The Surface/Subsurface Relationship Between Drainage and Buried Faults As Observed in the Andean Foreland of Central-Western Argentina

Home , Blind thrust earthquake, Mendoza River, Neotectonics

THE SURFACE/SUBSURFACE RELATIONSHIP BETWEEN DRAINAGE AND BURIED FAULTS AS OBSERVED IN THE ANDEAN FORELAND OF CENTRAL-WESTERN ARGENTINA

Thesis

Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University

Peter Andreas Enderlin, B.S.

Graduate Program in Geological Sciences

The Ohio State University

2010

Master’s Examination Committee:

Dr. Lindsay Schoenbohm, Advisor Dr. Ian Howat Dr. Lawrence Krissek

Peter Andreas Enderlin

2010

ABSTRACT

The Andean foreland of central-western Argentina (30°-35°S) is characterized by the interaction of the east-vergent, thick-skinned Sierras Pampeanas and the west-vergent, thin-skinned Precordillera. Blind thrust faults are associated with the transition between these structural provinces, and large earthquakes have resulted from their interplay beneath the cities of Mendoza and San Juan. This study develops and applies a geomorphic approach to reveal buried tectonic features at both the scale of individual structures and the regional-scale. We interpret changes in bank heights and sinuosity from three rivers located between the Cerro Salinas and Montecito anticlines to suggest the existence of a third, buried structure. Inflections in elevation swaths indicate these three structures may be connected by the southern continuation of the Cerro Salinas thrust, which would tie the three to the Sierras Pampeanas structural province. Regional- scale drainage in the Andean foreland shows that neither current- nor paleorivers have flowed across the Alto del Desaguadero area. Inflections in W-E and N-S elevation swaths across this area suggest the influence of tectonic forcing, possibly due to a rising basement structure similar to the Sierra Pie de Palo to the north.

ii ACKNOWLEDGEMENTS

First and foremost I thank my advisor, Dr. Lindsay Schoenbohm, for her guidance, encouragement, flexibility, and for giving me this opportunity.

I would also like to thank my committee members, Dr. Ian Howat and Dr.

Lawrence Krissek, as well as Dr. Terry Wilson, for their feedback, contributions and time.

Thanks to my collegues in Argentina for their assitance: Dr. Carlos Costa and

Emillio Ahumada, of the Universidad Nacional de San Luis and Dr. Jorge Baron of

CEDIAC. Also, a big thank you goes to Cesar Distante for his help in the field, his humor, and his friendship.

Finally, a very special thanks to my family for all their support, and to Ellyn

McFadden for keeping me smiling through it all.

Funding provided by NSF Grant #EAR-60014033

and by AAPG Ohio Geological Society Named Grant.

iii VITA

January 18, 1983…………………………………………………Born – Staten Island, NY

2001……………………………………………………….Morristown-Beard High School

September 2004……………………………………………..Poster, GSA Annual Meeting

2005………………………....…B.S. Geology/Environmental Science, Dickinson College Graduated with Departmental Honors

2005-2006……………………Geologist, Science Applications International Corporation

2006-2008……………………Geologist, Langan Engineering & Environmental Services

2008-2009……………………...Graduate Teaching Associate, The Ohio State University

May 2009………………………………… AAPG Ohio Geological Society Named Grant

December 2009…………...…………………………………….Poster, AGU Fall Meeting

2009-present…………………....Graduate Research Associate, The Ohio State University

FIELDS OF STUDY

Major Field: Geological Sciences

iv TABLE OF CONTENTS

Abstract……………………………………………………………………………………ii Acknowledgements………………………………………………………………………iii Vita………………………………………………………………………………………..iv List of Tables…………………………………………………………………………….vii List of Figures…………………………………………………………………………...viii

Chapters:

1. Introduction and Background……………………………………………………..1 1.1 Purpose………………………………………………………………………...1 1.2 Tectonic Setting……………………………………………………………….3 1.3 Climate………………………………………………………………………...9 1.4 Rivers………………………………………………………………………...11 1.5 River Response to Uplift……………………………………………………..14

2. The Cerro Salinas Thrust Case Study……………………………………………18 2.1 Methods………………………………………………………………………22 2.2 Results………………………………………………………………………..25 2.3 Discussion……………………………………………………………………32

3. Regional-Scale Drainage Deflection……………………………………………..38 3.1 River Deflections…………………………………………………………….38 3.1.1 Methods…………………………………………………………….38 3.1.2 Results……………………………………………………………...42 3.1.3 Discussion………………………………………………………….50 3.2 Alto del Desaguadero………………………………………………………...52 3.2.1 Methods…………………………………………………………….52 3.2.2 Results……………………………………………………………...54 3.2.3 Discussion………………………………………………………….58

v 4. Conclusions………………………………………………………………………61

References………………………………………………………………………………..64

Appendix A: Drainage anomaly data…………………………………………………….69

vi LIST OF TABLES

Table Page

2.1. Bank Heights of Rivers 1, 2, and 3………………………………………………….26

2.2. Sinuosity Indices of Rivers 1, 2, and 3……………………………………………...28

vii LIST OF FIGURES

Figure Page

1.1. Global distribution of earthquakes caused by blind or buried thrust faults…………..2

1.2. Regional map of study area…………………………………………………………...4

1.3. Schematic drawing of flat slab and steep subduction regions in South America…….6

1.4. Cerro Salinas study area………………………………………………………………8

1.5. Distribution of annual precipitation of south-western South America……………...10

1.6. Current and paleodrainage of the study area………………………………………...12

1.7. Important drainage ditches and irrigation canals of Mendoza, circa 1761………….14

2.1. Interpretation of seismic profile 31017……………………………………………...20

2.2 Structural interpretation of the Cerro Salinas study area…………………………….21

2.3. Thrust-related tectonic topography curve…………………………………………...24

2.4. Bank height plot of Rivers 1 through 3……………………………………………...27

2.5. Sinuosity plot of Rivers 1 through 3………………………………………………...27

2.6. Elevation swath profiles across the projected Cerro Salinas thrust...... 31

2.7. Schematic cross section inferred from seismic profile 31017………………………37

3.1. Example of HydroSHEDS stream-network vectors deviating from the ASTER imagery beyond the 2-km buffer……………………………………………………..40 viii 3.2. Tools used for stream deflection identification……………………………………..42

3.3. Trans-contour method identified anomalies, 5-km tool, 20-m contour interval, HydroSHEDS elevation model………………………………………………………44

3.4. Result comparison of different variables in a limited test area using the HydroSHEDS elevation model………………………………………………………45

3.5. Burrato-method identified anomalies, 5-km tool, 10-m contour interval, HydroSHEDS elevation model………………………………………………………47

3.6. Trans-contour method identified anomalies, 5-km tool, 20-m contour interval, ERSDAC elevation model…………………………………………………………..48

3.7. Burrato-method identified anomalies, 5-km tool, 10-m contour interval, ERSDAC elevation model………………………………………………………………………49

3.8. Alto del Desaguadero elevation swath and elevation inflection point locations……53

3.9. W-E elevation swath profiles across the Alto del Desaguadero…………………….55

3.10. N-S elevation swath profiles across the Alto del Desaguadero……………………57

ix CHAPTER 1:

INTRODUCTION AND BACKGROUND

1.1 Purpose

Blind thrust faults are faults that have not propagated to intersect the Earth’s surface. The

growth of these faults has resulted in numerous moderate- to large-scale earthquakes throughout the world (Fig.1.1). The explicit danger with these earthquakes is that the buried faults are often not recognized until they rupture. Highly populated metropolitan areas, such as Los Angeles (pop. 10 million), that are situated in a tectonically active

zone are constantly at risk of earthquakes. The most significant blind thrust earthquake

(M 5.9) on record for Los Angeles was the Whittier Narrows earthquake, which occurred

on October 1, 1987. This event resulted in 8 deaths, several hundred injuries, and over

$360 million in property damages (Bilodeau et al., 2007; USGS website).

The Andean foreland of central-western Argentina is among the most seismically active

regions in the world (Siame et al., 2006). Underlying blind thrusts pose significant risk to

the cities of Mendoza and San Juan as they are capable of generating large earthquakes.

One of the largest on record, a magnitude 7.4 earthquake, occurred in 1944 under the city of San Juan, resulting in over 10,000 deaths (Siame et al., 2006). In 1861, a magnitude

7.0 earthquake practically destroyed the city of Mendoza (USGS website). Although

earthquakes cannot be prevented, monitoring stress in active faults can be used to indicate

when an earthquake may occur.

Figure 1.1 Locations of earthquakes caused by blind or buried thrust faults. Some dots represent more than one event. The area of interest is boxed in red. Modified from Lettis et al. (1997).

Blind thrust faults are difficult to monitor because they must first be identified. The

identification of these faults has traditionally been limited to seismic exploration and/or

the recognition of anticlinal hills above the projected fault tip. However, even if there is

no topographic expression, blind thrust faults can be identified geomorphically (e.g.

Burrato et al., 2003). Deviations in drainage patterns, such as longitudinal and lateral

changes in stream gradient (i.e. river diversions, shifts in sinuosity, and gradient

changes), as well as overall changes in basin shape, have been associated with tectonics.

Areas of low-gradient, such as the Andean foreland, are especially sensitive to vertical

deformation. Furthermore, the rivers in this region flow from the Andes Mountains across

active blind thrust faults before reaching the foreland. This presents an ideal study

location to refine our methods for recognizing previously unidentified blind thrusts by

examining ephemeral streams.

In this study, we develop a method to indentify blind thrust faults by their geomorphic

expressions. The Cerro Salinas case study shows how data that can easily be collected in the field (i.e. bank height and sinuosity) can be used to confirm the existence of a buried thrust below ephemeral rivers. The regional-scale approach tests whether subtle tectonic uplift can be recognized either by drainage deflections in the geomorphology or by topographic inflections in elevation swaths in the central-western Argentine foreland. The

approach developed herein can be applied elsewhere to identify blind or buried structures

remotely, which could be beneficial for hazard assessment, understanding deformation

history, and hydrocarbon exploration.

1.2 Tectonic Setting

Mountain building processes in the Central Andes (4°-46°S) are dominated by subduction

of the Nazca Plate beneath the South American Plate (Fig. 1.2a; Barazangi and Isacks,

1976; Allmendinger et al., 1997; Costa et al., 2006). Two regions in the Central Andes,

the Peruvian (4°-14°S) and Pampean (27°-33°S) flat-slabs, are associated with a gap in

active arc volcanism, deformation, and late-Cenozoic arc volcanism (Fig. 1.3; Ramos et

3 al., 2002; Lamb and Davis, 2003). South of 33°S, the subducting plate resumes a steeper dip (25° to 30°) (Barazangi and Isacks, 1976; Siame et al., 2005).

