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1.
Soil‐mantled pole‐facing hillslopes on Earth tend to be steeper, wetter, and have more vegetation cover compared with adjacent equator‐facing hillslopes. These and other slope aspect controls are often the consequence of feedbacks among hydrologic, ecologic, pedogenic, and geomorphic processes triggered by spatial variations in mean annual insolation. In this paper we review the state of knowledge on slope aspect controls of Critical Zone (CZ) processes using the latitudinal and elevational dependence of topographic asymmetry as a motivating observation. At relatively low latitudes and elevations, pole‐facing hillslopes tend to be steeper. At higher latitudes and elevations this pattern reverses. We reproduce this pattern using an empirical model based on parsimonious functions of latitude, an aridity index, mean‐annual temperature, and slope gradient. Using this empirical model and the literature as guides, we present a conceptual model for the slope‐aspect‐driven CZ feedbacks that generate asymmetry in water‐limited and temperature‐limited end‐member cases. In this conceptual model the dominant factor driving slope aspect differences at relatively low latitudes and elevations is the difference in mean‐annual soil moisture. The dominant factor at higher latitudes and elevations is temperature limitation on vegetation growth. In water‐limited cases, we propose that higher mean‐annual soil moisture on pole‐facing hillslopes drives higher soil production rates, higher water storage potential, more vegetation cover, faster dust deposition, and lower erosional efficiency in a positive feedback. At higher latitudes and elevations, pole‐facing hillslopes tend to have less vegetation cover, greater erosional efficiency, and gentler slopes, thus reversing the pattern of asymmetry found at lower latitudes and elevations. Our conceptual model emphasizes the linkages among short‐ and long‐timescale processes and across CZ sub‐disciplines; it also points to opportunities to further understand how CZ processes interact. We also demonstrate the importance of paleoclimatic conditions and non‐climatic factors in influencing slope aspect variations. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

2.
Wildfire denudes vegetation and impacts chemical and physical soil properties, which can alter hillslope erosion rates. Post‐wildfire erosion can also contribute disproportionately to long‐term erosion rates and landscape evolution. Post‐fire hillslope erosion rates remain difficult to predict and document at the hillslope scale. Here we use 210Pbaex (lead‐210 mineral‐adsorbed excess) inventories to describe net sediment erosion on steep, convex hillslopes in three basins (unburned, moderately and severely burned) in mountainous central Idaho. We analyzed nearly 300 soil samples for 210Pbaex content with alpha spectrometry and related net sediment erosion to burn severity, aspect, gradient, curvature and distance from ridgetop. We also tested our data against models for advective, linear and non‐linear diffusive erosion. Statistically lower net soil losses on north‐ versus south‐facing unburned hillslopes suggest that greater vegetative cover and soil cohesion on north‐facing slopes decrease erosion. On burned hillslopes, erosion differences between aspects were less apparent and net erosion was more variable, indicating that vegetation influences erosion magnitude and fire drives erosion variability. We estimated net soil losses throughout the length of unburned hillslopes, including through a footslope transition to concave form. In contrast, on burned hillslopes, the subtle shift from convex to concave form was associated with deposition of a post‐fire erosion pulse. Such overall patterns of erosion and deposition are consistent with predictions from a non‐linear diffusion equation. This finding also suggests that concave sections of overall convex hillslopes affect post‐disturbance soil erosion and deposition. Despite these patterns, no strong relationships were evident between local net soil losses and gradient, curvature, distance from ridgetop, or erosion predicted with advection or diffusion equations. The observed relationship between gradient and erosion is therefore likely more complex or stochastic than often described theoretically, especially over relatively short timescales (60–100 years). Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post‐orogenic landscape remain enigmatic. The non‐glaciated Cullasaja River basin of south‐western North Carolina, with uniform lithology, frequent debris flows, and the availability of high‐resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post‐orogenic landscape through the lens of hillslope–channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km2, a conservative estimate of the transition from fluvial to debris‐flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint‐driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area–elevation and slope distributions is presented that may be representative of post‐orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel–hillslope coupling is an important factor in tectonically‐inactive (i.e. post‐orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering‐limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
The advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium. If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering—however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither “runaway weathering” to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1‐D rock weathering can be extended to consider lateral flow in a 2‐D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: “diffusing up,” where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; “draining down,” where solutes are advected primarily downward into the unweathered bedrock; and “draining along,” where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady‐state hillslope profile.  相似文献   

