The Cenozoic history of the Tibetan Plateau topography is critical for understanding the evolution of the Indian-Eurasian collision, climate, and biodiversity. However, the long-term growth and landscape evolution of the Tibetan Plateau remains ambiguous, it remains unclear if plateau uplift occurred soon after the India-Asia collision in the Paleogene or later in the Neogene. As the landscape evolution is controlled mainly by mountain uplift and surface processes, the present-day river profiles and the drainage basin geometries preserve important information that can be extracted to infer the long-term history of mountain uplift with numerical models. Here we focus on the southeastern (SE) Tibetan Plateau where three of the world’s largest rivers draining the Tibetan Plateau (the Yangtze, Mekong, and Salween Rivers, i.e., Three Rivers) have incised deep valleys with distinctive geomorphic signatures. We reproduce the uplift history of the SE Tibetan Plateau using a 2D landscape evolution model, which simultaneously solves fluvial erosion and sediment transport processes in the drainage basins of the Three Rivers region. Our model was optimized through a formal inverse analysis with a large number of forward simulations, which aims to reconcile the transient states of the present-day river profiles. The modeling results were ultimately compared to existing thermochronologic and paleoelevation datasets to help decipher between competing tectonic models that predict contrasting topographic evolutions. Our results suggest initially low elevations during the Paleogene, followed by a gradual southeastward propagation of topographic uplift of the plateau margin until present day. The modeling thus does not support Paleogene formation of the SE Tibetan Plateau with a major subsequent degradation via upstream fluvial erosion. The scenario with pre-existing high-elevation plateau or plateau degradation will result in much wider river channels with knickpoints that propagated upstream much further away from the plateau margin compared to observed river profiles. The quantitative constraints on landscape evolution achieved based on drainage patterns in SE Tibet indicate a powerful tool potentially applicable to other regions to infer important implications for the evolution of Indian-Eurasian collision, Asian monsoons, and biodiversity, as well as the geodynamic forces involved in collisional orogens.

How to cite: Yuan, X., Jiao, R., Dupont-Nivet, G., and Shen, X.: Southeastern Tibetan Plateau growth revealed by inverse analysis of landscape evolution model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2764, https://doi.org/10.5194/egusphere-egu23-2764, 2023.

Proposed drivers of eastern Andean Plateau river incision in the Pliocene include climate change, dynamically driven plateau uplift, and long-wavelength surface uplift above deep basement structures. However, the evaluation of each mechanism has been hampered in previous studies due to the lack of along-strike data on the timing and extent of canyon incision. In addition, the magnitude of exhumation, permissible structural geometries, and integration of the long-term deformation, erosion, exhumation, and sedimentation histories remain poorly understood.

This presentation focuses on two balanced geologic cross-sections and thermochronologic bedrock sample transects across the Andean Plateau, Eastern Cordillera, and Subandes in southern Peru. Based on (i) age-distance and age-elevation patterns of >80 new thermochronologic dates (apatite and zircon (U-Th)/He and fission-track) from plateau, interfluve, and canyon sample locations; (ii) inverse thermal history model results; and (iii) flexural and thermo-kinematic modeling, we highlight similarities and differences in thermochronometric age patterns, exhumation magnitude, structural geometries, and shortening rates between each section.

Results show that the first-order thermochronometric age pattern is a function of rocks' vertical and lateral movement over basement ramps and resulting exhumational erosion. This pattern is superimposed with a regional and synchronous incision-related exhumation signal since the Pliocene. While this incision occurred independent of structural deformation, the exhumation magnitude and difference in interfluve and canyon thermochronometric ages require the presence of a tectonic contribution to exhumation. We conclude that uplift over a basement ramp in the Eastern Cordillera and a decrease in shortening rates since ~10 Ma set the stage for climate-enhanced incision to occur in southern Peru.

How to cite: Falkowski, S., Glover, C., Buford Parks, V., McQuarrie, N., Perez, N., and Ehlers, T. A.: Drivers of eastern Andean Plateau incision from integrated thermochronology and thermo-kinematic modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12157, https://doi.org/10.5194/egusphere-egu23-12157, 2023.