Figure 1.2. a) Map of South America with the South American and Nazca Plates labeled and study area indicated by red box. b) Location map showing Andes, Cordillera, Precordillera, and Sierras Pampeanas after Ramos et al. (2002). c) Regional map of the Andean foreland of central-western Argentina showing current drainage, paleochannels, and tectonic structures. Keys: CST, Cerro Salinas Thrust; LPT, Las Peñas Thrust; LHT, Las Higueras Thrust. Shaded relief DEM from HydroSHEDS data (http://hydrosheds.cr.usgs.gov). Major regional faults are modified from Vergés et al. (2001) and Siame et al. (2005). 4

The Argentine Precordillera (27°-33°S) of the Andes Mountains is subdivided, from west to east, into the Western Precordillera, Central Precordillera, and Eastern Precordillera

(Fig. 1.2), which are generally thin-skinned thrust belts. East of the Andean foreland is the Sierras Pampeanas structural province (Fig. 1.2b), which is thick-skinned, involving basement rocks in deformation (Allmendinger et al., 1997; Ramos et al., 2002; Costa et al., 2006). The deformation and faulting of these basement blocks are characteristic of flat-slab subduction (Barazangi and Isacks, 1976; Ramos et al., 2002; Siame et al., 2006).

Tectonic activity in the Pampean flat-slab region (27°-33°S) is concentrated in the

Andean foreland between the eastern foothills of the Andes and the western Sierras

Pampeanas structural province (Costa et al., 2000a; Costa et al., 2006). The Western and

Central Precordillera behave as thin-skinned, east-vergent (Andean-type) thrust belts and the Sierras Pampeanas behave as a thick-skinned, west-vergent (Pampean-type) thrust belt (Fig. 1.3). Although the Central and Eastern Precordilleras show parallel fault trends, the Eastern Precordillera structures result from west-vergent compressive reverse faulting

(Fig. 1.2c; Siame et al., 2002; Costa et al., 2006; Vergés et al., 2007). The convergent thrusting of these structures forms a thick-skinned triangle zone bounded by oppositely verging thrusts (Zapata and Allmendinger, 1996). The deformation of this region is represented by neotectonic structures and small fault traces resulting from distributed bedding plane slip within flexural-slip folds (Fig. 1.2c; Ramos et al., 2002; Costa et al.,

2006; Siame et al. 2006; Vergés et al., 2007). South of ~32°S, deformation is transferred

5 to emerging or blind thrust faulting, and the thick-skinned triangle zone dies out south of

32°30’ S (Costa et al., 2006).

Figure 1.3. Schematic drawing comparing cross sections of the Pampean flab-slab (28°-33°S) and steep subduction (33°-40°S) regions. Cross section A-A’ shows the subsurface convergence of the east-vergent, thin skinned Precordillera and the west-vergent, thick-skinned Sierras Pampeanas. Modified from Ramos and Nullo (1993).

Much of the 200-km-long Andean front between the cities of Mendoza and San Juan is dominated by blind thrust faults extending to depths of 20-km and more (Vergés et al.,

2007). Faults associated with the interactions between the western Sierras Pampeanas and 6 the Eastern Precordillera, such as the Cerro Salinas and the Las Peñas-Las Higueras thrusts, have been mapped and projected in the subsurface between these two cities (Fig.

1.2c). Interpretation of multichannel seismic lines (MCS) by Vergés et al. (2007) suggests that the lateral extent of the deep structure associated with this thrust is linked to tectonic structures such as the Sierra de Pie de Palo to the north and the Cerro Salinas and

Montecito anticlines and the Sierra de Las Peñas-Las Higueras to the south (Fig. 1.2c).

The Sierra Pie de Palo is a 35x80-km elongated dome trending NNE with a maximum elevation over 3-km AMSL (Siame et al., 2006). The uplift of Pie de Palo is controlled by an east-vergent, basement wedge (Ramos et al., 2002; Siame et al., 2006). Pie de Palo is an important structure because the majority of present-day tectonics and uplift of the central Sierras Pampeanas are concentrated in the complex (Ramos et al., 2002). Despite the numerous earthquakes associated with the growth of this complex, there have been very few surface ruptures (Smalley et al., 1993), suggesting the faults associated with the growth are mostly buried (Siame et al., 2006).

The Cerro Salinas and Montecito anticlines lie in the southern section of the triangle zone. Both structures are north-south oriented, parallel to the fault trends of the Central and Eastern Precordillera (Fig. 1.2c). The Cerro Salinas anticline is formed above the west-vergent Cerro Salinas thrust as a highly asymmetric, thin-skinned footwall anticline

(Vergés et al., 2007). The thrust is exposed along the western flank of Cerro Salinas, but surface expression disappears beyond the southern tip of the structure (Fig. 1.4). The

Montecito structure is a symmetric doubly plunging anticline (Costa et al., 2000b) believed to be the southern continuation of the Cerro Salinas thrust (Vergés et al., 2007).

Figure 1.4. Map of the Cerro Salinas study area. Fault and structural positions are modified from Vergés et al. (2007).

West of the Montecito anticline, located between 32°15’ and 32°40’S, lies the Sierra de

Las Peñas (Costa et al., 2000a). This range is oriented NNW and is considered an

imbricate system of western-dipping reverse faults (Costa et al., 2000a). The junction of the east-vergent Las Peñas thrust and west-vergent Cerro Salinas/Montecito thrust forms

a Y-shape of overlapping geometry that defines the southern extent of the triangle

deformation zone (Fig. 1.4; Ahumada and Costa, 2009).

1.3 Climate

The Andes Mountains run approximately 7,000-km north-south with peak elevations

above 6-km (Strecker et al., 2007). Due to orographic effects, pronounced moisture

gradients exist between the eastern and western flanks of the Andes (Fig. 1.5;

Montgomery et al., 2003; Strecker et al., 2007). For example, the eastern facing slopes of

the southern central Andes (~10°-25°S) block moisture-bearing tropical easterly winds,

resulting in humid eastern flanks and arid western flanks (Harris and Mix, 2002; Strecker

et al., 2007). Alternatively, the western-facing slopes of the southern Andes (~35°-55°S) block the prevailing westerly winds, resulting in humid western flanks and arid eastern flanks (Strecker et al., 2007). Asymmetry in precipitation has also resulted in differences in weathering, erosion, and sediment transport (Montgomery et al., 2003; Strecker et al.,

2007).

Central-western Argentina (30°-35°S) is located at the easterly/westerly transition zone, which is strongly influenced by seasonality. For example, during the austral winter, atmospheric circulation and precipitation is dominated by the westerlies, whereas during

the austral summer it is controlled by the subtropical high-pressure belt (Hoke et al.,

2009). This results in a pronounced wet/dry season (Hoke et al., 2009). Central-western

Argentina has an arid climate, receiving less than 200 mm of precipitation per year

(Strecker et al., 2007; Hoke et al., 2009). Most of this falls during the austral winter in the

form of snow when the westerly flow across the Andes is enhanced. Therefore,

streamflow in central-western Argentina is strongly correlated with the amount of snow

that falls and is stored in the mountains during the austral winter (Masiokas et al., 2006).

Figure 1.5. Map of south-western South America showing the distribution of annual precipitation overlain on a shaded- relief map. Note the low precipitation in the area of interest (black box). Modified from Strecker et al. (2007). 10

1.4 Rivers Regional drainage in the Mendoza Province is comprised of four major rivers: the Ríos

Mendoza, San Juan, Desaguadero, and Tunuyán (Fig. 1.2c). The Río Mendoza presently

drains from the Andes through the city of Mendoza. The river flows approximately 45

km east before turning north and continuing for about 120 km until it intersects the Río

San Juan. From this confluence, the Río San Juan flows ESE for about 95 km until it

joins the south-flowing Río Desaguadero. These rivers flow around the periphery of an

area called the Alto del Desaguadero (Fig. 1.1c). The headwaters for the Río Tunuyán

also begin in the Andes, entering the eastern foreland about 100 km south of the Río

Mendoza. The Río Tunuyán flows north until it encounters a hydroelectric dam and

forms a reservoir. Downstream of this reservoir, the Río Tunuyán flows ESE until

converging with the Río Desaguadero, approximately 150 km south of the Río San Juan

confluence.

Despite the relatively erosive environment associated with eolian processes in deserts,

paleochannels from these major rivers are preserved in the eastern foreland. Although to

our knowledge these channels have not been dated absolutely, relative dating techniques

suggest the Ríos Mendoza and Tunuyán once flowed together northward during the

Pleistocene (Rodríguez and Barton, 1993; Martínez et al., 2008). Since that time,

paleochannels of the Río Tunuyán suggest that the river split off and migrated to its

current position. However, no paleochannels have been identified flowing across the Alto

del Desaguadero. Similarly, paleochannels of both the Ríos Mendoza and San Juan

11 indicate drainage has been deflected around and/or avulsed away from the Alto del

Desaguadero (Fig. 1.6; Rodríguez and Barton, 1993; Perucca, 1994).

Figure 1.6. Regional map of the Andean foreland showing the current drainage and occupational order of paleochannels. Paleochannels numbered 1 – 4 correspond with Pleistocene through Middle-Early Holocene ages, although exact ages are unknown. Note that drainage does not enter or cross the projected Alto del Desaguadero location. Paleochannel location and occupation order modified from Rodríguez and Barton (1993) and Perucca (1994), major regional faults are modified from Vergés et al. (2002) and Siame et al. (2005). 12

In the cities of Mendoza and San Juan, rivers are diverted into concrete irrigation canals

in order to maximize distribution (Fig. 1.6) and in order to ensure proper irrigation

practices. This management prohibits the natural flow and drainage development of the

region’s rivers. With limited rainfall, it is little surprise that the primary source of water

for agriculture is irrigated snowmelt runoff from the Andes (Bertranou et al., 1983;

Masiokas et al., 2006). This hydraulic supply is controlled by decentralized agencies,

owned and operated by the provincial government. Users’ associations are then allocated

to regulate water at the secondary and tertiary canal level (Chambouleyron, 1989). Water is also used for the generation of hydroelectric power. Between 1986 and 2003, hydroelectric plants have accounted for an average of 62% of the total domestic energy generated in the province of Mendoza (Masiokas et al., 2006). Therefore, the volume of water flowing through the irrigation canals is also impacted when the government decides to install a new hydroelectric dam.

Anthropogenic impact on the natural courses of the region’s rivers is not a modern phenomenon. When the Spanish Conquistadores arrived to this area in 1561, they found the natives living along the Río Mendoza irrigating the river to grow allochthonous crops

otherwise unsuited for the dry climate (Chambouleyron, 1989). The Spaniards took

advantage of this by building an irrigation network of channels and ditches onto the

existing infrastructure (Fig. 1.7; Prieto, 1999). By the end of the eighteenth century, the

city’s inhabitants had learned to regulate the seasonal variability of river flow with a

series of dams placed within the irrigation canals (Prieto, 1999). Due to this long-

13 standing anthropogenic influence on the natural flow of the region’s rivers, we limit our analysis to outside the irrigation canal-dominated drainage area (Fig. 1.6).

Figure 1.7. Schematic map of the Mendoza region circa 1761 showing important drainage ditches and irrigation canals. By the end of the eighteenth century the Spanish Conquistadores had learned to regulate the seasonal variability of river flow with a series of dams placed within the irrigation canals. Modified from Prieto (1999).

1.5 River Response to Uplift

Changes in planform drainage pattern and the gradient of a river can provide information on external forces. The forces causing these changes can be natural (climatic, tectonic) or anthropogenic (Burnett and Schumm, 1983; Schumm, 1985; Burrato et al., 2003).

