# Plio-Quaternary Landscape Evolution of the Northern Altiplano, Peru: Structural and Climatic Controls on Orogenic Plateau Capture

Benjamin Gérard, Xavier Robert, Laurence Audin, Pierre Valla

► To cite this version:

Benjamin Gérard, Xavier Robert, Laurence Audin, Pierre Valla. Plio-Quaternary Landscape Evolution of the Northern Altiplano, Peru: Structural and Climatic Controls on Orogenic Plateau Capture. 2025. [hal-05397332](https://hal.science/hal-05397332v1)

HAL Id: hal-05397332

https://hal.science/hal-05397332v1

Preprint submitted on 4 Dec 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
1 Plio-Quaternary Landscape Evolution of the Northern Altiplano, Peru:

2 Structural and Climatic Controls on Orogenic Plateau Capture

3

4 B. Gérard¹,², X. Robert², L. Audin² and P.G. Valla²

5 ¹Institute of Seismology, Department of Geosciences and Geography, University of Helsinki,

6 Helsinki, Finland

7 ²Institute of Earth Sciences (ISTerre), Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS,

8 IRD, Univ. Gustave Eiffel, Grenoble, France

9

10 Corresponding author: Benjamin Gérard (benjamin.gerard@helsinki.fi)
11 Abstract

The Central Andean Altiplano, second highest and widest orogenic plateau on Earth, remained endorheic for at least 8 Ma. However, its northern extension, corresponding to the High Peruvian Plateaus, has been dissected by exorheic drainage systems with rivers flowing toward the Amazon Basin. This region, known as the Abancay Deflection, provides a natural laboratory to investigate the mechanisms controlling the preservation and erosion of intra-montane plateaus. By analyzing the spatial distribution of topographic reliefs and their associated morphometric metrics, including slope, relief, knickpoints, normalized steepness index (k<sub>sn</sub>), and χ values, we identify several evidence for a Pliocene to Quaternary topographic reorganization in this high-elevation low-relief area. We propose that the paleo-Altiplano once formed a continuous endorheic system, extending up to 3° of latitude farther north than its present-day limit. This paleo-plateau was progressively captured by eastward-draining river systems, transitioning to an exorheic configuration. Since the Pliocene, the plateau margin has been retreating at an average rate of 34 ± 10 mm/yr. We suggest that such drainage reorganization and enhanced river incision were driven by two primary and complementary factors: (1) the intensification of the South American Monsoon and global climatic changes during the Pliocene, which likely enhanced headward river incision and promoted integration of formerly-isolated endorheic basins; and (2) the unique tectonic configuration of the Abancay Deflection, which is associated with the active crustal-scale Apurimac fault system and overall oblique to the main structural trend of the Andes, likely played a key role in focusing regressive river incision and plateau capture.

31

32

33
34

**Keywords**

35

Andes, Altiplano, geomorphology, regressive erosion, exorheism, endorheism, plateau capture

36

37

**Highlights:**

38

* Late Cenozoic paleo-Altiplano extended ~3° farther north.

39

* Paleo-Altiplano captured by Apurimac and Urubamba rivers at ca. 5 Ma.

40

* Southern Peru shifted from endorheic to exorheic drainage settings.

41

* Capture enhanced by stronger erosion during wetter Pliocene climate.

42

* Capture also guided by fault corridors focusing regressive incision.

43

44

**1 Introduction and settings**

45

46

47

48

49

50

51

52

53

In the Central Andes, the Altiplano is the second highest and widest orogenic plateau on
Earth with a mean elevation of around 4 km a.s.l. and a maximum width of 400 km (Figure 1).

This geomorphological domain, located between the Western and Eastern Cordilleras, is characterized by Cenozoic low-relief surfaces and Quaternary glacial landscapes underpinned by an over-thickened crust (~60 km thickness; Allmendinger et al., 1997). In such ocean-continent convergence margin, the mechanisms responsible for the uplift of the Altiplano remain debated.

Several hypotheses have been proposed, including crustal shortening (e.g. Barnes & Ehlers, 2009), lithospheric delamination (Garzione et al., 2017; Pons et al., 2022), crustal channel flow (Husson and Sempere, 2003) and lithospheric dripping (Göğüş et al., 2022; McMillan et al., 2023).
54
Paleoaltimetry data (Picard et al., 2008; Sundell et al., 2019) and biodiversity record (Hoorn et al.,
55
2010; Martínez et al., 2020) demonstrate that the northern Altiplano and the High Peruvian
56
Plateaus (HPP; Figure 1) acquired their present-day mean elevation (~4 km) by at least 5 Ma. The
57
long-term survival of the Altiplano and HPP raises fundamental questions about the mechanisms
58
controlling their preservation.

59
Significant differences in drainage network distribution and dynamics exist between the
60
HPP (north of 14°S) and the Altiplano (south of 14°S), with the Abancay Deflection region
61
marking the transition area (Figures 1 and 2a; Gérard et al., 2021). The HPP are today exorheic,
62
with rivers flowing eastward toward the Amazon basin and ultimately reaching the Atlantic Ocean.
63
These hydrographic networks have breached the natural barrier of the Eastern Cordillera, focusing
64
erosión within deeply-incised canyons (see swath profiles in Figure 1c). Sedimentary evidence and
65
incision dating suggest that parts of the HPP were endorheic prior to late-Pliocene (~2.8 Ma),
66
before being captured by the Mantaro river to the east (Figure 1; up to 11°S; Wise & Noble, 2008).
67
Additionally, local studies also evidenced that parts of the Abancay Deflection were associated
68
with the morphological Altiplano in an endorheic environment before ~5 Ma (Gérard et al., 2020;
69
Sundell et al., 2018).

70
In contrast, the Altiplano has remained endorheic since ~10-8 Ma (Allmendinger et al.,
71
1997; Garzione et al., 2006) with lake Titicaca (3.8 km of elevation) as regional base level in its
72
northern part (Figure 1). Hydrographic networks draining toward the Amazon basin have carved
73
canyons exceeding 2 km in depth within the Eastern Cordillera but have not yet crossed the latter
74
(Figure 1), preventing the capture of the Altiplano. Thermochronological data and exhumation rate
75
estimates suggest that canyon incision initiated at 5 ± 3 Ma, likely triggered and/or amplified by
76
wetter climatic conditions during the Pliocene (Buford Parks et al., 2023; Falkowski et al., 2023;
Gérard et al., 2020; Lease and Ehlers, 2013). This period coincides with the onset of convective precipitation along the eastern flank of the Central Andes, driven by orogenic-orographic feedback (Insel et al., 2010; Poulsen et al., 2010). Since then, the Eastern Cordillera acted as an effective moisture barrier, producing a strong precipitation gradient from >2 m/yr in the east and <1 m/yr in the west (Figure 2b; Bookhagen & Strecker, 2008).

Previous studies on climate-tectonic feedbacks, surface uplift and landscape evolution in the Central Andes have primarily focused on the Western and Eastern Cordilleras. For instance, using morphometric analyses of river channels draining the Cordilleras, Norton & Schlunegger (2011) demonstrated that the active tectonic shortening shift from the Western to the Eastern Cordillera appears to be primarily driven by changes in erosion patterns associated with the onset of intense precipitation to the east. As a result, the Eastern Cordillera experienced an increase in rock uplift and exhumation rates since the Pliocene (Evenstar et al., 2023). However, these morphometric analyses are to be considered with caution as spatial variations in rock uplift and rainfall rates strongly impact channel concavity and steepness indices ($k_{sn}$; Gasparini & Whipple, 2014; Leonard et al., 2023). Still in the Eastern Cordillera, Plasterr et al. (2025) demonstrated numerically that a decrease in shortening rates after 10 Ma allowed rivers to overcome surface uplift, promoting two major phases of upstream endorheic sub-basin capture (7-5 Ma and 3.5-0.5 Ma). These capture events, amplified by wetter Pliocene conditions, triggered 2-3 km of canyon incision on the eastern margin of the plateau. Yet, this work focuses on a unique catchment of the Eastern Cordillera and does not address the full spatial extent of the endorheic Altiplano system. In contrast, in the drier peruvian Western Cordillera, it has been shown that canyon carving are related to a major phase of uplift during the Miocene (Audin et al., 2023; Schildgen et al., 2007),
and that ongoing erosion still responds today to the Miocene disturbance in these areas (Trauerstein et al., 2013).