5.
Snowmelt water supplies streamflow and growing season soil moisture in mountain regions, yet pathways of snowmelt water and their effects on moisture patterns are still largely unknown. This study examined how flow processes during snowmelt runoff affected spatial patterns of soil moisture on two steep sub‐alpine hillslope transects in Rocky Mountain National Park, CO, USA. The transects have northeast‐facing and east‐facing aspects, and both extend from high‐elevation bedrock outcrops down to streams in valley bottoms. Spatial patterns of both snow depth and near‐surface soil moisture were surveyed along these transects in the snowmelt and summer seasons of 2008–2010. To link these patterns to flow processes, soil moisture was measured continuously on both transects and compared with the timing of discharge in nearby streams. Results indicate that both slopes generated shallow lateral subsurface flow during snowmelt through near‐surface soil, colluvium and bedrock fractures. On the northeast‐facing transect, this shallow subsurface flow emerged through mid‐slope seepage zones, in some cases producing saturation overland flow, whereas the east‐facing slope had no seepage zones or overland flow. At the hillslope scale, earlier snowmelt timing on the east‐facing slope led to drier average soil moisture conditions than on the northeast‐facing slope, but within hillslopes, snow patterns had little relation to soil moisture patterns except in areas with persistent snow drifts. Results suggest that lateral flow and exfiltration processes are key controls on soil moisture spatial patterns in this steep sub‐alpine location. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

6.
Infrequent, high‐magnitude events cause a disproportionate amount of sediment transport on steep hillslopes, but few quantitative data are available that capture these processes. Here we study the influence of wildfire and hillslope aspect on soil erosion in Fourmile Canyon, Colorado. This region experienced the Fourmile Fire of 2010, strong summer convective storms in 2011 and 2012, and extreme flooding in September 2013. We sampled soils shortly after these events and use fallout radionuclides to trace erosion on polar‐ and equatorial‐facing burned slopes and on a polar‐facing unburned slope. Because these radionuclides are concentrated in the upper decimeter of soil, soil inventories are sensitive to erosion by surface runoff. The polar‐facing burned slope had significantly lower cesium‐137 (137Cs) and lead‐210 (210Pb) inventories (p < 0.05) than either the polar‐facing unburned slope or equatorial‐facing burned slope. Local slope magnitude does not appear to control the erosional response to wildfire, as relatively gently sloping (~20%) polar‐facing positions were severely eroded in the most intensively burned area. Field evidence and soil profile analyses indicate up to 4 cm of local soil erosion on the polar‐facing burned slope, but radionuclide mass balance indicates that much of this was trapped nearby. Using a 137Cs‐based erosion model, we find that the burned polar‐facing slope had a net mean sediment loss of 2 mm (~1 kg m?2) over a one to three year period, which is one to two orders of magnitude higher than longer‐term erosion rates reported for this region. In this part of the Colorado Front Range, strong hillslope asymmetry controls soil moisture and vegetation; polar‐facing slopes support significantly denser pine and fir stands, which fuels more intense wildfires. We conclude that polar‐facing slopes experience the most severe surface erosion following wildfires in this region, indicating that landscape‐scale aridity can control the geomorphic response of hillslopes to wildfires. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

7.
The volumes, rates and grain size distributions of sediment supplied from hillslopes represent the initial input of sediment delivered from upland areas and propagated through sediment routing systems. Moreover, hillslope sediment supply has a significant impact on landscape response time to tectonic and climatic perturbations. However, there are very few detailed field studies characterizing hillslope sediment supply as a function of lithology and delivery process. Here, we present new empirical data from tectonically‐active areas in southern Italy that quantifies how lithology and rock strength control the landslide fluxes and grain size distributions supplied from hillslopes. Landslides are the major source of hillslope sediment supply in this area, and our inventory of ~2800 landslides reveals that landslide sediment flux is dominated by small, shallow landslides. We find that lithology and rock strength modulate the abundance of steep slopes and landslides, and the distribution of landslide sizes. Outcrop‐scale rock strength also controls the grain sizes supplied by bedrock weathering, and influences the degree of coarsening of landslide supply with respect to weathering supply. Finally, we show that hillslope sediment supply largely determines the grain sizes of fluvial export, from catchments and that catchments with greater long‐term landslide rates deliver coarser material. Therefore, our results demonstrate a dual control of lithology on hillslope sediment supply, by modulating both the sediment fluxes from landslides and the grain sizes supplied by hillslopes to the fluvial system. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

