurs when positive values are calculated. When negative values are calculated
for the water deficit in this equation (ó: P(ef) + S(a)mes-1 > ETp and Eta = ETp) then these values
are reclassified as zero (for calculation purposes).
It should be understood as the water deficit the amount of water that the plants in the survey area
require, according to their spatial and temporal presence, for their normal development. However,
deficit levels do not mean that plants reach the point of permanent wilting, but that they suffer water
stress, which is reflected in plant development and production.
Month Superficial
runoff
(hm3)
Inf_Alm
(hm3)
ETP (hm3) Deficit
(hm3)
Supply
(hm3)
Supply
(l/sec)
January 5,81 3,14 16,74 11,57 7,86 2,93
February 3,22 1,75 14,56 12,81 1,55 0,64
March 0,46 0,25 15,93 15,68 0,21 0,08
April 0,00 0,00 12,19 12,19 0,00 0,00
May 0,00 0,00 1,39 7,39 0,00 0,00
June 0,02 0,01 0,78 0,78 0,01 0,00
Therefore, the actual evapotranspiration is the amount of water that really
evaporates from the plants and the bare soil. In case there is enough water to
evaporate (or in situations of excess), the potential evapotranspiration is equal
to the actual evapotranspiration (ETp = ETr). If there is not enough water
available then ETr < ETp. Due to the high water deficit of the survey area, the
actual evapotranspiration is much lower than the potential evapotranspiration.
The calculations begin in December (generally the first month with precipitation).
The actual retention for November is then used for the following calculations
that begin in December.
3.14. Water deficit
The amount of soil moisture will be reduced when the effective precipitation
is less than the potential evapotranspiration. At a certain moment the amount
of water retained is zero and the vegetation still requires evaporation. Then
there is a deficit. The deficit in this survey does not refer to the stress situation
of the plants or to the point of permanent wilting, but to a moment of water
stress suffered by the plants. This can also be expressed in an equation:
The deficit only occurs when positive values are calculated. When negative
values are calculated for the water deficit in this equation (ó: P(ef) + S(a)mes-
1 > ETp and Eta = ETp) then these values are reclassified as zero (for calculation
purposes).
It should be understood as the water deficit the amount of water that the
plants in the survey area require, according to their spatial and temporal presence,
for their normal development. However, deficit levels do not mean that
plants reach the point of permanent wilting, but that they suffer water stress,
which is reflected in plant development and production.
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241
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
July 0,02 0,01 1,60 1,59 0,01 0,00
August 0,01 0,00 3,11 3,10 0,00 0,00
September 0,00 0,00 8,75 8,75 0,00 0,00
October 0,00 0,00 12,18 12,18 0,00 0,00
November 0,00 0,00 14,19 14,19 0,00 0,00
December 16,62 0,05 16,62 16,56 0,05 0,02
Table 3.13: Statistical analysis of the area of the Silala springs (in hm3 and in l / sec)
Figure 3.8: Map of Annual Water Supply (m/year)
3.15. Water surplus
When the effective precipitation is greater than the potential evapotranspiration, the amount of
moisture retained will increase. Water will be retained up to the maximum amount of potential
storage capacity (S(a) = S(p)). If more water enters the soil, it will percolate as surplus. The
following equation expresses this relation:
Subsurface Water Surplus = P(ef) - ETr + S(a)mes-1
Where: ETr = ETp and S(a) = S(p)
When negative values are calculated with the equation (P(ef) - ETp + S(a)mes-1 < S(p) there is no
surplus. Negative values must be reclassified as zero. In the survey area, due to the incipient amount
of this factor, it can be considered 0.
3.16. Water supply
July 0,02 0,01 1,60 1,59 0,01 0,00
August 0,01 0,00 3,11 3,10 0,00 0,00
September 0,00 0,00 8,75 8,75 0,00 0,00
October 0,00 0,00 12,18 12,18 0,00 0,00
November 0,00 0,00 14,19 14,19 0,00 0,00
December 16,62 0,05 16,62 16,56 0,05 0,02
Table 3.13: Statistical analysis of the area of the Silala springs (in hm3 and in l / sec)
Figure 3.8: Map of Annual Water Supply (m/year)
3.15. Water surplus
When the effective precipitation is greater than the potential evapotranspiration, the amount of
moisture retained will increase. Water will be retained up to the maximum amount of potential
storage capacity (S(a) = S(p)). If more water enters the soil, it will percolate as surplus. The
following equation expresses this relation:
Subsurface Water Surplus = P(ef) - ETr + S(a)mes-1
Where: ETr = ETp and S(a) = S(p)
When negative values are calculated with the equation (P(ef) - ETp + S(a)mes-1 < S(p) there is no
surplus. Negative values must be reclassified as zero. In the survey area, due to the incipient amount
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stress suffered by the plants. This can also be expressed in an equation:
The deficit only occurs when positive values are calculated. When negative values are calculated
for the water deficit in this equation (ó: P(ef) + S(a)mes-1 > ETp and Eta = ETp) then these values
are reclassified as zero (for calculation purposes).
It should be understood as the water deficit the amount of water that the plants in the survey area
require, according to their spatial and temporal presence, for their normal development. However,
deficit levels do not mean that plants reach the point of permanent wilting, but that they suffer water
stress, which is reflected in plant development and production.
Month Superficial
runoff
(hm3)
Inf_Alm
(hm3)
ETP (hm3) Deficit
(hm3)
Supply
(hm3)
Supply
(l/sec)
January 5,81 3,14 16,74 11,57 7,86 2,93
February 3,22 1,75 14,56 12,81 1,55 0,64
March 0,46 0,25 15,93 15,68 0,21 0,08
April 0,00 0,00 12,19 12,19 0,00 0,00
May 0,00 0,00 1,39 7,39 0,00 0,00
June 0,02 0,01 0,78 0,78 0,01 0,00
3.15. Water surplus
When the effective precipitation is greater than the potential evapotranspiration,
the amount of moisture retained will increase. Water will be retained up
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to the maximum amount of potential storage capacity (S(a) = S(p)). If more
water enters the soil, it will percolate as surplus. The following equation expresses
this relation:
When negative values are calculated with the equation (P(ef) - ETp + S(a)mes-
1 < S(p) there is no surplus. Negative values must be reclassified as zero. In the
survey area, due to the incipient amount of this factor, it can be considered 0.
3.16. Water supply
The water supply of the survey area will be equal to the sum of the surface runoff
plus the surplus of the subsurface water and is expressed as:
WATER SUPPLY = SURFACE RUNOFF + SUB-SUPERFICIAL SURPLUS
The calculation was made in each of the 625 m2 area pixels, which allows us
to establish the supply of surface water at the exit of artificial canals. For this,
it is sufficient to make the summation of all the pixels that contribute with their
―SUPPLY‖ when leaving the survey area (see Figure 3.8 and Annex C2).
Once the water supply of the survey area has been calculated, this volume is
2.93 l/sec for the month of January and 0.64 l/sec for the month of February,
making a total of 3.67 l/sec per year. The rest of the months are considered 0 l/
sec, since the supply values obtained are insignificant (see Table 3.13 and Annex
C4).
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Figure 3.8: Map of Annual Water Supply (m/year)
3.15. Water surplus
When the effective precipitation is greater than the potential evapotranspiration, the amount of
moisture retained will increase. Water will be retained up to the maximum amount of potential
storage capacity (S(a) = S(p)). If more water enters the soil, it will percolate as surplus. The
following equation expresses this relation:
Subsurface Water Surplus = P(ef) - ETr + S(a)mes-1
Where: ETr = ETp and S(a) = S(p)
When negative values are calculated with the equation (P(ef) - ETp + S(a)mes-1 < S(p) there is no
surplus. Negative values must be reclassified as zero. In the survey area, due to the incipient amount
of this factor, it can be considered 0.
3.16. Water supply
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Conclusions CHAPTER III (WATER MODELING)
The georeferencing of the satellite image has allowed the interpretation of
the image with the reallocation of values and indexes for several parameters
that have to do with the water balance and the estimate of water supply. These
indexes and parameters were corroborated with the fieldwork.
The study basin area was rasterized in pixels of 25*25 m, which allowed a
detailed analysis of the water supply.
The ratio Monthly Precipitation versus Potential Evapotranspiration is from 1
to 5. This means that for every millimeter of rain, 5mm evaporates; this leads
to a superficial water deficit in the survey area.
The water supply or surface runoff generated by the precipitation of the survey
area only has a maximum flow of 2.93 l/sec for the month of January and
0.64 l/sec for the month of February, 0.08 l/sec for the month of March and
0.02 l/sec in the month of December. The rest of the months have a contribution
of 0 l/sec.
In total the contribution of rainwater precipitation does not exceed 3.67 l/sec,
throughout the year, a volume that is insignificant compared to the average
200 l/sec, evacuated through the artificial canals into Chilean territory.
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Recommendations
Install a digital meteorological station and digital piezometers in order to
obtain up-to-date information on the surface water-groundwater ratio, in order
to obtain updated information.
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Chapter IV
Hydrochemistry
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INDEX
4.1. Introduction
4.1.1. Spring water
4.2. Theoretical basis
4.2.1. Water chemical analysis
4.2.2. Water classification by its use
4.2.3. Groundwater geochemical composition
4.3. Laboratory chemical analysis
4.4. Sampling Methodology - Monitoring
4.5. Field Methodology
4.6. Procedure – Hydro-chemical Interpretation
4.6.1. Collective Diagrams
4.7. Interpretation and evaluation of results
4.7.1. Chemical-Physical Analysis
4.7.2. Behavior of Anions
4.7.3. Behavior of Cations
4.8. Interpretation Techniques – Hydro-chemical Diagrams
4.8.1. Stiff Diagram
4.8.2. Piper Diagram
4.8.3. Wilcox Diagram
4.9. Anomalies maps
4.10. Analysis of Volcanic Soils
4.10.1. Physical and Chemical Properties of the Soil
Conclusions
Recommendations
PHOTOGRAPHS
Photograph 4.1. Atomic Adsorption Team
Photograph 4.2. Portable equipment for measuring physical-chemical parameters on site
247
Photograph 4.3. Water sampling
Photograph 4.4. Sampling of volcanic soils
FIGURES
Figure 4.1. pH concentrations in the Silala Springs
Figure 4.2. Sulfate concentrations mg/l (see Annex D.3.4)
Figure 4.3. Chlorides concentrations mg/l
Figure 4.4. Bicarbonate concentrations mg/l (see Annex D.3.1)
Figure 4.5. Carbonate concentrations mg/l
Figure 4.6. Sodium concentrations mg/l (see Annex D.3.2)
Figure 4.7. Calcium concentrations mg/l
Figure 4.8. Potassium concentrations mg/l (see Annex D.3.3)
Figure 4.9. Stiff Diagrams of the survey area
Figure 4.10. Piper Diagram of the survey area
Figure 4.11. SAR Wilcox Diagram
Figure 4.12. Classification of Soils by the Textural Triangle (USDA)
Tables
Table 4.1. Behavior of Hydro-chemical Areas in the Silala Springs
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4.9. Anomalies maps
4.10. Analysis of Volcanic Soils
4.10.1. Physical and Chemical Properties of the Soil
Conclusions
Recommendations
PHOTOGRAPHS
Photograph 4.1. Atomic Adsorption Team
Photograph 4.2. Portable equipment for measuring physical-chemical parameters on site
248
CHAPTER IV: HYDROCHEMISTRY OF THE WATERS OF THE SILALA
SPRINGS
4.1. Introduction
Hydro-geochemistry is an interdisciplinary science that studies the chemical
properties of surface and underground water, and its relation with regional geology.
Analyzes the ions dissolved in water and the water–solid interaction
processes.
It is the compilation of several sciences, such as the chemistry of water, which
concerns the study of chemical processes and reactions that affect the distribution
and circulation of dissolved species in natural waters, combined with geology
and biology, because during the hydrological cycle water interacts directly
with the biosphere.
The chemical quality of surface and groundwater is determined by the amount
and concentration of dissolved substances in them.
The aquifer systems are conditioned by the constant interaction between a solid
phase formed by rocks and minerals, a gas phase and a liquid phase. As a result
of this relation, groundwater acquires a defined chemical composition and is
characteristic of the system in which it is immersed. In this context, the study
of the chemical composition of water can contribute to the knowledge and determination
of its origin, directions of flow, extension of aquifer systems and
the possible underground connection between hydrographically independent
basins.
The information will allow a classification of waters affected mainly by evaporation
processes, flows between basins and their concordance with numerical
flow models, which are based on meteorological, hydrological, piezometric
and geophysical information.
4.1.1. Spring Water
Water that spontaneously emerges to the surface of the earth with a flow determined
by the hydrological cycle, after being captured through works carried
out for its exploitation. It does not have the properties of mineral water and is
of good quality.
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4.2. Theoretical basis
4.2.1. Water chemical analysis
The determination of the chemical-physical properties of natural water is an essential
tool for the analysis of water quality.
For the application of hydro-geochemical methods, the water solution, water balance
and geochemical parameters that characterize each system must be taken into
account, relating the volume of infiltration, circulation of the water with the chemical
composition of the same in the discharge area of the aquifers.
The second phase of the work will consist of selecting points or stations of systematic
observation, where the necessary registration or measurement equipment
is installed for the control of the flows and the chemical composition of the waters.
The chemical composition of meteoric waters is controlled by the chemical balances
of carbonates and other minerals and varies over time. For this reason, chemical
analyzes and pH measurements, as well as electrical conductivity, must be done
―in situ‖.
Anions
a) Chloride Ion, comes from:
Washing of land of marine origin: The waters and fossils can provide
important amounts. Rainwater and its concentration in the terrain.
Mixture with seawater in coastal regions.
More rarely it can come from gases and liquids associated with
volcanic emanations.
It is the most abundant anion in seawater, but may be the least important
of the fundamentals in inland waters. It almost never saturates and is
very difficult to alter by ionic or other type of action.
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b) Sulfate Ion, comes from:
Washing of lands formed in conditions of great aridity or in a marine
environment.
Oxidation of igneous rock sulfides, metamorphic sedimentary rocks.
Concentration of rainwater in the soil.
c) Bicarbonate and Carbonate Ions, come from:
Dissolution of atmospheric CO2 or soil.
d) Ion Nitrate, comes from:
Processes of natural nitrification, decomposition of organic matter and
urban, industrial and livestock pollution.
In small proportion of rainwater, volcanic emanations and washing of old
soils.
It is often an indicator of pollution, in which case it is usually stratified,
dominating the higher concentrations in the upper part of the free aquifer.
Cations
a) Sodium, comes from:
Attack of feldspars, feldspatoids and other silicates. Locally of the solution
of germ salt or natural sodium sulfate. Rarely of emanations and phenomena
related to magmatic processes.
Concentration of rainwater, is the most abundant cation in seawater, is very
affected by the change of bases.
b) Potassium, comes from:
Attack of the orthoclase and other silicates (micas, clays, etc.). Locally of
the dissolution of natural potassium salts (silvinite, carnallite, etc.). In small
amount of rainwater contributions.
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c) Calcium, comes from:
Dissolution of limestones, dolomites, gypsum and anhydrite. Attack of
feldspars and other calcium silicates. Dissolution of calcareous cement of
many rocks. Concentration of rainwater. It is frequently in a saturated
state and its stability in solution depends on the equilibrium
C02- C03HC03. It can precipitate easily and is very affected by the ionic
change.
d) Magnesium, comes from:
Dissolution of dolomites and dolomite limestones; attack of magnesium
and ferromagnetic silicates. Locally washed magnesium evaporite rocks
(carnallite, kaiserite, etc.).
It dissolves more slowly than calcium and tends to remain in solution
when it precipitates. It is affected by the ionic change.
e) Iron, comes from:
Attack of ferric silicates, attack of sulfides and iron oxides, attack of most
sedimentary rocks. Its stability depends fundamentally on the redox
potential; it solubilizes and precipitates easily. Only minimal amounts of
dissolved iron are present in oxidizing media.
Sodic Bicarbonated Waters.
The main action of these waters is of digestive type. They are used mainly
in drinks, in doses of 100 to 200 ml before breakfast, lunch and dinner, until
reaching a total dose of 1000 to 1500 ml per day. In general, these waters behave
as antacids, acting as neutralizers of gastric acidity and because of their
buffering capacity they also favor the action of pancreatic enzymes and the saponifying
power of bile. They also have a cholecystokinetic action. They are
favorable for the treatment of hepatopancreatic disorders.
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4.2.2. Water classification by its use
The chemical composition of natural water, according to the use that is given
to it, is called water quality, and there are a series of norms that regulate the
permissible concentrations that each element or indicator of quality must have
according to the different uses.
In addition to the chemical-physical quality of the waters, it is necessary to
control the bacteriological quality. The contamination of water by pathogenic
organisms is mainly due to dumping or percolation of urban or agro-industrial
waste, since this type of microorganism does not originate in natural conditions.
4.2.3. Groundwater geochemical composition
In natural groundwater, most dissolved substances are in the ionic state, most
of the hydro- geochemical aspects will be about these ions.
In groundwater, the elements to be analyzed in the field are the following:
PH
Temperature
Total dissolved solids
Conductivity
Hardness
Taste
Odor
4.3. Laboratory chemical analysis
Six samples were analyzed in the Laboratories dependent on the Tomas Frias
Autonomous University – JICA; where 10 important ions were programmed
with different analysis methods: Potentiometric, Gravimetric, Colorimetric,
Volumetric, Atomic Absorption and chemical physical parameters in situ with
the HATCH portable equipment (see Photograph 4.1).
As a comparison parameter to those reported by the laboratory, it shows a
good relation within the permissible ranges.
