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The onset of glaciation in the late Cenozoic caused rapid bedrock erosion above the snowline; however, whether the influx of eroded sediment is recorded in continental weathering and basin accumulation rates is an ongoing debate. We propose that the transport of glacially eroded bedrock through the fluvial system damps the signal of rapid headwater erosion and results in steady basin‐integrated sediment flux. Using a numerical model with integrated glacial and fluvial erosion, we find that headwater bedrock erosion rates increase rapidly at the onset of glaciation and continue to fluctuate with climatic oscillation. However, bedrock erosion rates decrease in the downstream fluvial system because larger grain sizes from glaciers result in an increase in sediment cover effect. When erosion and sediment flux rates are averaged, long‐term sediment flux is similar to nonglacial flux values, while localized bedrock erosion rates in the glaciated landscape are elevated 2–4 times compared to nonglacial values. Our simulated values are consistent with field measurements of headwater bedrock erosion, and the pattern of sediment flux and fluvial erosion matches paraglacial theory and terrace aggradation records. Thus, we emphasize that the bedload produced from glacial erosion provides a missing link to reconcile late Cenozoic erosion records. Plain Language Summary: Glaciers are effective erosion agents and the start of mountain glaciation is thought to correspond to higher alpine erosion rates. However, at the landscape‐scale, there is little to no change in erosion rates across the start of glaciation. In order to connect across these scales, we use a computer model to calculate erosion rates and sediment transfer rates. We find that the increase in sediment size from glaciation will lower erosion rates in rivers. Larger sediment sits on the riverbed and protects the underlying rock from erosion. Despite rapid erosion by glaciers upstream of the river, the slower erosion rates in the river result in a constant rate of sediment transferred out. Therefore, sediment transfer from glacier to river systems is an important process for understanding erosion across landscape scales. Key Points: Bedrock erosion downstream of glaciers is damped through an increase in sediment cover effect caused by glacier‐produced sedimentBasin‐wide sediment flux is similar to unglaciated sediment flux at timescales of >100 kyGlacially derived bedload provides a missing link between rapid bedrock erosion rates and steady basin accumulation and weathering rates [ABSTRACT FROM AUTHOR]

Dam failures due to changing hydroclimate and ageing infrastructure pose a significant threat to downstream river systems and communities. The detailed geomorphic effects of catastrophic dam failures are not well known because of a lack of high‐resolution topographic data before and after failures. On 19 May 2020, the 17‐m‐tall Edenville and 11‐m‐tall Sanford dams near Midland, Michigan, USA, failed as a result of significant rainfall over the preceding 2 days. We analysed the geomorphic impacts of these failures using a pre‐failure airborne lidar dataset and three uncrewed aerial vehicle (UAV)‐based lidar surveys collected 2 weeks, 3 months and 11 months after failure. Our survey following the dam failure revealed 47 100 ± 11 900 m3 of net floodplain erosion and 17 300 ± 4200 m3 of net deposition downstream of the Edenville and Sanford dam breaches, respectively. Over the year following failure, most geomorphic change was confined to new knickpoints migrating slowly through underlying glacial till substrate, with little change to riverbanks or surrounding floodplains. A lack of impounded reservoir sediment and antecedent downstream topography, including valley width and the location of the breaches relative to the river below the dams, contributed to relatively modest geomorphic changes despite the magnitude of water released. We provide insight into how landscapes are shaped by catastrophic floods, which are likely to become more common with ageing dams and a changing hydroclimate. [ABSTRACT FROM AUTHOR]

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]

Windthrow, or the uprooting of trees by extreme wind gusts, is a natural forest disturbance that creates microhabitats, turns over soil, alters hydrology, and removes carbon from the above-ground carbon stock. Long recurrence intervals between extreme wind events, however, make direct observations of windthrow rare, challenging our understanding of this important disturbance process. To overcome this difficulty, we present an approach that uses the geomorphic record of hillslope topographic roughness as a proxy for the occurrence of windthrow. The approach produces a probability function of the number of annual windthrow events for a maximum wind speed, allowing us to explore how windthrow or tree strengths may change due to shifting wind climates. Slight changes to extreme wind speeds may drive comparatively large changes in windthrow production rates or force trees to respond and change the distribution. We also highlight that topographic roughness has the potential to serve as an important archive of extreme wind speeds. [ABSTRACT FROM AUTHOR]