8.
Landscape curvature evolves in response to physical, chemical, and biological influences that cannot yet be quantified in models. Nonetheless, the simplest models predict the existence of equilibrium hillslope profiles. Here, we develop a model describing steady‐state regolith production caused by mineral dissolution on hillslopes which have attained an equilibrium parabolic profile. When the hillslope lowers at a constant rate, the rate of chemical weathering is highest at the ridgetop where curvature is highest and the ridge develops the thickest regolith. This result derives from inclusion of all the terms in the mathematical definition of curvature. Including these terms shows that the curvature of a parabolic hillslope profile varies with distance from the ridge. The hillslope model (meter‐scale) is similar to models of weathering rind formation (centimeter‐scale) where curvature‐driven solute transport causes development of the thickest rinds at highly curved clast corners. At the clast scale, models fit observations. Here, we similarly explore model predictions of the effect of curvature at the hillslope scale. The hillslope model shows that when erosion rates are small and vertical porefluid infiltration is moderate, the hill weathers at both ridge and valley in the erosive transport‐limited regime. For this regime, the reacting mineral is weathered away before it reaches the land surface: in other words, the model predicts completely developed element‐depth profiles at both ridge and valley. In contrast, when the erosion rate increases or porefluid velocity decreases, denudation occurs in the weathering‐limited regime. In this regime, the reacting mineral does not weather away before it reaches the land surface and simulations predict incompletely developed profiles at both ridge and valley. These predictions are broadly consistent with observations of completely developed element‐depth profiles along hillslopes denuding under erosive transport‐limitation but incompletely developed profiles along hillslopes denuding under weathering limitation in some field settings. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
The role of solar‐induced thermal stresses in the mechanical breakdown of rock in humid‐temperate climates has remained relatively unexplored. In contrast, numerous studies have demonstrated that cracks in rocks found in more arid mid‐latitude locations exhibit preferred northeast orientations that are interpreted to be a consequence of insolation‐related cracking. Here we hypothesize that similar insolation‐related mechanisms may be efficacious in humid temperate climates, possibly in conjunction with other mechanical weathering processes. To test this hypothesis, we collected rock and crack data from a total of 310 rocks at a forested field site in North Carolina (99 rocks, 266 cracks) and at forested and unforested field sites in Pennsylvania (211 rocks, 664 cracks) in the eastern United States. We find that overall, measured cracks exhibit statistically preferred strike orientations (47° ± 16), as well as dip angles (52° ± 24°), that are similar in most respects to comparable datasets from mid‐latitude deserts. There is less variance in strike orientations for larger cracks suggesting that cracks with certain orientations are preferentially propagated through time. We propose that diurnally repeating geometries of solar‐related stresses result in propagation of those cracks whose orientations are favorably oriented with respect to those stresses. We hypothesize that the result is an oriented rock heterogeneity that acts as a zone of weakness much like bedding or foliation that can, in turn, be exploited by other weathering processes. Observed crack orientations vary somewhat by location, consistent with this hypothesis given the different latitude and solar exposure of the field sites. Crack densities vary between field sites and are generally higher on north‐facing boulder‐faces and in forested sites, suggesting that moisture‐availability also plays a role in dictating cracking rates. These data provide evidence that solar‐induced thermal stresses facilitate mechanical weathering in environments where other processes are also likely at play. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