Aggradation or degradation, as a result of changes in discharge or baselevel, can influence channel depth, whereas changes in gradient, sediment type, and sediment load 14

will alter channel shape and pattern (Burnett and Schumm, 1983; Schumm, 1985;

Holbrook and Schumm, 1999). The degree of geomorphic response depends on the rate

and amount of tectonic deformation (Bull and McFadden, 1977; Ouchi, 1985; Peakall et

al., 2000; van der Beek et al., 2002), the underlying lithology (Holbrook and Schumm,

1999; van der Beek et al., 2002; Harkins et al., 2005), and the type of river (Ouchi, 1985,

Schumm, 1985). Alluvial rivers are particularly responsive to these changes because the

bed and banks are primarily comprised of the sediment transported by the stream (Burnett

and Schumm, 1983; Schumm, 1985). Therefore, the drainage pattern and profile of an

alluvial river will adjust to tectonic deformation even if it is subtle (Ouchi, 1985; Burrato

et al., 2003, Vannoli et al., 2004; Stokes et al., 2008).

Tectonic activity can produce longitudinal (parallel to floodplain orientation) and lateral

(normal to floodplain orientation) pattern changes in drainage (Holbrook and Schumm,

1999; Burrato et al., 2003). According to Holbrook and Schumm (1999) there are five typical responses to longitudinal tilting: 1) drainage deflection (a shift of the drainage direction from directly downstream over a limited spatial distance), 2) longitudinal profile adjustment (changes in the channel profile to the regional average gradient), 3) variations of stream sinuosity (deviation of a path length from the shortest possible path),

4) cross-section adjustment (changes in width/depth ratios), and 5) sediment-size change.

Lateral tilting will result in channel migration through avulsion (abrupt shifting of a stream course toward the lower, down-tilted region) or combing (slow migration by

preferential downslope erosion and/or meander cutoff on one side of the river) (Holbrook

and Schumm, 1999; Peakall et al., 2000).

Areas of low gradient are especially sensitive to vertical deformation. Therefore, the

rivers draining across these regions are more likely to express surface tilting through

anomalies in their drainage patterns (Holbrook and Schumm, 1999). This was

documented in a study by Allen and Davis (2007) in the West Siberian Basin. They

examined the influence of lateral tilting on low-gradient rivers as seen in satellite

imagery. They recognized evidence for combing through the asymmetric development of

meander scars. The lateral tilting surface deformation was caused by previously unidentified subtle active faulting.

Rivers that maintain their course across geological structures, such as faults and folds, are known as antecedent or transverse rivers (Burbank et al., 1996; Twidale, 2004). When transverse drainage encounters a rising structure it can be diverted around the fold or fault tip or deflected into a neighboring water gap. However, if the incision rate is greater than the uplift rate, the river will incise through the uplifting fold (Burnett and Schumm, 1983;

Peakall et al., 2000; van der Beek et al., 2002; Burrato et al., 2003; Davis et al., 2003;

Stokes et al., 2008). Deflections in drainage are the clearest indicators that streams are

approaching a rising or propagating structure (Keller at al., 1999; Burrato et al., 2003;

Davis et al., 2003; Allen and Davis, 2007; Delcaillau et al., 2007). An example of the

influence of vertical surface movement attributed to buried faults was documented in the

Apennine Mountains, Italy. Vannoli et al. (2004) monitored several rivers draining from the mountains across the coastal slope to the Adriatic Sea. They identified zones of increased downcutting, river migration, and sediment accumulation in the low-gradient

piedmont. These changes in drainage were attributed to the growth of the coastal anticline

driven by the underlying blind thrust fault (Vannoli et al., 2004).

CHAPTER 2:

THE CERRO SALINAS THRUST CASE STUDY

The rivers draining the Precordillera flow SSE, perpendicular to the Cerro Salinas and

Las Peñas faults. Depending on their location relative to the tip of the growing

anticline, rivers located between ~32°10’ and 32°28’S have either incised into

Neogene sedimentary rocks or been deflected around the tip of the Cerro Salinas and

Montecito anticlines (Costa et al., 2000a; Vergés et al., 2007; Bohon, 2008). Studies

by Vergés et al. (2007) and Costa et al. (2000a) have confirmed that the Cerro Salinas

hanging wall thrust is being uplifted and that the Montecito anticline is actively growing, respectively. Therefore, examining the rivers flowing between the Cerro

Salinas and Montecito anticlines presents a unique opportunity to observe the influence of active tectonics on drainage and to document the geomorphic response.

The Cerro Salinas structure is a west-vergent, highly asymmetric anticline: the backlimb is over 6-km wide, dipping between 23° and 30° to the east, whereas the

forelimb is west-dipping 37° and ~300-m wide (Vergés et al., 2007). Folded and

faulted Quaternary gravel terraces overlie Neogene red beds. An uplift rate of 0.45 mm/yr has been inferred for the hanging wall thrust through the dating of volcanic

18 ash to ~8.5 Ma within the pre-growth strata (Vergés et al., 2007). Although Cerro

Salinas is associated with Eastern Precordillera thin-skinned deformation, MCS indicates this uplift is triggered by blind, thick-skinned thrust and tectonic wedging at depth, which suggests it is associated with the Sierras Pampeanas (Fig. 2.1; Meigs et al., 2006).

Since the Cerro Salinas anticline is an actively growing structure, the effect on drainage morphology serves as comparison to our observations/results. As identified by Vergés et al. (2007), the antecedent streams (A and B, Fig. 2.2) intersecting this uplifting anticline either cut across or deflect around the growing structure. Secondary streams A1 and A2 are relatively linear as they cross Cerro Salinas, whereas stream

A3 is deflected about 2-km before crossing. Secondary streams A1, A2, and A3 are incised into Neogene sedimentary rocks. Stream B, on the other hand, is diverted around the southern termination of Cerro Salinas (Fig. 2.2; Vergés et al., 2007).

Similar observations have been made for the drainage flowing across the Montecito anticline: Rivers being deflected around the growing structure on either end are the

Quebrada Ancha to the north and the Quebrada Sur to the south (Costa et al., 2000a;

Bohon, 2008). The antecedent drainages, Quebrada de las Vacas and Quebrada

Jejenes, have formed meandering water gaps across the structure (Fig. 2.2).

ofthe CerroSalinas anticline. Modified fromVergés et al.

most tip most - Interpretation of seismic profile 31017 where it cross the southern the cross it where 31017 profile seismic of Interpretation

Figure 2.1. (2007).

Figure 2.2. Map of the Cerro Salinas study area showing the position the thrust as suggested by the common bank height locations and common sinuosity locations, as well as the possible through-going fault connecting Cerro Salinas to Montecito as suggested by the elevation inflection points. Faults, seismic line position, and Cerro Salinas drainage modified from Vergés et al. (2007), Montecito drainage modified from Bohon (2008). 21

The surface expression of the Cerro Salinas thrust is located along the western forelimb of the Cerro Salinas anticline. The subsurface continuation of the thrust has been projected south, connecting to the Montecito anticline (e.g., Siame et al., 2006;

Vergés et al., 2007). However, the exact location of thrust has yet to be confirmed, and the Montecito anticline may instead be linked to eastward propagation of the Las

Peñas-Las Higueras thrust system (Vergés et al., 2007). Because the geomorphic expression of growing anticlines is recorded in the fluvial system of foreland basins

(e.g., Davis et al., 2003), we examined the rivers flowing between these structures for evidence that they are structurally linked.

2.1 Methods

As discussed in Section 1.5, when a transverse river approaches a rising structure it will either incise through it or be deflected around the tip. Therefore, we expect to observe either an increase in river incision (e.g. increase of bank height), a change in river sinuosity, or deflection as the rivers flowed across the projected subsurface

Cerro Salinas thrust.

Bank heights were measured from the channel bed using a measuring tape along the southern bank of each of three rivers across a ~4 km wide region to capture any blind thrusts between the Montecito and Cerro Salinas anticlines. In sections where the most recently occupied channel was not directly adjacent to the bank, bank height was measured using the eye-height technique with a Brunton compass. Measurements

were taken every 250 meters. I measured this distance linearly from one point to the

next (valley length) using a handheld GPS unit.

Although the distance between bank height measurement points was constant, the

segments between were not, and therefore I simultaneously mapped the channel

thalweg of the three ephemeral rivers using the GPS unit. Data were automatically

recorded every 10 seconds in a downstream to upstream walking traverse. In areas with multiple stream channels I chose the most recently-occupied channel in an effort to map the most modern thalweg, basing this assessment on the relative freshness of the fluvial bedforms and channel depth. The sinuosity index (the ratio of the valley length to the channel length) was calculated for each river as well as for each segment

between bank height measurement points.

Once the GPS data had been downloaded, I compared the three traced rivers. In order to facilitate comparison, I projected each river onto an average trend line of 108°. The data could then be shifted along the trend line to test the alignment of similar patterns in sinuosity and bank height between the three rivers. These alignments were used to

identify the fault trace. The positions of the observed similarities were spatially

projected in ArcMap.

I examined the topography beyond the river channels between Cerro Salinas and

Montecito for signs of uplift; according to Ellis and Densmore (2006), thrust-related

topography is asymmetric, where the steeper, narrower flank will face the direction of

the fault vergence (Fig. 2.3). In Matlab, using a 30-m resolution digital elevation model (DEM), I measured five 1-km wide elevation swaths perpendicular to the projected thrust fault (Fig. 2.2). The swaths show the maximum, minimum, and mean elevation (averaged from the 1-km wide area), and were examined for steep, abrupt

elevation inflections. The swath positions and inflection point locations were then

spatially projected in ArcMap.

Figure 2.3. Schematic drawing of a thrust-related tectonic topography curve, consisting of an asymmetric range in which the narrow and steeper flank faces the direction of fault vergence. Modified from Ellis and Densmore, 2006.

2.2 Results

The downloaded GPS river positions were projected in ArcMap, overlying the

ASTER imagery. The three mapped rivers all flow across the Sierra de Las Peñas and, as they enter the foreland, intersect the Las Peñas thrust. The drainage pattern changes from sinuous to reticulate/braided and then back to sinuous over the 15-km of foreland the rivers cross before being canalized for flood control. Although the three rivers flow roughly parallel to one another, in the sections that were measured

Rivers 1 and 3 exhibit a SE flow direction, whereas River 2 is oriented E (Fig. 2.2).

Overall, the three rivers’ bank heights increase upstream (Table 2.1). However, the heights varied between the rivers, as well as within the rivers. The maximum, minimum, and average bank heights above the river channel for River 1 are 4.2 m,

1.0 m, and 2.8 m respectively. In River 2, these values are 3.2 m, 0.2 m, and 1.7 m, and in River 3 these values are 2.8 m, 0.1 m, and 1.0 m. I projected the bank heights and aligned the first increase in bank height, which revealed a common rise and fall to approximately 3-m above the river channel in all three rivers (Fig. 2.4).