River morphology and dynamics are strongly influenced by active tectonics. We report channel dynamics for the Peikang River, which flows through the Hsuehshan Range in central Taiwan. Using a digital elevation model and field surveys, we constrain channel morphology for an ~90 km stretch of river to calculate unit stream power and boundary shear stress along the river path. Incision rates are estimated with optically stimulated luminescence dating of sand deposited on strath terraces. We find a strong correlation between unit stream power/ shear stress and incision rate, but only if variation in channel width is considered. A calibrated river incision rule implies river incision rates of ~9-13.5 mm/yr upstream of the Meiyuan and Tili faults and suggests that one or both of these structures are presently active. Our results indicate that the Shuilikeng fault is also actively deforming, as incision rates increase to ~6-10 mm/yr across it, compared to 1-4 mm/yr in adjacent reaches. Prominent narrowing across the Shuilikeng fault, and the absence of significant gradient variation indicate that channel width is a first-order morphological adjustment to differential incision. Only when the channel width-to-depth ratio reaches a minimum does the channel slope significantly adjust to local changes in base level, as is the case upstream of the Meiyuan and Tili faults. doi: 10.1130/B30035.1

Earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes, yet little work has focused on understanding how a bedrock river responds to a single large earthquake. Data from the 1999 [M.sub.w] = 7.6 Chi-Chi earthquake in central Taiwan show dramatic differences in river response that depend on the proximity to the rupture zone. Near the fault scarp, vertical ground deformation intensifies river incision on a time scale of years to decades, while distal to the fault, landslides induced by the earthquake mantle bedrock on the river bed with sediment, impeding incision for decades to centuries as the material is evacuated. This surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes. doi: 10.1130/G30883.1

Lithology is an important control on the efficiency of bedrock incision and thus the pace of landscape evolution. Rock strength is commonly considered the limiting lithologic factor that resists erosion. Yet, rock strength is a dynamic property that oscillates during advection of rock to the channel surface as damaging processes weaken rock and erosion exposes fresh rock. We approach the problem by investigating damage on bedrock surfaces that vary by the frequency they are eroded in channels of different lithologies. Our data set includes measurements of channel slope and width to characterize channel morphology, and Schmidt hammer rebound, P wave velocity, slake durability, and porosity to characterize the mechanical properties of channel surfaces. The average damage accumulation rate of lithologies ranges over 41% of the mean. We find a range of damage patterns among the different lithologies. Local surface damage increases with erosion frequency in channels comprised of coarse‐grained bedrock but decreases with erosion frequency in channels comprised of fine‐grained bedrock. We interpret these patterns to develop from lithological influences on weathering, abrasion, and the threshold of damage to erosion. The cross‐channel damage patterns between channel floors and margins are well correlated with stream power demonstrating links between microstructural rock properties, reach‐scale morphology, and landscape‐scale processes. We conclude that the morphodynamics of bedrock channels are sensitive to the lithological influences on the direction and magnitude of feedback in the coevolution of bedform morphology and the mechanical properties of the surface. Plain Language Summary: Rivers shape the landscape by carving out valleys into rock. Some types of rock are harder to carve than other types of rock, but it is not clearly understood why because there are many physical and chemical weathering processes that attack rock other than the river. Using several dry river channels, we take many measurements of rock strength along the bedrock surface that forms the river channels. We take advantage of the different channel surfaces that are either shielded or exposed to the downstream flow of river sediment to get a sense of how the bedrock is damaged by sediment impacts and by weathering. We find that the size and type of minerals that make up the bedrock influence the pattern of rock damage that develops through complex feedbacks that occur as bedrock material is either weakened or eroded thereby exposing fresher material that lies underneath. These damage patterns in turn control the shape of the channel, and therefore, the erosive potential of the flowing water. Our findings demonstrate how microscale rock properties can influence the shaping of landscapes. Key Points: Erosion frequency and surface damage modulate the spatial variability in mechanical properties of bedrock channelsGrain size and mineralogy control damage by weathering and abrasion, which influence the slope, width, and roughness of bedrock channelsThe relation between rock damage and rock‐erodibility is unique for different lithologies [ABSTRACT FROM AUTHOR]