Himalayan rivers transport approximately 10³ Mt of sediment annually from their source in the steep topography of the High Himalaya to ocean basins. However, the journey from source to sink is not necessarily a smooth one: on the way, sediment can become trapped in montane storage systems, such as river valleys or floodplains. While sediment is stored in valleys, climate and erosional signals that we may wish to read from the final sedimentary record can be modified or even destroyed. We therefore need to understand the spatial distribution, volume and longevity of these valley fills. However, controls on Himalayan valley location and geometry are unknown, and sediment volume estimates are based on relatively untested assumptions of valley widening processes.

In this work we use a new method of automatically detecting valley floors to extract 1,644,215 valley-floor width measurements across the Himalayan orogen. We use this dataset to explore the dominant controls on valley-floor morphology, and to test models of valley widening processes. We use random forest regression to estimate the importance of potential controlling variables, and find that channel steepness, a proxy for rock uplift, is a first-order control on valley-floor width. We also analyse a newly compiled dataset of 1,797 exhumation rates across the orogen and find that valley-floor width decreases as exhumation rate increases. We therefore suggest that valley-floor width is adjusted to long-term exhumation, controlled by tectonics, rather than being controlled by water discharge or bedrock erodibility. We also hypothesise that valley widening predominantly results from sediment deposition along low-gradient valley floors, controlled by the ratio of sediment to water discharge, rather than lateral bedrock erosion.

How to cite: Clubb, F., Mudd, S., Schildgen, T., van der Beek, P., Devrani, R., and Sinclair, H.: Controls on valley-floor width across the Himalayan orogen, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3502, https://doi.org/10.5194/egusphere-egu23-3502, 2023.

Stream networks are highly abundant across Earth’s surface, reflecting the tectonic and climatic history under which they have developed. Prior studies suggest that stream branching angles are strongly correlated with climatic aridity, with a tendency toward wider branching angles in more humid climates. However, branching angles are also shaped by topography and thus by tectonic forcing. The importance of climate relative to tectonics, especially in tectonically active regions, remains ambiguous. Here we evaluate the relative dominance of climatic aridity and channel slope in shaping the branching angles of stream networks on the eastern Tibetan Plateau, a region with complex tectonics, variable climate, and diverse landscapes. Climatic aridity and channel slopes vary systematically from the relatively flat, dry interior to the steep, wet margin. Our analysis shows that the correlation between branching angles and climatic aridity reverses between the relatively flat interior and the steep eastern margin and the shift is observed in the transitional zone at intermediate topographic slopes. In the flat interior, branching angles are wider in wetter climates, consistent with previous studies in other regions. As one approaches the Tibetan Plateau’s eastern margin, however, branching angles become narrower as climate becomes wetter and topographic gradients simultaneously become steeper. These general patterns also persist after removing side-branches. These results indicate that climatic controls on branching angles are gradually overwhelmed by tectonic controls as one goes from the relatively flat terrain of the interior to the steeper terrain of the tectonically active eastern margin. Our findings demonstrate the joint influence of tectonic forcing and climate in shaping river network morphology.

How to cite: Li, M., Seybold, H., Wu, B., Chen, Y., and Kirchner, J. W.: Interaction between tectonics and climate encoded in the planform geometry of stream networks on the eastern Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4241, https://doi.org/10.5194/egusphere-egu23-4241, 2023.

Mountain building has classically been linked with CO₂ drawdown from silicate weathering in the critical zone, although recent views on mountain building recognize the importance of rock-derived CO₂ emissions from other organic and inorganic carbon sources. However, the focus on critical zone weathering reactions during mountain building does not consider the emission of metamorphic CO₂ from subduction processes in the crust and mantle. Such deep carbon sources could outpace the surficial drawdown and release of carbon, in particular in actively extending mountain ranges that subduct large volumes of carbonate rock. Thus, accounting for weathering processes at depth and in the critical zone in parallel is crucial to fully assess how mountain-range uplift impacts the carbon cycle. Here, we quantify the exchange of CO₂ between rock and the atmosphere from subduction-related processes and from critical zone weathering reactions in two major river systems in the central Apennine Mountains of Italy. The catchments straddle a geodynamic gradient across the subduction zone that is expressed as changes in surface heat flow and crustal thickness, whereas climatic boundary conditions are relatively constant.  At the regional scale, we find that metamorphic CO₂ sources outpace critical zone inorganic carbon sources and sinks by 2 orders of magnitude above a window in the subducting slab that is characterized by high heat flow and low crustal thickness, and could have driven efficient degassing over the last 2 Ma. In contrast, surficial weathering processes dominate the carbon budget where crustal thickness is greater and heat flow is lower. Importantly, the difference in metamorphic degassing fluxes across the geodynamic gradient is multiple orders of magnitude larger than the difference in critical zone weathering fluxes. Thus, modulations of metamorphic decarbonation reactions are the most efficient process by which tectonics can regulate the inorganic carbon cycle in the Apennines. Both near-surface and deep sources of CO₂ must be considered when constructing the carbon budget of orogenic systems that include the subduction of carbonate rock.