A sinuosity index value of 1.3 is typically the boundary value separating straight from meandering channels (Assine, 2005). The average sinuosity indices for the entire length of Rivers 1and 3 is 1.2, and for River 2 is 1.1. Maximum indices calculated for segments range from 1.3 to 1.6 (Table 2.2). Aligning the projected sinuosity indices measured between segments reveals a trend where the rivers are relatively

River 1 River 2 Point Height Latitude Longitude Point Height Latitude Longitude R1_01 3.20 -32.3870 -68.6873 R2_N3 1.40 -32.3497 -68.7201 R1_02 2.30 -32.3863 -68.6898 R2_N2 1.55 -32.3484 -68.7223 R1_03 2.40 -32.3851 -68.6921 R2_N1 2.10 -32.3491 -68.7248 R1_04 2.20 -32.3836 -68.6941 R2_01 2.90 -32.3480 -68.7272 R1_05 2.90 -32.3822 -68.6962 R2_02 2.60 -32.3463 -68.7289 R1_06 2.40 -32.3805 -68.6980 R2_03 2.10 -32.3453 -68.7313 R1_07 2.80 -32.3806 -68.7007 R2_04 1.50 -32.3449 -68.7340 R1_08 3.00 -32.3804 -68.7033 R2_05 1.55 -32.3447 -68.7366 R1_09 3.40 -32.3791 -68.7056 R2_06 1.60 -32.3447 -68.7393 R1_10 2.90 -32.3775 -68.7075 R2_07 2.50 -32.3448 -68.7419 R1_11 3.30 -32.3762 -68.7097 R2_08 3.20 -32.3446 -68.7446 R1_12 3.80 -32.3743 -68.7111 R2_09 3.00 -32.3445 -68.7473 R1_13 3.20 -32.3729 -68.7132 R2_10 1.80 -32.3452 -68.7498 R1_14 4.10 -32.3722 -68.7157 R2_11 1.65 -32.3454 -68.7525 R1_15 3.90 -32.3723 -68.7183 R2_12 0.60 -32.3454 -68.7551 R1_16 4.20 -32.3707 -68.7202 R2_13 0.70 -32.3454 -68.7577 R1_17 2.80 -32.3685 -68.7206 R2_14 0.45 -32.3452 -68.7604 R1_18 2.80 -32.3688 -68.7232 R2_15 0.20 -32.3445 -68.7630 R1_19 3.25 -32.3670 -68.7247 R1_20 4.20 -32.3666 -68.7274 River 3 R1_21 3.20 -32.3661 -68.7301 Point Height Latitude Longitude R1_22 2.30 -32.3647 -68.7323 R3_01 0.15 -32.3337 -68.7259 R1_23 2.20 -32.3642 -68.7348 R3_02 0.90 -32.3319 -68.7275 R1_24 3.00 -32.3629 -68.7370 R3_03 1.65 -32.3316 -68.7302 R1_25 2.90 -32.3613 -68.7389 R3_04 1.80 -32.3306 -68.7326 R1_26 2.80 -32.3603 -68.7413 R3_05 2.80 -32.3285 -68.7344 R1_27 2.10 -32.3594 -68.7437 R3_06 1.70 -32.3280 -68.7368 R1_28 2.30 -32.3579 -68.7458 R3_07 0.60 -32.3272 -68.7393 R1_29 1.70 -32.3573 -68.7484 R3_08 0.90 -32.3265 -68.7418 R1_30 1.60 -32.3564 -68.7508 R3_09 0.40 -32.3264 -68.7445 R1_31 1.00 -32.3560 -68.7535 R3_10 0.35 -32.3269 -68.7472 R1_32 1.50 -32.3560 -68.7561 R3_11 0.25 -32.3264 -68.7498 R1_33 1.40 -32.3562 -68.7588 R3_12 0.10 -32.3262 -68.7525

Table 2.1. Bank heights measured in meters above the river channel in River 1, River 2, and River 3. Note that the first point (R#-01) is the furthest downstream, and the ID’s sequentially increase upstream.

Figure 2.4. Bank heights measured during the river trace in River 1, River 2, and River 3. The positions of Rivers 2 and 3 have been shifted to align the common bank height rise to ~3-m (circled in yellow). This location is spatially projected on Figure 2.2.

straight (index value ~1.1), then increase to ~1.4, and drop off sharply to ~1.1 again.

(Fig. 2.5).

Figure 2.5. Sinuosity indices measured between bank height measurement segments from River 1, River 2, and River 3. The positions of Rivers 2 and 3 have been shifted to align the common sinuosity rise-and-fall location (circled in blue). This location is spatially projected on Figure 2.2.

River 1 Segment Channel Measured Sinuosity Start End Distance (m) Distance (m) R1_01 R1_33 9278.39 7544.97 1.2 R1_01 R1_02 280.64 250.99 1.1 R1_02 R1_03 300.46 255.58 1.2 R1_03 R1_04 293.99 248.87 1.2 R1_04 R1_05 292.60 251.05 1.2 R1_05 R1_06 275.81 253.78 1.1 R1_06 R1_07 293.03 254.10 1.2 R1_07 R1_08 334.95 251.40 1.3 R1_08 R1_09 298.23 252.63 1.2 R1_09 R1_10 413.00 253.49 1.6 R1_10 R1_11 267.80 252.95 1.1 R1_11 R1_12 254.75 247.90 1.0 R1_12 R1_13 297.76 248.58 1.2 R1_13 R1_14 253.08 249.96 1.0 R1_14 R1_15 274.83 248.65 1.1 R1_15 R1_16 259.01 250.73 1.0 R1_16 R1_17 326.30 247.71 1.3 R1_17 R1_18 303.30 254.88 1.2 R1_18 R1_19 269.39 248.40 1.1 R1_19 R1_20 314.42 259.58 1.2 R1_20 R1_21 264.11 254.25 1.0 R1_21 R1_22 292.92 253.03 1.2 R1_22 R1_23 253.75 250.27 1.0 R1_23 R1_24 270.51 250.30 1.1 R1_24 R1_25 348.74 250.37 1.4 R1_25 R1_26 266.12 249.15 1.1 R1_26 R1_27 327.71 250.95 1.3 R1_27 R1_28 260.31 253.31 1.0 R1_28 R1_29 257.75 252.94 1.0 R1_29 R1_30 321.04 251.21 1.3 R1_30 R1_31 261.20 251.59 1.0 R1_31 R1_32 278.02 251.23 1.1 R1_32 R1_33 272.85 253.04 1.1 continued

Table 2.2. Sinuosity indices measured for River 1, River 2, and River 3. Note that the first point (R#-01) is the furthest downstream, and the ID’s sequentially increase upstream.

Table 2.2 continued.

River 2 Segment Channel Measured Sinuosity Start End Distance (m) Distance (m) R2_N3 R2_15 4603.32 4074.82 1.1 R2_N3 R2_N2 275.54 250.83 1.1 R2_N2 R2_N1 268.62 250.55 1.1 R2_N1 R2_01 268.94 253.11 1.1 R2_01 R2_02 283.45 251.44 1.1 R2_02 R2_03 255.43 250.89 1.0 R2_03 R2_04 256.34 252.16 1.0 R2_04 R2_05 260.25 249.73 1.0 R2_05 R2_06 330.65 251.26 1.3 R2_06 R2_07 276.15 249.78 1.1 R2_07 R2_08 260.60 254.53 1.0 R2_08 R2_09 272.47 249.67 1.1 R2_09 R2_10 266.11 251.29 1.1 R2_10 R2_11 260.22 251.73 1.0 R2_11 R2_12 265.32 249.45 1.1 R2_12 R2_13 253.83 244.68 1.0 R2_13 R2_14 285.14 259.20 1.1 R2_14 R2_15 264.24 252.09 1.0

River 3 Segment Channel Measured Sinuosity Start End Distance (m) Distance (m) R3_01 R3_12 3092.81 2641.30 1.2 R3_01 R3_02 270.96 251.96 1.1 R3_02 R3_03 258.93 253.93 1.0 R3_03 R3_04 270.14 253.19 1.1 R3_04 R3_05 354.66 250.76 1.4 R3_05 R3_06 314.49 249.10 1.3 R3_06 R3_07 269.16 251.30 1.1 R3_07 R3_08 266.51 250.97 1.1 R3_08 R3_09 288.76 253.18 1.1 R3_09 R3_10 269.34 253.01 1.1 R3_10 R3_11 262.18 253.88 1.0 R3_11 R3_12 267.67 253.42 1.1

The shapes of the swath profiles differ from north to south. The north-most swath (A-

A’), located closest to Cerro Salinas, shows an abrupt steepening in the maximum

elevation of ~7.7-m (Fig. 2.6). This was the largest elevation inflection identified in all five swaths. Smaller inflections ranging from ~1-m to ~1.2-m were observed in the maximum elevations of the other four swaths (Fig. 2.6). The observed inflections were inferred as tectonic topography, and the projected locations were used to connect the Cerro Salinas and Montecito structures.

continued

Figure 2.6. Elevation swaths measured between the Cerro Salinas and Montecito anticlines. Top and bottom gray lines show elevation maximums and minimums, respectively, within the 1-km wide swath, and black center lines show averages. Inflections in elevation are circled in green. The locations of these swaths and the inflection points are shown on Figure 2.2.

Figure 2.6. continued:

2.3 Discussion

The main feature of a stream’s response to uplift is incision in the uplifted area

(Ouchi, 1985). Furthermore, the development of positive topography above the depositional plane is due to uplift exceeding aggradation. In order for a transverse river to maintain a foreland-ward gradient across a rising fold/fault, erosion through the uplift crest must be achieved (Burbank et al., 1996). Therefore, we interpret the observed rise in bank height in all three rivers to ~3-m to be the rivers’ response to

uplift: in order to maintain baselevel, the rivers have incised into the foreland strata.

This also indicates the erosion rate of the rivers is greater than the uplift rate of the

foreland structure.

A river will degrade at the uplifted crest and aggrade directly upstream and

downstream in response to uplift. Channel straightening (sinuosity decrease) will

occur upstream from the uplift in response to decrease in channel gradient.

Downstream of the area of uplift, an increase in channel gradient will cause the river

to increase erosion in order to maintain gradient, which results in an increase in

sinuosity (Ouchi 1985). The trend in our data matches this description, which

suggests uplift is occurring directly downstream of the sites where sinuosity shows changes consistent between the three rivers.

An alternate explanation for the increase in sinuosity is related to geomorphic processes: channel patterns are controlled by discharge and load (Leopold and

Wolman, 1957), which are ultimately determined by slope (Twidale, 2004). As the streams flow from the Andes, the patterns shift from straight to anastomose form.

Anastomose type rivers are typical where flow strength and gradients are low

(Twidale, 2004). Therefore, the change in gradient as the rivers flow from the Andes onto the gentle foreland may explain the increase in sinuosity. However, we reject this hypothesis due to observations of increased bank height at the same location as the sinuosity shift.

We interpret the elevation inflections observed in the swaths as evidence for the continuation of the Cerro Salinas thrust beyond the southern tip of Cerro Salinas. In modeling surface behavior over a blind thrust fault, Ellis and Densmore (2006) show that thrust-related topography results in an asymmetric range, where the steeper, narrower flank faces in the direction of fault vergence (Fig. 2.3). The shapes of the elevation inflections identified in our swaths appear west-vergent (Fig. 2.6), which suggest the Cerro Salinas thrust is being expressed.

Additionally, Ellis and Densmore (2006) show that a greater ground displacement will be expressed when the buried fault tip is closer to the surface. We believe that if a buried fault is plunging that this would be reflected by the amount of displacement observed at the surface. Therefore, we reason that the inflection in the northern swath is larger than the inflections observed in the other swaths due to the depth of the plunging Cerro Salinas thrust. The smaller inflections observed in the other swaths could either be due to the depth of the thrust or that erosion is significant enough to prevent significant surficial expression.