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Odor
4.3. Laboratory chemical analysis
Six samples were analyzed in the Laboratories dependent on the Tomas Frias Autonomous
University – JICA; where 10 important ions were programmed with different analysis methods:
Potentiometric, Gravimetric, Colorimetric, Volumetric, Atomic Absorption and chemical physical
parameters in situ with the HATCH portable equipment (see Photograph 4.1).
As a comparison parameter to those reported by the laboratory, it shows a good relation within the
permissible ranges.
Cations.- Sodium, Potassium, Manganese, Cadmium, Copper, Calcium, Iron, Magnesium.
Anions.- Bicarbonate, Carbonate, Chlorine, Nitrate, Nitrite, Sulphate.
Photograph 4.1: Atomic adsorption equipment.
4.4. Sampling Methodology - Monitoring
The sampling methodology is defined from a monitoring scheme and respecting international
standards in order to minimize errors in the reading of elements (See Photograph 4.2). The analyzes
were carried out before 72 hours in compliance with the indicated norms, due to the distance effect,
preservatives had to be used and transferred to specialized laboratories of the UATF; for the
Chemical Analysis (see Annex 0.1).
The values of the chemical analyzes, reported by laboratory, were subjected to an ionic balance in
order to verify the quality of the same; with the analyzes that report an error of less than 10%, the
4.4. Sampling Methodology - Monitoring
The sampling methodology is defined from a monitoring scheme and respecting
international standards in order to minimize errors in the reading of elements
(See Photograph 4.2). The analyzes were carried out before 72 hours in
compliance with the indicated norms, due to the distance effect, preservatives
had to be used and transferred to specialized laboratories of the UATF; for the
Chemical Analysis (see Annex 0.1).
The values of the chemical analyzes, reported by laboratory, were subjected to
an ionic balance in order to verify the quality of the same; with the analyzes
that report an error of less than 10%, the water quality was determined, using
as comparison parameters the permissible limits established in the Regulation
of the Environment Law, with respect to Water Contamination (RMCH).
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water quality was determined, using as comparison parameters the permissible limits established in
the Regulation of the Environment Law, with respect to Water Contamination (RMCH).
Photograph 4.2: Portable equipment for measuring physical-chemical parameters in situ.
In the evaluation of the cations the following elements were considered: calcium, magnesium,
sodium, potassium and iron. For the evaluation of the anions, sulfates, chlorides, carbonates,
nitrates, bicarbonates were considered and to determine the physical-chemical parameters the pH,
TOS, conductivity, salinity and temperature were analyzed.
The classification of the waters, were made according to the rules of the Ministry of Sustainable
Development and Environment (MDSMA) such as:
CLASS A: Natural waters of the highest quality, which enables them as drinking water for human
consumption without any previous treatment, or with simple bacteriological disinfection in the
necessary cases verified by laboratory.
CLASS B: Waters of general utility, for human consumption, require physical treatment and
bacteriological disinfection.
CLASS C: Waters of general utility, which in order to be qualified for human consumption requires
complete physical-chemical treatment and bacteriological disinfection.
CLASS D: Waters of minimum quality, which for human consumption, in extreme cases of public
necessity, require an initial process of pre-sedimentation, since they can have a high turbidity due to
high TOS content and then complete physical-chemical treatment and special bacteriological
disinfection against eggs and intestinal parasites.
4.5. Field Methodology
In the field phase, a detailed inventory of water from the Silala springs was made of six samples in
surface water in waterbodies, such as the Inacaliri Volcano Sector and the SES sector, samples that
were obtained in order to know and differentiate the quality of them.
In the evaluation of the cations the following elements were considered:
calcium, magnesium, sodium, potassium and iron. For the evaluation of the
anions, sulfates, chlorides, carbonates, nitrates, bicarbonates were considered
and to determine the physical-chemical parameters the pH, TOS, conductivity,
salinity and temperature were analyzed.
The classification of the waters, were made according to the rules of the Ministry
of Sustainable Development and Environment (MDSMA) such as:
CLASS A: Natural waters of the highest quality, which enables them as
drinking water for human consumption without any previous treatment, or
with simple bacteriological disinfection in the necessary cases verified by
laboratory.
CLASS B: Waters of general utility, for human consumption, require physical
treatment and bacteriological disinfection.
CLASS C: Waters of general utility, which in order to be qualified for human
consumption requires complete physical-chemical treatment and bacteriological
disinfection.
CLASS D: Waters of minimum quality, which for human consumption, in
extreme cases of public necessity, require an initial process of pre-sedimentation,
since they can have a high turbidity due to high TOS content and then
complete physical-chemical treatment and special bacteriological disinfection
against eggs and intestinal parasites.
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Photograph 4.3: Water sampling.
4.6. Procedure – Hydro-chemical Interpretation
Techniques that helped classify the type of groundwater proposed by international organizations
such as WHO were used. For the global interpretation of the hydro-geochemical behavior of the
analyzes of surface waters and waters coming from the springs of the survey area, Collective
Diagrams were applied, such as the PIPER, SITFF, WILCOX, which allowed to see the behavior
and the comparison of the samples of the different samples in the springs, which allowed defining
its genesis and the behavior of the elements in a panoramic way.
At the same time, specialized software such as Excel, GWW, which served in the interpretation and
generation of thematic graphs and maps, etc., was used as tools.
For the global interpretation of the hydro-geochemical behavior of the analysis of surface waters
and those coming from the springs of the survey area, they were carried out with the application of
collective diagrams.
4.6.1. Collective Diagrams
Collective diagrams were made such as: Piper, Schoeller and Wilcox Diagrams and the logarithmic
classification, where the content of the ions is seen in relation to the permissible limits established
by the WHO, which allowed to see the behavior and the comparison of the samples of the different
samples in the springs, which allowed defining its genesis and the behavior of the elements in a
panoramic way.
4.7. Interpretation and evaluation of results
The tasks of water reconnaissance and sampling carried out during the field stage, complemented
by the laboratory analyzes, compatible with the parameters of permissible limits, allow an
evaluation of the characteristics and conditions of the hydro-geochemical behavior.
4.5. Field Methodology
In the field phase, a detailed inventory of water from the Silala springs was
made of six samples in surface water in waterbodies, such as the Inacaliri Volcano
Sector and the SES sector, samples that were obtained in order to know
and differentiate the quality of them.
4.6. Procedure – Hydro-chemical Interpretation
Techniques that helped classify the type of groundwater proposed by international
organizations such as WHO were used. For the global interpretation of
the hydro-geochemical behavior of the analyzes of surface waters and waters
coming from the springs of the survey area, Collective Diagrams were applied,
such as the PIPER, SITFF, WILCOX, which allowed to see the behavior
and the comparison of the samples of the different samples in the springs,
which allowed defining its genesis and the behavior of the elements in a
panoramic way.
At the same time, specialized software such as Excel, GWW, which served in
the interpretation and generation of thematic graphs and maps, etc., was used
as tools.
For the global interpretation of the hydro-geochemical behavior of the analysis
of surface waters and those coming from the springs of the survey area,
they were carried out with the application of collective diagrams.
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4.6.1. Collective Diagrams
Collective diagrams were made such as: Piper, Schoeller and Wilcox Diagrams
and the logarithmic classification, where the content of the ions is seen
in relation to the permissible limits established by the WHO, which allowed
to see the behavior and the comparison of the samples of the different samples
in the springs, which allowed defining its genesis and the behavior of the elements
in a panoramic way.
4.7. Interpretation and evaluation of results
The tasks of water reconnaissance and sampling carried out during the field
stage, complemented by the laboratory analyzes, compatible with the parameters
of permissible limits, allow an evaluation of the characteristics and
conditions of the hydro-geochemical behavior.
In order to analyze the geochemical behavior in the springs, the contents of
the calcium, magnesium, sodium and potassium cations, and the anions of
sulfates, chlorides, carbonates, bicarbonates were taken into account, which
allowed us to make the geochemical classification in springs. Likewise, the
chemical-physical parameters were determined by measuring the pH, TOS,
conductivity, salinity, with the portable equipment shown in the figure.
4.7.1. Chemical-Physical Analysis
a) pH: The behavior of the pH in the samples in the Silala Springs, is considered
as Alkaline pH between 8.0-8.40, which according to the permissible
limit is below the value, which indicates a type of alkaline water allowed (see
Figure 4.1).
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English translation prepared by DIREMAR. The original language text remains the authoritative one.
In order to analyze the geochemical behavior in the springs, the contents of the calcium,
magnesium, sodium and potassium cations, and the anions of sulfates, chlorides, carbonates,
bicarbonates were taken into account, which allowed us to make the geochemical classification in
springs. Likewise, the chemical-physical parameters were determined by measuring the pH, TOS,
conductivity, salinity, with the portable equipment shown in the figure.
4.7.1. Chemical-Physical Analysis
a) pH: The behavior of the pH in the samples in the Silala Springs, is considered as Alkaline pH
between 8.0-8.40, which according to the permissible limit is below the value, which indicates a
type of alkaline water allowed (see Figure 4.1).
Figure 4.1: Concentrations of pH in the Silala Springs.
4.7.2. Behavior of Anions
a) Sulfates (S04 Permissible limit 300 mg/l). The behavior of contents of S04 in all the samples
obtained in the different points does not exceed the limit between 5.4 - 15 < 300 mg/l, values that
are in the established range with the exception of sample MS-04 that results in a value of 400 > 300
mg/l that exceeds 33.33% more than indicated (see Figure 4.2).
4.7.2. Behavior of Anions
a) Sulfates (S04 Permissible limit 300 mg/l). The behavior of contents of
S04 in all the samples obtained in the different points does not exceed the
limit between 5.4 - 15 < 300 mg/l, values that are in the established range
with the exception of sample MS-04 that results in a value of 400 > 300 mg/l
that exceeds 33.33% more than indicated (see Figure 4.2).
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Figure 4.2: Sulphate Concentrations mg/l (see Annex D.3.4).
c) Chlorides (CI, Permissible limit 30 mg/l). The Chloride values in the water samples taken are
below the permissible limit, comprised between 1.9 – 55.67 < 30 mg/l, values obtained in the ranges
described.
d) Bicarbonate - Carbonates (HC03-C03 Allowable limit 500 (mg / l). The values of the samples
report values that do not exceed the limits between 3.43 – 7.43 mg/l < 500 mg/l. The contents of
anions are lower because salts and borates are not present in the vicinity of the lagoons. Sample
MS-04 exceeds the value with respect to the permissible limit 2215.35 > 500 mg/l (see Figure 4.3
and Figure 4.4).
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Figure 4.3. Chloride Concentrations mg/l.
Figure 4.4: Bicarbonate Concentrations mg/l (see Annex D.3.1).
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Figure 4.4: Carbonate Concentrations mg/l.
4.7.3. Behavior of Cations
Sodium – Na (Permissible Limit 100 mg/l): The Na content exceeds the permissible limit
established in two samples M-1 and MS-04 between 343.3 - 1986.6 mg/l, obtaining a high
performance of this cation by the migration and chemical exchange of salts present and the
evaporation present in the surveyed site. The other samples are below the permissible limit of 20.6
94.7 mg/l < 100 mg/l (see Figure 4.6).
Calcium (Ca) (Permissible Limit 200 mg/l): According to the analysis obtained in these samples,
the concentrations obtained are between the ranges of 4.6 - 197.68 mg/l < 200 mg/l, values that do
not exceed the established permissible limit (see Figure 4.7).
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Figure 4.6. Sodium concentrations mg/l (see Annex D.3.2).
Figure 4.7: Calcium Concentrations mg/l.
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Potassium (K) (Permissible Limit 100 mg/l). The concentrations due to this cation do not exceed
their established limit, they are between values in mg/l of 1.2 - 128.34, except for sample MS-04
that exceeds the permissible limit and governs the concentration as it is one of the major ions
485.62 mg/l > 100 mg/l (see Figure 4.8).
Figure 4.8: Potassium Concentrations mg/l (see Annex D.3.3).
4.8. Interpretation Techniques – Hydro-chemical Diagrams
For the hydro-chemical and hydro-geochemical evaluation and interpretation of the composition of
natural waters, individual diagrams have been used (Stiff Diagrams) that allow us to represent the
chemical characteristics of a single sample. In order to compare the chemical characteristics of a
group of samples, the classic Piper triangular diagrams and the columnar Schoeller diagrams have
been used, and to determine the suitability of water for irrigation purposes, the Wilcox diagram has
been used. The classification of waters according to the sampling in the Silala springs includes a
methodology of analysis of cations and anions based on the majority presence of each element.
4.8.1. Stiff Diagram
The Stiff diagram is a variety of horizontal diagrams, where the results are represented in four
horizontal lines, equally spaced and divided by a vertical median. The cations are represented on the
left and the anions on the right. The concentration of the different ions is expressed in milliliters
equivalent per liter. On a horizontal axis, the scale is normal, which allows us to compare the
composition of the samples with each other by size.
4.8. Interpretation Techniques – Hydro-chemical Diagrams
For the hydro-chemical and hydro-geochemical evaluation and interpretation
of the composition of natural waters, individual diagrams have been used (Stiff
Diagrams) that allow us to represent the chemical characteristics of a single
sample. In order to compare the chemical characteristics of a group of samples,
the classic Piper triangular diagrams and the columnar Schoeller diagrams have
been used, and to determine the suitability of water for irrigation purposes, the
Wilcox diagram has been used. The classification of waters according to the
sampling in the Silala springs includes a methodology of analysis of cations
and anions based on the majority presence of each element.
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4.8.1. Stiff Diagram
The Stiff diagram is a variety of horizontal diagrams, where the results are
represented in four horizontal lines, equally spaced and divided by a vertical
median. The cations are represented on the left and the anions on the right.
The concentration of the different ions is expressed in milliliters equivalent per
liter. On a horizontal axis, the scale is normal, which allows us to compare the
composition of the samples with each other by size.
According to the Stiff diagrams shown in Figure 4.9, in the upwelling waters
that contribute to the Silala springs, Samples MS_01, MSN_01 for the predominant
ion are classified as Bicarbonated – Sodic – Potassium (see Figure 4.9).
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According to the Stiff diagrams shown in Figure 4.9, in the upwelling waters that contribute to the
Silala springs, Samples MS_01, MSN_01 for the predominant ion are classified as Bicarbonated –
Sodic – Potassium (see Figure 4.9).
Figure 4.9: Stiff diagrams of the survey area.
4.8.2. Piper Diagram
In order to represent the chemical characteristics of the waters of the Silala springs, Piper’s
triangular diagrams have been used. The anions and cations have been represented in two different
triangles, with a central rhomboidal field, where a third point deducted from those representing
cations and anions is represented, the concentration is represented in % of meq/l.
According to the Piper diagram, the waters of the Silala springs correspond to BICARBONATE –
SODIUM POTASSIUM hydro-chemical facies, as shown in Figure 4.10.
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Figure 4.9: Stiff diagrams of the survey area.
4.8.2. Piper Diagram
In order to represent the chemical characteristics of the waters of the Silala springs, Piper’s
triangular diagrams have been used. The anions and cations have been represented in two different
triangles, with a central rhomboidal field, where a third point deducted from those representing
cations and anions is represented, the concentration is represented in % of meq/l.
According to the Piper diagram, the waters of the Silala springs correspond to BICARBONATE –
SODIUM POTASSIUM hydro-chemical facies, as shown in Figure 4.10.
Code Name Piper Diagram Stiff Diagram Water Type
MS-01 NORTH-EAST
SPRINGS
BICARBONATE –
SODIUM
POTASSIUM
BICARBONATE –
SODIUM
POTASSIUM
SPRINGS
MSN-
01
SOUTH-EAST
SPRINGS
BICARBONATE –
SODIUM
POTASSIUM
BICARBONATE –
SODIUM
POTASSIUM
SPRINGS
M-1 INACALIRI
VOLCANO
SULPHATE –
MAGNESIUM
SULPHATE –
MAGNESIUM
LAGOON –
CRATER
MS-03 SOUTH SPRINGS BICARBONATE –
SODIUM
POTASSIUM
BICARBONATE –
SODIUM
POTASSIUM
SPRINGS
MS-04 SOUTH SPRINGS BICARBONATE –
SODIUM
POTASSIUM
BICARBONATE –
SODIUM
POTASSIUM
SPRINGS
MS-05 SOUTH SPRINGS BICARBONATE –
SODIUM
POTASSIUM
BICARBONATE –
SODIUM
POTASSIUM
SPRINGS
Table 4.1: Behavior of the Hydro-chemical Areas in the Silala Springs.
4.8.2. Piper Diagram
In order to represent the chemical characteristics of the waters of the Silala springs,
Piper’s triangular diagrams have been used. The anions and cations have been
represented in two different triangles, with a central rhomboidal field, where a third
point deducted from those representing cations and anions is represented, the concentration
is represented in % of meq/l.
According to the Piper diagram, the waters of the Silala springs correspond to
BICARBONATE – SODIUM POTASSIUM hydro-chemical facies, as shown in
Figure 4.10.
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BICARBONATE – SODIUM POTASSIUM
Figure 4.10: Piper Diagram of the survey area.
Both the PIPER diagram and the STIFF diagram give the same type of water with its predominant
concentrations coming from the springs belonging to the Silala as shown in Table 4.1.
From the analysis of the table, it is concluded that there is no difference between the classifications
of Piper and Stiff.
4.8.3. Wilcox Diagram
The classification established by the SAR index Wilcox diagram, and the salt coefficient is based on
the following characteristics:
The total concentration of soluble salts expressed by the electrical conductivity in
micromhos per cm at 25 °C.
The relative concentration of sodium with respect to calcium and magnesium called the
SAR index (Sodium Absorption Radius), based on the following formula:
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For the index to be representative, precipitation of calcium or magnesium salts should not occur as a
consequence of evapotranspiration.
Figure 4.11: SAR Wilcox Diagram
To the waters of a constant SAR are attributed a greater danger of alkalizing of the soil the greater
the total concentration (According to Custodian, page 1980).