10.
In Mediterranean regions, hillslopes are generally considered to be a mosaic of sink and source areas that control runoff generation and water erosion processes. These hillslopes used to be characterized by a complex hydrological and erosive response combining Hortonian and saturation excess overland flows. The hydrological response of soils is highly dependent on the soil surface components (e.g. vegetation patches, bare soil, rock fragment cover, crusts), which each one of them is dominated by a certain hydrological process. One of these soil surface components, not widely considered in studies of soil hydrology under Mediterranean conditions, is the accumulation of litter beneath shrubs enhancing water repellency in soils. This study investigates the influence of soil surface components, especially the litter accumulated beneath Cistus spp., in the hydrological and erosive responses of soils on two Mediterranean hillslopes having different exposures. The study was performed by means of rainfall simulation experiments and the Water Drop Penetration Time for measuring water repellency of soils, both techniques being carried out at the end of summer (September 2010) with very dry soils. The results indicate that (i) soil surface components from the north facing hillslope are characterized by a more uniform hydrological and erosive response than those from the south‐facing ones; (ii) the water repellency is more influential on the hydrological response of the north‐facing hillslope due to a greater accumulation of organic rest on the soils as the vegetation cover is also higher; (iii) the south‐facing hillslope seemed to follow the fertility island theory with very degraded bare soil areas, which are the most generated areas of runoff and mobilized sediments; (iv) the experimental area can be considered as a threshold area between the semiarid and subhumid Mediterranean environments, with the south‐facing hillslope being comparable with the former and the north facing one with the latter. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

11.
The long‐term evolution of channel longitudinal profiles within drainage basins is partly determined by the relative balance of hillslope sediment supply to channels and the evacuation of channel sediment. However, the lack of theoretical understanding of the physical processes of hillslope–channel coupling makes it challenging to determine whether hillslope sediment supply or channel sediment evacuation dominates over different timescales and how this balance affects bed elevation locally along the longitudinal profile. In this paper, we develop a framework for inferring the relative dominance of hillslope sediment supply to the channel versus channel sediment evacuation, over a range of temporal and spatial scales. The framework combines distinct local flow distributions on hillslopes and in the channel with surface grain‐size distributions. We use these to compute local hydraulic stresses at various hillslope‐channel coupling locations within the Walnut Gulch Experimental Watershed (WGEW) in southeast Arizona, USA. These stresses are then assessed as a local net balance of geomorphic work between hillslopes and channel for a range of flow conditions generalizing decadal historical records. Our analysis reveals that, although the magnitude of hydraulic stress in the channel is consistently higher than that on hillslopes, the product of stress magnitude and frequency results in a close balance between hillslope supply and channel evacuation for the most frequent flows. Only at less frequent, high‐magnitude flows do channel hydraulic stresses exceed those on hillslopes, and channel evacuation dominates the net balance. This result suggests that WGEW exists mostly (~50% of the time) in an equilibrium condition of sediment balance between hillslopes and channels, which helps to explain the observed straight longitudinal profile. We illustrate how this balance can be upset by climate changes that differentially affect relative flow regimes on slopes and in channels. Such changes can push the long profile into a convex or concave condition. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

12.
Most hillslope studies examining the interplay between climate and earth surface processes tend to be biased towards eroding parts of landscapes. This limitation makes it difficult to assess how entire upland landscapes, which are mosaics of eroding and depositional areas, evolve physio‐chemically as a function of climate. Here we combine new soil geochemical data and published 10Be‐derived soil production rates to estimate variations in chemical weathering across two eroding‐to‐depositional hillslopes spanning a climate gradient in southeastern Australia. At the warmer and wetter Nunnock River (NR) site, rates of total soil (–3 to –14 g m‐2 yr‐1; negative sign indicates mass loss) and saprolite (–18 to –32 g m‐2 yr‐1) chemical weathering are uniform across the hillslope transect. Alternatively, the drier hillslope at Frog's Hollow (FH) is characterized by contrasting weathering patterns in eroding soils (–30 to –53 g m‐2 yr‐1) vs. depositional soils (+91 g m‐2 yr‐1; positive sign indicates mass addition). This difference partly reflects mineral grain size sorting as a result of upslope bioturbation coupled with water‐driven soil erosion, as well as greater vegetative productivity in moister depositional soils. Both of these processes are magnified in the drier climate. The data reveal the importance of linking the erosion–deposition continuum in hillslope weathering studies in order to fully capture the coupled roles of biota and erosion in driving the physical and chemical evolution of hillslopes. Our findings also highlight the potential limitations of applying current weathering models to landscapes where particle‐sorting erosion processes are active. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