Despite significant advances in understanding the morpho-tectonic evolution of the Cordilleras flanking the HPP and the Altiplano, the Abancay Deflection area, exhibiting the transition from exorheism northward (HPP) and endorheism southward (Altiplano), has not been investigated from a geomorphological perspective. Given its striking and contrasting landscapes, this study area represents an ideal natural laboratory for investigating mechanisms of preservation and erosion of intra-mountainous plateaus. Similar issues of plateau and basin preservation and erosion have been discussed in other high-elevation regions worldwide. In Tibet, late Cenozoic river incision locally exceeded 2-3 km over the past ~10 Ma along the plateau margins, while large portions of the interior surface have remained remarkably stable (Clark and Royden, 2000; Hoke et al., 2014; Lease et al., 2007; van der Beek et al., 2009). In southern Africa, the Highveld and Drakensberg escarpments record extremely low long-term denudation rates of 5-20 m/Myr over the past 100 Myr, despite dynamic topography and ongoing escarpment retreat, pointing to the key role of lithological resistance and inherited planation surfaces in maintaining plateau elevations (Braun et al., 2014; Moore and Blenkinsop, 2002). Conversely, in tectonically active settings such as the NW Himalaya, drainage-capture events can generate rapid, localized incision and exhumation (Genge et al., 2025), illustrating how hydrological reorganization can affect and destabilize plateau margins over <1 Myr timescales. These cases illustrate how the balance between uplift, lithospheric and climate dynamics, and erosion governs plateau preservation, highlighting the importance of constraining the controls on long-term plateau stability worldwide.

In this study, we analyze the geomorphology of the Abancay Deflection by extracting morphometric parameters such as slopes, relief, knickpoints, channel steepness (Kirby and
122 Whipple, 2012) and $\chi$ (Perron and Royden, 2013; Willett et al., 2014). These metrics allow us to
123 identify Pliocene to Quaternary drivers of topographic reorganization in the watersheds of the
124 endorheic Altiplano and the exorheic Apurimac, Urubamba and Madre de Dios rivers (Figure 2a).

125

<figure><img src="image_2.png" /></figure>
**Figure 1.** Geomorphological and structural settings. a) Location of the study area (black rectangle) in the Central Andes and South America. b) Zoom on the Abancay Deflection area exhibiting the transition from exorheic High Peruvian Plateaus (HPP) and the endorheic Altiplano. Orogenic plateaus are highlighted in grey between the two Cordilleras. Major fault systems are indicated in red (from 1/100 000 and 1/50 000 INGEMMET maps: https://geocatmin.ingemmet.gob.pe/geocatmin/). c) Topographic swath profiles AA', BB' and CC' (see locations in Fig. 1b) extracted along rectangles (20-km width, 2-km sampling interval) using the PySwath program (Robert, 2019).
<figure><img src="image_3.png" /><figcaption>**Figure 2.** Geological and climatic settings of the study area. a) Locations of the Apurimac (1), Urubamba (2) and Madre de Dios (3) watersheds and simplified geological map of the study area (from 1/100 000 and 1/50 000 INGEMMET maps: https://geocatmin.ingemmet.gob.pe/geocatmin/). Cz: Cenozoic; Mz: Mesozoic; Pz: Paleozoic. b) Mean annual rainfall rates (1998 – 2009) from the Tropical Rainfall Measuring Mission (TRMM; Simpson et al., 1996) and topographic swath profile of southern Peru ([AB] box in Fig. 1a).</figcaption></figure>
143 **2 Material and Methods**

144 **2.1 DEM preparation and analysis**

145 We used a 1 arc-second (~30-m resolution) digital elevation model (DEM) derived from
146 the Shuttle Radar Topography Mission (SRTM V4; Reuter et al., 2007) to construct swath profiles
147 and to extract topographic slopes and relief metrics. 12-m resolution TanDEM-X data (with a UTM
148 18S reference projection; Rizzoli et al., 2017) were collected to perform the river-channel
149 morphometric analysis (knickpoints, ksn, χ) for the three analyzed watersheds (Apurimac,
150 Urubamba and Madre de Dios, Figure 2). Swath profiles were extracted from these DEMs using
151 the PySwath program (Figure 1; Robert, 2019). Slopes and relief metrics were derived using
152 dedicated modules implemented in QGIS via GDAL (GDAL/OGR Contributors, 2021). Relief
153 was calculated as the standard deviation of topographic elevation within a 200-m radius moving
154 window across the DEMs (Lindsay et al., 2015). To correct potential elevation biases, we applied
155 the method proposed by Purinton & Bookhagen (2017) using Topotoolbox v2 program
156 (Schwanghart and Kuhn, 2010; Schwanghart and Scherler, 2014). Watershed boundaries were
157 delineated using Whitebox GAT 3.4 (Lindsay, 2016; Figure 3). The outlets of the Apurimac,
158 Urubamba, and Madre de Dios watersheds were manually adjusted upstream of their confluence,
159 before crossing the tectonically active Sub-Andean zone, to prevent potential disturbances due to
160 acknowledged surface uplift (Gautheron et al., 2013). These adjustments allow us to focus on
drainage reorganization along the Altiplano margin and within the Eastern Cordillera, where active deformation is also accommodated by the Apurimac fault system (Figure 2).

## 2.2 Knickpoint extraction, k<sub>sn</sub> and χ analysis

River knickpoints and knickzones were identified using the ChiProfiler Matlab module (Gallen and Wegmann, 2017) implemented in Topotoolbox v2 (Schwanghart and Kuhn, 2010). A total of 553, 752 and 38 channels were analyzed for the Apurimac, Urubamba and Madre de Dios watersheds, respectively. Knickpoints were manually selected at the upstream inflection points along river profiles (Figure 3). To characterize their relative importance, we classified knickpoints into four categories based on the vertical offset between adjacent upstream and downstream channel segments at the break in slope (A > 0.5 km; 0.25 < B < 0.5 km; 0.1 < C < 0.25 km; D < 0.1 km; Pangaea dataset; Figure 3b). Additionally, we categorized knickpoints according to their likely origin, based on field verification, geological maps, and inspection using online satellite imagery database such as Google Earth imagery. Categories included anthropogenic features (e.g. dams, reservoirs), lithologic or structural controls (e.g. bedrock erodibility contrasts, faults), and glacial knickpoints (e.g. moraines, glacial locks). We also identified topographic knickpoints associated with hanging low-relief surfaces that reflect long-term landscape inheritance. For the purpose of this study, we focused exclusively on glacially-related knickpoints and those linked to hanging low-relief surfaces. Tectonically-induced knickpoints (i.e. at fault locations) are briefly acknowledged but remain outside the main scope of this study, as their analysis would require a more focused investigation within specific sub-catchments.

The normalized steepness index (k<sub>sn</sub>) quantifies river gradients variations corrected for upstream drainage area. This tool is useful to identify abnormally steep sections of channels and
knickzones (Kirby and Whipple, 2012). Spatial variation in k<sub>sn</sub> values within a watershed can highlight active faults and the edges of hanging surfaces undergoing regressive erosion (Kirby et al., 2003; Wobus et al., 2006). We extracted k<sub>sn</sub> values using Topotoolbox v2 (Schwanghart and Scherler, 2014) for the three watersheds, applying a reference mean concavity value of θ<sub>ref</sub> = 0.45 (Leonard et al., 2023; Wobus et al., 2006).

The $\chi$ parameter represents the normalized integrated drainage area at any given point in an hydrographic system (Perron & Royden, 2013; Whipple et al., 2017). Variations in $\chi$ values along watershed divides can indicate ongoing drainage divide stability or migration (Willett et al., 2014). When combined with independent geomorphological evidence, such patterns provide insights into recent drainage reorganizations. We computed $\chi$ values for the three watersheds and neighboring drainage basins using Topotoolbox v2 (Schwanghart and Scherler, 2014). Since $\chi$ calculations following Willett et al. (2014) require a common base level for channel outlets, we used two elevation reference elevations: (i) at 0.6 km to assess the stability of the drainage divide of the exorheic Apurimac, Urubamba, and Madre de Dios watersheds; (ii) at 3.8 km to investigate the reorganization of drainage divides between the exorheic basins to the north and the endorheic Altiplano to the south. All $\chi$ computations were performed using a standard concavity value of $\theta_{ref} = 0.45^\circ$ (Wobus et al., 2006).