What is shown in the following graph is the Wilcox diagram. Classifying these waters according to
the norms as:
SAMPLE MSN 01 (Springs South – East) According to the diagram, it is classified as CI-S2 with
a SAR index of 11.32 what corresponds to be a type of water of low salinity with medium sodium
content, with some danger of sodium accumulation in highly textured soils with low permeability.
SAMPLE MS-01 (Springs North - East) With a SAR index of 12.82 classified as water according
to the graph type C2-S4 medium salinity waters and high sodium content, for this reason it is not
advisable to use for irrigation in general.
4.9. Anomalies maps
Water anomalies
From the analysis of the table, it is concluded that there is no difference between
the classifications of Piper and Stiff.
4.8.3. Wilcox Diagram
The classification established by the SAR index Wilcox diagram, and the salt
coefficient is based on the following characteristics:
The total concentration of soluble salts expressed by the electrical conductivity
in micromhos per cm at 25 °C.
The relative concentratxion of sodium with respect to calcium and magnesium
called the SAR index (Sodium Absorption Radius), based on the following
formula:
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To the waters of a constant SAR are attributed a greater danger of alkalizing
of the soil the greater the total concentration (According to Custodian, page
1980).
What is shown in the following graph is the Wilcox diagram. Classifying
these waters according to the norms as:
SAMPLE MSN 01 (Springs South – East) According to the diagram, it is
classified as CI-S2 with a SAR index of 11.32 what corresponds to be a type
of water of low salinity with medium sodium content, with some danger of
sodium accumulation in highly textured soils with low permeability.
SAMPLE MS-01 (Springs North - East) With a SAR index of 12.82 classified
as water according to the graph type C2-S4 medium salinity waters and
high sodium content, for this reason it is not advisable to use for irrigation in
general.
4.9. Anomalies maps
Water anomalies
An anomalous distribution of elements in subterranean and meteoric waters is
called hydro- geochemical anomaly. As the elements are generally transported
in dissolved form in natural waters, the most suitable elements for geochemical
exploration of waters are the relatively mobile elements.
A very successful application of geochemical water exploration consists of
the determination of U in groundwater and meteoric waters.
Abnormalities in Drainage Sediments
Sediment from springs, lakes, floodplains, active sediments of water currents
and sediments, which act as filters for water, belongs to drainage sediments.
Drainage systems often start from springs. The sediments located in the
vicinity of the springs and the filtration sediments tend to exhibit appreciable
anomalies and therefore these sediments are useful for a geochemical exploration.
The active sediments of water currents include elastic and
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hydromorphic material from the filtration sectors, the elastic material eroded
from the banks of detrital material located in riverbeds and hydromorphic material
absorbed or precipitated by the upwelling waters. The anomalies developed
in these active sediments can extend several ten kilometers with respect
to their source. Studies of these anomalies are used frequently and preferably
to achieve general recognition. In the case of lakes, the elastic components
and the material absorbed or precipitated from the sediments are studied. In
areas with a high number of lakes such as in the Precambrian shield area of
Canada modeled by glaciers, the geochemical survey of lake sediments may
be the most economical and effective method for a general survey.
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4.10. Analysis of Volcanic Soils
4.10.1. Physical and Chemical Properties of the Soil
Soil is a normal constituent of nature, with mineral and organic components
and a biological component formed by organisms that live in it and the physical,
chemical and biochemical alteration of the rocks causes the formation of
new highly reactive mineral constituents.
The soil is the surface covering of most of the continental surface of the Earth.
It is an aggregate of unconsolidated minerals and organic particles produced by
the combined action of wind, water and the processes of organic disintegration.
4.10.2. Textures Triangle
The texture indicates the relative content of different sized particles, such as
sand, silt and clay, in the soil. The texture has to do with the ease with which the
soil can be worked, the amount of water and air that it retains and the velocity
with which the water penetrates the soil and passes through it.
The textural triangle method is based on the system applied by the USDA according
to the size of the particles, in which the following classification is used:
Silt, all particles whose size varies from 0.002 to 0.05 mm;
Clay, all particles less than 0.002 mm.
In the field phase, 4 soil samples were obtained from the Silala springs.
The 1st sample Ssee-SUE01, taken on 23 October 2016 at 09:25 am, indicates
SILT-LOAMY as type of soil, with a higher percentage of 55.8% silt, 40.3% sand
and 3.9% clay.
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The 1st sample Ssee-SUE01, taken on 23 October 2016 at 09:25 am, indicates SILT-LOAMY as
type of soil, with a higher percentage of 55.8% silt, 40.3% sand and 3.9% clay.
Photographs 4.4 - 4.5: Sampling of volcanic soils.
The 2nd sample Ssee-SUE02, taken on 23 October 2016 at 10:50 am, indicates SILT-LOAMY as
type of soil, with a higher percentage of 54.2% silt, 44.4% sand and 1.4% clay.
The 3rd sample SnWW-SUE01, was taken on 24 October, 2016 at 12:43 pm, indicates SILTLOAMY
as type of soil, with a higher percentage of 73.7% silt, 24.6% sand and 1.7% clay.
The 4th sample SnWW-SUE02, was taken on 24 October 2016 at 14:42 pm, indicates SILTLOAMY
as type of soil, with a higher percentage of 60.3% silt, 20.1% sand and 19.6% clay.
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Figure 4.12. Classification of Soils by the Textural Triangle (USDA)
Conclusions CHAPTER IV (HYDROCHEMISTRY)
The presence of older and recent volcanic deposits in the area is evidenced, which alter the
composition, hydro-chemical migration in the waterbody.
The geo-morphological features reflect units of volcanic origin - denudational, alluvial,
lacustrine and fluvial–lacustrine.
The soils determined in the area are deep and very susceptible to wind erosion and due to
their chemical characteristics present limitations in their agricultural use.
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Conclusions CHAPTER IV (HYDROCHEMISTRY)
The presence of older and recent volcanic deposits in the area is evidenced,
which alter the composition, hydro-chemical migration in the waterbody.
The geo-morphological features reflect units of volcanic origin - denudational,
alluvial, lacustrine and fluvial–lacustrine.
The soils determined in the area are deep and very susceptible to wind erosion
and due to their chemical characteristics present limitations in their agricultural
use.
It is evidenced by the results of the hydrogeological survey that most of the
contributions of the springs are of underground origin because they are found
as means of discharge to depths and located in ignimbrite rocks due to the effect
of fracturing and secondary permeability.
The hydro-chemical facie of the waterbody in the North-northeast and South-
East springs; they are classified as SODIUM BICARBONATED POTASSIUM
waters, reflecting low conductivities between 110 - 140 ms/cm and almost neutral
pH; showing a type A cationic stability, classified as suitable for human
consumption and used for irrigation.
For the samplings carried out in the Inacaliri volcano, in the center of the
volcano, they are classified as SULPHATED – MAGNESIAN waters. This behavior
is due to the effects of migration and disintegration of volcanic activity.
Recommendations
Due to the monitoring and control established for this period, a periodic
control over these canals is recommended in order to evaluate the isotopic behavior.
Expand the research to the other sub-basins in order to obtain information on
the quality of hydro-chemical profiles in water resources.
Recommend, at the request of the Governorate, the preservation of natural
resources (Water - Soil), as it is an important reserve for future generations.
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CHAPTER V
HYDROGEOLOGY
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INDEX
5.1. Introduction
5.2. Definition of fundamental concepts
5.3. Survey Objective
5.4. Survey Scope
5.5 Hydro-morphological Parameters of the Surveyed Basin
5.6. Hydrogeological Survey
5.7. Obtaining Hydrogeological Parameters
5.7.1. Hydrogeological Parameters of Unconsolidated Deposits
5.7.2. Hydrogeological Parameters of the Miocene Ignimbrite Formation
5.7.3. Hydrogeological Parameters of Volcanic Lava Formation
5.8. Hydrogeological Map of the Silala Springs
Conclusions and Recommendations
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FIGURES
Figure 5.1: Diagram of the Hydrological Cycle
Figure 5.2: Location of the Survey Area, Silala Springs
Figure 5.3: Area of the Survey Area, Silala Springs
Figure 5.4: Digital Elevation Model of the Silala Springs
Figure 5.5: Reclassification of the DEM in ranges of 200 meters from the Silala Springs
Figure 5.6: Hypsometric Curve of the Silala Area
Figure 5.7: Soil Sampling Points from the Silala Springs
Figure 5.8: Location of Infiltration Test Points
Figure 5.9: Location of Permeability Test Points
TABLES
Table 5.1: Calculation of the Slope Average Inclination of the Silala Area
Table 5.2: Textural Classification of Soils
Table 5.3: Results of Infiltration Tests
Table 5.4: Results of Permeability Tests
Table 5.5: Storage and Permeability of Volcanic Rocks (Source: Custodio (1996), Sanders & Smith
(1998), Morris & Johnson (1982))
Table 5.6: Hydrogeological Units of the Silala Area
MAPS
Map 5.1: Hydrogeological Map of the Silala Springs
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CHAPTER V: HYDROGEOLOGICAL CHARACTERIZATION OF
THE SILALA SPRINGS
5.1. Introduction
Hydrogeology is that part of hydrology that corresponds to the storage, circulation
and distribution of terrestrial waters in the saturated area of geological
formations, taking into account the physical and chemical properties, their interactions
with the physical and biological environment and their reactions to
the action of men.
The HYDROGEOLOGICAL CHARACTERIZATION has allowed defining
different variables such as: geological, geo-morphological, geophysical, hydrogeochemical,
hydrological, hydrogeological, which have allowed quantifying
the volume of surface water and the volume of groundwater, as well as the
quality and the hydraulic-genetic relation in the Silala springs.
For the hydrogeological characterization of the Silala springs, field mapping
was carried out in detail, which allowed determining the lithology, the structural
interpretation from the mapping of 1,500 fractures present in the survey
area, which allowed determining the type of fracture, the frequency of them,
which condition the secondary permeability in the area.
Geophysical profiles (SEV) were also carried out; the same ones that allowed
determining the thicknesses of the different geological structures and the depth
of them, with their petro-physical characteristics, that allowed elaborating the
stratovolcanic columns.
Due to the lack of meteorological information in the survey area, water modeling
was carried out through a Geographical Information System (ILWIS -
LOCCLIM), which allowed determining the water supply and the volume of
runoff.
The hydro-geochemical analysis of the waters of the Silala springs, both in
the southeast-east sector and in the northwest-west sector, which allowed determining
the quality of the same classifying them as SODIC-POTASSIC BICARBONATED
waters, which allowed us differentiating from the waterbodies
present at higher altitudes such as the Inacaliri Volcano (5,570 m.a.s.l.), which
has a classification of MAGNESIUM-SULFATED water, which does not corresponds
to the quality of the spring water.
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5.2. Definition of fundamental concepts
Spring: It is a point or area of the surface of the terrain in which an appreciable
amount of water from an aquifer flows naturally to the surface.
Slope: Inclined plane that allows the runoff of water.
Bofedals: Ever-green physiognomy associations that generally have high
groundwater levels and permanent surface runoff.
River: More or less abundant water current that continues flowing naturally and
that ends in another basin or in the sea.
International Course River: It is defined as a watercourse that crosses or separates
the territories of two or more States.
Fossil water: Groundwater that remains for millennia, millions of years under
the subsoil in aquifers and that was sealed by geological processes preventing
its recharge.
Permafrost soils: It is the soil layer permanently frozen but not permanently
covered with ice or snow from very cold or periglacial regions such as the
tundra.
The hydrological cycle
The hydrological cycle is fundamental in hydrology; it is a continuous process
without beginning or end. The concept of a hydrological cycle involves the
movement or transfer of water masses from one place to another and from one
state to another.
The hydrological cycle aims to characterize quantitatively important factors
within the water balance of the survey area, such as precipitation (P), evapotranspiration
(Evt), runoff and variations of the water reserve in the soil (ΔR or
infiltration – storage).
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snow from very cold or periglacial regions such as the tundra.
The hydrological cycle
The hydrological cycle is fundamental in hydrology; it is a continuous process without beginning or
end. The concept of a hydrological cycle involves the movement or transfer of water masses from
one place to another and from one state to another.
The hydrological cycle aims to characterize quantitatively important factors within the water
balance of the survey area, such as precipitation (P), evapotranspiration (Evt), runoff and variations
of the water reserve in the soil ( R or infiltration – storage).
Figure 5.1: Hydrological Cycle (Environmental Sciences – Mcgraw Hill).
To calculate the water balance through modeling, the following equation was applied (see Figure
5.):
P = Ev + ETP + Ese+ + I
Where:
P = Precipitation
Ev = Evaporation
ETP = Potential Evapotranspiration
Esc = Surface runoff (supply)
= Surface storage
I = Infiltration
Also for the underground water balance the following equation was used (see Figure 5).
I = EscSub + EVT + Cc + Im + R
Where:
I = Infiltration
EscSub = Sub-surface runoff
EVT = Evapotranspiration
Cc = Field capacity
Im = Wilting Index
R = Recharge to the aquifer
However, the recharge factor R, is the most important parameter in the variation of the piezometric
and phreatic levels, and can be expressed as:
R = I - EscSub - EVT - Cc – Im
Where:
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Also for the underground water balance the following equation was used (see Figure 5).
I = EscSub + EVT + Cc + Im + R
Where:
I = Infiltration
EscSub = Sub-surface runoff
EVT = Evapotranspiration
Cc = Field capacity
Im = Wilting Index
R = Recharge to the aquifer
However, the recharge factor R, is the most important parameter in the variation of the piezometric
and phreatic levels, and can be expressed as:
R = I - EscSub - EVT - Cc – Im
Where:
R = Recharge to the aquifer
I = Infiltration
EscSub = Sub-surface runoff
EVT = Evapotranspiration
Cc = Field capacity
Im = Wilting Index
Variables that allowed operationalizing the thematic maps of the modeling, which allowed
obtaining the water balance of whose results it was defined that there is a WATER DEFICIT (see
Figure 5.2).
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Figure 5.2: Diagram of the Hydrological Cycle in relation to Precipitation, Infiltration and
Recharge.
5.3. Survey Objective
The objective of this survey was the hydrogeological characterization of the Silala springs,
understanding methodologically as a characterization to define, analyze and establish hydrological
relations.
5.4. Survey Scope
The physical characterization of the survey area, allowed defining –from the topographic highs– the
survey area surrounding the Silala springs (see Figure 5.3), in order to define the type of recharge.
5.5. Hydro-morphological Parameters of the Survey Area
The physical characteristics of an area are elements that have a great importance in the superficial
hydrological behavior of the same and have their direct impact on the hydrogeology of the survey
area. These physical characteristics are classified into two types according to their impact in the
survey area: those that condition the volume of runoff and infiltration, as well as the area and type
of soil, and those that determine the velocity of response, as well as the length of the canal, the
average inclination of the slope and the hypsometric curve that allows determining the average
elevation of the survey area. However, in the absence of a river, the survey of the length of the
canal and the slope of the canal has no relevance.
There is a close correspondence between the hydrological regime and the physical characterization
of the survey area, for which the knowledge of these has great practical utility, since in establishing
relations and comparisons between them with known, modeled and calculated hydrological data,
hydrological values could be determined indirectly in sections of practical interest where data are
5.3. Survey Objective
The objective of this survey was the hydrogeological characterization of the
Silala springs, understanding methodologically as a characterization to define,
analyze and establish hydrological relations.
5.4. Survey Scope
The physical characterization of the survey area, allowed defining –from the
topographic highs– the survey area surrounding the Silala springs (see Figure
5.3), in order to define the type of recharge.
5.5. Hydro-morphological Parameters of the Survey Area
The physical characteristics of an area are elements that have a great importance
in the superficial hydrological behavior of the same and have their direct
impact on the hydrogeology of the survey area. These physical characteristics
are classified into two types according to their impact in the survey area: those
that condition the volume of runoff and infiltration, as well as the area and type
of soil, and those that determine the velocity of response,
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lacking or where, for reasons of physiographic or economic nature, the installation of hydrometric
stations is not feasible (see Chapter III).
Figure 5.3: Location of the Survey Area, Silala Springs.
Area of the Survey Area
The area of the survey area is of great importance because it serves as a basis for determining other
elements such as: parameters, coefficients, relations, and classification of the type of the survey
area. On the other hand, in general, runoff and supply flows decrease as the area of the survey area
decreases. The growth of the area acts as a compensation factor so that it is more common to detect
instantaneous increases and immediate response in the survey areas.
The systematization of all the information indicated through a GIS has allowed us obtaining the
area of the Silala area of 249319375 m2, equivalent to 249.31 km2 (see Figure 5.4). The area was
obtained from the processing of ASTER satellite information.
Figure 5.4: Area of the Survey Area – Silala Springs.
as well as the length of the canal, the average inclination of the slope and the
hypsometric curve that allows determining the average elevation of the survey
area. However, in the absence of a river, the survey of the length of the canal
and the slope of the canal has no relevance.
There is a close correspondence between the hydrological regime and the physical
characterization of the survey area, for which the knowledge of these has
great practical utility, since in establishing relations and comparisons between
them with known, modeled and calculated hydrological data, hydrological values
could be determined indirectly in sections of practical interest where data
are lacking or where, for reasons of physiographic or economic nature, the
installation of hydrometric stations is not feasible (see Chapter III).
Area of the Survey Area
The area of the survey area is of great importance because it serves as a basis
for determining other elements such as: parameters, coefficients, relations, and
classification of the type of the survey area. On the other hand, in general,
runoff and supply flows decrease as the area of the survey area decreases. The
growth of the area acts as a compensation factor so that it is more common to
detect instantaneous increases and immediate response in the survey areas.
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Figure 5.3: Location of the Survey Area, Silala Springs.