In most landscape evolution models, extreme rainfall enhances river incision. In steep landscapes, however, these events trigger landslides that can buffer incision via increased sediment delivery and aggradation. We quantify landslide sediment aggradation and erosional buffering with a natural experiment in southern Taiwan where a northward gradient in tectonic activity drives increasing landscape steepness. We find that landscape response to extreme rainfall during the 2009 typhoon Morakot varied along this gradient, where steep areas experienced widespread channel sediment aggradation of >10 m and less steep areas did not noticeably aggrade. We model sediment export to estimate a sediment removal timeline and find that steep, tectonically active areas with the most aggradation may take centuries to resume bedrock incision. Expected sediment cover duration reflects tectonic uplift. We find that despite high stream power, sediment cover may keep steep channels from eroding bedrock for up to half of a given time period. This work highlights the importance of dynamic sediment cover in landscape evolution and suggests a mechanism by which erosional efficiency in tectonically active landscapes may decrease as landscape steepness increases. [ABSTRACT FROM AUTHOR]

The isotopic composition of precipitation is used to trace water cycling and climate change, but interpretations of the environmental information recorded in central Andean precipitation isotope ratios are hindered by a lack of multi‐year records, poor spatial distribution of observations, and a predominant focus on Rayleigh distillation. To better understand isotopic variability in central Andean precipitation, we present a three‐year record of semimonthly δ18Op and δ2Hp values from 15 stations in southern Peru and triple oxygen isotope data, expressed as ∆′17Op, from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with δ18Op and that seasonal δ18Op variations are related to upstream rainout and local convection. Spatial δ18Op variations and atmospheric back trajectories show that both eastern‐ and western‐derived air masses bring precipitation to southern Peru. Seasonal d‐excessp cycles record moisture recycling and relative humidity at remote moisture sources, and both d‐excessp and ∆′17Op clearly differentiate evaporated and non‐evaporated samples. These results begin to establish the natural range of unevaporated ∆′17Op values in the central Andes and set the foundation for future paleoclimate and paleoaltimetry studies in the region. This study highlights the hydrologic understanding that comes from a combination of δ18Op, d‐excessp, and ∆′17Op data and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes. Key Points: The isotopic composition of central Andean precipitation records upstream precipitation, local convection, and remote moisture sourcesPrecipitation on the flank of the western central Andes is sourced from the Pacific Ocean∆'17O can separate evaporated and non‐evaporated samples and provides key baseline information for Andean paleoclimate and paleoaltimetry [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]

Landscape morphology reflects drivers such as tectonics and climate but is also modulated by underlying rock properties. While geomorphologists may attempt to quantify the influence of rock strength through direct comparisons of landscape morphology and rock strength metrics, recent work has shown that the contact migration resulting from the presence of mixed lithologies may hinder such an approach. Indeed, this work counterintuitively suggests that channel slopes within weaker units can sometimes be higher than channel slopes within stronger units. Here, we expand upon previous work with 1-D stream power numerical models in which we have created a system for quantifying contact migration over time. Although previous studies have developed theories for bedrock rivers incising through layered stratigraphy, we can now scrutinize these theories with contact migration rates measured in our models. Our results show that previously developed theory is generally robust and that contact migration rates reflect the pattern of kinematic wave speed across the profile. Furthermore, we have developed and tested a new approach for estimating kinematic wave speeds. This approach utilizes channel steepness, a known base-level fall rate, and contact dips. Importantly, we demonstrate how this new approach can be combined with previous work to estimate erodibility values. We demonstrate this approach by accurately estimating the erodibility values used in our numerical models. After this demonstration, we use our approach to estimate erodibility values for a stream near Hanksville, UT. Because we show in our numerical models that one can estimate the erodibility of the unit with lower steepness, the erodibilities we estimate for this stream in Utah are likely representative of mudstone and/or siltstone. The methods we have developed can be applied to streams with temporally constant base-level fall, opening new avenues of research within the field of geomorphology. [ABSTRACT FROM AUTHOR]

Landslide dam outburst floods have a significant impact on landform evolution in high mountainous areas. Historic landslide dams on the Yigong River, southeastern Tibet, generated two outburst superfloods > 105 m3/s in 1902 and 2000 AD. One of the slackwater deposits, which was newly found immediately downstream of the historic dams, has been dated to 7 ka BP. The one-dimensional backwater stepwise method gives an estimate of 225,000 m3/s for the peak flow related to the paleo-stage indicator of 7 ka BP. The recurrence of at least three large landslide dam impoundments and super-outburst floods at the exit of Yigong Lake during the Holocene greatly changed the morphology of the Yigong River. More than 0.26 billion m3 of sediment has been aggraded in the dammed lake while the landslide sediment doubles the channel slope behind the dam. Repeated landslide damming may be a persistent source of outburst floods and impede the upstream migration of river knickpoints in the southeastern margin of Tibet. [ABSTRACT FROM AUTHOR]