This geomorphic study is not designed to provide precise quantifications of parameters such as rock uplift and/or erosion rates, as performed in smaller areas, where most of the parameters were known, quantified and/or spatially uniform (e.g. Kirby & Whipple, 2001). Instead, the spatial relationships among geomorphic metrics used here are suitable for identifying large-scale, post-Pliocene landscape reorganization, as demonstrated in previous studies of the Western Cordillera of Peru (Hoke et al., 2007; Trauerstein et al., 2013).
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Spatial mapping of main river channels (left panels) and associated river profiles (right panels) for three the studied watersheds: a) Apurimac, b) Urubamba, and c) Madre de Dios. A selection of a few representative tributaries are displayed for clarity.</figcaption></figure>

206

207

208

209
210

# 3 Results

211

## 3.1 Watersheds and hydrographic networks

212

213

214

215

216

217

218

219

220

221

222

Considering the locations of the outlets, the Apurimac, Urubamba and Madre de Dios watersheds, drain approximately 65 000 km², 33 000 km² and 7 500 km², respectively. To the southeast, the endorheic Altiplano bounds both the exorheic Apurimac and Urubamba basins. To the northwest, the Apurimac watershed is bordered by the exorheic Mantaro basin (Figure 2a). The Apurimac and Urubamba watersheds have an elongated shape, extending deep into the range after crossing the Eastern Cordillera, following a SE-NW axis that is slightly oblique to the main elongation axis of the orogen (Figures 2a & 3). Although not analyzed in detail here, the Mantaro watershed displays morphological characteristics comparable to the Apurimac and Urubamba watersheds, including an elongated shape crossing the Eastern Cordillera and the preservation of hanging low-relief surfaces (Figure 4; Wise & Noble, 2008). However, it is not included in our morphometric analysis, and is therefore only considered here for regional context.

223

224

225

226

227

228

Focusing on the Apurimac watershed, the channel network exhibits a dendritic pattern upstream, transitioning to a trellis pattern downstream, characterized by sharp changes in flow direction as the rivers cross inherited and sometimes active faults (Apurimac fault system; Figures 2a & 3a; Gérard et al., 2020). The watershed is notably asymmetric, with extensively developed left-bank tributaries (>200 km in length), whereas, right-bank tributaries do not exceed 30 km and have steeper long profiles (Figure 3a).

229

230

231

In the Urubamba basin, the watershed also narrows along the Apurimac fault system, with channels presenting a dendritic pattern at the headwaters and evolving downstream into a trellis-like network (Figure 3b). The tributaries within this trellis pattern display a characteristic bow-
shaped curvature, likely reflecting structural inheritance associated with the Miocene rotation of
the crustal block defining the Abancay Deflection (Marocco, 1971). These morphological
characteristics contrast with those of the Madre de Dios watershed. Here, the upstream channels
exhibit a parallel layout and drain only the Eastern Cordillera, flowing perpendicular to the range's
elongation axis, similar to other rivers further south that drain the Eastern Cordillera in Peru and
Bolivia (Figure 3c; Gasparini & Whipple, 2014; Whipple & Gasparini, 2014).

## 3.2 Topography, relief and slopes

In the Altiplano/HPP domains (south of the Apurimac fault system), elevations range from
1.0 to 5.4 km (Figure 1). Slope and relief maps reveal two distinct morphological domains: First,
hanging surfaces above 3.8 km of elevation, characterized by slopes <10° (Figure 4a) and low
relief (<50 m; Figure 4b). Second, deeply-incised landforms, with slopes >25° (Figure 4a) and
reliefs exceeding 200 m (Figure 4b), corresponding to the valleys of the Apurimac river and its
tributaries (Figure 3a). The Eastern Cordillera domain (north of the Apurimac fault system; Figure
2), presents higher maximum elevation peaks (e.g., Nevado Salcantay >6 km; Figure 1) in
comparison to the Altiplano domain. It is primarily drained by the Urubamba channel network,
with almost the entire downstream area exhibiting slopes >30° (Figure 4a) and relief exceeding
200 m (Figure 4b). However, remnants of hanging surfaces are preserved in the upstream reaches
of the Urubamba watershed (Figure 4).
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Spatial mapping of slopes (a) and relief computed as the standard deviation of topographic elevation within a 200-m radius moving window (b) of southern Peru. Studied watersheds are outlined in blue. Hanging surfaces were mapped using a slope threshold of <10°, following common criteria for identifying planation surfaces in the Andes (e.g., Kennan et al., 1997). The hanging surface mask was generated at pixel scale (30-m resolution), and polygons were subsequently adjusted manually to retain only coherent patches consistent with DEM slope inspection. AFS: Apurimac fault system; AD: Abancay Deflection; HPP: High Peruvian Plateaus.</figcaption></figure>
258

## 3.3 Knickpoints and knickzones

259

260

261

262

263

264

265

266

267

268

269

Two groups of knickpoints can be distinguished. First, glacially-induced knickpoints with offsets <250 m, associated with moraines and glacial locks (Figure 5). Their distribution is heterogeneous, but they are more densely concentrated in high-elevation areas around watershed heads and in an E-W band along the drainage divide between the Urubamba and Apurimac watersheds (Figure 5). These knickpoints are not present below 3.6 km in elevation. A second group is identified, with geomorphically significant topographic knickpoints showing offsets >500 m, associated with upstream hanging surfaces (Figure 5). These topographic knickpoints occur at similar elevations (3.6-4 km) between 13°S and 14.5°S, corresponding to the present-day Altiplano/HPP mean elevation. North of 13°S, their elevations drop sharply from around 3 to 1 km (Figure 5b). The Madre de Dios watershed contains no significant knickpoint for this study (offset < 0.1 km).
<figure><img src="image_6.png" /><figcaption>**Figure 5.** Knickpoint spatial distribution over the study area. a) Spatial locations of glacial knickpoints and knickpoints associated with low-relief surfaces upstream (topographic knickpoints) in the three studied watersheds (outlined in blue). b) Knickpoints distribution along the topographic swath profile ([AB] box in “a”).</figcaption></figure>
275

**3.4 Spatial patterns of river k<sub>sn</sub> values**

276

277

278

279

280

281

282

283

284

285

286

287

288

289

In an undisturbed watershed, the highest k<sub>sn</sub> values are typically found near the drainage divide, which is the case for the Madre de Dios drainage basin, where ksn values range from 10 to 100 m<sup>0.9</sup> (Figure 6a). The Apurimac and Urubamba watersheds exhibit clearly different patterns. In the Apurimac watershed, the highest k<sub>sn</sub> values (20-500 m<sup>0.9</sup>) are concentrated along tributaries below ~4 km in elevation, forming a dendritic pattern. Above 4 km-elevation, k<sub>sn</sub> values are much lower (0.01-10 m<sup>0.9</sup>), corresponding to the HPP and Altiplano morphological domains. The transition from low to high k<sub>sn</sub> values is often marked by major topographic knickpoints (Figures 5 and 6). In the Urubamba watershed, the highest k<sub>sn</sub> values (>1000 m<sup>0.9</sup>) are found along a SW-NE band perpendicular to the main drainage direction, associated with major upstream topographic knickpoints. However, the spatial relationships between topographic knickpoints and high k<sub>sn</sub> values are less straightforward than in the Urubamba watershed, reflecting a more complex behavior that may also involve tectonic forcing on river incision dynamics. Upstream of these knickpoints, k<sub>sn</sub> values are much lower (<1 m<sup>0.9</sup>), also corresponding to hanging low-relief surfaces (Figure 6).
<figure><img src="image_7.png" /><figcaption>**Figure 6.** Spatial distribution of k<sub>sn</sub> values. a) Map of k<sub>sn</sub> values for the Apurimac, Urubamba and Madre de Dios watersheds. b) 3D topographic diagram (location in “a”) of a tributary of the Apurimac river showing the respective distribution of k<sub>sn</sub> values (channels), locations of hanging surfaces and major topographic knickpoints.</figcaption></figure>

290

291

292

293

294
295

**3.5 Spatial patterns of χ values**

296

297

298

299

300

301

302

303

304

305

306

Along the drainage divide between the Apurimac watershed and the Pacific-draining basins, χ values are higher in the Apurimac domain (~10⁵ m) compared to the Pacific-draining watersheds (~10⁴ m; Figure 7a). A similar pattern is observed along the Urubamba drainage divide, where χ values (~10⁴ m) are higher than in adjacent watersheds (Apurimac and Madre de Dios), which exhibit χ values of ~10³ m (Figure 7a). Along the divide between the Apurimac and Mantaro watersheds, χ values on both sides are of similar magnitude, showing no significant differences across the divide. This pattern suggests limited or no recent migration of the drainage boundary between these two exorheic basins. Finally, along the drainage divide between the exorheic basins and the endorheic Altiplano, χ values are two orders of magnitude higher in the endorheic Altiplano (~10⁵ m) than in the exorheic area (~10³ m; Figure 7b).
<figure><img src="image_8.png" /><figcaption>**Figure 7.** Spatial distribution of χ values. a) Map of χ values associated with outlets at 0.6 km of elevation to investigate drainage divide stability between the exorheic watersheds. b) Map of χ values associated with outlets at 3.8 km of elevation to investigate drainage divide stability between exorheic basins northward and the endorheic Altiplano southward.</figcaption></figure>
312

# 4 Discussion

313

## 4.1 Limitations of the morphometric approach

314

Our study area extends over 100 000 km², encompassing a wide range of lithologies, as well as in contrasts in erodibility, surface uplift, precipitation, and thus in erosion rates. Such spatial variability affects the calculation of morphometric metrics, which are known to be sensitive to both precipitation and rock uplift rates at least (Leonard et al., 2023), potentially leading to interpretative biases. To minimize these effects, we restricted our analysis to areas where precipitation has remained relatively stable and homogeneous over the last ca. 5 Ma (~1 m/yr; Insel et al., 2010; Poulsen et al., 2010). We thus excluded major topographic knickpoints located in the northeastern part of the Urubamba basin (Figure 5) from our interpretation, as this area experiences significantly different climatic conditions, particularly much higher precipitation (Figure 2). In addition, we focused on the Altiplano and Eastern Cordillera domains separated by the Apurimac Fault System to avoid further tectonic interferences related to the Subandes active fold and thrust belt (Espurt et al., 2011).