Area of the Survey Area
The area of the survey area is of great importance because it serves as a basis for determining other
elements such as: parameters, coefficients, relations, and classification of the type of the survey
area. On the other hand, in general, runoff and supply flows decrease as the area of the survey area
decreases. The growth of the area acts as a compensation factor so that it is more common to detect
instantaneous increases and immediate response in the survey areas.
The systematization of all the information indicated through a GIS has allowed us obtaining the
area of the Silala area of 249319375 m2, equivalent to 249.31 km2 (see Figure 5.4). The area was
obtained from the processing of ASTER satellite information.
Figure 5.4: Area of the Survey Area – Silala Springs.
The systematization of all the information indicated through a GIS has allowed
us obtaining the area of the Silala area of 249319375 m2, equivalent to 249.31
km2 (see Figure 5.4). The area was obtained from the processing of ASTER
satellite information.
Average slope steepness
The average slope inclination of the survey area was calculated according to
the following equation:
Where:
Sm = Average inclination of the slope
DA = Total drainage area
Si = Average slope of each sub-area in which the basin is
reclassified
DAi = Each of the reclassified sub-areas
Average slope steepness
The average slope inclination of the survey area was calculated according to the following equation:
Where:
Sm = Average inclination of the slope
DA = Total drainage area
Si = Average slope of each sub-area in which the basin is reclassified
DAi = Each of the reclassified sub-areas
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Where:
Sm = Average inclination of the slope
DA = Total drainage area
Si = Average slope of each sub-area in which the basin is reclassified
DAi = Each of the reclassified sub-areas
Figure 5.5: Digital Elevation Model of the Silala Springs.
Elevation
Ranges
Average
Slope
Area (m2) Average
Slope with
Area
Product
Accumulated
Area
Percentage
of
Accumulated
Area
Average
Elevation
(m)
4400 13,8 1577500 21769500 1577500 0,6 4.300
4400 – 4600 26,2 65798125 1723910875 67375625 27,4 4.500
4600 – 4800 29,6 120144375 3556273500 187520000 76,4 4.700
4800 – 5000 30,2 46436875 1402393625 233956875 95,3 4.900
5000 – 5200 32,6 7070000 230482000 241026875 98,2 5.100
5200 – 5400 32,8 3253750 106723000 244280625 99,5 5.300
5400 – 5600 47,8 1037500 49592500 245318125 99,9 5.500
5600 – 5800 37 237500 8787500 245555625 100 5.700
Summation 245555625 7099932500
Average inclination of the slope (%) 28,9
Table 5.1: Calculation of the average slope inclination of the Silala area
The Digital Elevation Model (DEM) of the survey area (see Figure 5.5) was
reclassified into sub- areas of level ranges or topographic heights. In the case of
the Silala area, it was divided into 200- meter ranges (see Figure 5).
Once all the calculations have been made, the ―average inclination of the
slope‖ is 28.9% (see Figure 5.6).
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Figure 5.7: Hypsometric Curve of the Silala Area.
It is interesting to know how the area of the survey area is distributed at different topographic
levels, in order to compare storage characteristics. This is achieved from the hypsometric curve.
From Figure 5.7, it can be deduced that it is a curve that reflects a basin with a minimum erosive
potential. This aspect corroborates the existence of minimum volumes of surface runoff.
5.6. Hydrogeological Survey
Geological units of the Silala area
From the interpretation of the geology of the survey area, which was carried out in Chapters I, II
and III of this report, the presence of three geological units was defined: Mio-Pliocene Volcanic
Lavas, Rhyolitic Ignimbrites (Welded Tuffs) and Pleistocene Unconsolidated Deposits.
The unit that occupies the largest area is the Mio-Pliocene Volcanic Lavas, occupying 105.16 km2,
representing 42.2% of the survey area. The second unit in importance is the Rhyolitic Ignimbrites
(Welded Tuffs), with a total of 87 km2, representing 34.9% of the total area. Finally, the third unit
has an area of 57.2 km2, representing 22.9% of the survey area; we have the Pleistocene
Unconsolidated Deposits (see Chapter III, Map 3.1, p. 68).
5.7. Obtaining Hydrogeological Parameters
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The Digital Elevation Model (DEM) of the survey area (see Figure 5.5) was reclassified into subareas
of level ranges or topographic heights. In the case of the Silala area, it was divided into 200-
meter ranges (see Figure 5).
Once all the calculations have been made, the a“verage inclination of the slope” is 28.9% (see
Figure 5.6).
Figure 5.6: Reclassification of the Digital Elevation Model (DEM) in ranges of 200 meters from
the Silala springs.
Hypotometric curve
From Table 5.1, and taking into account the columns “ Percentage of accumulated area” and
“Average height”, the hypsometric curve is obtained. The distribution of the area of the survey area
is obtained at different topographic levels, in order to compare storage and flow characteristics in
the basin (see Figure 5).
Hypotometric curve
From Table 5.1, and taking into account the columns ―Percentage of accumulated
area‖ and ―Average height‖, the hypsometric curve is obtained. The
distribution of the area of the survey area is obtained at different topographic
levels, in order to compare storage and flow characteristics in the basin (see
Figure 5).
It is interesting to know how the area of the survey area is distributed at different
topographic levels, in order to compare storage characteristics. This is
achieved from the hypsometric curve.
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From Figure 5.7, it can be deduced that it is a curve that reflects a basin with a
minimum erosive potential. This aspect corroborates the existence of minimum
volumes of surface runoff.
5.6. Hydrogeological Survey
Geological units of the Silala area
From the interpretation of the geology of the survey area, which was carried out
in Chapters I, II and III of this report, the presence of three geological units was
defined: Mio-Pliocene Volcanic Lavas, Rhyolitic Ignimbrites (Welded Tuffs)
and Pleistocene Unconsolidated Deposits.
The unit that occupies the largest area is the Mio-Pliocene Volcanic Lavas, occupying
105.16 km2, representing 42.2% of the survey area. The second unit in
importance is the Rhyolitic Ignimbrites (Welded Tuffs), with a total of 87 km2,
representing 34.9% of the total area. Finally, the third unit has an area of 57.2
km2, representing 22.9% of the survey area; we have the Pleistocene Unconsolidated
Deposits (see Chapter III, Map 3.1, p. 68).
5.7. Obtaining Hydrogeological Parameters
In order to obtain the parameters of permeability, it was necessary to resort to
different direct and indirect methods, applied mainly to the Ignimbrite formations
considered as Aquifers.
Unconsolidated deposit formations, because they have more or less favorable
levels of effective porosity for the storage of groundwater, are considered as
Aquitards.
The compact volcanic lava formations do not have expected levels of porosity,
they are classified as Aquifuges.
5.7.1. Hydrogeological Parameters of Unconsolidated Deposits
For the hydrogeological characterization of the unconsolidated deposits of the
Silala springs, we proceeded to obtain the soil texture, perform infiltration velocity
tests, through the infiltration test
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by the Double Ring Method based on the Kostiakov Equation and the permeability tests at greater
depth through the Descending Level Method (see Annex E.1 – Infiltration Test Tables).
5.7.1.1. Soil Texture
The texture of the soil indicates the relative content of different sized particles, such as sand, silt
and clay. As it also has to do with the amount of water and air it retains and the velocity with which
water penetrates the ground and passes through it.
In the survey area, soil samples were taken at four points that after having been analyzed in
laboratories resulted in a SILTY- LOAMY texture (see Figure 5.8, Table 5.2).
Figure 5.8: Soil sampling points from the Silala springs.
SAMPLE TEXTURE
Ssee-SUE01 Silt-Loamy
Ssee-SUE02 Silt-Loamy
Snww-SUE01 Silt-Loamy
Snww-SUE02 Silt-Loamy
Table 5.2: Textural Classification of Soils
Geological formations that are composed of silt contents are classified as Aquitards (See Annex
0.1., Soil Certificate).
5.7.1.2. Infiltration Velocity Tests
It is called “in ltration” to the process of vertical migration through which water penetrates the
surface, a process that allows saturating the geological formations.
The infiltration test by the double ring method consists of saturating a portion of the soil limited by
two concentric rings so that the variation of the water level in the inner cylinder can then be
measured. Through the Kostiakov Equation, the infiltration velocity was obtained. This information
defined the soil type for a range of 30–50 cm, on average, from which results average values of
infiltration velocity were obtained with a permeability calculated in the southeast-east sector of
1.08 m/day and in the northwest-west sector of 2.44 m/day (see Annex E.1., Infiltration Tests).
by the Double Ring Method based on the Kostiakov Equation and the permeability
tests at greater depth through the Descending Level Method (see Annex
E.1 – Infiltration Test Tables).
5.7.1.1. Soil Texture
The texture of the soil indicates the relative content of different sized particles,
such as sand, silt and clay. As it also has to do with the amount of water and air
it retains and the velocity with which water penetrates the ground and passes
through it.
In the survey area, soil samples were taken at four points that after having been
analyzed in laboratories resulted in a SILTY- LOAMY texture (see Figure 5.8,
Table 5.2).
Geological formations that are composed of silt contents are classified as Aquitards
(See Annex D.1., Soil Certificate).
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Photograph 5.1: Infiltration Tests by the Double Ring Method.
Figure 5.9: Location of Infiltration Test Points
As shown in Figure 5.9, three infiltration tests were carried out on the points coded as: Snww
INF04, Ssee INF02 and Ssee INF01.
The results of these soil tests shown in Table 5.3, classify them as Aquitards.
POINT Infiltration
m/day
Snww INF04 2,4337
Ssee INF02 0,0901
Ssee INF01 1,0769
Table 5.3: Results of the Infiltration Test.
5.7.1.3. Permeability Tests
5.7.1.2. Infiltration Velocity Tests
It is called ―infiltration‖ to the process of vertical migration through which
water penetrates the surface, a process that allows saturating the geological
formations.
The infiltration test by the double ring method consists of saturating a portion
of the soil limited by two concentric rings so that the variation of the water level
in the inner cylinder can then be measured. Through the Kostiakov Equation,
the infiltration velocity was obtained. This information defined the soil type for
a range of 30–50 cm, on average, from which results average values of infiltration
velocity were obtained with a permeability calculated in the southeast-east
sector of 1.08 m/day and in the northwest-west sector of 2.44 m/day (see Annex
E.1., Infiltration Tests).
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Photograph 5.1: Infiltration Tests by the Double Ring Method.
Figure 5.9: Location of Infiltration Test Points
As shown in Figure 5.9, three infiltration tests were carried out on the points coded as: Snww
INF04, Ssee INF02 and Ssee INF01.
The results of these soil tests shown in Table 5.3, classify them as Aquitards.
POINT Infiltration
m/day
Snww INF04 2,4337
Ssee INF02 0,0901
Ssee INF01 1,0769
Table 5.3: Results of the Infiltration Test.
5.7.1.3. Permeability Tests
Permeability is the ability of a material to allow a flow to pass through it without altering its internal
structure. It is stated that a material is permeable if it allows an appreciable amount of fluid to pass
through it in a given time.
The coefficient of permeability can be expressed according to the following equation:
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Photograph 5.1: Infiltration Tests by the Double Ring Method.
Figure 5.9: Location of Infiltration Test Points
As shown in Figure 5.9, three infiltration tests were carried out on the points coded as: Snww
INF04, Ssee INF02 and Ssee INF01.
The results of these soil tests shown in Table 5.3, classify them as Aquitards.
POINT Infiltration
m/day
Snww INF04 2,4337
Ssee INF02 0,0901
Ssee INF01 1,0769
Table 5.3: Results of the Infiltration Test.
5.7.1.3. Permeability Tests
Permeability is the ability of a material to allow a flow to pass through it without altering its internal
structure. It is stated that a material is permeable if it allows an appreciable amount of fluid to pass
through it in a given time.
The coefficient of permeability can be expressed according to the following equation:
As shown in Figure 5.9, three infiltration tests were carried out on the points
coded as: Snww INF04, Ssee INF02 and Ssee INF01.
The results of these soil tests shown in Table 5.3, classify them as Aquitards.
5.7.1.3. Permeability Tests
Permeability is the ability of a material to allow a flow to pass through it without
altering its internal structure. It is stated that a material is permeable if it
allows an appreciable amount of fluid to pass through it in a given time.
The coefficient of permeability can be expressed according to the following
equation:
k= Q / IA
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k = Q / I A
Where:
k: coefficient of permeability or hydraulic conductivity [m/s]
Q: flow rate [m3/s]
I: gradient
A: section [m2]
For the calculation of this permeability value of the unconsolidated formations of the colluvialalluvial
material, the Descendant Level Method was applied to a depth of 1.5–2 meters (see Figure
5 and Figure 5.10), with a constant load at four points in the survey area, whose results are shown in
Table 5.4 (see Annex E.2., Permeability Tests).
Photograph 5.2: Permeability Tests.
POINT PERMEABILITY
cm/min
PERMEABILITY
cm/min
PERMEABILITY
cm/sec
PERMEABILITY
cm/day
Snww
PERM01
0,3348 3,3480 0,00006 4,8211
Ssee
PER02
0,3348 3,3480 0,00006 4,8211
Ssee
PER03
0,2259 2,2590 0,000004 3,2530
Ssee
PER04
0,4326 4,3260 0,000007 6,2294
Table 5.4: Results of the Permeability Tests.
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Figure 5.10: Location of Permeability Test points.
The permeability and storage coefficient of volcanic rocks is mainly a function of the degree of
fracture or secondary porosity, as an effect of the tectonism of the survey area. However, there are
calculated average values that are compatible with Table 5.6 –that according to Custodio (1996)–
Ignimbrites are classified as Regular to Good Aquifers, according to Table 5.5.
Permeability
m/day
10-6 10-5 10-4 10-3 10-2 10-1 1 4.607 10 102 103
Rating Impermeable Low
permeability
Somewhat
permeable
Permeable Very
permeable
Aquifer rating Aquiclude Aquitard Poor Aquifer Aquifer from
regular to
good
Excellent
Aquifer
Type of
materials
Compact clay
Shale
Granite
Silt
Sandy
Silt
Clay
Silty
Fine sand
Silty Sand
Fractured
limestone
Clean sand
Gravel and
sand
Fine sand
Clean sand
Table 5.5: Classification of terrains by permeability (according to Custodio and Llamas)
5.7.2. Hydrogeological Parameters of the Miocene Ignimbrite Formation
The hydrogeological survey in volcanic rocks is a very special case since they are not part of the
typical fissured or porous aquifers. Recent volcanic materials encompass rocks of different nature
around the Siloli Chico Hill volcanic dome.
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Photograph 5.3: Siloli Chico Hill volcanic dome.
From the interpretation of the structural geology of the survey area, we have a Domain 1,
characterized by fractures of extension of courses, which fluctuate from N 81-85° E, coinciding
with the direction of the topographic depression through which the springs flow, with a preferred
course of N 81° E. These geological structures are located in the Ignimbrites of the survey area, so
this formation can be classified as a secondary porosity aquifer. However, as seen in the Chapter on
“Modeling the Water Supply”, the recharge from meteoric waters is null, so it can be affirmed
that the origin of the water from the springs also has another source that is located outside the
survey area, in Bolivian territory of higher elevations; consequently they cannot be considered fossil
waters.
5.7.3. Hydrogeological Parameters of Volcanic Lava Formation
This formation, correspond to Domain 2, which are characterized by the presence of shear fractures.
From the interpretation of the Frequency Rosette it can be perceived predominance of course with a
range of N 0-10° W, which coincides with compression fractures, as well as a fracturing frequency
in a range of N 60-68° W, which coincides with shear fractures. For all the above, it can be
explained in the section of Domain 2 that there are no springs, since there is a preference for closed
fractures unlike Domain 1 and 4, which are extension fractures. Consequently, it can be affirmed
that this formation behaves like an Aquifuge.
5.8. Hydrogeological Map of the Silala Springs
Once the geological formations have been characterized –from the hydrogeological point of view–
based on the type of soil texture, infiltration, permeability and the interpretation of structural
geology, we proceeded with obtaining the geological map that served as the basis for developing the
hydrogeological map of the survey area. Where three hydrogeological units are presented, which in
order of importance for the area they occupy, are: Aquifuge, Aquifer of Secondary Porosity and
Aquitard.
The Aquifuge of the Silala area is non-fractured volcanic rock, it occupies an area of 104.98 km2,
and representing 42.11% of the total area (see Table 5.5). This hydrogeological unit is located in the
From the interpretation of the structural geology of the survey area, we have
a Domain 1, characterized by fractures of extension of courses, which fluctuate
from N 81-85° E, coinciding with the direction of the topographic depression
through which the springs flow, with a preferred course of N 81° E.
These geological structures are located in the Ignimbrites of the survey area,
so this formation can be classified as a secondary porosity aquifer. However,
as seen in the Chapter on ―Modeling the Water Supply‖, the recharge from
meteoric waters is null, so it can be affirmed that the origin of the water from
the springs also has another source that is located outside the survey area, in
Bolivian territory of higher elevations; consequently they cannot be considered
fossil waters.
5.7.3. Hydrogeological Parameters of Volcanic Lava Formation
This formation, correspond to Domain 2, which are characterized by the presence
of shear fractures. From the interpretation of the Frequency Rosette it
can be perceived predominance of course with a range of N 0-10° W, which
coincides with compression fractures, as well as a fracturing frequency in a
range of N 60-68° W, which coincides with shear fractures. For all the above,
it can be explained in the section of Domain 2 that there are no springs, since
there is a preference for closed fractures unlike Domain 1 and 4, which are
extension fractures. Consequently, it can be affirmed that this formation behaves
like an Aquifuge.
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5.8. Hydrogeological Map of the Silala Springs
Once the geological formations have been characterized –from the hydrogeological
point of view– based on the type of soil texture, infiltration, permeability
and the interpretation of structural geology, we proceeded with obtaining
the geological map that served as the basis for developing the hydrogeological
map of the survey area. Where three hydrogeological units are presented,
which in order of importance for the area they occupy, are: Aquifuge, Aquifer
of Secondary Porosity and Aquitard.