Understanding bed load impact dynamics on exposed bedrock in rivers is crucial to quantifying the erosive energy of a stream. Observations of the bed load saltation trajectories and impact energies are lacking, particularly in channels with nonplanar bed topography. In this study, we performed four flume experiments of saltating gravel to offer new insights on the dependence of particle impact dynamics on transport stage and bed topography. Our experiments used two different boundary shear stresses (τb = 36.5 and 25.4 Pa) and two different bed configurations, planar and nonplanar (bedrock disks uniformly oriented at 10° from the bed surface). For each experiment, we indirectly estimated the impact energies from the trajectories of particles with high‐speed video imaging and measured the erosion rates of rock samples embedded in the flume floor. The planar and nonplanar beds had negative and constant relationships, respectively, between energy delivered to the bed and transport stage. The nonplanar bed had a heavier tailed distribution of impact energy than the planar bed, which implies a greater number of rare highly erosive impacts. Probabilistic formulations of particle trajectories better predict the increase or decrease in erosion rate across experiments than deterministic regression equations. Our findings suggest that bedrock erosion models should consider a distribution of possible bed load impact energies, particularly for natural river channels that have rough surfaces. Key Points: Flume experiments reveal how erosion rates and saltation trajectories vary for smooth and rough beds for 17 rock typesImpact energy rates of gravel at set flow conditions vary over 4 orders of magnitude and may follow heavy‐tailed distributionsThe change in erosion rate across experiments is better predicted with probability functions than with deterministic regression equations [ABSTRACT FROM AUTHOR]

Meandering river sinuosity increases until the channel erodes into itself (neck cutoff) or forms a new channel over the floodplain (chute cutoff) and sinuosity is reduced. Unlike neck cutoff, which can be measured or modelled without considering overbank processes, chute cutoff must be at least partially controlled by channel‐forming processes on the floodplain. Even though chute cutoff controls meandering river form, the processes that cause chute cutoff are not well understood. This study analyses the morphology of two incipient chute cutoffs along the East Fork White River, Indiana, USA, using high temporal and spatial resolution UAS‐based LiDAR and aerial photography. LiDAR and aerial imagery obtained between 1998 and 2019 reveals that large scour holes formed in the centre of both chutes sometime after chute channel initiation. A larger analysis within the study watershed reveals that scour holes within incipient chutes can be stable or unstable, and tend to stabilize when the chute is colonized by native vegetation and forest. When the scour holes form in farmed floodplain, they enlarge rapidly after initial formation and contribute to complete chute cutoff. In addition, this study shows that the formation of scour holes can occur in response to common, relatively low‐magnitude floods and that the amount of incipient chute erosion does not depend on peak flood magnitude. The role of scour holes in enlarging chute channels could be an important mechanism for chute channel evolution in meandering rivers. This study also confirms that understanding the relationships among flow, land cover, and cutoff morphology is substantially improved with on‐demand remote sensing techniques like integrated UAS and LiDAR. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Landscape evolution is driven by factors like tectonics and climate, and unraveling such factors can reveal the history recorded in landscape morphology. The northern U.S. Cordillera features many potential drivers, such as the Yellowstone plume, the extrusion of a large igneous province, and the drainage of large lakes. Among this complex geologic history, the drivers of transient incision in the Clearwater and Salmon watersheds of central Idaho are not well understood. To constrain the pattern of regional incision, we analyze the morphologies of 80 individual tributaries underlain by single lithologies. From north to south across our study area, knickpoint elevations increase from about 800 to 2,200 m, and incision depths increase from about 300 to 1,200 m. We use both numerical and analytical models to demonstrate that such a gradient could represent spatial variations in rock uplift. These findings suggest that transience is driven by a spatially variable increase in rock uplift that has disrupted a low‐relief paleolandscape, and the high steepness values of main drainages suggest that high rock‐uplift rates are still maintained to the present. Changes in rock uplift may be related to interactions between the Yellowstone plume and the lithosphere, although base level fall from the drainage of the Lake Idaho down the proto‐Snake River may be superimposed over these patterns in rock uplift. We show that careful, quantitative analyses of river profiles in geologically complex regions can differentiate between the influences of rock uplift and far‐field base level changes. Key Points: Knickpoint elevations and incision depths of individual tributaries in the Clearwater and Salmon watersheds increase from north to southBedrock river morphologies indicate that a spatially variable increase in rock uplift caused the dissection of a low‐relief paleolandscapeWe support our findings with numerical model simulations and a review of previous analytical work on transient bedrock river behavior [ABSTRACT FROM AUTHOR]

