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Few studies have constrained the magnitudes and timescales associated with large‐scale drainage captures (areas >103 km2), even though these constraints are crucial to reconstruct sediment budgets, assess the potential for drainage reorganization to be preserved in the rock record, and determine the extent to which environmental signals (i.e., structures, composition and fossil assemblages within sedimentary rocks that are influenced by sediment supply and transport) are representative of conditions during deposition. In this work, we characterize the Pleistocene capture of the Zhada Basin, an ~23 000 km2 extensional basin in southern Tibet, by the Sutlej River, a prominent tributary to the Indus River. We quantify the magnitudes and timescales of capture‐driven erosion using knickpoint celerity modelling, paleotopographic reconstructions, 10Be‐derived denudation rates, and topographic analyses of drainage divides. We find that capture has removed 2010 ± 400 km3 of sediment from the Zhada Basin, increasing sediment supply to the Sutlej network by 17%–29% since 735 ± 269 ka. This work represents a crucial step towards reconstructing the Pleistocene sediment budget of the Indus sedimentary system and identifying potential impacts from sediment redistribution. We also identify several plausible tectonic or autogenic mechanisms that may have facilitated capture of the Zhada Basin, including: (1) preferential erosion of weak lithologies along active faults, (2) headward erosion in response to prior capture of the Spiti River and (3) headward erosion generated by breaching of a structural culmination downstream (the Kullu‐Rampur Window). This provides a framework to assess the mechanistic links between arc‐parallel extension, large‐scale drainage capture, landscape evolution and orogenic wedge deformation. [ABSTRACT FROM AUTHOR]

Bedrock rivers are the pacesetters of landscape evolution in uplifting fluvial landscapes. Water discharge variability and sediment transport are important factors influencing bedrock river processes. However, little work has focused on the sensitivity of hillslope sediment supply to precipitation events and its implications on river evolution in tectonically active landscapes. We model the temporal variability of water discharge and the sensitivity of sediment supply to precipitation events as rivers evolve to equilibrium over 106 model years. We explore how coupling sediment supply sensitivity with discharge variability influences rates and timing of river incision across climate regimes. We find that sediment supply sensitivity strongly impacts which water discharge events are the most important in driving river incision and modulates channel morphology. High sediment supply sensitivity focuses sediment delivery into the largest river discharge events, decreasing rates of bedrock incision during floods by orders of magnitude as rivers are inundated with new sediment that buries bedrock. The results show that the use of river incision models in which incision rates increase monotonically with increasing river discharge may not accurately capture bedrock river dynamics in all landscapes, particularly in steep landslide prone landscapes. From our modeling results, we hypothesize the presence of an upper discharge threshold for river incision at which storms transition from being incisional to depositional. Our work illustrates that sediment supply sensitivity must be accounted for to predict river evolution in dynamic landscapes. Our results have important implications for interpreting and predicting climatic and tectonic controls on landscape morphology and evolution. Plain Language Summary: Rivers that carve rock are often used as markers of climate, tectonic, and rock‐type controls in evolving landscapes. To back out these controls from the present form of rivers which erode rock, thorough knowledge of how they evolve and how they respond to changes in climate and tectonics is required. Most models for the evolution of bedrock rivers assume that the rate of erosion always increases with river discharge, as the weight of water on the riverbed increases. Here, we challenge this assumption using a new model for river evolution which accounts for short‐timescale variations in river discharge and supply of sediment from hillslopes to channels. We find that in these systems, the largest floods may be less erosive than one would expect because they must transport large volumes of sediment, which makes it harder for them to erode fresh bedrock in channels. Our results are important because models of river evolution inform much of our understanding of interactions between Earth's surface and its atmosphere in rapidly changing parts of our planet. Key Points: We present a bedrock river evolution model that accounts for sediment supply sensitivity to precipitation events over long timescalesWhen sediment supply is highly sensitive to large precipitation events, bedrock incision is inhibited by sediment cover during floodsWe find evidence of an upper limit on water discharge for river incision driven by increased sediment cover in channels [ABSTRACT FROM AUTHOR]

Wind‐driven tree throw is an observable and consequential process that suddenly moves soil downslope, inverts the soil column, and roughens the surface with pit‐mound topography. Quantifying fluxes due to tree throw is complicated by its stochastic nature and estimation requires averaging over a large area or long time. Here, we develop a theory that leads to a dimensionless metric directly measurable from high resolution topographic data. The theory explains the flux and topographic roughness as a function of tree throw production and decay rate by creep‐like processes. We then form a measurable dimensionless variable that is the ratio of fluxes due to tree throw versus creep‐like processes. Applying the theory to hillslopes in Southern Indiana, we find that tree throw accounts for 11%–18% of the hillslope sediment flux. The theoretical and observational findings provide important constraints on quantifying Critical Zone function from topographic parameters such as roughness. Plain Language Summary: When trees fall on hillslopes, they often uproot a volume of soil that is attached to the roots. Because trees usually fall downslope, this uprooted soil also moves down the hillslope, contributes to erosion, and leaves characteristic pit and mound shapes on the surface. Despite the topographic signature of the process, quantifying how much dirt trees move downslope is complicated by the randomness that drives the process. We develop a theory that explains the roughness of hillslope topography and how it relates to sediment transport rates driven by tree throw. We then map topographic roughness over a county in southern Indiana and demonstrate that tree throw accounts for 11%–18% of the sediment motions on hillslopes. Further, we demonstrate that east‐facing hillslopes tend to have more tree throw events, which coincides with the dominant wind directions and illustrates that extreme wind events drive most tree throw events in southern Indiana. Key Points: Tree throw accounts for 11%–18% of the hillslope sediment flux in southern IndianaThe expected topographic variance is a function of the ratio of tree throw rates to creep‐like diffusivityTree throw occurs more frequently on steep, east‐facing hillslopes, which is consistent with the dominant wind directions in Indiana [ABSTRACT FROM AUTHOR]

Abstract: We use the two-dimensional (2D) electrical resistivity imaging (ERI) method to detect the contact between sediment and bedrock in a modern fluvial system. We performed eight 2D electrical resistivity surveys along the Peikang River in Kuohsing area, central Taiwan, with a pole–pole array of 1-m electrode spacing to produce a spatial resolution of about 1 m. The resistivity data were inverted into subsurface electrical structures using the least-squares inversion techniques. Then, the contact between the bedrock and sediment was found by using an image processing technique called Laplacian edge detection (LED), which represents an objective approach in interpreting various geophysical images. Numerical modeling demonstrates that isoresistivity lines are not in good agreement with the hypothetical interfaces between the bedrock and sediment, but the zero-lines of the Laplacian operation are strikingly accurate. Our results indicate a well-defined boundary in the resistivity structure that can be used to estimate the quantity of sediments covering bedrock, thus highlighting the utility of this technique in studies of landscape evolution, sediment transport, and sediment budgets. [Copyright &y& Elsevier]