The Aquifuge of the Silala area is non-fractured volcanic rock, it occupies an
area of 104.98 km2, and representing 42.11% of the total area (see Table 5.5).
This hydrogeological unit is located in the north, northeast and south of the
survey area (see Map 5.1), these are Mio-Pliocene Volcanic Lavas with very
low permeability.
The second hydrogeological unit is a secondary porosity aquifer, which occupies
86.95 km2, representing 34.87% of the total area (see Table 5.5). This
hydrogeological unit is located mostly in the eastern sector of the survey area.
Another important sector of emplacement of this unit is the North, Center
and South (See Map 5.1). Lithologically it is formed by Ignimbrites that have
been affected by an intense jointing, having identified a ―Domain 1‖ of open
jointing, which gives a secondary porosity. Since it is a cracked aquifer, the
water content depends on the degree and distribution of the fracture. However,
the recharge conditions, due to the effect of meteoric waters, are incipient
(WATER DEFICIT), so they are not likely to contribute any amount of water
to the artificial drainage canals to Chile.
The third unit, in order of importance for the area it occupies, is an Aquitard,
which occupies 57.39 km2, and representing 23.02% of the total area
(see Table 5.5). This hydrogeological unit is formed by river deposits (in the
ravines), morrhenic deposits, colluvial, colluvial-fluvial deposits and alluvial
deposits. The survey area is mainly located in the central part (see Map 5.1).
For all the above we can point out that the surface hydrogeological map does
not contribute to the upwelling of the Silala springs. Due to the volumes that
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representing 34.87% of the total area (see Table 5.5). This hydrogeological unit is located mostly in
the eastern sector of the survey area. Another important sector of emplacement of this unit is the
North, Center and South (See Map 5.1). Lithologically it is formed by Ignimbrites that have been
a ected by an intense jointing, having identi ed a D“omain 1” of open jointing, which gives a
secondary porosity. Since it is a cracked aquifer, the water content depends on the degree and
distribution of the fracture. However, the recharge conditions, due to the effect of meteoric waters,
are incipient (WATER DEFICIT), so they are not likely to contribute any amount of water to the
artificial drainage canals to Chile.
The third unit, in order of importance for the area it occupies, is an Aquitard, which occupies 57.39
km2, and representing 23.02% of the total area (see Table 5.5). This hydrogeological unit is formed
by river deposits (in the ravines), morrhenic deposits, colluvial, colluvial-fluvial deposits and
alluvial deposits. The survey area is mainly located in the central part (see Map 5.1).
For all the above we can point out that the surface hydrogeological map does not contribute to the
upwelling of the Silala springs. Due to the volumes that have been gauged in a range of 160 to 250
l/s, consequently the recharge to the aquifers comes from Bolivian territory with higher elevations
than those of the survey area.
Hydrological Unit Area (m2) Area (km2) % Area
Aquifuge 104977500 104,98 42,11
Aquifer of secondary
porosity
86949375 86,95 34,87
Aquitard 57392500 57,39 23,02
TOTAL 249319375 249,32 100,0
Table 5.5: Hydrogeological Units of the Silala Area.
The detailed geological mapping in the survey area has allowed the elaboration of the structural
geological map (see Annex A.2 – Map 2/8 – Chapter 1), which has allowed the strato-volcanic
column to be elaborated (see Table 5.6).
These thematic maps allowed validating the hypothesis of the geological and hydrogeological
history and its relation with the geomorphology and the materials present in the survey area. This
has allowed classifying correspondingly the permeability of all the formations present in the survey
area classified as: Aquifuges, Aquitards and regular to good Aquifers.
have been gauged in a range of 160 to 250 l/s, consequently the recharge to
the aquifers comes from Bolivian territory with higher elevations than those
of the survey area.
The detailed geological mapping in the survey area has allowed the elaboration
of the structural geological map (see Annex A.2 – Map 2/8 – Chapter 1),
which has allowed the strato-volcanic column to be elaborated (see Table 5.6).
These thematic maps allowed validating the hypothesis of the geological
and hydrogeological history and its relation with the geomorphology and the
materials present in the survey area. This has allowed classifying correspondingly
the permeability of all the formations present in the survey area classified
as: Aquifuges, Aquitards and regular to good Aquifers.
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ERA AGE PERIOD ROCK
TYPE
LITHOLOGY STORAGE
(%)
PERMEABILITY
(m/day)
Table 5.6: Storage and permeability of volcanic rocks (Source: Custodio (1996), Sanders & Smith
(1998), Morris & Johnson (1982)).
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Map 5.1: Hydrogeological Map of the Silala Springs.
Conclusions CHAPTER V (HYDROGEOLOGY)
The recharge of the Ignimbrite aquifer is not possible under the hydrological regime of the survey
area, since the meteoric water volumes are minuscule, there is a Water Deficit, therefore the
volumes of permanent variable flow that are evacuated towards the artificial canals are validated
according to the results of the survey of the superficial hydrological modeling and the gauges
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Conclusions CHAPTER V (HYDROGEOLOGY)
The recharge of the Ignimbrite aquifer is not possible under the hydrological
regime of the survey area, since the meteoric water volumes are minuscule,
there is a Water Deficit, therefore the volumes of permanent variable flow that
are evacuated towards the artificial canals are validated according to the results
of the survey of the superficial hydrological modeling and the gauges carried
out in the sector.
The ignimbrite volcanic rock formation is a secondary permeability aquifer due
to the degree of fracturing it presents, which come from geological formations
that are below the ignimbrite layer, whose recharge is in Bolivian territory at
higher elevations than in the survey area.
The piezometric levels of the bofedals present in the area were depressed in
anthropogenic form in order to increase the upwelling of the groundwater towards
the canals.
Considering an average flow of 200 l/sec, flowing through artificial canals, the
surface water supply of the survey area only represents 1.4% of these flows.
The remaining 98.6% comes from deep underground aquifers, which migrate
their waters through two spring systems structurally controlled by extension
fractures in Domain 1, southeast-east springs, and by the shear fractures product
of efforts of cupola Domain 4 and faults present in the northwest-west
springs, which also conditioned the topographic depression.
The chemical analyzes carried out in the Silala springs define them as SODICPOTASSIC
BICARBONATED waters, and the chemical analyzes carried out
in natural and permanent waterbodies with higher elevations classify them as
MAGNESIUM-SULFATED waters, consequently, there is no hydro-geochemical
relations.
Due to the geological, hydrogeological and topographic characteristics of the
survey area, it can be concluded that it is a confined aquifer with secondary
permeability.
Due to all the hydrological and hydrogeological characteristics, we can conclude
that it is not a shared aquifer, that there is a water deficit, that the recharge
is in Bolivian territory and that there is no international course river.
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Recommendations
It is recommended to carry out geophysical surveys by the seismic method in
order to determine the thickness of the Ignimbrite layer and, in turn, to define
the geological formations that lie below the plate.
An exploration stage should be planned based on the geophysical drilling
results that allow samples of the deep geological formations to be correlated
stratigraphically with the aquifers present in Bolivian territory.
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300
GENERAL CONCLUSIONS
CHAPTER I: GEOLOGY
From the structural mapping of 1,500 fractures and the processing of these
data, 4 domains were identified, which represent the dominant structural areas
of geological behavior, which defines the upwelling of the Silala springs.
There are extension fractures whose courses fluctuate between N 81°-85° E,
coinciding with the direction of the topographic depression; where the springs
flow.
The directions frequency rosette of Domain 1 shows a preferential fracturing
in a range of N 80°-85° W, that respond to fractures of extension, which is why
they facilitate the migration of the springs because they are open fractures.
The frequency rosette of Domain 4 shows a fracture preference of N 50-60°
W, fractures that respond to decuple shear stress, that conditioned faults of a N
50° E direction, with a dip of 48° SE and a striation of S 45° W direction, and a
trend of 11°; efforts that conditioned the current geomorphology of topographic
depression (see Annex A.3, planes 6/8, 7/8 and 8/8), where are the outcrops of
the Silala Sector north-northwest springs (see Annex A.2 planes 2/8, 3/8 and
4/8).
CHAPTER II: GEOPHYSICS
In the study area, 15 Vertical Electrical Probes (SEV) were carried out; in the
southeast- east sector and in the northwest-west sector, where the upwelling of
the springs are located, an average horizontal linear laying of 250 meters and
a depth investigated AB/2 of 90 meters, with an average range of 100 to 1000
Ohm-m, having been determined 2 to 4 lithological layers.
In the 6 geo-electric profiles executed in the southeast-east sector, four lithological
units (A, B, C and D) of variable thickness were determined. Unit A presents
saturated alluvial material and weathered Ignimbrite with a thickness of
5.25 meters. Unit B presents consolidated Ignimbrite material with a thickness
of 4.66 meters at a depth of 9.92 meters. Unit C reflects Ignimbrite materials
with a thickness of 20.79 meters at a depth of 30.71 meters. Unit D corresponds
to the last geo-electric layer, with a thickness of 40.21 meters and a depth of
less than 70.91 meters (SEV3),
301
having as maximum depth of the profiles executed up to 90 meters, whose resistivities
are similar to the final layer with fractured Ignimbrite material.
The wet zone detected from the interpretation of the 6 profiles, has a depth
range of 0.28 to 0.50 meters, average thickness of the bofedals.
In the 9 geo-electrical profiles executed from the northwest-west sector, three
lithological units (A, B and C) were determined. Unit A presents alluvial material
saturated with clay sediments and weathered ignimbrite with a thickness
of 4.04 meters. Unit B with sandy- clayey sediments with a thickness of 41.65
meters at a depth of 45.69 meters. Unit C presents fractured ignimbrite material
with a thickness of 23.61 meters at a depth of 69.3 meters.
The wet zone detected from the interpretation of the 9 profiles is found at
0.40 meters.
The calibration of the equipment was carried out in the outcropping horizons
in the survey area, which in turn allowed reconstructing the strato-volcanic
column (see Annex A.3, planes 6/8, 7/8 and 8/8).
CHAPTER III: MODELING
The georeferencing of the satellite image through a Geographic Information
System (ILWIS) has allowed the generation of thematic maps such as:
Geological, Topographic Map, Vegetation, Permeability, Slope, Soil Texture,
Stoniness, Effective Depth of Plant Roots. The same ones that were verified
through a detailed field mapping in the survey area.
The ratio of Monthly Precipitation versus Potential Evapotranspiration is
from 1 to 5, this means that for every millimeter of rain, 5mm evaporates; this
leads to a superficial water deficit in the survey area. Values that ratify the annual
reports of SENAMHI (Colorada Lagoon Station), where they report average
values of 80 mm of precipitation and a potential evaporation of 580 mm.
The water supply or surface runoff generated by the precipitation in the survey
area only has a maximum flow of 2.83 l/sec for the month of January and
0.64 l/sec for the month of February. The rest of the months have 0 l/sec of
surface water supply to the artificial drainage canals. The total annual flow is
3.67 l/sec.
302
CHAPTER IV: HYDROCHEMISTRY CAPÍTULO IV: HIDROQUÍMICA
The hydro-chemical quality of the springs’ water in the southeast-east and
northwest-west sectors, reflect SODIUM BICARBONATED POTASSIUM facies,
classified as type A, (suitable for human consumption, according to Law
N° 1333).
There are several waterbodies such as Blanca and Chica lagoons with (4,600
m.a.s.l.) and Kara with (4,509 m.a.s.l.) which, due to their quality of BRACKISH
WATER, cannot be recharge areas. At the same time samplings were carried
out in the INACALIRI Volcano, which are classified as SULPHATED
– MAGNESIAN waters, which do not show quality relation with the spring
waters.
CHAPTER V: HYDROGEOLOGY
The recharge of the Ignimbrite aquifer is not possible under the hydrological
regime of the survey area, since the volumes of meteoric water are minimal
–there is a water deficit– therefore the volumes of permanent variable flow of
the springs that are evacuated towards the artificial canals; they are validated
according to the historical data reported by the Meteorological Station of the
Colorada Lagoon and the results of the surveyy of the superficial hydrological
modeling, as well as the results of the gauging by the windlass
method executed in the sector.
The formation of Ignimbrite volcanic rock behaves as a permeable medium,
due to the secondary porosity that results from fracturing. Consequently, the
outcrops of the Silala springs come from deep aquifers of the geological formations
that are below the igneous layer, whose recharge is found in natural
and permanent bodies in Bolivian territory with higher elevations than in the
survey area.
The piezometric levels of the bofedals present in the area were depressed in
an anthropic form in order to increase the outcrop of the underground water of
the canals towards lower elevations.
303
Considering an average flow of 200 l/sec, flowing through artificial canals,
the surface water supply of the survey area only represents 1.4% of these flows.
The remaining 98.6% comes from deep underground aquifers, which migrate
their waters through two spring systems, structurally controlled by extension
fractures in the southeast-east springs of Domain 1, and by the shear fractures
product of efforts of coupe Domain 4 and faults present in the northwest-west
springs that also conditioned the topographic depression present in the area.
The chemical analyzes carried out in the Silala springs define them as SODIC-
POTASSIC BICARBONATED waters, and the chemical analyzes carried
out in natural and permanent waterbodies with higher elevations classify them
as MAGNESIUM-SULFATED waters, consequently, there is no hydraulic relation
with surface waters of the springs.
Throughout the hydrological and hydrogeological characterization we can
conclude that it is not a shared aquifer, that there is a water deficit, that the
recharge is located in Bolivian territory, that they cannot be considered fossil
waters and that there is no international course river.
RECOMENDACIONES
It is recommended to carry out geophysical surveys by the seismic method in
order to determine the thickness of the Ignimbrite layer and, in turn, to define
the geological formations that lie below.
An exploration stage must be planned based on the geophysical results by the
seismic method, drillings that will allow obtaining samples of deep geological
formations (aquifers) to correlate stratigraphically with the aquifers present in
Bolivian territory.
304 24
English translation prepared by DIREMAR. The original language text remains the authoritative one.
ANNEX A.
GEOLOGY
305
ANNEX A. 1.
STRUCTURAL
INTERPRETATION
1ST DOMAIN JOINTS
SILALA PROJECT
306
26
English translation prepared by DIREMAR. The original language text remains the authoritative one.
1ST DOMAIN JOINTS SILALA PROJECT
INTERPRETATION
Based on the structural interpretation, it can be perceived that fractures ―b‖
and ―c‖ respond to shear fractures in relation to the main axis of a NE 81°
trend; fractures ―a‖ and ―b‖ respond to second order sheers in relation to
shear stress.
There are fractures of angle strike extension, which fluctuate from 81° N – 85°
E and concur with the direction of the topographic depression of the area in
which the springs flow, with a preferential Rb [direction] of N 81° E.
From an interpretation of the Rose diagram, it can be perceived that the ruling
fracture direction is 80° N – 85° W. The latter is the reason why the flow of the
SEE sector springs has a higher rate, inasmuch as water always flows to areas
where there is less resistance. These extension fractures are open fractures that
enable the upwelling of the springs because of their high secondary permeability
rate.
28 307
English translation prepared by DIREMAR. The original language text remains the authoritative one.
1ST DOMAIN JOINTS
SILALA PROJECT
308
29
English translation prepared by DIREMAR. The original language text remains the authoritative one.
1ST DOMAIN JOINTS
CUTTINGS
309 30
English translation prepared by DIREMAR. The original language text remains the authoritative one.
FREQUENCY DIAGRAM
1ST DOMAIN
ROSE DIAGRAM
1ST DOMAIN
310
31
English translation prepared by DIREMAR. The original language text remains the authoritative one.
2ND DOMAIN JOINTS
SILALA PROJECT
INTERPRETATION
2nd Domain: it is characterized for having a 1st δ (maximum effort axis) of an 85°
NE direction and a Plungeof12°NE,a2nd δofan85°NEdirectionandaPlungeof78°SW,
anda3rd δofan5°NW direction and a Horizontal Plunge. These caused fractures ―b‖
and ―e‖ to be shear fractures, fractures ―a‖ to be compression (closed) fractures,
and ―e‖ to be second order shear fractures.
From an interpretation of the Rose diagram (see, Annex A. l., p. 29), it is possible to
perceive a predominant Rb [Direction] in a range of 0° N – 10° W, which matches
the compression fractures, and a fracture frequency in a range of 60° N – 68 ° W—
matching the shear fractures.
The above provides an explanation as to why the 2nd domain section does not comprise
any springs, i.e. this domain presents closed fractures, unlike the 1st Domain.
311 33
English translation prepared by DIREMAR. The original language text remains the authoritative one.
2ND DOMAIN JOINTS
SILALA PROJECT
312
34
English translation prepared by DIREMAR. The original language text remains the authoritative one.
2ND DOMAIN JOINTS
CUTTINGS
313
35
English translation prepared by DIREMAR. The original language text remains the authoritative one.
2ND DOMAIN JOINTS
CUTTINGS
314
36
English translation prepared by DIREMAR. The original language text remains the authoritative one.
2ND DOMAIN
FREQUENCY DIAGRAM
2ND DOMAIN
ROSE DIAGRAM
315
37
English translation prepared by DIREMAR. The original language text remains the authoritative one.
3RD DOMAIN JOINTS
SILALA PROJECT
INTERPRETATION
3rd domain: it is characterized for presenting a 1st δ of a 75° NE direction and a
Plunge of 10° SW, a 2nd δofa75°NEdirectionandaPlungeof80°NE,anda3rd
δofa15°NWdirectionanda Horizontal Plunge. These caused fractures ―a‖ and ―d‖ to
be first order shear fractures, fractures ―b‖ and ―c‖ to be second order shear fractures,
and fracture ―e‖ to be compression fractures.