Applying our methodology to observations reported by Bohon (2008) suggests that similar forcings are at play west of the Montecito anticline. Before crossing the structure, rivers have incised the alluvial fans upstream from the west limb.

Downstream of this, sinuosity indices of ~1.6 and 1.4 were measured in the Quebrada

34 de las Vacas and Quebrada Jejenes, respectively (Bohon, 2008). The geomorphic signature of incision upstream and increased sinuosity downstream indicates the projection of the blind thrust fault associated with Montecito along the west flank of the anticline (Fig. 2.2).

The common changes in bank heights and sinuosity indices of three rivers are nearly coincident along their lengths. When connected, the common bank height locations and sinuosity maxima are approximately parallel to the faults associated with the

Central and Eastern Precordilleras, but form an en echelon trend with the Cerro

Salinas and Montecito thrusts (Fig. 2.2). Because we argue the changes in bank height and sinuosity reflect uplift along a blind thrust, we interpret these as evidence for the presence of a buried thrust located between the Cerro Salinas and Montecito structures (Fig. 2.2). This would indicate three individual structures are present in this region.

Alternatively, the three faults (the Cerros Salinas thrust, projected Montecito fault, and the newly identified fault) lie approximately parallel to one another. The elevation inflections suggest a connection by a through-going buried fault: the largest inflection was observed in the swath closest to the southern tip of the Cerro Salinas structure, whereas smaller inflections were expressed in the four other swaths. We interpret this as the southern continuation and plunging of the Cerro Salinas thrust south of the structure. However, due to limited constraints, we have projected the

35 through-going continuation of the Cerro Salinas fault as a straight line trending 57° from the southern tip of Cerro Salinas to the northern tip of the projected Montecito thrust (Fig. 2.2).

Whether there are three individual, en echelon structures or one structure connected by a through-going fault, we suggest the structures are related to the west-vergent

Sierras Pampeanas. This agrees with Vergés et al. (2007), who describe a low-angle, east vergent blind fore thrust ramp connecting with the Cerro Salinas thrust, forming a west-vergent back thrust (Fig. 2.7). Since we suggest the Cerro Salinas and

Montecito structures may be connected by the southern continuation of the Cerro

Salinas thrust, the uplift of Montecito also may be controlled by a west-vergent tectonic wedge at depth. Extending the Cerro Salinas thrust increases the tectonic threat for the region because a through-going structure between San Juan and

Mendoza enhances the potential for large earthquakes under these cities.

The existence and position of the buried Cerro Salinas thrust fault could be supported with seismic reflection data. However, until MCS data becomes available, our results remain unconfirmed.

alinas alinas

Schematic cross section along MCS profile 31017 showing the tectonic wedge at depth below the Cerro S Cerro the below depth at wedge tectonic the showing 31017 profile MCS along section cross Schematic

. Figure 2.7Figure 2007. al., et Vergés from Modified monocline.

CHAPTER 3:

REGIONAL-SCALE DRAINAGE DEFLECTIONS

3.1River Deflections

Deflection is a typical response for a river that encounters a longitudinal change in grade. Whether this occurs away from an uplifting fault/fold tip or into a zone of subsidence, the result is an abrupt shift in the drainage direction from perpendicular to the average gradient over a limited spatial distance (Holbrook and Schumm, 1999).

An observed change in a river’s course, such as a deflection, is considered to be an anomalous occurrence. Mapping and plotting a region’s drainage anomalies can be a way to diagnose the transient state of a tectonically active region (Wobus et al.,

2006). Burrato et al. (2003) examined the distribution of drainage anomalies to identify blind thrust faults in the Po Valley, Italy. Our approach applied and extends their methodology to the Andean foreland by examining the drainage for deflection anomalies.

3.1.1 Methods

A regional examination for drainage anomalies in the form of river deflections was conducted. Elevation data for the study area was obtained from two online sources:

HydroSHEDS (Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales; http://hydrosheds.cr.usgs.gov) and ERSDAC (Earth Remote

Sensing Data Analysis Center; http://www.gdem.aster.ersdac.or.jp/index.jsp).

HydroSHEDS elevation data was derived from SRTM DEMs (Shuttle Radar

Topography Mission Digital Elevation Model) with 90-m resolution. ERSDAC

elevation data was derived from ASTER GDEM (Global Digital Elevation Model)

with 30-m resolution. ASTER imagery with 15-m resolution was also acquired for the area of interest.

HydroSHEDS data includes stream-network vectors derived from elevation data with algorithms already applied, including void-filling, filtering, stream burning, and upscaling techniques. These algorithms were applied to improve the original SRTM data (Lehner et al., 2006). In contrast, the elevation data obtained from ERSDAC was less processed. Using ArcTools, I applied a void-filling algorithm to the GDEM prior to building a drainage direction map. From the drainage direction map, stream- network vectors were derived.

Comparison of the stream-network vectors to rivers seen on the ASTER imagery revealed some discrepancies (Fig. 3.1). This is because regions with low relief are susceptible to errors in the drainage extraction algorithm (Lehner et al., 2006).

Streams sections that deviated more than 2 km from their positions in the ASTER images were laterally adjusted by hand tracing to match the DEM-based river

network and the image-derived rivers as closely as possible. A 2-km buffer was

chosen because it required adjustment of approximately 10% of the stream-network

vectors.

Figure 3.1. Map showing sections of river (yellow boxes) where the HydroSHEDS stream-network vectors (blue lines) deviated from the ASTER imagery beyond the 2-km buffer (black dashed lines). Areas such as these were adjusted to match the HydroSHEDS and ERSDAC stream-network vectors and the image-derived river as closely as possible.

River deflections were determined using adjusted stream positions. We defined a

drainage anomaly as a drainage divergence from the average topographic gradient

greater than 10° persisting for more than 5-km. Deflections were measured as a

drainage vector intersected a 10-m contour interval. Drainage anomalies were

identified using two methods which we call the trans-contour method and the

Burrato-method. The trans-contour method examined a 5-km reach of stream, 2.5-km

upstream and 2.5-km downstream of the river-contour intersection, and defined the

average flow direction as being perpendicular to a 1-km contour interval average

(Fig. 3.2a,b). The Burrato-method, modified from Burrato et al. (2003), examined a

5-km reach of stream downstream of the contour interval. The average flow direction was determined to be perpendicular to the average-strike contour of the down-slope contour (Fig. 3.2c,d).

Figure 3.2. Schematic drawings of the tools used to measure stream divergences and examples of how these tools were used to identify stream deflections. a) The trans-contour method tool measured divergences greater than 10° over 2.5 km upstream and 2.5 km downstream of the contour intersection, totaling a 5 km reach. b) Two examples showing how the tool was used to measure stream divergences, showing an anomaly where stream 2 crosses the 120-m contour line. c) The Burrato- method tool measured divergences greater than 10° over a 5 km reach in the flowing direction of the drainage network. d) Two examples showing how the tool was used to measure stream divergences, showing an anomaly where stream 2 crosses the 120-m contour line.

3.1.2 Results

As one purpose of this study is to refine the methods for identifying and interpreting drainage anomalies, we here present methods and data sets which did not produce useful data, including our findings from longer (10 km) and shorter (2 km) stream reach measurements. We also compare HydroSHEDS and GDEM results.

The HydroSHEDS drainage vectors were examined for a study area of 31°30’ to

34°S latitude and 67° to 69°30’W longitude. The trans-contour method was applied

along a 5 km reach to identify river deflections of the HydroSHEDS drainage vectors

at 20 m contour intervals. This identified 174 anomalies, of which approximately

13% are located in currently occupied channels (Fig. 3.3).

Variables, such as the stream length reach and the contour interval frequency, were

explored in order to refine the methodology. I limited my study area to the foreland

between 32°30’ to 33°30’S latitude and 67° to 68°15’W longitude. This limited area

was chosen because 20 anomalies had been identified and it contained original and

adjusted HydroSHEDS rivers (Fig. 3.4a). Increasing the stream reach to 10 km, the

20 previously identified anomaly locations were retested, which reduced the anomaly frequency to 17 locations (Fig. 3.4b). Decreasing the stream reach to 2 km identified

30 anomalies (20, 5 km reach anomalies and 10 new locations; Fig. 3.4c). Increasing the contour interval to 10 m and testing for anomalies along a 5 km reach identified

39 anomalies (20, 20 m interval and 19, 10 m interval anomalies; Fig. 3.4d).

Figure 3.3. Regional map showing the distribution of anomalies identified using the trans-contour method, 5 km tool, 20 m contour interval, and the HydroSHEDS elevation model-derived drainage- vectors and topographic contours.

Figure 3.4. Maps showing the limited test area and variables used for the trans-contour drainage deflection method: a) 5 km tool, 20 m contour interval, b) 10 km tool, 20 m contour interval, c) 2 km tool, 20 m contour interval, d) 5 km tool, 10 m contour interval. Note that despite the changes, no spatial distribution pattern is observed. 45

Changing the variables revealed consistent findings with the trans-contour anomaly locations. Due to the low relief of the foreland, only by increasing the contour density did I find additional information that I felt was relevant. Therefore, I systematically determined that examining a 5 km reach of river at the 10 m contour intervals would be the optimal combination for this investigation. Using this combination of reach length and contour interval, I also applied the Burrato-method to HydroSHEDS rivers located downstream of the irrigation-dominated areas. This identified 78 anomaly locations, of which approximately 13% are located in currently occupied channels

(Fig. 3.5).

The ERSDAC drainage vectors were derived for a study area between 32°’ to 34°S latitude and 67° to 69°W longitude. This study area is more limited than the study area discussed above due to a lack of anomalous drainage deflections identified during the HydroSHEDS investigation. Furthermore, although the trans-contour method was applied to the entire study area, the Burrato-method was only applied to the foreland downstream of the irrigation-dominated areas. The trans-contour method identified 106 anomalies (Fig. 3.6) and the Burrato-method identified 70 anomalies

(Fig. 3.7). Approximately 27% and 26%, respectively, of the identified anomalies were located in currently occupied channels.

Detailed information pertaining to the drainage anomalies identified above is provided as Appendix A.

Figure 3.5. Regional map showing the distribution of anomalies identified using the Burrato-method, 5 km tool, 10 m contour interval, and the HydroSHEDS elevation model-derived drainage-vectors and topographic contours.

Figure 3.6. Regional map showing the distribution of anomalies identified using the trans-contour method, 5 km tool, 10 m contour interval, and the ERSDAC elevation model-derived drainage-vectors and topographic contours.

Figure 3.7. Regional map showing the distribution of anomalies identified using the Burrato-method, 5 km tool, 10 m contour interval, and the ERSDAC elevation model-derived drainage-vectors and topographic contours.

3.1.3 Discussion

Locations where both the trans-contour and Burrato-methods identified drainage

anomalies were limited. The HydroSHEDS data shows ~5% overlap (12 overlapping

locations) and the ERSDAC data shows ~7% overlap (12 overlapping locations). This

indicates the two methods (trans-contour and Burrato) identify different types of river deflections. This is most obvious in the distribution of anomalies across the Alto del

Desaguadero: for example, using the ERSDAC data, 19% (13 locations) of the anomalies identified using the Burrato-method are located within the Alto del

Desaguadero boundaries, versus 9% (10 anomaly locations) identified using the trans- contour method.