How to cite: Erlanger, E., Bufe, A., Paris, G., D'Angeli, I., Pisani, L., Kemeny, P., Stammeier, J., Haghipour, N., and Hovius, N.: Building the inorganic carbon budget of a young, actively extending carbonate-rich mountain range:  the interplay between chemical weathering and tectonics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5452, https://doi.org/10.5194/egusphere-egu23-5452, 2023.

Determination of the depositional age of sediments provides the basis for much of the current understanding of tectonic processes, paleoclimate, and other aspects that relate to time. Integrated the high-resolution magnetostratigraphy with independent means of age control (e.g., biostratigraphy, tephrostratigraphy), the age model of the sedimentary sequences can generally be constrained. However, as the paleomagnetic correlation to the Geomagnetic Polarity Time Scale (GPTS) is usually non-unique, magnetostratigraphy alone usually leads to dramatically different age models for the siliclastic sequences in the absence of fossils or volcanic ash layers, likely resulting in diverse tectonic and paleoclimate reconstructions. This challenge presented by different age models is well-exemplified in the debated Cenozoic terrestrial strata in Central Asia, resulting in competing models that account for the growth of the Tibetan plateau and its association with aridification history of Central Asia. Here we develop a new approach to evaluate the age model of the tephras- and fossils-free strata by checking the potential link between syntectonic sedimentation in the basin and the rapid exhumation of basement rocks. By comparing the initiation of growth strata with the onset timing of the rapid exhumation revealed by the low-temperature thermochronology, we validate this method in the regions (e.g., Zagros fold-and-thrust belt and Ruby Mountains metamorphic core complex) where the age models for the strata have been well-constrained. Applying this approach to the debated age models of the strata in the Tarim and Qaidam basins, we constrain the depositional age of Paleogene syntectonic strata, indicating a Paleocene-Eocene initial and an Oligocene-Miocene intensified mountain building process along the northern margin of the Tibetan plateau. Integrating the timing of Paleogene tectonism along the northern Tibetan plateau with Proto-Paratethys Sea fluctuations history, we highlight the significant role of tectonism in the retreat of proto-Paratethys Sea as well as its influence on the aridification in Central Asia.

How to cite: Cheng, F., Zuza, A., Marc, J., and Guo, Z.: Testing age models for sedimentary sequences based on growth strata and the exhumation history of adjacent mountain ranges, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6921, https://doi.org/10.5194/egusphere-egu23-6921, 2023.

An interplay of rock uplift and glacial erosion shapes glacierized mountains across the globe. Under the simplifying assumption that subglacial bedrock erosion is proportional to the local ice flux, a steady balance between uplift and erosion is used to theoretically predict the elevation distribution (hypsometry) of glacier cover above the long-term snowline. When snow accumulation rates increase linearly with elevation, the theory predicts a half-normal distribution with a range that is proportional to the million-year scale local uplift rate. The theoretical form fits well the present-day hypsometry of glacier cover in glacierized mountain ranges across the globe, which may indicate a prevailing approximate long-term balance between glacial erosion and uplift. The fits obtain realistic estimates of the spatial patterns of uplift, which align well with geologic boundaries, and explain global variations in the maximum height of mountain peaks measured from the long-term local snowline. However, a comparison of hypsometry-derived uplift rates with thermochronology-derived exhumation rates yields large residuals, likely due to the simplifying assumptions and a poorly calibrated erosion law. Despite the limitations, the steady-state theory presented successfully describes both the glacier-cover hypsometry and the peak heights on a global scale, connecting them to the million-year scale local uplift rates.

How to cite: Scherler, D. and Banerjee, A.: Topographic signature of tectonics in glacial landscapes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7595, https://doi.org/10.5194/egusphere-egu23-7595, 2023.