From an interpretation of the Rose diagram, it can be perceived that there is a predominant
NS fracture Rb [direction], which corresponds to compression fractures, and NW
fractures that correspond to shear fractures, to a lesser degree. This is why springs do
not well up in this domain.
316
39
English translation prepared by DIREMAR. The original language text remains the authoritative one.
3RD DOMAIN JOINTS
SILALA PROJECT
317
40
English translation prepared by DIREMAR. The original language text remains the authoritative one.
3RD DOMAIN JOINTS
SILALA PROJECT
318
41
English translation prepared by DIREMAR. The original language text remains the authoritative one.
3RD DOMAIN JOINTS
SILALA PROJECT
319
42
English translation prepared by DIREMAR. The original language text remains the authoritative one.
FREQUENCY DIAGRAM
3RD DOMAIN
ROSE DIAGRAM
3RD DOMAIN
320
43
English translation prepared by DIREMAR. The original language text remains the authoritative one.
4TH DOMAIN JOINTS
SILALA PROJECT
INTERPRETATION
Fractures ―a‖, ―b‖ and ―c‖ are first order shear fractures, with respect to the 1st δ.
Fractures ―e‖ and ―d‖ are second order shear fractures activated by shear stresses.
These have activated the predominant faults in the 4th Domain, as a result of the action
of shear stresses, where a fault mirror was mapped with a dipping direction of
140°/148°, a 225° trend, a 11° plunge, and a SW 11° raque. This structural control
predetermines the emergence of the NWW sector springs.
45 321
English translation prepared by DIREMAR. The original language text remains the authoritative one.
4TH DOMAIN JOINTS
SILALA PROJECT
322 46
English translation prepared by DIREMAR. The original language text remains the authoritative one.
4TH DOMAIN JOINTS
CUTTINGS
323
47
English translation prepared by DIREMAR. The original language text remains the authoritative one.
4TH DOMAIN JOINTS
CUTINGS
324 48
English translation prepared by DIREMAR. The original language text remains the authoritative one.
FREQUENCY DIAGRAM
4TH DOMAIN
ROSE DIAGRAM
4TH DOMAIN
325
49
English translation prepared by DIREMAR. The original language text remains the authoritative one.
STRUCTURAL FAULT
SILALA PROJECT
CUTTINGS
INTERPRETATION
The position of the fault mirrors (striae) shows that the fractures of the 4th domain were activated by
the action of shear stresses, which formed the current geomorphology of the canyon (tectonic
pit/structural gully).
Fault mirror, Dip/Dir of 140/48, trend 225, plunge 110, raque of 11 SW. This structural control
conditions the emergence of the springs of the NWW sector.
326
327
328
329
330
331
332
333
334
335
336
ANNEX B.
GEOPHYSICS
337
ANNEX B.1.
GEOPHYSICAL SURVEYS
SEE SECTOR – SILALA SPRINGS
338
104
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Geophysical Line SEV-02SE
Location:
North Coordinate East Coordinate Height Wing
7565802 603017 4416 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 2: SEV-02SE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 19 7.0686 134.80
5 5.65 23.8238 134.60
7 2.61 48.9566 127.78
10 1.18 102.3638 120.79
15 496.23 233.2638 115.75
20 285.7 416.5238 119.00
25 192.2 652.1438 125.34
30 140.95 940.1238 132.51
40 85.69 1673.164 143.37
50 298.33 2615.644 156.45 210.77 2615.64 156.45
60 151 1123.12 169.54
75 101.16 1759.3 177.97
100 60.94 3133.75 190.97
125 41.38 4900.9 199.38 223.69 942.48 199.38
150 151.18 1374.45 207.79
175 113.02 1884.96 213.04
200 86.37 2474.01 213.68
250 55.51 3887.73 215.81
300 37.01 5615.61 207.83
339 105
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.1.1. Location of the transversal line with respect to the spring.
Graph B.1.1. Apparent Resistivity Values vs. AB/2
Graph B.1.2. Interpretation of Resistivity Model - Layers.
340
106
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N° of
LAYERS
Layer
Thickness
(m)
Approx.
Depth
(m)
Resist.
m
Characteristics Lithological
Description
1 5.255 -5. 255 137.8 The first layer with
resistivity of 137.8 Ohm-m
with depth of 5.255 meters
corresponds to alluvial
material saturated with
weathered ignimbrite.
2 4.664 -9.92 75.83 The second layer with
resistivity of 75.83 Ohm-m
corresponds to welded
ignimbrita.
3 20.79 -30.71 158.4 The third layer has a
resistivity of 158.4 Ohm-m
indicating the presence of
fractured medium-high
ignimbrite and has a depth of
-30.71 m.
4 191.2 -70.92 249.4 The last layer detected is
from -70.92 m, indicating
the existence of fractured
ignimbrite.
SEV-02SE analysis:
The 1st layer has a depth of 5,255 m, Resistivity of 137.8 Ohm-m indicating the presence of alluvial
material saturated with weathered ignimbrite, the 2nd layer with 9.92 meters deep, thickness of
4,664 m has a resistivity of 75.83 Ohm-m corresponding to welded ignimbrite.
The 3rd layer with 30. 71 m of depth has resistance of 158.4 Ohm-m this resistivity corresponds to
ignimbrite high medium saturated, which indicates the fracturing of the rock. Finally, the last layer
has a resistivity of 249.4 Ohm-m with a depth of 70.92 m indicates the presence of fractured
ignimbrite.
341
107
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV2_SE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
603017
Y
7565802
Z
4416.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
500.0
Horizontal
150.0
Geophysical Line SEV-03SE
Location:
342
North Coordinate East Coordinate Height Wing
7565913 603019 4419 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Area
N° of Survey 3: SEV-03SE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 17 7.0686 119.52
5 4.661 23.8238 111.04
7 2.2027 48.9566 107.84
10 1.1527 102.3638 117.99
15 573.54 233.2638 133.79
20 342.73 416.5238 142.76
25 233.32 652.1438 152.16
30 168.63 940.1238 158.53
40 104.77 1673.164 175.30
50 75.122 2615.644 185.12 250.04 777.546 185.12
60 174 1123.122 194.94
75 109.52 1759.296 192.68
100 54.957 3133.746 172.22
125 33.048 4900.896 184.88 207.43 942.48 184.88
150 143.72 1374.45 197.54
175 110.24 1884.96 207.80
200 81.935 2474.01 202.71
250 49.699 3887.73 193.22
300 32.321 5615.61 181.50
343
109
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photography 8.1.2. Location of the longitudinal line with respect to the spring.
Graph 8.1.3. Apparent Resistivity Values vs. AB/2
Graph 8.1.4. Interpretation of Resistivity Model - Layers.
344
110
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 1.8 -1.8 135.8 The first layer with a
resistivity of 135.8 Ohm-m
with a depth of 5,255 m
corresponds to alluvial
material saturated with
weathered ignimbrite.
2 1.962 -16.44 75.27 The second layer with a
resistivity of 75.27 Ohm-m
corresponds to welded
ignimbrite.
3 12.68 -34.35 145.2 The third layer has a
resistivity of 145.2 Ohm-m
indicating the presence of
medium high fractured
ignimbrite and has a depth of
-34.35 m.
4 17.91 -71.78 368.6 The last layer detected is
found from the
-71.78 m, indicates the
existence of fractured
ignimbrite
SEV-03SE Analysis:
The 1st layer with a depth of 5,255 m, has a Resistivity of 135.8 Ohm-m indicating the presence of
alluvial material saturated with weathered ignimbrite, the 2nd layer has a depth of 16.44 meters,
thickness of 1,962 m and resistivity of 75.27 Ohm-m corresponding to welded ignimbrite.
The 3rd layer with 34.35 m depth, the resistance is 145.2 Ohm-m this resistivity corresponds to
saturated medium high ignimbrite, which indicates the fracturing of the rock. The last layer has
depth of 71.78 m, thickness of 17.91 m and resistivity of 368.6 Ohm-m indicates presence of
fractured ignimbrite.
345
111
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV3_SE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
603019
Y
7565913
Z
4419.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
400.0
Horizontal
100.0
346
Geophysical Line SEV-04SE
Location:
North Coordinate East Coordinate Height Wing
7565866 603138 4417 200 m
CALCULATION OF APPARENT RESISTIVITY
Silala Area
No. of Survey 4: SEV-04SE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 25 7.0686 176.95
5 6.2189 23.8238 148.16
7 2.5414 48.9566 124.42
10 1.1576 102.3638 118.50
15 519.92 233.2638 121.28
20 294.53 416.5238 122.68
25 196.81 652.1438 128.35
30 149.72 940.1238 140.76
40 94.981 1673.164 158.92
50 67.96 2615.644 165.57 211.58 777.549 165.57
60 153 1123.122 172.22
75 97.202 1759.296 171.01
100 54.579 3133.746 171.04
125 31.29 4900.896 174.00 196.33 942.48 174.00
150 128.75 1374.45 176.96
175 102.69 1884.96 193.57
200 75.816 2474.01 187.57
347 113
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.1.3. Location of the longitudinal line with respect to the spring.
Graph B.1.5. Apparent Resistivity Values vs. AB / 2
Graph B.1.6. Interpretation of Resistivity Model - Layers.
348
114
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 2.697 -2.697 203.3 The first layer with a
resistivity of 203.3 Ohm-m
with a depth of -2697 m
corresponds to alluvial
material saturated with a
medium-high fractured
ignimbrite mixture.
2 1.628 -4.324 37.88 The second layer with
resistivity of 37.88 ohm
corresponds to welded
ignimbrite.
3 39.55 -43.88 206.1 The third layer has a
resistivity of 206.1 Ohm-m
indicating the presence of
fractured ignimbrite and
starts at a depth of -43.88 m.
SEV-04SE Analysis:
The 1st layer with a depth of 2,697 m, has a resistivity of 202.2 Ohm-m indicating the presence of
saturated alluvial material with a mixture of medium-high fractured ignimbrite, the 2nd layer with a
depth of 4,324 m and a thickness of 1,628 m has a resistivity of 37.88 Ohm-m corresponding to
welded material.
The 3rd layer with 43.88 m deep, 39.55 m thick resistance of 206.1 Ohm-m resistivity responding to
fractured ignimbrite, which indicates rock fracturing.
349
115
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV4_SE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
603138
Y
7565866
Z
4417.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
300.0
Horizontal
100.0
350
Geophysical Line SEV-05SE
Location:
North Coordinate East Coordinate Height Wing
7565850 603020 4415 200 m
CALCULATION OF APPARENT RESISTIVITY
Silala Area
No. of Survey 5: SEV-05SE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 19 7.0686 134.34
5 4.8079 23.8238 114.54
7 2.3482 48.9566 114.96
10 1.1169 102.364 114.33
15 530.17 233.264 123.67
20 320.4 416.524 133.45
25 218.6 652.144 142.56
30 162.27 940.124 152.55
40 95.884 1673.16 160.43
50 68.746 2615.64 146.55 240.16 777.546 146.55
60 170 1123.12 190.76
75 105.56 1759.3 185.71
100 62.885 3133.75 197.07
125 44.551 4900.9 199.38 244.92 942.48 199.38
150 167.84 1374.45 230.69
175 129.49 1884.96 244.08
200 97.735 2474.01 241.80
351 117
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Location of the longitudinal line with respect to the spring.
Graph. 8.1. 7. Apparent Resistivity Values vs. AB/2
Graph B.1.8. Interpretation of Resistivity Model - Layers.
352
118
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 1.5 -1.5 155.3 The first layer with a
resistivity of 155.3 ohm and
a depth of -1.5 m
corresponds to alluvial
material saturated with a
medium-high fractured
ignimbrite mixture.
2 5.944 -7.444 98.17 The second layer with
resistivity of 98.17 Ohm-m
corresponds to welded
ignimbrita with thickness of
5.944
3 45.55 -52.99 176.4 The last layer has a
resistivity of 176.4 Ohm-m
indicating the presence of
fractured ignimbrite and
starts at a depth of -52.99 m.
SEV-05SE Analysis:
The 1st layer has a depth of 1.5 m, with resistivity of 155.3 Ohm-m indicates the presence of
saturated alluvial material with a mixture of fractured medium-high ignimbrite, the 2nd layer has a
depth of 4,324 meters thick of 1,628 m with resistivity of 37.88 Ohm corresponding to welded
ignimbrite.
The 3rd with a depth of 43.88 m thickness of 45.55 m and resistivity of 206.1 Ohm-m responds to
fractured ignimbrite, which indicates the fracturing of the rock.
353
119
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV5_SE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
603020
Y
7565850
Z
4415.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
350.0
Horizontal
50.0
354
Geophysical Line SEV-06SE
Location:
North Coordinate East Coordinate Height Wing
7565769 602815 4414 150 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 6: SEV-06SE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 24 7.0686 171.05
5 5.97 23.8238 142.23
7 2.4681 48.9566 120.83
10 365.05 102.3638 37.37
15 255.54 233.2638 59.61
20 161.92 416.5238 67.44
25 163.53 652.1438 106.65
30 102.18 940.1238 96.06
40 65.535 1673.164 109.65
50 46.072 2615.644 118.73 171.85 2615.644 118.73
60 114 1123.122 127.81
75 73.082 1759.296 128.57
100 45.266 3133.746 141.85
125 30.815 4900.896 145.39 166.06 942.48 145.39
150 108.36 1374.45 148.94
355
121
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.1.5. Location of the longitudinal line with respect to the spring.
Graph B.1.9. Apparent Resistivity Values vs. AB / 2
Graph B.1.1 O. Interpretation of Resistivity Model - Layers.
356
122
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 3.174 -3.174 207.3 The first layer with a
resistivity of 207.3 Ohm-m
with a depth of -3.174 m
corresponds to alluvial
material saturated with a
medium-high fractured
ignimbrite mixture.
2 3.301 -3.31 13.22 The second layer with a
resistivity of 13.22 Ohm-m
corresponds to welded
ignimbrite with a thickness
of 3.301.
3 35.44 -35.43 604.2 The last layer has a
resistivity of 604.2 Ohm-m
that indicates the presence of
fractured ignimbrite and
starts at a depth of 35.43 m.
SEV-06SE Analysis:
The 1st with depth of 3.174 m, has resistivity of 207.3 Ohm-m indicates presence of saturated
alluvial material with mixture of ignimbrite medium high fractured, the 2nd layer has 3.31 meters
deep thickness of 3.301 m and resistivity of 13.22 Ohm responds to welded material.
The last layer with 35.43 m depth and resistivity of 604.2 Ohm-m belongs to fractured ignimbrite
that indicates the fracturing of the rock.
357
123
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV6_SE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
602815
Y
7565769
Z
4414.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
300.0
Horizontal
50.0
358
ANNEX B.2.
GEOPHYSICAL SURVEYS
NWW SECTOR - SILALA SPRINGS
359
Geophysical Line SEV-02NE
Location:
North Coordinate East Coordinate Height Wing
7566387 601165 4392 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 2: SEV-02NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 470 7.0686 3323.16
5 134.01 23.8238 3192.63
7 59.018 48.9566 2889.32
10 23.157 102.3638 2370.44
15 7.5104 233.2638 1751.90
20 3.37 416.5238 1403.69
25 1.7533 652.1438 1211.56 6.4623 188.496 1211.56
30 4 274.89 1019.43
40 1.446 494.802 715.48
50 757.81 777.546 589.23
60 420.73 1123.122 472.53
75 250.08 1759.296 439.96
100 154.14 3133.746 483.04
125 86.14 4900.896 427.41 397.69 942.48 427.41
150 270.5 1374.45 371.79
175 217.2 1884.96 409.41
200 167.71 2474.01 414.92
250 104.63 3887.73 406.77
300 83.75 5615.61 470.31
360
126
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.2.1. Location of the longitudinal line with respect to the spring.
Graph 8.2.1. Apparent Resistivity Values vs. AB/2
Graph B.2.2. Interpretation of Resistivity Model - Layers.
127 361
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 14.39 -20.76 200.4 The first layer with a
resistivity of 200.4 Ohm-m
with a depth of -20.76 m
corresponds to alluvial
material saturated with clay
sediments and weathered
ignimbrite.
2 30.48 -62.55 901 The second layer with
resistivity of 901 Ohm-m
corresponds to fractured
ignimbrite with thickness of
16.04 and starts from -62.55
m.
SEV-02NE Analysis:
The 1st layer with resistivity of 200.4 Ohm-m and a depth of 20.76 m indicates the presence of
alluvial material saturated with clay sediments and weathered ignimbrites.
The last layer with 62.55 m depth and resistivity of 901 Ohm-m responds to fractured ignimbrite.
362
128
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV2_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
601165
Y
7566387
Z
4392.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
500.0
Horizontal
100.0
363
Geophysical Line SEV-03NE
Location:
North Coordinate East Coordinate Height Wing
7566500 601168 4401 125 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 3: SEV-03NE
AB/2
M/N2= 1.5 MN/2= 5,0
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 246 7.0686 1739.16
5 5.977 23.8238 142.39
7 35.619 48.9566 1743.79
10 16.156 102.364 1653.79
15 6.1773 233.264 1440.94
20 2.8114 416.524 1171.02
25 1.4821 652.144 1039.75 5.976 188.496 1039.75
30 3 274.89 908.48
40 1.2962 494.802 641.36
50 681.95 777.546 530.25
60 258.3 1123.122 290.10
75 145.95 1,759.30 525.46
100 44.663 3133.746 139.96
125 26.176 4900.896 128.29
364
130
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 8.2.2. Location of the longitudinal line with respect to the spring.
Figure 8.2.3. Apparent Resistivity Values vs. A8 / 2
Graph B.2.4. Interpretation of Resistivity Model - Layers.
365
131
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 15.87 -22.7 1167 The first layer with a
resistivity of 1167 Ohm-m
with a depth of -22.7 m
corresponds to alluvial
material saturated with clay
sediments and weathered
ignimbrite.