315

316

317

318

319

320

321

322

323

324

325

326

Also, erodibility contrasts due to lithological variability can affect spatial patterns of k<sub>sn</sub> values distribution and knickpoint locations (Duvall et al., 2004). In the Urubamba watershed, major knickzones and highest k<sub>sn</sub> values align along a SW-NE trend of the Apurimac fault system (Figure 6a). Field investigations reveal these features are located on both plutonic and metasedimentary units, suggesting their locations are not primarily controlled by lithology. Thus, this pattern likely reflects a broader geomorphological or structural transition. In the Apurimac watershed, detailed analysis of geological maps and field data indicate that major knickpoints coincide with the boundary of an erosional window separating upstream Eocene volcanoclastic

327

328

329

330

331

332

333
rocks from downstream Mesozoic sedimentary units (Figures 2a and 6a). However, these erodibility contrasts alone cannot account for knickzone offsets exceeding 500 m, and may instead be related to a geomorphological transition potentially driven by regressive erosion.

Glaciations are another potential factor influencing landscape evolution, as they could enhance erosion and may trigger postglacial isostatic rebound, as observed in fully glaciated regions such as the Cordillera Blanca in northern Peru (Margirier et al., 2016). In this study, no glacial knickpoints were identified below 3.6 km, and most are found above 4.2 km elevation (Figure 5) reflecting the maximum ice extend. Based on present-day topography, this suggests that during peak glaciation, ice likely covered up a maximum of 35%, and more conservatively about 15%, of the Apurimac and Urubamba basins (Fox and Bloom, 1994). Given the intertropical setting, where fluvial erosion is the dominant process, and considering the scale of our study area, we assume that the influence of past glaciations on topographic disturbance has been negligible for the purpose of this study.

Finally, since the Madre de Dios watershed exhibits no major evidence for geomorphic disequilibrium compared to the Apurimac and Urubamba basins, it will be used as a control basin in the remainder of the discussion to enable clearer comparisons between the two other catchments.

## 4.2 Interpretation of morphometric metrics

In the Apurimac and Urubamba watersheds, major topographic knickpoints, associated with >500 m of vertical offset, are all encountered at similar elevation between 3.6 and 4.0 km (Figure 5), which corresponds to the average elevation of the present-day HPP and Altiplano domains (Figure 1). These knickpoints are associated with upstream hanging low-relief surfaces (Figures 4 and 5) attributed to the HPP and Altiplano, suggesting they mark the morphological boundary of
these domains. Given their consistent elevation and magnitude of offset, we consider it unlikely
that these features result from localized tectonic structures; their occurrence is too systematic to
be accounted for by structural deformation alone. We interpret these topographic knickpoints
(Figure 6) as resulting from base-level fall in the Urubamba and Apurimac watersheds due to
regressive erosion and the capture of a formerly elevated area: the paleo-Altiplano or HPP. In this
context, the knickpoints are remnants of a paleo-Altiplano/HPP that once extended farther north-
west.

Regarding ksn values distribution in the Apurimac waterhed, the highest ksn values are
distributed in a dendritic pattern downstream of major knickpoints (Figure 6), indicating that the
observed morphological disequilibrium is driven by regressive erosion rather than active tectonics
(Figure 8b). Indeed, if tectonic processes were responsible, high ksn values and major knickpoints
should be aligned along active fault systems (Kirby & Whipple, 2012). The spatial association of
both topographic knickpoints and high ksn values downstream supports the hypothesis of a
drainage capture of the HPP and the Altiplano. In contrast, in the Urubamba watershed, the highest
ksn values form a SW-NE trending band, which is orthogonal to the main axis of the watershed
(Figure 6). This band corresponds to the area of greatest morphological anomaly across the study
area, characterized by steep slopes and high relief (Figure 4), and suggesting a tectonic
disequilibrium (Kirby & Whipple, 2012; Whipple & Tucker, 1999). The Urubamba basin therefore
records a complex evolution involving both plateau capture and active tectonics, as evidenced by
the spatial distribution of high ksn values (Figure 6). Two tectonic models can explain the ksn
pattern observed in the Urubamba watershed: (1) tectonic uplift along a ramp located beneath the
Eastern Cordillera associated with the active Subandean front (Espurt et al., 2011; Gotberg et al.,
2010), or (2) backthrust activity along the Apurimac fault system (Gérard et al., 2021). Given that
379 the high k<sub>sn</sub> values are oriented perpendicular to the Subandean thrust but parallel to the Apurimac
380 fault system, we favor the latter hypothesis involving backthrust-related uplift along the Apurimac
381 fault.

382 Finally, χ values are used to identify drainage divide migration, as divides tend to shift
383 from areas of lower χ values toward areas of higher χ values (Whipple et al., 2017; Willett et al.,
384 2014). Among the exorheic watersheds, the Apurimac appears to be undergoing headward erosion
385 by adjacent Pacific-draining watersheds (Figure 7a), while the Urubamba watershed is being
386 progressively captured by both the Apurimac and Madre de Dios watersheds (Figure 7a). Although
387 χ values distributions suggest a northward migration of the Apurimac drainage divide toward the
388 Urubamba (Figure 7a), the northern divide of the Apurimac basin shows limited expansion
389 compared to its southern part (Figure 3a). This asymmetric pattern likely reflects the truncation of
390 the right-bank tributaries by the Apurimac fault system, further supporting the influence of this
391 active structure in exhuming the Eastern Cordillera domain (Gérard et al., 2021). Lastly and
392 importantly, the endorheic Altiplano is being actively attacked by all neighboring watersheds
393 (Figure 7b).
394

## 4.3 Pliocene paleogeography of Southern Peruvian Andes

395

The present-day exorheic Apurimac and Urubamba watersheds are bounded to the south by the endorheic Altiplano and to the north by the exorheic Mantaro watershed (Figure 2a). Sedimentary records from intermontane basins (Junin, Huancayo and Ayacucho basins; Figure 8) within the Mantaro watershed indicate that the upper course of the river is juvenile (<2 Ma; Wise & Noble, 2008). Through regressive erosion, the Mantaro river and its tributaries progressively captured these intermontane basins and opened a formerly endorheic area as part of the HPP, toward the Amazon basin (Figure 8; Wise & Noble, 2008).

396

397

398

399

400

401

402

Further south, in the Apurimac watershed, provenance studies conducted in the intramontane Paruro basin (Figure 8; Sundell et al., 2018) suggest that bedrock lithologies from the Eastern Cordillera contributed to the sediment supply of the Altiplano basin during the late Miocene (~9 to 7 Ma). In contrast, sediments produced in the Eastern Cordillera are now exported toward the Amazon foreland via the modern Apurimac drainage network (Figure 2a). This contrast indicates a major drainage reversal since the late Miocene, implying that endorheic conditions were more extensive northward at that time (Figure 8).

403

404

405

406

407

408

409

These interpretations all support a paleogeographic connection between the formerly endorheic HPP northward (currently drained by the Mantaro hydrographic system) and the present-day endorheic Altiplano, through the intervening Apurimac and Urubamba watersheds (Figure 8). The spatial correlation of major knickpoints, along with $k_{sn}$ and $\chi$ values distribution, indicates a wave of erosion propagating upstream along the Apurimac and Urubamba tributaries, capturing the endorheic HPP and Altiplano domains (Figures 6 and 7).