13.
Hillslopes have complex three‐dimensional shapes that are characterized by their plan shape, profile curvature of surface and bedrock, and soil depth. To investigate the stability of complex hillslopes (with different slope curvatures and plan shapes), we combine the hillslope‐storage Boussinesq (HSB) model with the infinite slope stability method. The HSB model is based on the continuity and Darcy equations expressed in terms of storage along the hillslope. Solutions of the HSB equation account explicitly for plan shape by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function. The presented model is composed of three parts: a topography model conceptualizing three‐dimensional soil mantled landscapes, a dynamic hydrology model for shallow subsurface flow and water table depth (HSB model) and an infinite slope stability method based on the Mohr–Coulomb failure law. The resulting hillslope‐storage Boussinesq stability model (HSB‐SM) is able to simulate rain‐induced shallow landsliding on hillslopes with non‐constant bedrock slope and non‐parallel plan shape. We apply the model to nine characteristic hillslope types with three different profile curvatures (concave, straight, convex) and three different plan shapes (convergent, parallel, divergent). In the presented model, the unsaturated storage has been calculated based on the unit head gradient assumption. To relax this assumption and to investigate the effect of neglecting the variations of unsaturated storage on the assessment of slope stability in the transient case, we also combine a coupled model of saturated and unsaturated storage and the infinite slope stability method. The results show that the variations of the unsaturated zone storage do not play a critical role in hillslope stability. Therefore, it can be concluded that the presented dynamic slope stability model (HSB‐SM) can be used safely for slope stability analysis on complex hillslopes. Our results show that after a certain period of rainfall the convergent hillslopes with concave and straight profiles become unstable more quickly than others, whilst divergent convex hillslopes remain stable (even after intense rainfall). In addition, the relation between subsurface flow and hillslope stability has been investigated. Our analyses show that the minimum safety factor (FS) occurs when the rate of subsurface flow is a maximum. In fact, by increasing the subsurface flow, stability decreases for all hillslope shapes. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

14.
Landscape evolution and surface morphology in mountainous settings are a function of the relative importance between sediment transport processes acting on hillslopes and in channels, modulated by climate variables. The Niesen nappe in the Swiss Penninic Prealps presents a unique setting in which opposite facing flanks host basins underlain by identical lithologies, but contrasting litho‐tectonic architectures where lithologies either dip parallel to the topographic slope or in the opposite direction (i.e. dip slope and non‐dip slope). The north‐western facing Diemtigen flank represents such a dip slope situation and is characterized by a gentle topography, low hillslope gradients, poorly dissected channels, and it hosts large landslides. In contrast, the south‐eastern facing Frutigen side can be described as non‐dip slope flank with deeply incised bedrock channels, high mean hillslope gradients and high relief topography. Results from morphometric analysis reveal that noticeable differences in morphometric parameters can be related to the contrasts in the relative importance of the internal hillslope‐channel system between both valley flanks. While the contrasting dip‐orientations of the underlying flysch bedrock has promoted hillslope and channelized processes to contrasting extents and particularly the occurrence of large landslides on the dip slope flank, the flank averaged beryllium‐10 (10Be)‐derived denudation rates are very similar and range between 0.20 and 0.26 mm yr?1. In addition, our denudation rates offer no direct relationship to basin's slope, area, steepness or concavity index, but reveal a positive correlation to mean basin elevation that we interpret as having been controlled by climatically driven factors such as frost‐induced processes and orographic precipitation. Our findings illustrate that while the landscape properties in this part of the northern Alpine border can mainly be related to the tectonic architecture of the underlying bedrock, the denudation rates have a strong orographic control through elevation dependent mean annual temperature and precipitation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