Despite using two sets of elevation data and two drainage deflection identification methods, the distribution of four sets of anomalies does not reveal any sort of spatial pattern that suggests tectonic forcing. This indicates that either 1) there is no tectonic activity in the Andean foreland or 2) this approach does not work to infer uplift in this region. If the latter, we believe this could result from the methodology limiting our deflection locations (to drainage/contour intersections), our scale (too small to examine regional patterns), and/or not examining the vertical component (incision) associated with a river’s response to uplift.

Regional-scale drainage shows the Río Mendoza shifting direction ~90° to flow north as it drains from the Andes. When it joins with the Río San Juan, it changes direction

~90° to flow east, then bends ~45° south of east before converging with the Río

Desaguadero. At this confluence, another ~90° turn to the south is seen. Abrupt shifts like these are typical in rivers flowing around an uplift or into a zone of subsidence

(Holbrook and Schumm, 1999). Alternatively, shifting of channels by avulsion is also commonly observed in alluvial megafans; note that the Ríos Mendoza and Tunuyán flow within 15-km of one another, but instead of continuing on its northward course, the Río Tunuyán bends ~45° to flow SE until joining the Río Desaguadero. The fan- shaped topography extending into the foreland from this deflection point suggests the presence of a megafan: a large (103 to 105-km2) fan-shaped clastic deposit at the outflow point of mountainous drainages (Horton and DeCelles, 2001). Whether the

forces driving the changes in regional drainage are tectonic or geomorphic could not

be determined by this drainage-deflection approach.

The DEM-derived rivers were manually edited to better overlap with the ASTER

image-derived rivers; this prevented the extraction of stream gradient data from the

DEM. Therefore, we did not include channel longitudinal profiles in our

investigation, foregoing the possibility of discovering vertical anomalies (such as

knickpoints or changes in gradient). The spatial projection of vertical drainage

anomalies has been used in past studies to diagnose the transient state of a region and

to delineate tectonic boundaries (Wobus et al., 2006).

The lower resolution of the HydroSHEDS elevation models compared to the

ERSDAC elevation models is reflected in the drainage vectors and elevation

topography lines. This was evident as the drainage vectors derived from the ERSDAC

elevation models required less manual editing to overlap with the ASTER image-

derived rivers than those derived from HydroSHEDS.

3.2 Alto del Desaguadero

Perhaps the most obvious regional-scale drainage anomaly in the study area is the

Alto del Desaguadero. The drainage-vectors derived from both the HydroSHEDS and

ERSDAC elevation models predict that rivers should be draining across this area (e.g.

Fig. 3.3; Fig. 3.6), yet we observe the current river courses and paleochannels have

3 2 been deflected around this 3x10 km area since the Pleistocene (Fig. 1.2c; Fig. 1.6).

Because of this discrepancy, this area was further investigated. Our approach

addresses two of the weaknesses of the drainage deflection methods discussed above:

we investigate drainage on the regional-scale and consider vertical shifts in topography.

3.2.1 Methods

Since the limits of the Alto del Desaguadero have not been defined, I attempted this based on changes in elevation that may be associated with a rising tectonic structure.

In Matlab, using the ERSDAC elevation model, I extracted six 1-km wide W-E elevation swaths and four 1-km wide N-S elevation swaths across the approximate

Figure 3.8. Elevation swath and elevation inflection point locations across the Alto del Desaguadero. The shape of the Alto del Desaguadero (black dashed lined) was inferred from the locations of the inflection points.

53 location of the Alto del Desaguadero (Fig. 3.8). The ERSDAC elevation model was used because of its higher resolution compared to the HydroSHEDS elevation model.

These swaths show the maximum, minimum, and mean elevation (averaged from the

1-km wide area). The plots were examined for narrow, steep elevation inflections, especially on the western flank, which we interpret as the topographic divide between the forelimb and backlimb associated with a buried thrust (Fig. 2.2; Ellis and

Densmore, 2006). These inflections were then spatially projected in ArcMap to approximate the limits of the Alto del Desaguadero.

3.2.2 Results

The shapes of the W-E swaths are similar to one-another in that, from west to east, we observe a steep, narrow increase in elevation before a long elevation decrease (Fig.

3.9). We interpret these to be the western edge of the Alto del Desaguadero. Further east from the decreasing elevation segment, another elevation inflection was interpreted as the eastern boundary of the Alto del Desaguadero (Fig. 3.9). East of this point is the Río Desaguadero floodplain. The inflection points were used to delineate the western and eastern boundaries of the Alto del Desaguadero (Fig. 3.8).

continued

Figure 3.9. W-E elevation swath profiles measured across the Alto del Desaguadero. Inflections in elevation are circled in green and the approximate Río Desaguadero location is indicated by the blue arrow. The locations of these swaths and the inflection points are shown on Figure 3.8.

Figure 3.9. continued:

continued

Figure 3.10. N-S elevation swaths measured across the Alto del Desaguadero. Inflections in elevation are circled in green. The locations of these swaths and the inflection points are shown on Figure 3.8.

Figure 3.10. continued:

In contrast to the W-E swaths, the N-S swaths are parallel to the regional topographic

gradient. Because the overall change in elevation across the swath is gradual, the

inflections are less apparent. However, inflections could still be identified (Fig. 3.10)

and used to define the northern and southern boundaries of the Alto del Desaguadero

(Fig. 3.8).

3.2.3 Discussion

Although tectonic activity is not prevalent under the Alto del Desaguadero (Siame et

al., 2006), I argue that the topographic shape and lack of drainage flowing across the

Alto del Desaguadero could be caused by the basement uplift associated with the

thick-skinned Sierras Pampeanas. We interpret the inflections observed in our swaths

as the topographic response to uplift. The spatial distribution of these inflection points

delineates a rectangular shape in the Andean foreland. Connecting these points

provides the boundaries for the Alto del Desaguadero, an area approximately 3x103- 58

km2 (Fig. 3.8). This is comparable to the Sierra Pie de Palo is size, shape, and structure.

Paleochannels indicate that the Ríos Mendoza and Tunuyán once flowed together

northward towards the Río San Juan during the Pleistocene (Stage 1, Fig. 1.6;

Perucca, 1994). These rivers split and began to circumvent the area we now call the

Alto del Desaguadero (Stage 2, Fig. 1.6). The Río Mendoza continued to be diverted

to the west away from this area, whereas the Río Tunuyán migrated to the south

(Stages 3&4, Fig. 1.6). Current channels of the Ríos Mendoza and Tunuyán continue

to flow around the periphery of the Alto del Desaguadero (Fig. 1.6). The Río

Desaguadero is also shifted away from the Alto del Desaguadero, shown by its

position to the east in its floodplain in the W-E swaths (Fig. 3.9).

A similar influence on drainage is recorded in the paleodrainage flowing around the

Sierra Pie de Palo. The Río San Juan was once located along the west-flank of the structure (Stage 2, Fig. 1.6), but has migrated to the west to its present position. North of its confluence with the Río San Juan, paleochannels of the Río Desaguadero also indicate a shift to the east, away from the Pie de Palo. The resemblance to the current drainage pattern and to paleochannels flowing around the Alto del Desaguadero corroborate our hypothesis that a rising structure would cause rivers to avulse toward the lower/downtilted side of the floodplain.

The possibility for a growing basement wedge in the Andean foreland implies increased seismic hazards for the surrounding areas. Furthermore, rapid uplift like the

1.2-m vertical displacement of Pie de Palo, caused by the 1977 M 7.4 earthquake

(Martínez et al., 2008), could have dire consequences. Additional data, such as MCS profiles, constraints on paleochannels ages, and Alto Desaguadero uplift rates, would help determine if a tectonic threat is buried beneath the Andean foreland.

CHAPTER 4:

CONCLUSIONS

The connection of the Cerro Salinas and Montecito anticlines by the southern extension of the Cerro Salinas thrust has been previously suggested (e.g. Vergés et al., 2007) but never confirmed. If the thrust is indeed propagating south, we expected to see the influence of uplift in the geomorphology of the rivers flowing between these structures. The mapping of these rivers indicates a change in river pattern from straight to anastomose form, as well as increases in sinuosity and bank height. We interpret these changes as the rivers’ response to uplift of the buried Cerro Salinas thrust: the change in river pattern results from a change in gradient across the thrust, and the increase in bank height is indicative of the incision through the uplifted foreland strata. Additionally, the shape and direction of the elevation inflections identified in the elevation swaths between the Cerro Salinas and Montecito structures supports this hypothesis. Although it does not confirm the connection of Cerro

Salinas and Montecito, it provides evidence for a subsurface, west-vergent structure beyond the southern tip of Cerro Salinas, which we interpret to be the subsurface continuation of the Cerro Salinas thrust.

At the regional scale, drainage anomalies identified from deflections in drainage

yielded inconclusive results as the spatial distribution of four sets of anomalies does

not reveal any sort of pattern suggestive of tectonic forcing. We believe this was

either due to the lack of tectonic activity in the study area, or from our methodology

limiting our scale and omitting the vertical component (incision) associated with a

river’s response to uplift.

To resolve the two shortcomings in the drainage deflection approach, we increased

our scale to examine the region’s drainage as a whole. Modern- and paleochannels

reveal the absence of drainage flowing across the Alto del Desaguadero, and

paleochannel occupation order indicates the Ríos Mendoza, Tunuyán, and

Desaguadero have shifted away from this area over time. This is similar to the

paleochannel patterns of the Ríos San Juan and Desaguadero shifting away from the

rising Sierra Pie de Palo. Inflections in W-E and N-S swaths across this area suggest

the influence of from tectonic forcing, possibly due to a rising basement structure

similar to the Sierra Pie de Palo.

Unlike the traditional methods to identify subsurface tectonic features, which have

generally been limited to seismic exploration and/or the recognition of anticlinal hills above the projected fault tip, our study indicates that a geomorphic approach can be used to reveal buried tectonic features at both the individual structural-scale and the regional-scale. However, because our methods are limited to surface exploration and

62 data collection, confirmation of our results relies on additional data, such as MCS profiles.