410

411

412

413

414
We propose that the endorheic paleo-Altiplano formed a continuous system that extended up to 3° of latitude farther north than today (Figure 8), at least since the Pliocene. This paleo-Altiplano domain, that included the HPP northward, was subsequently captured in multiple locations by the Mantaro, Apurimac, and Urubamba rivers. The drainage-capture process is ongoing, as evidenced by the spatial distribution of χ values (Figure 7b), which points to a southeastward migration of the drainage divide, indicating the expansion of the Urubamba and Apurimac watersheds at the expense of the present-day endorheic Altiplano (Figure 8).

In the Apurimac watershed, where active tectonics plays a limited role, we use knickpoint retreat as a proxy to estimate the long-term regressive incision rate along the margins of the HPP and the Altiplano. Our calculation is anchored at the Apurimac triple junction (Fig. 9), which coincides with a sampling site of apatite fission-track (AFT) ages reported by van Heiningen et al. (2005). At this locality, AFT ages are broadly consistent within analytical uncertainty. Considering that exhumation in this sector of the Altiplano has been steady since ~40 Ma (Gérard et al., 2021), we interpret the clustered AFT cooling ages (9.3-5.1 Ma) as reflecting exhumation linked to the onset of canyon incision and, by inference, to the drainage capture of the paleo-Altiplano. Using this time window and the distances from the triple junction to the major upstream knickpoints, we obtain average regressive incision rates of 34 ± 10 mm/yr (Figure 9). Our estimates are about one order of magnitude lower than the high knickpoint migration rates reported for the Salween River in southeastern Tibet (180-205 mm/yr; Yang et al., 2016), yet remain within the range expected for transient knickpoint retreat in orogenic plateau settings. Although analogue models (e.g., De Lavaissière et al., 2022) indicate that knickpoints retreat faster than drainage divides migrate, our estimates provide a first-order approximation of Altiplano northern margin erosion and migration.

437
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

438

439 **Figure 8.** Paleogeographic evolution of southern Peru since the Pliocene. a) Reconstructed paleo-elevation map of southern Peru ca. 5 Ma ago, generated using bicubic Tikhonov spline interpolation based on the elevations of major knickpoints identified in this study and those of captured intermontane basins reported by Wise & Noble (2008) (Junin, Huancayo, and Ayacucho) and Sundell et al. (2018) (Paruro). b) Present-day topography and drainage pattern of southern Peru.
<figure><img src="image_11.png" /><figcaption>**Figure 9.** Major knickpoint retreat map within the Apurimac watershed. Retreat rates were calculated by dividing the distance measured along the present-day hydrographic networks between each major knickpoint and the downstream triple junction (red star) by the estimated age of the Altiplano capture of $7.2 \pm 2.1$ Ma (van Heiningen et al., 2005).</figcaption></figure>

**4.4 Climatic and structural controls for the capture of the endorheic paleo-Altiplano/HPP**

To the north, Wise & Noble (2008) proposed that the proto-Mantaro river captured the paleo-HPP prior to 2 Ma. In the Apurimac watershed, apatite fission-track data interpretation favors a capture onset for the paleo-Altiplano between ~9 and 5 Ma, i.e. during the Late Miocene (van Heiningen et al., 2005). Supporting this timeframe, the detrital record of the Paruro Basin
(Sundell et al., 2018) indicates that the capture of the endorheic paleo-Altiplano by the Apurimac river occurred after 7 Ma, consistent with phases of incision and the capture of a smaller endorheic sub-basin (San Gaban) that initiated also at that time farther south along the Eastern Cordillera in Bolivia (Plasterr et al., 2025). These timings match with the incision history in the Urubamba watershed with an initiation of paleo-plateau capture at $5 \pm 2$ Ma (Gérard et al., 2020). Despite timing uncertainties, it appears that the paleo-Altiplano and HPP were captured by the hydrographic networks around 5 Ma.

Regionally, this late-Miocene to Pliocene period coincides with the intensification of the South American monsoon (Poulsen et al., 2010), which likely enhanced erosion on the eastern flank of the Eastern Cordillera. Such enhanced erosion have allowed rivers to breach the topographic barrier, facilitating headward erosion and drainage integration (Plasterr et al., 2025). Globally, Pliocene climatic cooling (Peizhen et al., 2001) may have further accelerated these erosional processes, as proposed to explain canyon carving in the Eastern Cordillera of southern Peru (Lease and Ehlers, 2013).

Yet, this raises the question of why rivers draining the Eastern Cordillera, farther south in southern Peru and northern Bolivia, did not similarly captured the endorheic Altiplano, despite experiencing similar climatic forcings (Fedorov et al., 2013; Insel et al., 2010; Lease and Ehlers, 2013; Uba et al., 2007). A possible explanation lies in the unique structural and climatic setting of the Abancay deflection area (Figure 1; Gérard et al., 2021), which is oblique to the general Andean trend. This geometry likely exposed a larger area of the Eastern Cordillera to Amazonian moisture fluxes (Vera et al., 2006), enhancing erosion efficiency. Furthermore, the crustal-scale Apurimac fault system, appears to have played a critical role in guiding regressive erosion, at least for the Apurimac and Urubamba hydrographic systems (Gérard et al., 2020). Fault-related rock
weakening likely localized erosion along fault gouge zones, facilitating river capture over the past
~5 Ma. Similar structural controls may also apply in the Mantaro basin, which is influenced by the
active crustal-scale Huaytapallana fault (Dorbath et al., 1990) in the continuation of the Apurimac
fault system northward.

The Abancay deflection region appears to have provided both a climatic and structural
advantage for endorheic plateau capture. The interplay of intensified wetter conditions in Pliocene,
active faulting (Gérard et al., 2021), and favorable topography, have promoted regressive erosion
leading to the capture of the endorheic paleo-Altiplano/HPP in southern Peru since ca. 5 Ma.

5 Conclusions

Our integrated analysis of morphometric metrics, including slope, knickpoints, normalized
steepness index (k<sub>sn</sub>), and χ values, sheds new light on the Plio-Quaternary paleogeographic
evolution of the southern Peruvian Andes. We propose that the present-day endorheic Altiplano
once formed a continuous endorheic intra-montane plateau extending up to 3° latitude farther north
than today. This plateau was progressively dissected and captured by the Mantaro, Apurimac, and
Urubamba river systems, a process still underway as evidenced by χ gradients indicating active
drainage divide migration southward. Based on the location of major knickpoints along the
tributaries of the Apurimac River, we estimate that the plateau margin has been retreating at an
average rate of 34 ±10 mm/yr since the Pliocene.

The onset timing for this major capture event, around 5 Ma, appears to coincide with the
intensification of the South American monsoon and a global trend toward Pliocene cooling. These
climatic changes likely enhanced erosional efficiency on the eastern flank of the Andes, promoting headward incision and basin integration through regressive erosion. Additionally, the structural configuration of the Abancay deflection and the presence of crustal-scale fault systems, such as the Apurimac fault system, likely played a key role in focusing regressive erosion and guiding fluvial capture pathways.

Together, these climatic and structural factors created favorable conditions for the integration of formerly endorheic basins into the Amazonian drainage. Our results highlight the sensitivity of Andean landscape evolution to both climatic variability and tectonic architecture and provide new constraints on the timing and mechanisms of plateau dissection in inter-tropical orogenic settings.

## 511 Acknowledgments

This work was supported by the IRD (Institut de Recherche pour le Développement), ISTerre and the INSU (Institut National des Sciences de l'Univers). We also thank Cécile Gautheron, Sébastien Carretier, Brian Horton and Peter van der Beek for helpful discussions that reinforced the scope of this paper.

## 517 Open Research

Datasets for this research are available at PANGAEA® - Data Publisher for Earth & Environmental Science doi:XXX), [Creative Commons Attribution License].

## 521 References
522 Allmendinger, R.W., Jordan, T.E., Kay, S.M., Isacks, B.L., 1997. The Evolution of the

523 Altiplano-Puna Plateau of the Central Andes. Annu Rev Earth Planet Sci 25, 139–174.

524 https://doi.org/10.1146/annurev.earth.25.1.139

525 Audin, L., Gérard, B., Gautheron, C., Schwartz, S., Benavente, C., Robert, X., van der Beek, P.,

526 Pinna-Jamme, R., Balvay, M., Bernet, M., Margirier, A., Zerathe, S., 2023. Burial in the

527 western Central Andes through Oligocene to Miocene ignimbrite flare-ups recorded by low-

528 temperature thermochronology in the Cañete Canyon, Peru. Terra Nova 35, 488–497.

529 https://doi.org/10.1111/ter.12669

530 Barnes, J.B., Ehlers, T.A., 2009. End member models for Andean Plateau uplift. Earth Sci Rev

531 97, 105–132. https://doi.org/10.1016/j.earscirev.2009.08.003

532 Bookhagen, B., Strecker, M.R., 2008. Orographic barriers, high-resolution TRMM rainfall, and

533 relief variations along the eastern Andes. Geophys Res Lett 35, 1–6.