Abstract: Intense precipitation or seismic events can generate clustered mass movement processes across a landscape. These rare events have significant impacts on the landscape, however, the rarity of such events leads to uncertainty in how they impact the entire geomorphic system over a range of timescales. Taiwan is steep, tectonically active, and prone to landslide and debris flows, especially when exposed to heavy rainfall events. Typhoon Morakot made landfall in Taiwan in August of 2009, causing widespread landslides in southern Taiwan. The south to north trend in valley relief in southern Taiwan leads to spatial variability in landslide susceptibility providing an opportunity to infer the long‐term impact of such landslide events on channel morphology. We use pre‐ and post‐typhoon imagery to quantify the propagating impact of this event on channel width as the debris is routed through the landscape. The results show the importance of cascading hazards from landslides on landscape evolution based on patterns of channel width (both pre‐ and post‐typhoon) and hillslope gradients in 20 basins along strike in southern Taiwan. Prior to Typhoon Morakot, the river channels in the central part of the study area were about 3–10 times wider than the channels in the south. Following the typhoon, aggradation and widening was also a maximum in these central to northern basins where hillslope gradients and channel steepness is high, accentuating the pre‐typhoon pattern. The results further show that the narrowest channels are located where channel steepness is the lowest, an observation inconsistent with a detachment‐limited model for river evolution. We infer this pattern is indicative of a strong role of sediment supply, and associated landslide events, on long‐term channel evolution. These findings have implications across a range of spatial and temporal scales including understanding the cascade of hazards in steep landscapes and geomorphic interpretation of channel morphology. Copyright © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The evolution of rivers in eroding landscapes plays a key role in determining landscape relief and modulating climate‐tectonic interactions. A common approach to quantifying river system evolution uses a one‐dimensional, detachment‐limited stream power equation. One potential drawback of this model is that it does not incorporate the effects of changes in channel width or the role of sediment transport dynamics. Here I present a new method for modeling the influence of channel width on river dynamics to explore how variable width and sediment transport impact river profile evolution. With this approach, vertical river erosion can operate based on any number of river erosion models, such as a simple shear stress model (e.g., detachment limited), sediment cover‐shear stress hybrid models, or mechanistic saltation‐abrasion models. I explore the sensitivity of these three models to increases in rock‐uplift rate (i.e., 2, 3, 5, 10, and 20× increase). Generally, the results show that incorporating channel width adjustment or sediment transport dynamics lowers the sensitivity of a river profile to rock‐uplift rate. For the sediment transport‐dependent models, the degree of sensitivity depends on whether the system is limited by bedrock exposure or erosion potential (i.e., detachment potential). The approach produces transient responses that reveal distinct patterns of width and slope, which may provide valuable insight into the limiting physical mechanisms of bedrock erosion in a region. The implications of the work are broad and include the potential to distinguish underlying erosion controls from field observations of width and slope as well as understanding climate‐tectonic interactions. [ABSTRACT FROM AUTHOR]

Landscape evolution is a product of the forces that drive geomorphic processes (e.g., tectonics and climate) and the resistance to those processes. The underlying lithology and structural setting in many landscapes set the resistance to erosion. This study uses a modified version of the Channel-Hillslope Integrated Landscape Development (CHILD) landscape evolution model to determine the effect of a spatially and temporally changing erodibility in a terrain with a complex base level history. Specifically, our focus is to quantify how the effects of variable lithology influence transient base level signals. We set up a series of numerical landscape evolution models with increasing levels of complexity based on the lithologic variability and base level history of the Jura Mountains of northern Switzerland. The models are consistent with lithology (and therewith erodibility) playing an important role in the transient evolution of the landscape. The results show that the erosion rate history at a location depends on the rock uplift and base level history, the range of erodibilities of the different lithologies, and the history of the surface geology downstream from the analyzed location. Near the model boundary, the history of erosion is dominated by the base level history. The transient wave of incision, however, is quite variable in the different model runs and depends on the geometric structure of lithology used. It is thus important to constrain the spatiotemporal erodibility patterns downstream of any given point of interest to understand the evolution of a landscape subject to variable base level in a quantitative framework. [ABSTRACT FROM AUTHOR]