2 23.89 -46.59 31.23 The second layer with
resistivity of 31.23 Ohm-m
corresponds to fractured
ignimbrite with thickness of
23.89 and starts from -46.59
m.
SEV-03NE Analysis:
The 1st layer with resistivity of 1167 Ohm-m and depth of 22. 7 m indicates the presence of alluvial
material saturated with clay sediments and weathered ignimbrite.
The last layer with 46.59 m depth and resistivity of 31.23 Ohm-m responds to fractured ignimbrite.
366
132
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV3_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
601168
Y
7566500
Z
4401.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
300.0
Horizontal
80.0
367
Geophysical Line SEV-04NE
Location:
North Coordinate East Coordinate Height Wing
7566370 601020 4383 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 4: SEV-04NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 43 7.0686 305.99
5 12.072 23.8238 287.60
7 6.4835 48.9566 317.41
10 3.3325 102.364 341.13
15 1.5365 233.264 358.41
20 857.88 416.524 357.33
25 557.45 652.144 374.92 2.113 188.496 374.92
30 1 274.89 392.52
40 802.35 494.802 397.00
50 499.57 777.546 388.44
60 352.93 1123.12 396.38
75 191.95 1759.3 337.70
100 108.7 3133.75 340.64
125 81.807 4900.9 324.22 356.87 942.48 324.22
150 223.94 1374.45 307.79
175 163 1884.96 307.25
200 131.24 8474.01 324.69
250 89.775 3887.73 348.94
300 73.135 5615.61 410.70
368
134
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 8.2.3. Location of the longitudinal line with respect to the spring.
Graph 8.2.5. Apparent Resistivity Values vs. AB/2
Graph 8.2.6. Interpretation of Resistivity Model - Layers.
369
135
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 4.044 -4.044 257.4 The first layer with a
resistivity of 257.4 Ohm-m
with a depth of -4.044 m
corresponds to alluvial
material saturated with sandy
sediments.
2 41.65 -45.69 429.6 The second layer with
resistivity of 429.6 Ohm-m
corresponds to sand-clay
sediments with a thickness of
41.65 m.
3 123.5 -69.3 200.8 The last layer has a
resistivity of 200.8 Ohm-m
indicating the presence of
fractured ignimbrite and
starts at a depth of -35.43 m.
SEV-04NE Analysis:
The 1st layer with a depth of 4,044 m and resistivity of 257.4 Ohm-m indicates the presence of
alluvial material saturated with sandy sediments. The 2nd layer with a depth of 45.69 m, thickness
of 41.65 m and resistivity of 429.6 Ohm-m corresponding to sand-clay sediments.
The 3rd layer with 69.3 m depth and resistance of 200.8 Ohm-m responds to fractured ignimbrite,
which indicates rock fracturing.
370
136
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV4_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
601020
Y
7566370
Z
4383.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
500.0
Horizontal
100.0
371
137
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Geophysical Line SEV-05NE
Location:
North Coordinate East Coordinate Height Wing
7566293 600873 4373 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 5: SEV-05NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 42.81 7.0686 302.61
5 29.223 23.824 696.20
7 6.4503 48.957 315.78
10 3.1399 102.36 321.41
15 1.4431 233.26 336.62
20 812.75 416.52 338.53
25 503.2 652.14 347.26 1.8405 188.496 347.26
30 1.295 274.89 355.98
40 749.95 494.802 371.08
50 468.05 777.546 363.93
60 346.44 1123.122 389.09
75 172.5 1759.296 303.48
100 100.98 3133.746 316.45
125 66.809 4900.896 312.62 361.12 942.48 312.62
150 224.67 1374.45 308.80
175 162.89 1884.96 307.04
200 118.38 2474.01 292.87
250 73.551 3887.73 285.95
300 40.48 5615.61 227.32
372
138
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.2.4. Location of the longitudinal line with respect to the spring.
Graph B.2.7. Apparent Resistivity Values vs. AB/2
Graph B.2.8. Interpretation of Resistivity Model - Layers.
373 139
English translation prepared by DIREMAR. The original language text remains the authoritative one.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 11.45 -11.45 295.6 The first layer with a
resistivity of 295.6 Ohm-m
with a depth of 11.45 m
corresponds to alluvial
material saturated with sandy
sediments.
2 15.5 -26.96 600.9 The second layer with
resistivity of 600.9 Ohm-m
corresponds to sand-clay
sediments with a thickness of
15.5 m and a depth of -26.96
m.
3 27.32 -54.27 141.9 The last layer has a
resistivity of 141.9 Ohm-m
which indicates the presence
of fractured ignimbrite and
starts at a depth of -54.27 m.
SEV-05NE Analysis:
The 1st layer has a depth of 11.45 m and resistivity of 295.6 Ohm-m indicating the presence of
alluvial material saturated with sandy sediments, the 2nd layer with a depth of 26.96 m thick of 15.5
m and resistivity of 600.9 Ohm-m corresponding to sand-clay sediments.
The last layer is 54.27 m deep and has a resistance of 141.9 Ohm-m responds to fractured
ignimbrite, which indicates rock fracturing.
374
140
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV5_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
600873
Y
7566293
Z
4373.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
400.0
Horizontal
50.0
375
141
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Geophysical Line SEV-06NE
Location:
North Coordinate East Coordinate Height Wing
7566277 600875 4374 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 5: SEV-05NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 33.057 7.0686 233.67
5 12.823 23.8238 305.49
7 6.0706 48.9566 297.20
10 3.105 102.3638 317.84
15 1.4663 233.2638 342.03
20 839.91 416.5238 349.84
25 537.72 652.1438 356.16 1.8742 188.5 356.16
30 1.3186 274.89 362.47
40 723.82 494.8 358.15
50 461.33 777.55 358.71
60 298.74 1123.1 335.52
75 178.52 1759.3 314.07
100 103.65 3133.7 324.81
125 66.622 4900.9 323.06 371.06 942.48 323.06
150 233.77 1374.45 321.31
175 170.43 1884.96 321.25
200 121.39 2474.01 300.32
250 66.35 3887.73 257.95
300 24.879 5615.61 139.71
376
142
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.2.5. Location of the longitudinal line with respect to the spring.
Graph B.2.9. Apparent Resistivity Values vs. AB/2
Graph B.2.1 O. Interpretation of Resistivity Model - Layers.
377 143
English translation prepared by DIREMAR. The original language text remains the authoritative one.
SEV-06NE Analysis:
The 1st layer with a depth of 3,622 m and resistivity of 239 Ohm-m indicates the presence of
alluvial matter saturated with sandy sediments, the 2nd layer has a depth of 63.25 meters thick of
59.63 m and resistivity of 780.1 Ohm-m corresponding to sand-clay sediments.
The 3rd layer with 59.52 m depth and resistivity of 780.01 Ohm-m responds to fractured ignimbrite,
which indicates rock fracturing.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 3.622 -3.622 239 The first layer with
resistivity of 239 Ohm-m
corresponds to alluvial
material saturated with
sandy sediments.
2 59.63 -63.25 342.4 The second layer with
resistivity of 342.4 Ohmm
corresponds to sandclay
sediments with a
thickness of 59.63 m and
a depth of -63.25 m.
3 40.11 -69.52 780.1 The last layer has a
resistivity of 780.1 Ohmm
indicating the presence
of ignimbrite and starts at
a depth of -69.52m.
378
144
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV6_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
600875
Y
7566277
Z
4374.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
500.0
Horizontal
100.0
379
145
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Geophysical Line SEV-07NE
Location:
North Coordinate East Coordinate Height Wing
7566335 600875 4377 300 m
CALCULATION OF APPARENT RESISTIVITY
Silala Area
No. of Survey 7: SEV-07NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 68.702 7.0686 485.63
5 18.855 23.8238 449.20
7 9.0481 48.9566 442.96
10 4.3893 102.364 449.31
15 2.0722 233.264 483.37
20 1.1291 416.524 470.30
25 650.32 652.144 470.03 2.4771 188.496 470.03
30 1.7089 274.89 469.76
40 813.36 494.802 402.45
50 496.31 777.546 385.90
60 345.16 1123.122 387.66
75 178.25 1759.296 313.59
100 97.212 3133.746 304.64
125 63.757 4900.896 284.86 297.92 942.48 284.86
150 192.87 1374.45 265.09
175 140.57 1884.96 264.97
200 103.66 2474.01 256.46
250 70.583 3887.73 274.41
300 42.48 5615.61 238.55
380
146
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.2.6. Location of the longitudinal line with respect to the spring
Graph B.2.11. Apparent Resistivity Values vs. AB/2
Graph B.2.12. Interpretation of Resistivity Model - Layers.
147 381
English translation prepared by DIREMAR. The original language text remains the authoritative one.
SEV-07NE Analysis:
The 1st layer with a depth of 10.12 m and resistivity of 392.9 Ohm-m indicates the presence of
alluvial material saturated with sandy sediments, the 2nd layer is 17.48 m deep and 7.363 m thick
and resistivity of 112 Ohm-m corresponding to sand-clay sediments.
The last layer has a depth of 42.81 m and resistivity of 154.4 Ohm-m responds to fractured
ignimbrite, which indicates rock fracturing.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 10.12 -10.12 392.9 The first layer with
resistivity of 239.9 m
corresponds to alluvial
material saturated with
sandy sediments.
2 7.363 -17.48 1112 The second layer with a
resistivity of 1112 Ohmm
corresponds to sandclay
sediments with a
thickness of 7.363 m and
a depth of -17.48 m.
3 25.33 -42.81 154.4 The last layer has a
resistivity of 154.4 Ohmm
which indicates the
presence of fractured
ignimbrite with a
thickness of 25.33 m.
382
148
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Geophysical Line SEV-08NE
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV7_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
600857
Y
7566335
Z
4377.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
300.0
Horizontal
50.0
383
149
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Location:
North Coordinate East Coordinate Height Wing
7566170 600668 4362 250 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 8: SEV-08NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 87.347 7.0686 617.42
5 18.258 23.8238 434.97
7 7.3165 23.9566 434.97
10 2.7933 102.3638 285.93
15 1.0777 233.2638 251.39
20 539.72 416.5238 224.81
25 338.57 652.1438 220.80
30 241.66 940.1238 227.19
40 134.65 1673.164 238.64 490.44 494.802 238.64
50 321.65 777.546 250.10
60 219.89 1123.122 246.96
75 131.17 1759.296 230.77
100 83.435 3133.746 261.46
125 63.238 4900.896 266.99 285.95 942.48 266.99
150 198.27 1374.45 272.51
175 159.7 1884.96 301.03
200 126.48 2474.01 312.91
250 46.413 3887.73 180.44
384
150
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.2.7. Location of the longitudinal line with respect to the spring.
Graph B.2.13. Apparent Resistivity Values vs. AB/2
Graphic B.2.14. Interpretation of Resistivity Model - Layers
151 385
English translation prepared by DIREMAR. The original language text remains the authoritative one.
SEV-08NE Analysis:
The 1st layer with a depth of 2,368 m and resistivity of 694.9 Ohm-m indicates the presence of
alluvial material saturated with sand-clay sediments, the 2nd layer has a depth of 58.47 m thick of
60.36 m and resistivity of 223.6 Ohm-m corresponding to the fractured ignimbrite.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 2.368 -2.368 694.9 The first layer with
resistivity of 694.9 m
corresponds to alluvial
material saturated with
sand-clay sediments.
2 60.36 -58.47 223.6 The last layer has a
resistivity of 223.6 Ohmm
corresponds to
fractured ignimbrite with
a thickness of 60.36 m
from a depth of -58.47 m.
386
152
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV8_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
600668
Y
7566170
Z
4362.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 11: xxx
Geological-Environmental Research Institute Vertical
400.0
Horizontal
100.0
387
153
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Geophysical Line SEV-09NE
Location:
North Coordinate East Coordinate Height Wing
7566312 600730 4376 250 m
CALCULATION OF APPARENT RESISTIVITY
Silala Zone
No. of Survey 9: SEV-09NE
AB/2
M/N2= 1.5 MN/2= 5,0 MN/2= 25
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
RESIST.
V/I
FACTOR
K
RESIST.
AP
3 39.305 7.0686 277.831
5 10.916 23.8238 260.061
7 5.3234 48.9566 260.616
10 2.7383 102.364 280.303
15 1.2611 233.264 294.169
20 717.74 416.524 298.956
25 470.13 652.144 306.592
30 334.03 940.124 314.030
40 196.76 1673.16 330.007 728.16 494.802 330.077
50 445.15 777.546 346.124
60 275.78 1123.122 309.735
75 146.39 1759.296 257.543
100 71.558 3133.746 267.001 431.83 589.05 267.001
125 293.33 942.48 276.001
150 191.09 1374.45 262.6436
175 132.24 1884.96 249.2671
200 103.2 2474.01 255.3178
250 57.475 3887.73 223.4473
388
154
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph B.2.8. Location of the longitudinal line with respect to the spring
Graph B.2.15. Apparent Resistivity Values vs AB/2 values.
Graph B.2.16. Interpretation of Resistivity Model – Layers
389
155
English translation prepared by DIREMAR. The original language text remains the authoritative one.
SEV-09NE Analysis:
The 1st with a depth of 1,831 m and resistivity of 161.3 Ohm-m indicates the presence of alluvial
material saturated with sand-clay sediments, the 2nd layer has a depth of 67.65 m thick of 65.82 m
and resistivity of 330.4 Ohm-m corresponding to fractured ignimbrite material.
N°
LAYERS
Layer
Thickness.
(m)
Approx.
Depth.
(m)
Resist.
m
Characteristics Lithological
Description
1 2.181 -1.831 161.3 The first layer with
resistivity of 161.3 m
corresponds to alluvial
material saturated with
sand-clay sediments.
2 65.82 -67.65 330.4 The last layer has a
resistivity of 330.4 Ohmm
corresponds to
fractured ignimbrite with
thickness of 65.82 m
from a depth of -67.65
m.
390
156
English translation prepared by DIREMAR. The original language text remains the authoritative one.
LITHOLOGICAL COLUMN OF RESISTIVITIES
Name
SEV9_NE
HYDROGEOLOGICAL CHARACTERIZATION PROJECT OF THE SILALA
SPRINGS
Coordinates Date
X
600730
Y
7566312
Z
4376.00
Meas. Pt. Elev.
Faculty of Geological Engineering Scale 1: xxx
Geological-Environmental Research Institute
Vertical
450.0
Horizontal
50.0
391
ANNEX B.3.
RESISTIVITY PROFILES - SILALA SPRINGS
392
158
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex B.3.1.
Resistivity Profile 1
393
159
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex B.3.2
Resistivity Profile 2
394
160
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex B.3.3
Resistivity Profile 3
395
161
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex B.3.4.
Resistivity Profile 4
Annex B.3.5.
396
162
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Resistivity Profile 5
397
163
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex B.3.6.
Resistivity Profile 6
398
399
400
401
402
403
404
405
171
English translation prepared by DIREMAR. The original language text remains the authoritative one.
ANNEX B.5.
NWW LONGITUDINAL AND TRANSVERSAL CUTS - SEE
406
172
English translation prepared by DIREMAR. The original language text remains the authoritative one.
METERS
References
SEV SE Locations
Cable Distance SEV
Contour Lines
Cuts
407
173
English translation prepared by DIREMAR. The original language text remains the authoritative one.
References
SEV SE Locations
Cable Distance SEV
Contour Lines
Cuts
408
204
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex C.
Modeling
409 205
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Annex C.1.
Photographs
410 206
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 1: In the Silala Springs.
Photograph 2: Artificial canals that drain the waters of the Silala springs towards Chile.
411
207
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 3: Water of very good quality and quantity that is poured into the Republic of Chile.
Photograph 4: Weir for the Measurement of Flows.
412
208
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 5: Performing Infiltration Tests.
Photograph 6: Performing Infiltration Tests.
413
209
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 7: Infiltration Tests by the Double Ring Method.
Photograph 8: Performance of Permeability Tests on the substrate.
414
210
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 8: Performance of Permeability Tests on the substrate.
Photograph 9: Taking soil samples.
Photograph 10: Measurement of the root depth of plants.
415
ANNEX C.2.
Monthly maps of surface runoff (in mm)
416 213
English translation prepared by DIREMAR. The original language text remains the authoritative one.
417 214
English translation prepared by DIREMAR. The original language text remains the authoritative one.
418
ANNEX C.3.
Monthly maps of potential evaporation (in mm)
419 216
English translation prepared by DIREMAR. The original language text remains the authoritative one.
420 217
English translation prepared by DIREMAR. The original language text remains the authoritative one.
421
ANNEX C.4.
Map of annual water supply (mm / year)
422
423
ANNEX D.
HYDROCHEMISTRY
424
244
ANNEX D.1.
LABORATORY CERTIFICATES
425
245
English translation prepared by DIREMAR. The original language text remains the authoritative one.
TOMAS FRIAS AUTONOMOUS UNIVERSITY
GEOLOGICAL ENGINEERING FACULTY
POTOSI – BOLIVIA
N° 001132
GEOCHEMICAL LABORATORY
ANALYSIS CERTIFICATE
Requested by: Project: Silala Springs (Research Institute)
N° ORIGIN AND DETAIL LAWS
PARAMETER UNIT SI – N° 01 SI – N° 02 SI – N° 03
Bicarbonate mg/l
Carbonate mg/l
Chloride mg/l
Nitrite mg/l
Nitrate mg/l
Sulfate mg/l
pH
Conductivity uS/cm
Temperature °C
Suspended Sol. mg/l
Dissolved Sol. mg/l
Total Sol. mg/l
Calcium mg/l
Magnesium mg/l
Sodium mg/l
Potassium mg/l
*******************************************************************************
SI – N° 01 Silala; 16:30; 22/09/17
SI – N° 02 Silala; 17:30; 22/09/17
SI – N° 03 Silala; 18:30; 22/09/17
Note.- Water sampling carried out by Eng. Juan Carlos Erquicia. Reception in the laboratory on
11/26/17 at 4:30 p.m.