534 https://doi.org/10.1029/2007GL032011

535 Braun, J., Guillocheau, F., Robin, C., Baby, G., Jelsma, H., 2014. Rapid erosion of the Southern

536 African plateau as it climbs over a mantle superswell. J Geophys Res Solid Earth 119,

537 6093–6112. https://doi.org/10.1002/2014JB010998

538 Buford Parks, V.M., McQuarrie, N., Falkowski, S., Perez, N.D., Ehlers, T.A., 2023. Timing and

539 drivers of exhumation and sedimentation in the eastern Peruvian Andes: Insights from

540 thermokinematic modelling. Earth Planet Sci Lett 620.

541 https://doi.org/10.1016/j.epsl.2023.118355

542 Clark, M.K., Royden, L.H., 2000. Topographic ooze: Building the eastern margin of Tibet by

543 lower crustal flow. Geology 28, 703–706.
544 De Lavaissière, L., Bonnet, S., Guyez, A., Davy, P., 2022. Autogenic knickpoints in laboratory
545 landscape experiments. Earth Surface Dynamics 10, 229–246. https://doi.org/10.5194/esurf-
546 10-229-2022

547 Dorbath, C., Dorbath, L., Cisternas, A., Deverchère, J., Sebrier, M., 1990. Seismicity of the
548 huancayo basin (central Peru) and the huaytapallana fault. J South Am Earth Sci 3, 21–29.
549 https://doi.org/10.1016/0895-9811(90)90015-S

550 Duvall, A., Kirby, E., Burbank, D.W., 2004. Tectonic and lithologic controls on bedrock channel
551 profiles and processes in coastal California. J Geophys Res 109, 1–18.
552 https://doi.org/10.1029/2003jf000086

553 Espurt, N., Barbarand, J., Roddaz, M., Brusset, S., Baby, P., Saillard, M., Hermoza, W., 2011. A
554 scenario for late Neogene Andean shortening transfer in the Camisea Subandean zone
555 (Peru, 12°S): Implications for growth of the northern Andean Plateau. Bulletin of the
556 Geological Society of America 123, 2050–2068. https://doi.org/10.1130/B30165.1

557 Evenstar, L.A., Hartley, A.J., Mather, A.E., 2023. Orogenic-orographic feedback and the rise of
558 the Central Andes. Earth Planet Sci Lett 602. https://doi.org/10.1016/j.epsl.2022.117931

559 Falkowski, S., Ehlers, T.A., McQuarrie, N., Glover, C.O., Perez, N.D., Buford Parks, V.M.,
560 2023. Exhumation and incision of the eastern Central Andes, southern Peru: Low-
561 temperature thermochronology observations. Earth Planet Sci Lett 620.
562 https://doi.org/10.1016/j.epsl.2023.118299

563 Fedorov, A. V., Brierley, C.M., Lawrence, K.T., Liu, Z., Dekens, P.S., Ravelo, A.C., 2013.
564 Patterns and mechanisms of early Pliocene warmth. Nature 496, 43–49.
565 https://doi.org/10.1038/nature12003
566 Fox, N., Bloom, A., 1994. Snowline Altitude and Climate in the Peruvian Andes (5-17°S) at
567 Present and during the Latest Pleistocene Glacial Maximum. Journal of Geography 103,
568 867-885.

569 Gallen, S.F., Wegmann, K.W., 2017. River profile response to normal fault growth and linkage:
570 An example from the Hellenic forearc of south-central Crete, Greece. Earth Surface
571 Dynamics 5, 161-186. https://doi.org/10.5194/esurf-5-161-2017

572 Garzione, C.N., McQuarrie, N., Perez, N.D., Ehlers, T.A., Beck, S.L., Kar, N., Eichelberger, N.,
573 Chapman, A.D., Ward, K.M., Ducea, M.N., Lease, R.O., Poulsen, C.J., Wagner, L.S.,
574 Saylor, J.E., Zandt, G., Horton, B.K., 2017. Tectonic Evolution of the Central Andean
575 Plateau and Implications for the Growth of Plateaus. Annu Rev Earth Planet Sci 45, 529-
576 559. https://doi.org/10.1146/annurev-earth-063016-020612

577 Garzione, C.N., Molnar, P., Libarkin, J.C., MacFadden, B.J., 2006. Rapid late Miocene rise of
578 the Bolivian Altiplano: Evidence for removal of mantle lithosphere. Earth Planet Sci Lett
579 241, 543-556. https://doi.org/10.1016/j.epsl.2005.11.026

580 Gasparini, N.M., Whipple, K.X., 2014. Diagnosing climatic and tectonic controls on topography:
581 Eastern flank of the northern Bolivian Andes. Lithosphere 6, 230-250.
582 https://doi.org/10.1130/L322.1

583 Gautheron, C., Espurt, N., Barbarand, J., Roddaz, M., Baby, P., Brusset, S., Tassan-Got, L.,
584 Douville, E., 2013. Direct dating of thick- and thin-skin thrusts in the Peruvian Subandean
585 zone through apatite (U-Th)/He and fission track thermochronometry. Basin Research 25,
586 419-435. https://doi.org/10.1111/bre.12012

587 GDAL/OGR Contributors, 2021. GDAL/OGR Geospatial Data Abstraction software Library.
588 Open source Geospatial Foundation.
589 Genge, M.C., Adeoti, B., Webb, A.A.G., Huang, Y., Wang, F., Wu, L., Colleps, C.L., Singh,

590 B.P., Thiede, R.C., McKenzie, N.R., Vlaha, D.R., 2025. Apatite (U-Th)/He

591 Thermochronometry Along the Sutlej River, NW India Himalaya: Pleistocene River

592 Capture Events Accelerated River Anticline Development. Tectonics 44.

593 https://doi.org/10.1029/2025TC008983

594 Gérard, B., Audin, L., Robert, X., Gautheron, C., van der Beek, P., Bernet, M., Benavente, C.,

595 Delgado, F., 2020. Pliocene river capture and incision of the northern Altiplano: Machu

596 Picchu, Peru. J Geol Soc London jgs2020-100. https://doi.org/10.1144/jgs2020-100

597 Gérard, B., Robert, X., Audin, L., Valla, P.G., Bernet, M., Gautheron, C., 2021. Differential

598 Exhumation of the Eastern Cordillera in the Central Andes: Evidence for South-Verging

599 Backthrusting (Abancay Deflection, Peru). Tectonics 40, 1-29.

600 https://doi.org/10.1029/2020TC006314

601 Göğüş, O.H., Sundell, K., Uluocak, E.Ş., Saylor, J., Çetiner, U., 2022. Rapid surface uplift and
602 crustal flow in the Central Andes (southern Peru) controlled by lithospheric drip dynamics.

603 Sci Rep 12. https://doi.org/10.1038/s41598-022-08629-8

604 Gotberg, N., McQuarrie, N., Caillaux, V.C., 2010. Comparison of crustal thickening budget and
605 shortening estimates in southern Peru (12 14°S): Implications for mass balance and
606 rotations in the “Bolivian orocline.” Bulletin of the Geological Society of America 122,
607 727-742. https://doi.org/10.1130/B26477.1

608 Hoke, G.D., Isacks, B.L., Jordan, T.E., Blanco, N., Tomlinson, A.J., Ramezani, J., 2007.

609 Geomorphic evidence for post-10 Ma uplift of the western flank of the central Andes 18°30'

610 - 22°S. Tectonics 26, 1-17. https://doi.org/10.1029/2006TC002082
611 Hoke, G.D., Liu-Zeng, J., Hren, M.T., Wissink, G.K., Garzione, C.N., 2014. Stable isotopes
612 reveal high southeast Tibetan Plateau margin since the Paleogene. Earth Planet Sci Lett 394,
613 270–278. https://doi.org/10.1016/j.epsl.2014.03.007

614 Hoorn, C., Wesselingh, F.P., Ter Steege, H., Bermudez, M.A., Mora, A., Sevink, J., Sanmartín,
615 I., Sanchez-Meseguer, A., Anderson, C.L., Figueiredo, J.P., Jaramillo, C., Riff, D., Negri,
616 F.R., Hooghiemstra, H., Lundberg, J., Stadler, T., Särkinen, T., Antonelli, A., 2010.
617 Amazonia through time: Andean uplift, climate change, landscape evolution, and
618 biodiversity. Science (1979). https://doi.org/10.1126/science.1194585