Landscapes are sculpted by a complex response of surface processes to external forcings, such as climate and tectonics. Several major stream captures have been documented on the Southeast Tibetan Plateau, leading to the hypothesis that the region experiences exceptionally high rates of drainage reorganization driven by horizontal shortening and propagating uplift. Here we determine the prevalence, intensity, and spatial patterns of ongoing drainage reorganization on the Southeast Tibetan Plateau and evaluate the relative time scales of this transience by comparing drainage divide asymmetry for four geomorphic metrics that operate at different spatial and temporal scales. Specifically, we evaluate drainage divide asymmetry in catchment-restricted topographic relief, hillslope gradient, normalized channel steepness (k_sn), and χ. k_sn and χ are both precipitation-corrected to account for the strong precipitation gradient across the region. We calculate the migration direction and Scherler & Schwanghart (2020)’s divide asymmetry index (DAI) in each metric for drainage divides across the entire region in order to analyze how well the asymmetry in these metrics agree along divides and where consistent divide movement is inferred. We find a high incidence of strongly asymmetric divides in all metrics across the entire Southeast Tibetan Plateau. While the magnitude of asymmetry varies significantly between metrics, a majority of divides agree on divide migration direction across all metrics. Divides with higher magnitudes of asymmetry are more likely to agree on migration direction across multiple metrics. While χ agrees least often with the other metrics on migration direction, it agrees on direction >90% of the time when low DAI divides are excluded. We also establish that disagreement in predicted divide migration directions between χ and the other geomorphic metrics can be interpreted as evidence of localized variations in tectonic uplift or erodibility, glacial alteration, or recent lateral stream capture. Our work confirms the high incidence of drainage reorganization across the Southeast Tibetan Plateau and highlights both transient and stable areas in the landscape with unprecedented resolution. In addition, we propose how to combine geomorphic metrics to ascertain how drainage divides migrate across different timescales and identify local deviations in tectonic uplift and erodibility.

How to cite: Gelwick, K. D., Willett, S. D., and Wang, Y.: Drainage divide asymmetry as an indicator of large-scale landscape transience on the Southeast Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7931, https://doi.org/10.5194/egusphere-egu23-7931, 2023.

Multiple uplift events, either by discrete earthquakes or creep, will steepen and thus apparently rejuvenate fault scarps, raising the possibility that fault slip history leaves a hidden morphological signature. Here we explore this idea by proposing a new analytical formulation to simulate the scarp degradation generated by faulting at regular intervals. Our formulation fills the gap between the single rupture and the creeping fault proposed solutions. We show that the morphology of degrading fault scarps generated by one major or multiple minor earthquakes with the same final total uplift deviates by as much as 10-20%. Our inversion approach highlights the importance of trade-offs between fault slip history and erosion intensity. An identical topographic profile can be obtained either with a stable creep and an intense erosion or with a single seismic event and a weak erosion. Finally, our findings reveal that the previously noticed variation of the diffusion coefficient with time may be an artifact related to the kinematics of faulting. These inferences, derived from the simplest possible diffusion model, are likely to be even more pronounced in nature.

How to cite: Steer, P., Holtmann, R., Cattin, R., and Simoes, M.: Revealing the hidden signature of fault slip history in the morphology of degrading scarps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9275, https://doi.org/10.5194/egusphere-egu23-9275, 2023.

The legacy of tectonic deformation affects geomorphic and biological dynamics, even in post-orogenic mountain ranges. As ancient geologic structures originally created through tectonic deformation are exhumed through erosion, rocks with different chemical and physical properties are exposed at the surface of the landscape. We propose that this process not only influences landscape dynamics but is also a mechanism for speciation in freshwater fish.  As rivers erode through layers of different kinds of rock, the spatial distribution of rocks at the surface of the landscape changes. For fish with habitat specificity linked to rock type, erosion can progressively expose either favorable or unfavorable rock types, creating either barriers to or corridors for dispersal. The underlying structural geology will dictate which of those scenarios occurs. We present two case-studies that illustrate each scenario from the southeast United States, a freshwater biodiversity hotspot. First, we show that populations of the Greenfin Darter (Nothonotus chlorobranchius) are genetically isolated within tributaries flowing over the metamorphic rocks making up the thrust sheets of the Blue Ridge geologic province. In contrast, they are not found in rivers flowing over sedimentary rock of the Valley and Ridge. We show that over time, more sedimentary rock has been exposed, which has progressively isolated N. chlorobranchius populations from one another. In this case, river incision is introducing more barriers (sedimentary rock) into the landscape, leading to lineage diversification (i.e., speciation). In the second case-study, we explore the diversification of the Vermilion Darter complex that includes the federally endangered Vermilion Darter (Etheostoma chermocki) and the closely related Warrior Darter (E. bellator). Unique lineages of this species complex are restricted to tributaries flowing over carbonate rocks in the Black Warrior River. In contrast to the N. chlorobranchius case-study, here river incision is progressively expanding habitat by exposing more carbonate rock, driving dispersal-mediated allopatric speciation within the Vermilion Darter complex. Our results suggest that in bedrock-dominated rivers found throughout much of the Appalachian Mountains, erosion through ancient geologic structures can drive the diversification of freshwater fish, highlighting links between tectonic deformation, surface processes, and biological evolution in an ancient mountain range.