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APPENDIX A:

DRAINAGE ANOMALY DATA

HydroSHEDS; Trans-contour method; 5-km tool; 20-m contours River: Adjusted or Topo Line Anomaly ID HydroSHEDS Latitiude Longitude Crossed Original L1 520 Adjusted -33.966 -67.752 L2 580 Adjusted -33.915 -67.939 L3 880 HydroSHEDS -33.852 -68.440 L4 1000 Adjusted -33.846 -68.506 L5 960 Adjusted -33.827 -68.468 L6 980 Adjusted -33.818 -68.473 L7 1000 Adjusted -33.807 -68.476 L8 800 HydroSHEDS -33.831 -68.331 L9 820 Adjusted -33.802 -68.412 L10 840 Adjusted -33.801 -68.427 L11 860 Adjusted -33.800 -68.441 L12 920 Adjusted -33.785 -68.471 L13 780 Adjusted -33.827 -68.314 L14 800 Adjusted -33.808 -68.328 L15 620 Adjusted -33.724 -68.084 L16 860 HydroSHEDS -33.740 -68.374 L17 880 HydroSHEDS -33.731 -68.401 L18 920 HydroSHEDS -33.716 -68.439 L19 1060 HydroSHEDS -33.719 -68.539 L20 580 HydroSHEDS -33.606 -68.053 L21 740 HydroSHEDS -33.712 -68.263 L22 820 HydroSHEDS -33.673 -68.332 L23 600 HydroSHEDS -33.500 -68.133 L24 1040 HydroSHEDS -33.606 -68.526 L25 940 HydroSHEDS -33.514 -68.467 L26 1060 HydroSHEDS -33.527 -68.575 L27 920 HydroSHEDS -33.494 -68.455 L28 640 HydroSHEDS -33.376 -68.297 L29 640 HydroSHEDS -33.352 -68.319 L30 760 Adjusted -33.351 -68.349 L31 840 HydroSHEDS -33.426 -68.430 L32 680 Adjusted -33.328 -68.407 L33 440 HydroSHEDS -33.867 -67.116 L34 480 Adjusted -33.692 -67.420 L35 500 Adjusted -33.652 -67.564 L36 560 HydroSHEDS -33.462 -67.922 L37 560 HydroSHEDS -33.381 -67.906 L38 580 HydroSHEDS -33.348 -68.018 L39 820 HydroSHEDS -33.306 -68.563 L40 920 HydroSHEDS -33.368 -68.577 L41 740 HydroSHEDS -33.255 -68.680 L42 780 HydroSHEDS -33.295 -68.690 L43 860 Adjusted -33.356 -68.678 L44 880 Adjusted -33.367 -68.675 L45 900 Adjusted -33.379 -68.669 L46 820 HydroSHEDS -33.365 -68.694 L47 960 Adjusted -33.535 -68.772 L48 820 HydroSHEDS -33.430 -68.840 L49 1000 HydroSHEDS -33.565 -68.768 continued

70 HydroSHEDS; Trans-contour method; 5-km tool; 20-m contours continued L50 1020 HydroSHEDS -33.573 -68.751 L51 1060 HydroSHEDS -33.581 -68.718 L52 1000 HydroSHEDS -33.587 -68.779 L53 880 HydroSHEDS -33.512 -68.860 L54 980 HydroSHEDS -33.621 -68.852 L55 1120 HydroSHEDS -33.706 -68.807 L56 1100 Adjusted -33.716 -68.871 L57 860 HydroSHEDS -33.502 -68.985 L58 860 HydroSHEDS -33.531 -68.990 L59 880 HydroSHEDS -33.569 -69.002 L60 900 HydroSHEDS -33.621 -68.999 L61 980 HydroSHEDS -33.723 -69.090 L62 920 Adjusted -33.655 -69.057 L63 1040 HydroSHEDS -33.694 -69.190 L64 880 HydroSHEDS -33.556 -69.031 L65 920 HydroSHEDS -33.539 -69.080 L66 1020 HydroSHEDS -33.485 -69.157 L67 880 HydroSHEDS -33.487 -69.009 L68 1000 HydroSHEDS -33.416 -69.119 L69 880 HydroSHEDS -33.472 -68.986 L70 900 Adjusted -33.459 -68.996 L71 820 Adjusted -33.333 -68.788 L72 840 Adjusted -33.310 -68.812 L73 1060 HydroSHEDS -33.293 -68.985 L74 1080 HydroSHEDS -33.293 -69.000 L75 1000 Adjusted -33.282 -68.952 L76 1020 Adjusted -33.275 -68.961 L77 820 HydroSHEDS -33.314 -68.777 L78 900 HydroSHEDS -33.222 -68.873 L79 1000 HydroSHEDS -33.169 -68.964 L80 1040 Adjusted -33.154 -68.981 L81 780 HydroSHEDS -33.226 -68.709 L82 460 Adjusted -33.550 -67.188 L83 460 Adjusted -33.508 -67.172 L84 500 Adjusted -33.443 -67.503 L85 580 HydroSHEDS -33.265 -67.976 L86 460 HydroSHEDS -33.427 -67.143 L87 480 Adjusted -33.392 -67.364 L88 620 HydroSHEDS -33.134 -68.170 L89 500 Adjusted -33.287 -67.483 L90 460 HydroSHEDS -33.242 -67.181 L91 460 Adjusted -33.210 -67.202 L92 460 HydroSHEDS -33.116 -67.192 L93 580 HydroSHEDS -33.136 -67.914 L94 620 HydroSHEDS -33.065 -68.172 L95 540 Adjusted -32.997 -67.646 L96 600 Adjusted -33.046 -67.935 L97 620 Adjusted -33.071 -68.025 L98 480 HydroSHEDS -32.860 -67.469 L99 540 HydroSHEDS -32.934 -67.737 L100 560 Adjusted -32.904 -67.825 L101 580 Adjusted -32.891 -67.907 L102 520 HydroSHEDS -32.858 -67.667 L103 560 HydroSHEDS -32.794 -67.860 L104 580 HydroSHEDS -32.845 -67.982 L105 500 HydroSHEDS -32.789 -67.586 L106 500 HydroSHEDS -32.722 -67.596 L107 500 HydroSHEDS -32.605 -67.615 L108 480 HydroSHEDS -32.696 -67.352 L109 480 Adjusted -32.578 -67.259 L110 520 Adjusted -32.363 -67.764 L111 500 HydroSHEDS -32.395 -67.509 L112 520 Adjusted -32.268 -67.789 continued

71 HydroSHEDS; Trans-contour method; 5-km tool; 20-m contours continued L113 580 HydroSHEDS -32.556 -68.298 L114 600 HydroSHEDS -32.723 -68.321 L115 660 HydroSHEDS -33.042 -68.571 L116 740 Adjusted -33.120 -68.702 L117 880 HydroSHEDS -33.056 -68.798 L118 900 HydroSHEDS -33.060 -68.804 L119 900 HydroSHEDS -33.060 -68.817 L120 940 HydroSHEDS -33.069 -68.861 L121 560 HydroSHEDS -32.376 -68.345 L122 880 HydroSHEDS -32.963 -68.855 L123 960 Adjusted -33.027 -68.887 L124 980 Adjusted -33.036 -68.903 L125 1000 Adjusted -33.045 -68.925 L126 820 Adjusted -32.921 -68.853 L127 1000 HydroSHEDS -32.942 -68.904 L128 720 Adjusted -32.863 -68.819 L129 620 Adjusted -32.723 -68.668 L130 900 Adjusted -32.819 -68.899 L131 600 Adjusted -32.631 -68.669 L132 720 HydroSHEDS -32.670 -68.789 L133 1000 HydroSHEDS -32.547 -68.890 L134 580 Adjusted -32.434 -68.658 L135 580 Adjusted -32.389 -68.630 L136 820 HydroSHEDS -32.291 -68.813 L137 620 Adjusted -32.298 -68.674 L138 620 Adjusted -32.247 -68.643 L139 560 HydroSHEDS -32.005 -68.473 L140 580 Adjusted -31.978 -68.498 L141 740 HydroSHEDS -31.952 -68.627 L142 700 HydroSHEDS -31.890 -68.586 L143 640 Adjusted -31.878 -68.553 L144 640 Adjusted -31.870 -68.565 L145 780 Adjusted -31.879 -68.619 L146 820 Adjusted -31.888 -68.632 L147 840 Adjusted -31.890 -68.637 L148 900 Adjusted -31.900 -68.658 L149 580 Adjusted -31.769 -68.520 L150 560 Adjusted -31.858 -68.375 L151 540 HydroSHEDS -32.054 -68.063 L152 620 HydroSHEDS -31.740 -68.115 L153 660 HydroSHEDS -31.728 -68.102 L154 700 HydroSHEDS -31.719 -68.098 L155 540 Adjusted -32.005 -68.017 L156 540 HydroSHEDS -31.984 -67.965 L157 500 Adjusted -32.341 -67.459 L158 500 HydroSHEDS -32.246 -67.377 L159 500 HydroSHEDS -32.232 -67.331 L160 540 Adjusted -32.273 -67.218 L161 600 HydroSHEDS -32.273 -67.160 L162 560 HydroSHEDS -32.427 -67.149 L163 600 HydroSHEDS -32.408 -67.104 L164 480 HydroSHEDS -32.595 -67.182 L165 660 HydroSHEDS -32.489 -67.076 L166 660 HydroSHEDS -32.490 -67.063 L167 520 Adjusted -32.673 -67.098 L168 660 HydroSHEDS -32.706 -67.002 L169 620 HydroSHEDS -32.756 -66.972 L170 580 HydroSHEDS -32.849 -66.959 L171 640 HydroSHEDS -32.855 -66.914 L172 660 HydroSHEDS -32.847 -66.865 L173 560 Adjusted -33.366 -67.029 L174 580 Adjusted -33.351 -67.020 continued

72 HydroSHEDS; Trans-contour method; 10-km tool; 20-contours in isolated AOI River: Adjusted or Topo Line Anomaly ID HydroSHEDS Latitiude Longitude Notes Crossed Original A1 620 HydroSHEDS -33.134 -68.170 L88 A2 500 Adjusted -33.287 -67.483 L89 A3 460 Adjusted -33.210 -67.202 L91 A4 460 HydroSHEDS -33.116 -67.192 L92 A5 580 HydroSHEDS -33.136 -67.914 L93 A6 620 HydroSHEDS -33.065 -68.172 L94 A7 540 Adjusted -32.997 -67.646 L95 A8 600 Adjusted -33.046 -67.935 L96 A9 620 Adjusted -33.071 -68.025 L97 A10 480 HydroSHEDS -32.860 -67.469 L98 A11 540 HydroSHEDS -32.934 -67.737 L99 A12 560 Adjusted -32.904 -67.825 L100 A13 580 Adjusted -32.891 -67.907 L101 A14 520 HydroSHEDS -32.858 -67.667 L102 A15 560 HydroSHEDS -32.794 -67.860 L103 A16 500 HydroSHEDS -32.789 -67.586 L105 A17 500 HydroSHEDS -32.722 -67.596 L106

Trans-contour method; 2-km tool; 20-contours in isolated AOI River: Adjusted or Topo Line Anomaly ID HydroSHEDS Latitiude Longitude Notes Crossed Original B1 500 HydoSHEDS -33.343 -67.507 B2 620 HydroSHEDS -33.134 -68.170 L88, A1 B3 500 Adjusted -33.287 -67.483 L89, A2 B4 500 HydroSHEDS -33.250 -67.483 B5 460 HydroSHEDS -33.242 -67.181 L90 B6 460 Adjusted -33.210 -67.202 L91, A3 B7 480 HydroSHEDS -33.164 -67.342 B8 460 HydroSHEDS -33.146 -67.196 B9 460 HydroSHEDS -33.116 -67.192 L92, A4 B10 580 HydroSHEDS -33.136 -67.914 L93, A5 B11 620 HydroSHEDS -33.065 -68.172 L94, A6 B12 540 Adjusted -32.997 -67.646 L95, A7 B13 600 Adjusted -33.046 -67.935 L96, A8 B14 620 Adjusted -33.071 -68.025 L97, A9 B15 560 Adjusted -33.010 -67.810 B16 500 HydroSHEDS -33.027 -67.520 B17 480 HydroSHEDS -32.860 -67.469 L98, A10 B18 540 HydroSHEDS -32.954 -67.730 B19 540 HydroSHEDS -32.934 -67.737 L99, A11 B20 560 Adjusted -32.904 -67.825 L100, A12 B21 580 Adjusted -32.884 -67.887 B22 580 Adjusted -32.891 -67.907 L101, A13 B23 520 HydroSHEDS -32.858 -67.667 L102, A14 B24 560 HydroSHEDS -32.794 -67.860 L103, A15 B25 580 HydroSHEDS -32.845 -67.982 L104 B26 600 HydroSHEDS -32.891 -68.146 B27 500 HydroSHEDS -32.789 -67.586 L105, A16 B28 500 HydroSHEDS -32.722 -67.596 L106, A17 B29 500 HydroSHEDS -32.670 -67.617 B30 500 HydroSHEDS -32.605 -67.615 L107