619 Husson, L., Sempere, T., 2003. Thickening the Altiplano crust by gravity-driven crustal channel
620 flow. Geophys Res Lett 30, 1–4. https://doi.org/10.1029/2002GL016877

621 Insel, N., Poulsen, C.J., Ehlers, T.A., 2010. Influence of the Andes Mountains on South
622 American moisture transport, convection, and precipitation. Clim Dyn 35, 1477–1492.
623 https://doi.org/10.1007/s00382-009-0637-1

624 Kennan, L., Lamb, S.H., Hoke, L., 1997. High-altitude palaeosurfaces in the Bolivian Andes:
625 evidence for late Cenozoic surface uplift. Geological Society, London, Special Publications
626 120, 307–323. https://doi.org/10.1144/GSL.SP.1997.120.01.20

627 Kirby, E., Whipple, K., 2001. Quantifying differential rock-uplift rates via stream profile
628 analysis. Geology 29, 415–418. https://doi.org/10.1130/0091-
629 7613(2001)029<0415:QDRURV>2.0.CO;2

630 Kirby, E., Whipple, K.X., 2012. Expression of active tectonics in erosional landscapes. J Struct
631 Geol 44, 54–75. https://doi.org/10.1016/j.jsg.2012.07.009
Kirby, E., Whipple, K.X., Tang, W., Chen, Z., 2003. Distribution of active rock uplift along the eastern margin of the Tibetan Plateau: Inferences from bedrock channel longitudinal profiles. J Geophys Res Solid Earth 108. https://doi.org/10.1029/2001jb000861

Lease, R.O., Burbank, D.W., Gehrels, G.E., Wang, Z., Yuan, D., 2007. Signatures of mountain building: Detrital zircon U/Pb ages from northeastern Tibet. Geology 35, 239-242. https://doi.org/10.1130/G23057A.1

Lease, R.O., Ehlers, T.A., 2013. Incision into the eastern Andean Plateau during Pliocene cooling. Science (1979) 341, 774-776. https://doi.org/10.1126/science.1239132

Leonard, J.S., Whipple, K.X., Heimsath, A.M., 2023. Isolating climatic, tectonic, and lithologic controls on mountain landscape evolution. Sciences Advances 1-10. https://doi.org/10.1126/sciadv.add8915

Lindsay, J.B., 2016. Whitebox GAT: A case study in geomorphometric analysis. Comput Geosci 95, 75-84. https://doi.org/10.1016/j.cageo.2016.07.003

Lindsay, J.B., Cockburn, J.M.H., Russell, H.A.J., 2015. An integral image approach to performing multi-scale topographic position analysis. Geomorphology 245, 51-61. https://doi.org/10.1016/j.geomorph.2015.05.025

Margirier, A., Audin, L., Robert, X., Herman, F., Ganne, J., Schwartz, S., 2016. Time and mode of exhumation of the Cordillera Blanca batholith (Peruvian Andes). J Geophys Res Solid Earth 121, 6235-6249. https://doi.org/10.1002/2015JB012608.Received

Marocco, R., 1971. Etude géologique de la chaîne andine au niveau de la déflexion d'Abancay (Pérou). Cah. ORSTOM 3, 45-58.
Martínez, C., Jaramillo, C., Correa-Metrío, A., Crepet, W., Moreno, J.E., Aliaga, A., Moreno, F., Ibañez-Mejia, M., Bush, M.B., 2020. Neogene precipitation, vegetation, and elevation history of the Central Andean Plateau. Sci Adv 6. https://doi.org/10.1126/sciadv.aaz4724

McMillan, M., Schoenbohm, L.M., Tye, A.R., 2023. Plateau Formation Controlled by Lithospheric Foundering Under a Weak Crust. Geophys Res Lett 50. https://doi.org/10.1029/2023GL103996

Moore, A., Blenkinsop, T., 2002. The role of mantle plumes in the development of continental-scale drainage patterns: The southern African example revisited. South African Journal of Geology 105, 353–360.

Norton, K., Schlunegger, F., 2011. Migrating deformation in the Central Andes from enhanced orographic rainfall. Nat Commun 2. https://doi.org/10.1038/ncomms1590

Peizhen, Z., Molnar, P., Downs, W.R., 2001. Increased sedimentation rates and grain sizes 2-4 Ma ago due to the influence of climate change on erosion rates. Nature 410, 891–897. https://doi.org/http://www.nature.com/nature/journal/v410/n6831/suppinfo/410891a0_S1.ht ml

Perron, J.T., Royden, L., 2013. An integral approach to bedrock river profile analysis. Earth Surf Process Landf 38, 570–576. https://doi.org/10.1002/esp.3302

Picard, D., Sempere, T., Plantard, O., 2008. Direction and timing of uplift propagation in the Peruvian Andes deduced from molecular phylogenetics of highland biotaxa. Earth Planet Sci Lett 271, 326–336. https://doi.org/10.1016/j.epsl.2008.04.024

Plasterr, J., McQuarrie, N., Shelef, E., Falkowski, S., Eizenhöfer, P.R., Ehlers, T.A., 2025.

Drivers of canyon incision in the Peruvian Andes: Tectonics, precipitation, and drainage basin capture. Sci Adv 11. https://doi.org/10.1126/sciadv.adz9285
676 Pons, M., Sobolev, S. V., Liu, S., Neuharth, D., 2022. Hindered Trench Migration Due To Slab

677 Steepening Controls the Formation of the Central Andes. J Geophys Res Solid Earth 127.

678 https://doi.org/10.1029/2022JB025229

679 Poulsen, C.J., Ehlers, T.A., Insel, N., 2010. Onset of Convective Rainfall During Gradual Late
680 Miocene Rise of the Central Andes. Science (1979) 328, 490–494.

681 https://doi.org/10.1126/science.1185078

682 Purinton, B., Bookhagen, B., 2017. Validation of digital elevation models (DEMs) and
683 comparison of geomorphic metrics on the southern Central Andean Plateau. Earth Surface
684 Dynamics 5, 211–237. https://doi.org/10.5194/esurf-5-211-2017

685 Reuter, H.I., Nelson, A., Jarvis, A., 2007. An evaluation of void-filling interpolation methods for
686 SRTM data. International Journal of Geographical Information Science 21, 983–1008.

687 https://doi.org/10.1080/13658810601169899

688 Rizzoli, P., Martone, M., Gonzalez, C., Wecklich, C., Borla Tridon, D., Bräutigam, B.,
689 Bachmann, M., Schulze, D., Fritz, T., Huber, M., Wessel, B., Krieger, G., Zink, M.,

690 Moreira, A., 2017. Generation and performance assessment of the global TanDEM-X
691 digital elevation model. ISPRS Journal of Photogrammetry and Remote Sensing 132, 119–
692 139. https://doi.org/10.1016/j.isprsjprs.2017.08.008

693 Robert, X., 2019. Pyswath v2.02 (Python module).

694 https://doi.org/https://doi.org/10.5281/zenodo.2575054

695 Schildgen, T.F., Hodges, K. V., Whipple, P.W., Reiners, P.W., Pringle, M.S., 2007. Uplift of the
696 western margin of the Andean plateau revealed from canyon incision history, southern Peru.

697 Geology 35, 523–526. https://doi.org/10.1130/G23532A.1
Schwanghart, W., Kuhn, N.J., 2010. TopoToolbox: A set of Matlab functions for topographic analysis. Environmental Modelling and Software 25, 770–781.

https://doi.org/10.1016/j.envsoft.2009.12.002

Schwanghart, W., Scherler, D., 2014. Short Communication: TopoToolbox 2 - MATLAB-based software for topographic analysis and modeling in Earth surface sciences. Earth Surface Dynamics 2, 1–7. https://doi.org/10.5194/esurf-2-1-2014

Simpson, J., Kummerow, C., Tao, W.-K., Adler, R.F., 1996. On the Tropical Rainfall Measuring Mission (TRMM). Meteorology and Atmospheric Physics 60, 19–36.

https://doi.org/10.1007/BF01029783

Sundell, K.E., Saylor, J.E., Lapen, T.J., Horton, B.K., 2019. Implications of variable late Cenozoic surface uplift across the Peruvian central Andes. Sci Rep 9, 1–12.

https://doi.org/10.1038/s41598-019-41257-3

Sundell, K.E., Saylor, J.E., Lapen, T.J., Styron, R.H., Villarreal, D.P., Usnayo, P., Cárdenas, J., 2018. Peruvian Altiplano Stratigraphy Highlights Along-Strike Variability in Foreland Basin Evolution of the Cenozoic Central Andes. Tectonics 37, 1876–1904.

https://doi.org/10.1029/2017TC004775

Trauerstein, M., Norton, K.P., Preusser, F., Schlunegger, F., 2013. Climatic imprint on landscape morphology in the western escarpment of the Andes. Geomorphology 194, 76–83.

https://doi.org/10.1016/j.geomorph.2013.04.015

Uba, C.E., Strecker, M.R., Schmitt, A.K., 2007. Increased sediment accumulation rates and climatic forcing in the central Andes during the late Miocene. Geology 35, 979–982.

https://doi.org/10.1130/G224025A.1
720 van der Beek, P., Van Melle, J., Guillot, S., Pcher, A., Reiners, P.W., Nicolescu, S., Latif, M.,
721 2009. Eocene Tibetan plateau remnants preserved in the northwest Himalaya. Nat Geosci 2,
722 364–368. https://doi.org/10.1038/ngeo503

723 van Heiningen, P.S., Carlotto, V., Zuloaga, A.D., Romero, L., Andriessen, P.A.M., 2005.
724 Oligocene to Pleistocene exhumation patterns across the Apurimac River drainage basin,
725 southern Peru. 6th International Symposium on Andean Geodynamics (ISAG 2005,
726 Barcelona) 763–766.