How to cite: Stokes, M., Kim, D., Perron, J. T., and Near, T.: Erosion through ancient geologic structures as a mechanism for freshwater fish speciation in a post-orogenic mountain range, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9690, https://doi.org/10.5194/egusphere-egu23-9690, 2023.

Glacial-interglacial cycles have repeatedly perturbed climate and topography in many mid-latitude mountain ranges during the Quaternary. Glacial erosion can move drainage divides and induce fluvial adjustment downstream. Today and in the past, north-facing slopes in the Qilian Shan have accumulated more ice because they receive less solar insolation and more precipitation than south-facing slopes. The larger glaciers that form on north-facing slopes may enhance erosion and drive southward migration of drainage divides, particularly during glacial periods. We combine numerical simulations with topographic analyses to examine the influence of glacial erosion on divide mobility and postglacial landscape response to drainage reorganization. Our analyses suggest that asymmetric glaciation in the Qilian Shan has caused southward migration of the main drainage divide, prompting river channels below the extents of ice on north-facing slopes to become oversteepened relative to their drainage area. This oversteepening should accelerate postglacial fluvial incision, even in this region where topography has not been directly modified by glacial erosion. Numerical modeling suggests this enhanced incision persists for millions of years – much longer than the duration of recent glacial-interglacial cycles – implying a widespread and enduring influence of intermittent glaciations on landscape evolution in mid-latitude mountain ranges during the Quaternary.

How to cite: Lai, J. and Huppert, K.: Asymmetric glaciation, divide migration, and postglacial fluvial response times in the Qilian Shan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3099, https://doi.org/10.5194/egusphere-egu23-3099, 2023.

The first-order morphology of mountain ranges is controlled by the topologic complexity of the channel networks that drain them. Some networks are characterized by simple flow paths that follow the regional topographic gradient. Other networks are more complex, showing tortuous flow paths and asymmetric distribution of drainage area with respect to the main trunks. The degree of network complexity controls the distribution of slope magnitude and aspect, as well as the local relief of mountainous terrains, placing a strong control over their geomorphic, hydrologic, and ecologic functionality. 

Some of the variability in network complexity could be attributed to the level of heterogeneity in the environmental and boundary conditions. Spatial gradients in tectonics, climate, and lithology are likely linked to more complex network topology. However, previous numerical studies of landscape evolution showed that variability in complexity appears even when the environmental and boundary conditions are uniform. This means that drainage complexity could emerge from autogenic network dynamics.

To explore the controls over network complexity, we adopt a new metric that quantifies complexity as the distribution of differences in flow length between pairs of flow paths that diverge from a common divide and merge downstream. Symmetric flow lengths indicate low complexity, and increased flow-length asymmetry is indicative of a complex network. Consistent with previous numerical studies, we show, for the first time for natural mountain ranges, that plan-view network complexity, as expressed by lengthwise asymmetry, is a strong function of the concavity index that characterizes channel long profiles.

An analytic model of channel pairs that diverge from a stable drainage divide and obeys Hack’s law predicts that low concavity channels can sustain a stable divide only if they are lengthwise symmetric. In contrast, high concavity channels can sustain stable divides under a range of lengthwise symmetry conditions. The analytic model explains the increase in asymmetry (complexity) median and variance with increased channel concavity documented in both natural and numerical mountain ranges.

An optimal channel network perspective provides further intuition. Starting from a random network, the energy gain of reducing network complexity is high only when the concavity is low. Therefore, high-concavity, complex networks have a lower energetic incentive to reduce their complexity via changes in network topology. In contrast, complex networks of medium and low concavity tend to change their topology via drainage divide migration to achieve a less complicated and lower energy configuration.