Variation in the erodibility of rock units has long been recognized as an important determinant of landscape evolution but has been little studied in landscape evolution models. We use a modified version of the Channel-Hillslope Integrated Landscape Development (CHILD) model, which explicitly allows for variations in rock strength, to reveal and explore the remarkably rich, complex behavior induced by rock erodibility variations in even very simple geologic settings with invariant climate and tectonics. We study the importance of relative contrasts in erodibility between just two units, the order of these units (whether hard rocks overlie soft or soft rocks overlie hard) and the orientation of the contact between the two units. We emphasize the spatial and temporal evolution of erosion rates, which have important implications for basin analysis, detrital mineral records, and the interpretation of cosmogenic isotope concentrations in detrital samples. Results of the landscape evolution modeling indicate that the stratigraphic order of units in terms of erodibility, the gross orientation of the contact (i.e. dipping away or toward the outlet of the landscape) and the contact dip angle all have measurable effects on landscape evolution, including significant spatial and temporal variations in erosion rates. Steady-state denudation conditions are unlikely to develop in landscapes with significant contrasts in rock strength in horizontal to moderately tilted rock layers, at least at the scale of the entire landscape. Additionally, our results demonstrate that there is no general relation between rock erodibility and erosion rates in natural settings. Although rock erodibility directly controls the erosion rate constant in our models, it is not uncommon for higher erosion rates to occur in the harder, less erodible rock. Indeed erosion rates may be either greater or less than the rock uplift rate (invariant in time and space in our models) in both hard and soft rocks, depending on the local geology, topography, and the pattern of landscape evolution. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The processes that build and shape mountain landscapes expose important mineral resources. Mountain landscapes are widely thought to result from the interaction between tectonic uplift and exhumation by erosion. Both climate and tectonics affect rates of exhumation, but estimates of their relative importance vary. Porphyry copper deposits are emplaced at a depth of about 2 km in convergent tectonic settings; their exposure at the surface therefore can be used to track landscape exhumation. Here we analyse the distribution, ages and spatial density of exposed Cenozoic porphyry copper deposits using a global data set to quantify exhumation. We find that the deposits exhibit young ages and are sparsely distributed-both consistent with rapid exhumation-in regions with high precipitation, and deposits are older and more abundant in dry regions. This suggests that climate is driving erosion and mineral exposure in deposit-bearing mountain landscapes. Our findings show that the emplacement ages of porphyry copper deposits provide a means to estimate long-term exhumation rates in active orogens, and we conclude that climate-driven exhumation influences the age and abundance of exposed porphyry copper deposits around the world. [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]

Flow regulation by large dams affects downstream flow competence and channel maintenance. Debris flows from 740 tributaries in Grand Canyon, Arizona, transport coarse-grained sediment onto debris fans adjacent to the Colorado River. These debris fans constrict the river to form rapids and are reworked during river flows that entrain particles and transport them downstream. Beginning in 1963, flood control operations of Glen Canyon Dam limited the potential for reworking of aggraded debris fans. We analyzed change in debris fans at the mouths of 75-Mile and Monument Creeks using photogrammetry of aerial photography taken from 1965 to 2000 and supplemented with ground surveys performed from 1987 to 2005. Our results quantify the debris fan aggradation that resulted from debris flows from 1984 to 2003. Volume, area, and river constriction increased at both debris fans. Profiles of the two debris fans show that net aggradation occurred in the middle of debris fans at stages above maximum dam releases, and surface shape shifted from concave to convex. Dam releases above power plant capacity partially reworked both debris fans, although reworking removed much less sediment than what was added by debris flow deposition. Large dam releases would be required to create additional reworking to limit the rate of debris fan aggradation in Grand Canyon. [ABSTRACT FROM AUTHOR]

The article offers information about the landscape evolution under the southern Laurentide Ice Sheet. It discusses that document landscape evolution beneath the southern Laurentide Ice Sheet of North America since the end of the Pliocene by reconstructing the isostatically adjusted preglacial surface and modern bedrock topography at a horizontal resolution.