727 Vera, C., Higgins, W., Amador, J., Ambrizzi, T., Garreaud, R., Gochis, D., Gutzler, D.,
728 Lettenmaier, D., Marengo, J., Mechoso, C.R., Nogues-Paegle, J., Silva Dias, P.L., Zhang,
729 C., 2006. Toward a unified view of the American monsoon systems. J Clim 19, 4977–5000.
730 https://doi.org/10.1175/JCLI3896.1

731 Whipple, K.X., Forte, A.M., DiBiase, R.A., Gasparini, N.M., Ouimet, W.B., 2017. Timescales of
732 landscape response to divide migration and drainage capture: Implications for the role of
733 divide mobility in landscape evolution. J Geophys Res Earth Surf 122, 248–273.
734 https://doi.org/10.1002/2016JF003973

735 Whipple, K.X., Gasparini, N.M., 2014. Tectonic control of topography, rainfall patterns, and
736 erosion during rapid post–12 Ma uplift of the Bolivian Andes. Lithosphere 6, 251–268.
737 https://doi.org/10.1130/L325.1

738 Whipple, K.X., Tucker, G.E., 1999. Dynamics of the stream-power river incision model:
739 Implications for height limits of mountain ranges, landscape response timescales, and
740 research needs. J Geophys Res 104, 661–674.

741 Willett, S.D., McCoy, S.W., Perron, J., Goren, L., Chen, C.Y., 2014. Dynamic reorganization of
742 River Basins. Science (1979) 343. https://doi.org/10.1126/science.1248765
743 Wise, J.M., Noble, D.C., 2008. Late Pliocene inception of external drainage and erosion of
744 intermontane basins in the highlands of Central Perú. Revista de la Sociedad Geologica de
745 Espana 21, 73-91.

746 Wobus, C., Whipple, K.X., Kirby, E., Snyder, N., Johnson, J., Spyropolou, K., Crosby, B.,
747 Sheehan, D., 2006. Tectonics from topography: Procedures, promise, and pitfalls.
748 Geological Society of America Special Pa, 55-74. https://doi.org/10.1130/2006.2398(04)

749 Yang, R., Fellin, M.G., Herman, F., Willett, S.D., Wang, W., Maden, C., 2016. Spatial and
750 temporal pattern of erosion in the Three Rivers Region, southeastern Tibet. Earth Planet Sci
751 Lett 433, 10-20. https://doi.org/10.1016/j.epsl.2015.10.032

752
<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

Central Andes

<figure><img src="image_15.png" /></figure>

Western Cordillera

<figure><img src="image_16.png" /></figure>

Eastern Cordillera

AD: Abancay Deflection

HPP: High Peruvian Plateaus

AFS: Apurimac Fault System

<figure><img src="image_17.png" /></figure>

Endorheic

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>
<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>
<figure><img src="image_23.png" /><figcaption>a</figcaption></figure>

<figure><img src="image_24.png" /><figcaption>b</figcaption></figure>

<figure><img src="image_25.png" /></figure>

<figure><img src="image_26.png" /><figcaption>c</figcaption></figure>

<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /></figure>

Mean elevation of the Altiplano/HPP

reviewed
<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>
<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>
<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>
<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>
a ~5 Ma

<figure><img src="image_37.png" /></figure>

b Present-day

<figure><img src="image_38.png" /></figure>
<figure><img src="image_39.png" /></figure>

Mean knickpoint retreat rate = 34±10 mm/yr

Sampling site (van Heiningen et al. (2005))

xx±xx Knickpoint retreat rate (mm/yr)
# Plio-Quaternary Landscape Evolution of the Northern Altiplano, Peru:
## Structural and Climatic Controls on Orogenic Plateau Capture

**Figure captions:**

**Figure 1.** Geomorphological and structural settings. a) Location of the study area (black rectangle) in the Central Andes and South America. b) Zoom on the Abancay Deflection area exhibiting the transition from exorheic High Peruvian Plateaus (HPP) and the endorheic Altiplano. Orogenic plateaus are highlighted in grey between the two Cordilleras. Major fault systems are indicated in red (from 1/100 000 and 1/50 000 INGEMMET maps: https://geocatmin.ingemmet.gob.pe/geocatmin/). c) Topographic swath profiles AA', BB' and CC' (see locations in Fig. 1b) extracted along rectangles (20-km width, 2-km sampling interval) using the PySwath program (Robert, 2019).

**Figure 2.** Geological and climatic settings of the study area. a) Locations of the Apurimac (1), Urubamba (2) and Madre de Dios (3) watersheds and simplified geological map of the study area (from 1/100 000 and 1/50 000 INGEMMET maps: https://geocatmin.ingemmet.gob.pe/geocatmin/). Cz: Cenozoic; Mz: Mesozoic; Pz: Paleozoic. b) Mean annual rainfall rates (1998 – 2009) from the Tropical Rainfall Measuring Mission (TRMM; Simpson et al., 1996) and topographic swath profile of southern Peru ([AB] box in Fig. 2a).
**Figure 3.** Spatial mapping of main river channels (left panels) and associated river profiles (right panels) for three the studied watersheds: a) Apurimac, b) Urubamba, and c) Madre de Dios. A selection of a few representative tributaries are displayed for clarity.

**Figure 4.** Spatial mapping of slopes (a) and relief computed as the standard deviation of topographic elevation within a 200-m radius moving window (b) of southern Peru. Studied watersheds are outlined in blue. Hanging surfaces were mapped using a slope threshold of <10°, following common criteria for identifying planation surfaces in the Andes (e.g., Kennan et al., 1997). The hanging surface mask was generated at pixel scale (30-m resolution), and polygons were subsequently adjusted manually to retain only coherent patches consistent with DEM slope inspection. AFS: Apurimac fault system; AD: Abancay Deflection; HPP: High Peruvian Plateaus.

**Figure 5.** Knickpoint spatial distribution over the study area. a) Spatial locations of glacial knickpoints and knickpoints associated with low-relief surfaces upstream (topographic knickpoints) in the three studied watersheds (outlined in blue). b) Knickpoints distribution along the topographic swath profile ([AB] box in “a”).

**Figure 6.** Spatial distribution of k<sub>sn</sub> values. a) Map of k<sub>sn</sub> values for the Apurimac, Urubamba and Madre de Dios watersheds. b) 3D topographic diagram (location in “a”) of a tributary of the Apurimac river showing the respective distribution of k<sub>sn</sub> values (channels), locations of hanging surfaces and major topographic knickpoints.
**Figure 7.** Spatial distribution of χ values. a) Map of χ values associated with outlets at 0.6 km of elevation to investigate drainage divide stability between the exorheic watersheds. b) Map of χ values associated with outlets at 3.8 km of elevation to investigate drainage divide stability between exorheic basins northward and the endorheic Altiplano southward.

**Figure 8.** Paleogeographic evolution of southern Peru since the Pliocene. a) Reconstructed paleo-elevation map of southern Peru ca. 5 Ma ago, generated using bicubic Tikhonov spline interpolation based on the elevations of major knickpoints identified in this study and those of captured intermontane basins reported by Wise & Noble (2008) (Junin, Huancayo, and Ayacucho) and Sundell et al. (2018) (Paruro). b) Present-day topography and drainage pattern of southern Peru.

**Figure 9.** Major knickpoint retreat map within the Apurimac watershed. Retreat rates were calculated by dividing the distance measured along the present-day hydrographic networks between each major knickpoint and the downstream triple junction (red star) by the estimated age of the Altiplano capture of 7.2 ±2.1 Ma (van Heiningen et al., 2005).