Our findings provide a way to quantify channel concavity by evaluating the plan-form network complexity. Our results further imply that reduction in channel concavity, due to, for example, a transition to a drier climate, is expected to induce a phase of drainage reorganization that reduces the network complexity. In contrast, increased concavity is likely to cause minor or no changes in network topology and complexity.

How to cite: Goren, L. and Shelef, E.: Channel concavity controls drainage network complexity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12490, https://doi.org/10.5194/egusphere-egu23-12490, 2023.

The branching angles of stream network are the fingerprint of the processes that shape our landscape. However, the mechanisms that give rise to stream network patterns on Earth are not fully understood. Recent studies have shown controls of climate, tectonics, and lithology on channel incision and the planform geometry of stream networks. Our analysis of one million river junctions and over 4.2 million groundwater well observations across the contiguous United States shows for the first time that stream network branching angle vary systematically with the degree to which streams and groundwater interact.  Streams that are losing their water to groundwater exhibit narrow branching angles while streams that are gaining water from groundwater exhibit wide branching angles on average. We show that the correlation between branching angle and fraction of losing streams is stronger than branching angle and other controls of stream network planform geometry. The systematic relationship between branching angle and losing fraction persist across a range of topographic gradient and across several stream orders. Our findings brings forward a mechanistic linkage between previously shown correlation between branching angles and climate.

How to cite: Freund, E., Seybold, H., Jasechko, S., and Kirchner, J.: Groundwater-surface water interactions manifested on stream network geometry across United States, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13304, https://doi.org/10.5194/egusphere-egu23-13304, 2023.

The evolution and course of Himalayan rivers when exiting the orogen is controlled by the interplay between tectonics, climate, and associated sediment flux. We investigate these interactions by studying a Late Pleistocene deflection of the Sutlej River at the southern margin of the western Himalayan. This part of the Himalaya is also referred to as Kangra Recess. Late Quaternary faulting and folding along the Main Frontal Thrust and related back thrusts has created anticlinal structures in the south and piggyback basins in the north. Combined field observations and chronological constraints have shown that the anticline evolved as multiple fault segments, which grew through lateral propagation and led to the permanent deflection of the Sutlej River by ~ 50 km to the southeast. In this work, we present new luminescence and cosmogenic nuclide chronologies combined with previously published data to better identify the sedimentation history. Most importantly, we focus on the cause and final timing of the permanent river deflection. We show evidence for widespread aggradation and sediment deposition by the Sutlej River megafan and its tributaries starting before 47 ka and continuing until ~ 26 ka. Our ¹⁰Be and ²⁶Al results in combination with available OSL data document the last widespread throughflow of the Sutlej at ~ 30-25 ka. We argue that a combination of climate and tectonic factors, especially the variability of monsoonal strength, led to major changes in sediment supply at short time scales and therefore affected the course of the Sutlej River system.

How to cite: Kordt, J., Dey, S., Bookhagen, B., Rugel, G., Lachner, J., Vivo-Vilches, C., and Thiede, R.: Frontal fault growth and megafan construction control drainage development in the western Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14188, https://doi.org/10.5194/egusphere-egu23-14188, 2023.

Past studies indicate that landscape evolution on various timescales is influenced by vegetation cover. However, the linkages between vegetation, type, and species distribution and erosion processes and their relationships between landscape steepness and climate are not well understood. In this study, we focus on the active tectonic setting of the East-African Rift System and its complex climatic and biotic environment to explore linkages between millennial-scale denudation rates and landscape steepness, climate, and vegetation. We specifically focus on spaceborne vegetation-height and biomass measurements that may better reflect the impact of vegetation on geomorphic processes when compared to generally used vegetation cover measurements. We present 12 new in situ ¹⁰Be catchment-averaged denudation rates from the tectonically active Chew Bahir area in southern Ethiopia. The sampled catchments comprise a range of denudation rates over one order of magnitude from 0.01 to 0.1 mm/y and largely correlate with rainfall-weighted landscape steepness. We analyze the rates in comparison to previous studies (a) that evaluated the drier central and northern areas of the Kenya Rift to the south of Chew Bahir and (b) that measured denudation rates in the wetter, densely vegetated Rwenzori mountains in Uganda to the west. Rock-strength values between the sites are comparable, although the Rwenzori mountains have undergone rapid Miocene-Pliocene exhumation processes that may have been aided by ubiquitous fractured bedrock. Importantly, we observe a clear impact of biomass on denudation rates. For example, catchments with the same denudation rate and erosional integration timescale but higher biomass can sustain steeper fluvial channels as indicated by their river-steepness indices. We argue that high vegetation heights characterized by deep root structures lead to a stabilization of hillslopes and ultimately allow the formation of steeper channels. This in turn results in lower denudation rates comparable to less vegetated terrain where hillslopes destabilize more rapidly. We analyze the spatial distribution of hillslopes, river-steepness, rainfall, and vegetation biomass within catchments to elucidate their relative impact. This allows us demonstrate the usefulness of vegetation height and biomass measurements for assessing impacts on erosion rates and we explore different weighting schemes for digital elevation model analysis.