HydroSHEDS; Trans-contour method; 5-km tool; 10-m contours in isolated AOI River: Adjusted or Topo Line Anomaly ID* HydroSHEDS Latitiude Longitude Crossed Original T1 470 HydroSHEDS -32.980 -67.319 T2 570 HydroSHEDS -33.193 -67.871 continued

73 HydroSHEDS; Trans-contour method; 5-km tool; 10-m contours in isolated AOI contiuned T3 590 HydroSHEDS -33.122 -67.997 T4 610 HydroSHEDS -33.090 -68.107 T5 530 Adjusted -33.091 -67.645 T6 590 Adjusted -33.075 -67.906 T7 550 Adjusted -33.017 -67.752 T8 590 Adjusted -33.041 -67.896 T9 570 Adjusted -32.990 -67.837 T10 470 HydroSHEDS -32.902 -67.377 T11 470 HydroSHEDS -32.891 -67.385 T12 570 Adjusted -32.891 -67.860 T13 530 HydroSHEDS -32.835 -67.714 T14 550 HydroSHEDS -32.798 -67.808 T15 590 HydroSHEDS -32.868 -68.060 T16 490 HydroSHEDS -32.720 -67.538 T17 490 HydroSHEDS -32.721 -67.546 T18 490 HydroSHEDS -32.722 -67.557 T19 490 Adjusted -33.270 -67.423 *: Only newly identified anomalies are listed.

ERSDAC; Trans-contour method; 5-km tool; 20-contours Topo Line River: Adjusted or Anomaly ID Latitiude Longitude Crossed GDEM Original G-1 520 Adjusted -33.887 -67.780 G-2 560 Adjusted -33.883 -67.898 G-3 580 Adjusted -33.868 -67.971 G-4 740 GDEM -33.939 -68.292 G-5 820 GDEM -33.914 -68.416 G-6 920 GDEM -33.901 68.485 G-7 840 GDEM -33.863 -68.413 G-8 840 GDEM -33.862 -68.415 G-9 860 GDEM -33.851 -68.432 G-10 860 GDEM -33.852 -68.434 G-11 980 GDEM -33.820 -68.505 G-12 1080 Adjusted -33.784 -68.576 G-13 620 GDEM -33.777 -68.082 G-14 760 GDEM -33.746 -68.293 G-15 820 GDEM -33.739 -68.353 G-16 860 GDEM -33.734 -68.395 G-17 880 GDEM -33.730 -68.426 G-18 900 GDEM -33.717 -68.436 G-19 900 Adjusted -33.653 -68.419 G-20 580 Adjusted -33.487 -68.071 G-21 720 Adjusted -33.568 -68.268 G-22 820 Adjusted -33.514 -68.386 G-23 620 Adjusted -33.359 -68.297 G-24 640 Adjusted -33.352 -68.340 G-25 660 Adjusted -33.337 -68.386 G-26 500 Adjusted -33.513 -67.558 G-27 520 Adjusted -33.438 -67.712 G-28 520 Adjusted -33.435 -67.715 G-29 540 GDEM -33.410 -67.818 G-30 660 GDEM -33.198 -68.527 G-31 680 GDEM -33.200 -68.585 G-32 780 GDEM -33.298 -68.734 G-33 780 GDEM -33.384 -68.761 G-34 980 Adjusted -33.630 -68.846 G-35 900 GDEM -33.558 -68.875 G-36 820 Adjusted -33.468 -68.921 G-37 800 GDEM -33.318 -68.776 G-38 820 GDEM -33.291 -68.797 G-39 460 GDEM -33.484 -67.207 G-40 460 GDEM -33.488 -67.240 continued

74 ERSDAC; Trans-contour method; 5-km tool; 20-contours continued G-41 460 Adjusted -33.419 -67.205 G-42 460 Adjusted -33.303 -67.167 G-43 460 Adjusted -33.244 -67.179 G-44 460 Adjusted -33.220 -67.197 G-45 460 Adjusted -33.211 -67.207 G-46 460 Adjusted -33.107 -67.203 G-47 460 GDEM -33.071 -67.248 G-48 460 GDEM -33.071 -67.257 G-49 540 GDEM -33.181 -67.734 G-50 540 GDEM -33.181 -67.737 G-51 560 GDEM -33.168 -6.857 G-52 580 GDEM -33.135 -67.920 G-53 580 GDEM -33.130 -67.935 G-54 580 GDEM -33.130 -67.948 G-55 600 GDEM -33.102 -68.077 G-56 480 Adjusted -32.857 -67.529 G-57 580 GDEM -32.920 -67.971 G-58 520 GDEM -32.838 -67.707 G-59 580 Adjusted -32.859 -68.042 G-60 580 Adjusted -32.860 -68.044 G-61 580 Adjusted -32.852 -68.109 G-62 580 Adjusted -32.845 -68.118 G-63 580 Adjusted -32.840 -68.146 G-64 500 GDEM -32.726 -67.640 G-65 480 GDEM -32.626 -67.512 G-66 480 GDEM -32.611 -67.519 G-67 480 GDEM -32.594 -67.506 G-68 480 GDEM -32.588 -67.502 G-69 500 GDEM -32.489 -67.642 G-70 500 GDEM -32.494 -67.653 G-71 500 GDEM -32.386 -67.650 G-72 500 GDEM -32.380 -67.656 G-73 520 GDEM -32.327 -67.872 G-74 540 GDEM -32.311 -68.057 G-75 540 GDEM -32.312 -68.067 G-76 460 Adjusted -32.840 -67.194 G-77 460 Adjusted -32.835 -67.188 G-78 480 Adjusted -32.535 -67.278 G-79 500 Adjusted -32.356 -67.582 G-80 500 Adjusted -32.334 -67.610 G-81 500 Adjusted -32.242 -67.560 G-82 500 Adjusted -32.240 -67.588 G-83 520 Adjusted -32.205 -67.862 G-84 520 GDEM -32.079 -68.021 G-85 520 GDEM -32.077 -68.011 G-86 520 GDEM -32.075 -68.013 G-87 540 GDEM -32.276 -68.248 G-88 600 GDEM -32.814 -68.438 G-89 640 GDEM -33.013 -68.555 G-90 860 GDEM -33.057 -68.795 G-91 880 GDEM -33.060 -68.812 G-92 900 GDEM -33.063 -68.821 G-93 900 GDEM -33.062 -68.830 G-94 560 GDEM -32.507 -68.345 G-95 560 Adjusted -32.486 -68.372 G-96 580 Adjusted -32.651 -68.455 G-97 540 Adjusted -32.197 -68.500 G-98 600 Adjusted -32.750 -68.601 G-99 760 Adjusted -32.905 -68.830 G-100 580 Adjusted -32.575 -68.688 G-101 1040 GDEM -32.139 -68.812 G-102 1080 GDEM -32.138 -68.817 G-103 580 GDEM -32.128 -68.583 continued

75 ERSDAC; Trans-contour method; 5-km tool; 20-contours continued G-104 600 GDEM -32.105 -68.607 G-105 540 GDEM -32.275 -67.208 G-106 560 GDEM -32.354 -67.145

ERSDAC; Burrato-Method; 5-km tool; 10-m contours Topo Line River: Adjusted or Anomaly ID Latitiude Longitude Crossed GDEM Original C-1 460 Adjusted -33.669 -67.245 C-2 460 Adjusted -33.618 -67.230 C-3 460 Adjusted -33.621 -67.236 C-4 510 Adjusted -33.481 -67.615 C-5 520 Adjusted -33.436 -67.715 C-10 490 Adjusted -33.437 -67.482 C-11 520 Adjusted -33.359 -67.645 C-15 550 Adjusted -33.269 -67.800 C-18 470 Adjusted -33.200 -67.344 C-19 510 Adjusted -33.192 -67.546 C-20 480 Adjusted -33.153 -67.407 C-21 490 Adjusted -33.152 -67.458 C-23 470 Adjusted -33.123 -67.349 C-33 580 Adjusted -32.852 -68.108 C-46 480 Adjusted -32.553 -67.335 C-47 490 Adjusted -32.470 -67.374 C-48 500 Adjusted -32.362 -67.566 C-49 500 Adjusted -32.345 -67.591 C-50 490 Adjusted -32.433 -67.374 C-51 500 Adjusted -32.240 -67.547 C-52 500 Adjusted -32.238 -67.555 C-53 500 Adjusted -32.241 -67.561 C-55 500 Adjusted -32.284 -67.576 C-56 530 Adjusted -32.176 -68.238 C-6 580 GDEM -33.332 -68.005 C-7 590 GDEM -33.306 -68.052 C-8 590 GDEM -33.320 -68.083 C-9 470 GDEM -33.519 -67.325 C-12 480 GDEM -33.348 -67.412 C-13 490 GDEM -33.320 -67.485 C-14 540 GDEM -33.284 -67.760 C-16 580 GDEM -33.210 -67.941 C-17 590 GDEM -33.186 -67.994 C-22 460 GDEM -33.073 -67.271 C-24 540 GDEM -33.181 -67.732 C-25 570 GDEM -33.139 -67.907 C-26 600 GDEM -33.103 -68.077 C-27 500 GDEM -32.920 -67.600 C-28 540 GDEM -32.936 -67.763 C-29 550 GDEM -32.910 -67.816 C-30 510 GDEM -32.856 -67.667 C-31 520 GDEM -32.839 -67.707 C-32 530 GDEM -32.800 -67.775 C-34 500 GDEM -32.725 -67.640 C-35 530 GDEM -32.737 -67.777 C-36 550 GDEM -32.734 -67.858 C-37 490 GDEM -32.707 -67.612 C-38 490 GDEM -32.617 -67.618 C-39 480 GDEM -32.588 -67.503 C-40 500 GDEM -32.494 -67.652 C-41 500 GDEM -32.433 -67.604 C-42 530 GDEM -32.308 -67.970 C-43 540 GDEM -32.367 -68.027 C-44 540 GDEM -32.312 -68.067 C-45 540 GDEM -32.306 -68.088 continued

76 ERSDAC; Burrato-Method; 5-km tool; 10-m contours C-54 530 GDEM -32.237 -68.135 C-57 570 Adjusted -32.553 -68.289 C-58 570 Adjusted -32.558 -68.285 C-59 580 Adjusted -32.696 -68.297 C-60 550 Adjusted -32.384 -68.288 C-61 540 GDEM -32.269 -68.391 C-62 570 Adjusted -32.555 -68.297 C-63 570 Adjusted -32.571 -68.484 C-64 570 GDEM -32.443 -68.662 C-65 580 GDEM -32.361 -68.632 C-66 590 GDEM -32.344 -68.652 C-67 560 GDEM -32.241 -68.561 C-68 590 GDEM -32.241 -68.618 C-69 600 GDEM -32.251 -68.640 C-70 490 GDEM -32.493 -67.202