Potosi, 29 January 2018
426
427
246
English translation prepared by DIREMAR. The original language text remains the authoritative one.
TOMAS FRIAS AUTONOMOUS UNIVERSITY
FACULTY OF AGRICULTURAL SCIENCES AND LIVESTOCK
AGRONOMIC ENGINEERING MAJOR
CHEMICAL ANALYSIS LABORATORY: SOILS, WATER AND BROMATOLOGICAL
RESULTS REPORT
RECEPTION DATE 2 December 2016
DELIVERY DATE 28 March 2017
CLIENT INFORMATION:
Name Eng. Jorge Diaz
Survey Title CHARACTERIZATION OF THE SILALA
SPRINGS
Telephone
SAMPLE INFORMATION:
Analysis Type Soil
Sample N° 1
Department Potosi
Province South Lipez
Municipality San Pablo de Lipez
Community Quetena
Sampling Date 23 October 2016
Sampling Time 09:25 am
Physical Analysis of the Soil
ORIGINAL
CODE
PARAMETER UNIT HUMIDITY METHOD
Ssee-SUE01
Humidity % 3.788 Gravimetry
Bulk density g/cc 1.455 Gravimetry
Sand
%
40.3
Gravimetry
Silt 55.8
Clay 3.9
Texture % Silt-Loamy
Lic. Roxana Careaga Tapia
Head of the Soil Chemical Laboratory
428 247
English translation prepared by DIREMAR. The original language text remains the authoritative one.
TOMAS FRIAS AUTONOMOUS UNIVERSITY
FACULTY OF AGRICULTURAL SCIENCES AND LIVESTOCK
AGRONOMIC ENGINEERING MAJOR
CHEMICAL ANALYSIS LABORATORY: SOILS, WATER AND BROMATOLOGICAL
RESULTS REPORT
RECEPTION DATE 2 December 2016
DELIVERY DATE 28 March 2017
CLIENT INFORMATION:
Name Eng. Jorge Diaz
Survey Title CHARACTERIZATION OF THE SILALA
SPRINGS
Telephone
SAMPLE INFORMATION:
Analysis Type Soil
Sample N° 2
Department Potosi
Province South Lipez
Municipality San Pablo de Lipez
Community Quetena
Sampling Date 23 October 2016
Sampling Time 10:50 am
Physical Analysis of the Soil
ORIGINAL
CODE
PARAMETER UNIT HUMIDITY METHOD
Ssee-SUE02
Humidity % 0.423 Gravimetry
Bulk density g/cc 1.454 Gravimetry
Sand
%
44.4
Silt 54.2 Gravimetry
Clay 1.4
Texture % Silt-Loamy Gravimetry
Lic. Roxana Careaga Tapia
Head of the Soil Chemical Laboratory
429 248
English translation prepared by DIREMAR. The original language text remains the authoritative one.
TOMAS FRIAS AUTONOMOUS UNIVERSITY
FACULTY OF AGRICULTURAL SCIENCES AND LIVESTOCK
AGRONOMIC ENGINEERING MAJOR
CHEMICAL ANALYSIS LABORATORY: SOILS, WATER AND BROMATOLOGICAL
RESULTS REPORT
RECEPTION DATE 2 December 2016
DELIVERY DATE 28 March 2017
CLIENT INFORMATION:
Name Eng. Jorge Diaz
Survey Title CHARACTERIZATION OF THE SILALA
SPRINGS
Telephone
SAMPLE INFORMATION:
Analysis Type Soil
Sample N° 3
Department Potosi
Province South Lipez
Municipality San Pablo de Lipez
Community Quetena
Sampling Date 24 October 2016
Sampling Time 12:43
Physical Analysis of the Soil
ORIGINAL
CODE
PARAMETER UNIT HUMIDITY METHOD
Ssee-SUE02
Humidity % 0.447 Gravimetry
Bulk density g/cc 1.463 Gravimetry
Sand
%
24.6
Silt 73.7 Gravimetry
Clay 1.7
Texture % Silt-Loamy Gravimetry
Lic. Roxana Careaga Tapia
Head of the Soil Chemical Laboratory
430 249
English translation prepared by DIREMAR. The original language text remains the authoritative one.
TOMAS FRIAS AUTONOMOUS UNIVERSITY
FACULTY OF AGRICULTURAL SCIENCES AND LIVESTOCK
AGRONOMIC ENGINEERING MAJOR
CHEMICAL ANALYSIS LABORATORY: SOILS, WATER AND BROMATOLOGICAL
RESULTS REPORT
RECEPTION DATE 2 December 2016
DELIVERY DATE 28 March 2017
CLIENT INFORMATION:
Name Eng. Jorge Diaz
Survey Title CHARACTERIZATION OF THE SILALA
SPRINGS
Telephone
SAMPLE INFORMATION:
Analysis Type Soil
Sample N° 4
Department Potosi
Province South Lipez
Municipality San Pablo de Lipez
Community Quetena
Sampling Date 24 October 2016
Sampling Time 14:42
Physical Analysis of the Soil
ORIGINAL
CODE
PARAMETER UNIT HUMIDITY METHOD
Ssee-SUE02
Humidity % 57.504 Gravimetry
Bulk density g/cc 0.596 Gravimetry
Sand
%
20.1
Silt 60.3 Gravimetry
Clay 19.6
Texture % Silt-Loamy Gravimetry
Lic. Roxana Careaga Tapia
Head of the Soil Chemical Laboratory
431
ANNEX D.2
Sampling Points
432
433
434
ANNEX D.3.
ANOMALIES MAPS
435
436
437
438
439
440
441
ANNEX D.4.
PHOTOGRAPHIC REPORT
442 259
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph N° 1
Obtaining Infiltration Test Data
Photograph N° 2
Base point for obtaining Infiltration Data
443
260
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph N° 3
Infiltration Tests by the Double Ring Method
Photograph N° 4
Infiltration Velocity Test.
444
261
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph N° 5
Performance of Permeability Tests on the Substrate
Photograph N° 6
Settling of the PVC Tube for the Permeability Test
445 262
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph N° 7
Obtaining water parameters through the Multi-parameter Team
Photograph N° 8
Runoff from the springs from SEE - Measurement of Physicochemical Parameters
446
263
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph N° 9
Soil Sampling
Photograph N° 10
Measurement of the root depth of plants
447
264
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph N° 11
UATF-FAC Working Brigade of Geological Engineering in the Silala Springs
448
285
English translation prepared by DIREMAR. The original language text remains the authoritative one.
ANNEX E.
HYDROGEOLOGY
449
ANNEX E.1.
INFILTRATION TESTS
450 287
English translation prepared by DIREMAR. The original language text remains the authoritative one.
INFILTRATION TEST OF INFILTROMETER RINGS
SILALA WELL: Snww INF04
Coordinates: E: 600767,571
N: 7566500,704
Height: 4394.67 m.a.s.l.
TIME (min) Partial Sheet
(mm)
Infiltration
Velocity
(mm/min)
Accumulated
Time (min)
Accumulated
Sheet (mm)
0 0 0 0
0,5 2 4 0,5 2
0,5 1,4 2,8 1 3,4
0,5 1,1 2,2 1,5 4,5
0,5 1 2 2 5,5
0,5 1 2 2,5 6,5
0,5 1 2 3 7,5
0,5 0,9 1,8 3,5 8,4
0,5 0,9 1,8 4 9,3
0,5 0,8 1,6 4,5 10,1
0,5 0,7 1,4 5 10,8
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 m= -0,417
0,5 4 b= 3,3067
1 2,8 t= 5
1,5 2,2 KOSTIAKOV MODEL
2 2 Instant
infiltration
velocity
l= b*T (m)
2,5 2 l= 3.3067*(5-0.417)
3 2 l= 1.6901 mm/min
3,5 1,8
4 1,8
4,5 1,6
5 1,4
451 288
English translation prepared by DIREMAR. The original language text remains the authoritative one.
INFILTRATION TEST OF INFILTROMETER RINGS
SILALA WELL: Ssee INF01
Coordinates: E: 603064
N: 7566812
Height: 4416
TIME (min) Partial Sheet
(mm)
Infiltration
Velocity
(mm/min)
Accumulated
Time (min)
Accumulated
Sheet (mm)
0 0 0 0
0,5 0,7 1,4 0,5 1,7
0,5 0,3 0,6 1 1
0,5 1 2 1,5 2
0,5 0,5 1 2 2,5
0,5 0,5 1 2,5 3
0,5 0,7 1,4 3 3,7
0,5 0,3 0,6 3,5 4
0,5 1,4 2,8 4 5,4
0,5 0,8 1,6 4,5 6,2
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 m= -0,417
0,5 1,4 b= 3,3067
1 0,6 t= 5
1,5 2 KOSTIAKOV MODEL
2 1 Instant
infiltration
velocity
l= b*T (m)
2,5 1 l= 3.3067*(5-0.417)
3 1,4 l= 1.6901 mm/min
3,5 0,6
4 2,8
4,5 1,6
452
289
English translation prepared by DIREMAR. The original language text remains the authoritative one.
INFILTRATION TEST OF INFILTROMETER RINGS
SILALA WELL: Ssee INF02
Coordinates: E: 602988 602973
N: 7565669 7565834
Height: 442
TIME (min) Partial Sheet
(mm)
Infiltration
Velocity
(mm/min)
Accumulated
Time (min)
Accumulated
Sheet (mm)
0 0 0 0
0,5 0,4 0,8 0,5 0,4
0,5 0,3 0,6 1 0,7
0,5 0,2 0,4 1,5 0,9
0,5 0,3 0,6 2 1,2
0,5 0,3 0,6 2,5 1,5
0,5 0,2 0,4 3 1,7
0,5 0,3 0,6 3,5 2
0,5 0,3 0,6 4 2,3
0,5 0,2 0,4 4,5 2,5
0,5 0,2 0,4 5 2,7
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 m= -0,0509
0,5 0,8 b= 0,068
1 0,6 t= 5
1,5 0,4 KOSTIAKOV MODEL
2 0,6 Instant
infiltration
velocity
l= b*T (m)
2,5 0,6 l= 3.3067*(5-0.417)
3 0,4 l= 0.06265 mm/min
3,5 0,6
4 0,6
4,5 0,4
5 0,4
453
ANNEX E.2.
PERMEABILITY TESTS
454 291
English translation prepared by DIREMAR. The original language text remains the authoritative one.
PERMEABILITY TEST BY DESCENDING LEVEL
SILALA WELL: Ssee PERM03 Date: 26/Oct/2016
Coordinates: E: 603130,159
N: 7565778,9
Height: 4411,6 m.a.s.l.
TIME (min) Partial Sheet
(mm)
Accumulated
Time
Accumulated
Sheet
(h1/h2) Permeability
(cm/min)
0 0,1 0 0,1 1,000 0,000
3 0,5 3 0,5 0,200 0,965
3 0,6 6 1,1 0,455 0,473
3 0,4 9 1,5 0,733 0,186
3 0,3 12 1,8 0,833 0,109
3 0,4 15 2,2 0,818 0,120
3 0,3 18 2,5 0,880 0,077
3 0,5 21 3 0,833 0,109
3 0,3 24 3,3 0,909 0,057
3 0,6 27 3,9 0,846 0,100
3 0,4 30 4,3 0,907 0,059
Average= 0,226
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 0,000 m= -0,0139
3 0,965 b= 0,4142
6 0,473 t= 30
9 0,186 KOSTIAKOV MODEL
12 0,109 Instant
infiltration
velocity
l= b*T (m)
15 0,120 l= 0.4142*(30-0.0139)
18 0,077 l= 0.350 cm/min
21 0,109
24 0,057
27 0,100
30 0,059
292 455
English translation prepared by DIREMAR. The original language text remains the authoritative one.
PERMEABILITY TEST BY DESCENDING LEVEL
SILALA WELL: Ssee PERM04 Date: 26/Oct/2016
Coordinates: E: 603115.502
N: 7565860.414
Height: 4410,2 m.a.s.l.
TIME (min) Partial Sheet
(mm)
Accumulated
Time
Accumulated
Sheet
(h1/h2) Permeability
(cm/min)
0 0,1 0 0,1 1,000 0,000
2 5 2 5 0,020 3,519
2 2,5 4 7,5 0,667 0,365
2 2 6 9,5 0,789 0,213
2 2,2 8 11,7 0,812 0,187
2 1,3 10 13 0,900 0,095
2 1 12 14 0,929 0,067
2 2 14 16 0,875 0,120
2 1 16 17 0,941 0,055
2 1,5 18 18,5 0,919 0,076
2 1,3 20 19,8 0,934 0,061
Average = 0,4325
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 0,000 m= -0,0668
2 3,519 b= 1,1009
4 0,365 t= 20
6 0,213 KOSTIAKOV MODEL
8 0,187 Instant
infiltration
velocity
l= b*T (m)
10 0,095 l= 1.1009*(30-0.0668)
12 0,067 l= 0.90123 cm/min
14 0,120
16 0,055
18 0,076
20 0,061
456 293
English translation prepared by DIREMAR. The original language text remains the authoritative one.
PERMEABILITY TEST BY DESCENDING LEVEL
SILALA WELL: Ssee PERM01 Date: 26/Oct/2016
Coordinates: 603139
N: 7565802
Height: 4,426 m.a.s.l.
TIME (min) Partial Sheet
(mm)
Accumulated
Time
Accumulated
Sheet
(h1/h2) Permeability
(cm/min)
0 0,1 0 0,1 1,000 0,000
3 1,6 3 1,6 0,063 2,494
3 0,7 6 2,3 0,696 0,326
3 0,4 9 2,7 0,852 0,144
3 0,4 12 3,1 0,871 0,124
3 0,3 15 3,4 0,912 0,083
3 0,3 18 3,7 0,919 0,076
3 0,5 21 4,2 0,881 0,114
3 0,3 24 4,5 0,933 0,062
3 0,1 27 4,6 0,978 0,020
3 0,4 30 5 0,920 0,075
Average = 0,3199
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 0,000 m= -0,0316
3 2,494 b= 0,7938
6 0,326 t= 20
9 0,144 KOSTIAKOV MODEL
12 0,124 Instant
infiltration
velocity
l= b*T (m)
15 0,083 l= 0.7938*(30-0.0316)
18 0,076 l= 0.7221 cm/min
21 0,114
24 0,062
27 0,020
30 0,075
457 294
English translation prepared by DIREMAR. The original language text remains the authoritative one.
PERMEABILITY TEST BY DESCENDING LEVEL
SILALA WELL: Snww PERM01 Date: 26/Oct/2016
Coordinates: E: 603139 600877
N: 7565802 7566333
Height: 4,426 m.a.s.l.
TIME (min) Partial Sheet
(mm)
Accumulated
Time
Accumulated
Sheet
(h1/h2) Permeability
(cm/min)
0 0,1 0 0,1 1,000 0,000
0,5 0,8 0,5 0,8 0,125 1,871
0,5 0,8 1 1,6 0,500 0,624
0,5 0,5 1,5 2,1 0,762 0,245
0,5 1 2 3,1 0,677 0,350
0,5 0,3 2,5 3,4 0,912 0,083
0,5 0,6 3 4 0,850 0,146
0,5 0,4 3,5 4,4 0,909 0,086
0,5 0,6 4 5 0,880 0,115
0,5 0,5 4,5 5,5 0,909 0,086
0,5 0,5 5 6 0,917 0,078
Average = 0,3349
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 0,000 m= -0,1599
0,5 1,871 b= 0,7347 0,56799529
1 0,624 t= 20
1,5 0,245 KOSTIAKOV MODEL
2 0,350 Instant
infiltration
velocity
l= b*T (m)
2,5 0,083 l= 0.7938*(30-0.0316)
3 0,146 l= 0.5679 cm/min
3,5 0,086
4 0,115
4,5 0,086
5 0,078
458 295
English translation prepared by DIREMAR. The original language text remains the authoritative one.
PERMEABILITY TEST BY DESCENDING LEVEL
SILALA WELL: Ssee PERM02 Date: 26/Oct/2016
Coordinates: E: 603138
N: 7565808
Height: 4,426 m.a.s.l.
TIME (min) Partial Sheet
(mm)
Accumulated
Time
Accumulated
Sheet
(h1/h2) Permeability
(cm/min)
0 0,1 0 0,1 1,000 0,000
3 1,4 3 1,4 0,071 2,374
3 0,6 6 2 0,700 0,321
3 0,4 9 2,4 0,833 0,164
3 0,6 12 3 0,800 0,201
3 0,5 15 3,5 0,857 0,139
3 0,5 18 4 0,875 0,120
3 0,3 21 4,3 0,930 0,065
3 0,7 24 5 0,860 0,136
3 0,6 27 5,6 0,893 0,102
3 0,4 30 6 0,933 0,062
Average = 0,3349
Accumulated
Time
Infiltration
Velocity
(mm/min)
0 0,000 m= -0,0291
3 2,374 b= 0,7718 0,73648643
6 0,321 t= 5
9 0,164 KOSTIAKOV MODEL
12 0,201 Instant
infiltration
velocity
l= b*T (m)
15 0,139 l= 0.7718*(30-0.0291)
18 0,120 l= 0.73643 cm/min
21 0,065
24 0,136
27 0,102
30 0,062
459
Annex E.3.
Photographic Report
460 297
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 1: Measurement of Flows.
Photograph 2: Determination of the Infiltration Capacity.
461 298
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 3: Permeability Measurement (K)
462 299
English translation prepared by DIREMAR. The original language text remains the authoritative one.
Photograph 4: Permeability Measurement (K)
Volume 4 - Annexx 23.5