How to cite: Bookhagen, B., Erbello, A., Wittman, H., Melnick, D., and Strecker, M.: The impact of vegetation on erosion in the East-African Rift System: New insights from Chew Bahir, southern Ethiopia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14798, https://doi.org/10.5194/egusphere-egu23-14798, 2023.

Digital Elevation Models (DEMs) are a fundamental data source for the calculation of tectonogeomorphic indices in areas with active tectonic deformation. There are, however, hardly any studies available that compared the strength and weaknesses of the various, freely available medium-resolution DEMs for these kinds of applications. As such, it is difficult for researchers to make a well-informed choice regarding the most suitable DEM for their specific study. We have therefore carried out an exhaustive analysis of the five, most commonly used medium-resolution DEMs. These are the 30-m SRTM v.3.0, AW3D30, ASTER GDEM3, Copernicus and the 12-m TanDEM-X. We have analysed the performance of these DEMs by calculating the most commonly used tectonogeomorphic indices for 22 river basins in two geographically contrasting tectonic basins in the Peruvian Andes. Calculated metrics included drainage basin areas, fluvial network length and position, longitudinal profile and knickpoint representation, concavity indices θ and m/n, the normalised steepness index ksn and the Hypsometric integral. We also performed a mapping exercise of fluvio-tectonic landforms such as fluvial terraces, folds and fault traces. Statistical analysis were carried out to highlight similarities and differences in performance between the five DEMs. Copernicus and TanDEM-X were the best performing DEMs across the whole range of analysed metrics, closely followed by AW3D30. SRTM3 v. 3.0 and ASTER GDEM3 performed well in some of the tests, but lacked in other areas and are therefore not recommended. 

How to cite: Viveen, W., del Rosario González-Moradas, M., Vidal-Villalobos, R. A., and Villegas-Lanza, J. C.: An assessment of the most suitable DEM for tectonogeomorphic analysis in tectonic basins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17217, https://doi.org/10.5194/egusphere-egu23-17217, 2023.

The underground of the northern German lowlands, located in the Central European Basin System (CEBS), is characterized by numerous Permian Zechstein salt structures, which are found at depths of up to more than 2000m. The lowlands were transgressed several times by the Scandinavian Ice Sheet during the Pleistocene glacial cycles. Several researchers have noted that there seems to be a spatial correlation between the positions of Weichselian end moraines in Northern Germany and subsurface salt structures. Thus, it was assumed that the pressure of the advancing ice sheet triggers salt tectonic movements, which in return influences the spatial configuration of the ice extent.

Using high resolution laser scan digital elevation models, we have recently mapped more than 150 linear negative landforms (up to several km in length, up to 20 m in depth and up to more than 100 m in width) in northern Germany that we term “surface cracks” and which we interpret as surface expansion ruptures caused by ice sheet induced salt movements related to the last glacial cycle (Weichselian glaciation). This interpretation is based on: (1) geomorphological analyses, which also allow for a relative geochronological classification; (2) a reassessment of existing theoretical models on ice sheet induced salt movement, and; (3) new physical modeling experiments. Our results shed a new light on the geomorphology of the northern German young morainic landscapes, illustrating an active interplay between climate (glaciations) and loading-induced subsurface motions (buried salt structures).

How to cite: Hardt, J., Norden, B., Bauer, K., Dooley, T., and Hudec, M.: Ice sheet induced salt tectonics – the example of surface cracks in northern Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15122, https://doi.org/10.5194/egusphere-egu23-15122, 2023.