15.
Abstract

A physically-based hillslope hydrological model with shallow overland flow and rapid subsurface stormflow components was developed and calibrated using field experiments conducted on a preferential path nested hillslope in northeast India. Virtual experiments were carried out to perform sensitivity analysis of the model using the automated parameter estimation (PEST) algorithm. Different physical parameters of the model were varied to study the resulting effects on overland flow and subsurface stormflow responses from the theoretical hillslopes. It was observed that topographical shapes had significant effects on overland flow hydrographs. The slope profiles, surface storage, relief, rainfall intensity and infiltration rates primarily controlled the overland flow response of the hillslopes. Prompt subsurface stormflow responses were mainly dominated by lateral preferential flow, as soil matrix flow rates were very slow. Rainfall intensity and soil macropore structures were the most influential parameters on subsurface stormflow. The number of connected soil macropores was a more sensitive parameter than the size of macropores. In hillslopes with highly active vertical and lateral preferential pathways, saturation excess overland flow was not evident. However, saturation excess overland flow was generated if the lateral macropores were disconnected. Under such conditions, rainfall intensity, duration and preferential flow rate governed the process of saturation excess overland flow generation from hillslopes.
Editor D. Koutsoyiannis; Associate editor C. Perrin  相似文献   

16.
Decoupling the impacts of climate and tectonics on hillslope erosion rates is a challenging problem. Hillslope erosion rates are well known to respond to changes in hillslope boundary conditions (e.g. channel incision rates) through their dependence on soil thickness, and precipitation is an important control on soil formation. Surprisingly though, compilations of hillslope denudation rates suggest little precipitation sensitivity. To isolate the effects of precipitation and boundary condition, we measured rates of soil production from bedrock and described soils on hillslopes along a semi‐arid to hyperarid precipitation gradient in northern Chile. In each climate zone, hillslopes with contrasting boundary conditions (actively incising channels versus non‐eroding landforms) were studied. Channel incision rates, which ultimately drive hillslope erosion, varied with precipitation rather than tectonic setting throughout the study area. These precipitation‐dependent incision rates are mirrored on the hillslopes, where erosion shifts from relatively fast and biologically‐driven to extremely slow and salt‐driven as precipitation decreases. Contrary to studies in humid regions, bedrock erosion rates increase with precipitation following a power law, from ～1 m Ma?1 in the hyperarid region to ～40 m Ma?1 in the semi‐arid region. The effect of boundary condition on soil thickness was observed in all climate zones (thicker soils on hillslopes with stable boundaries compared to hillslopes bounded by active channels), but the difference in bedrock erosion rates between the hillslopes within a climate region (slower erosion rates on hillslopes with stable boundaries) decreased as precipitation decreased. The biotic‐abiotic threshold also marks the precipitation rate below which bedrock erosion rates are no longer a function of soil thickness. Our work shows that hillslope processes become sensitive to precipitation as life disappears and the ability of the landscape to respond to tectonics decreases. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

17.
The size distributions of sediment delivered from hillslopes to rivers profoundly influence river morphodynamics, including river incision into bedrock and the quality of aquatic habitat. Yet little is known about the factors that influence size distributions of sediment produced by weathering on hillslopes. We present results of a field study of hillslope sediment size distributions at Inyo Creek, a steep catchment in granitic bedrock of the Sierra Nevada, USA. Particles sampled near the base of hillslopes, adjacent to the trunk stream, show a pronounced decrease in sediment size with decreasing sample elevation across all but the coarsest size classes. Measured size distributions become increasingly bimodal with decreasing elevation, exhibiting a coarse, bouldery mode that does not change with elevation and a more abundant finer mode that shifts from cobbles at the highest elevations to gravel at mid elevations and finally to sand at low elevations. We interpret these altitudinal variations in hillslope sediment size to reflect changes in physical, chemical, and biological weathering that can be explained by the catchment's strong altitudinal gradients in topography, climate, and vegetation cover. Because elevation and travel distance to the outlet are closely coupled, the altitudinal trends in sediment size produce a systematic decrease in sediment size along hillslopes parallel to the trunk stream. We refer to this phenomenon as ‘downvalley fining.’ Forward modeling shows that downvalley fining of hillslope sediment is necessary for downstream fining of the long-term average flux of coarse sediment in mountain landscapes where hillslopes and channels are coupled and long-term net sediment deposition is negligible. The model also shows that abrasion plays a secondary role in downstream fining of coarse sediment flux but plays a dominant role in partitioning between the bedload and suspended load. Patterns observed at Inyo Creek may be widespread in mountain ranges around the world. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

18.
Nature can provide analogues for post‐mining landscapes in terms of landscape stability and also in terms of the rehabilitated structure ‘blending in’ with the surrounding undisturbed landscape. In soil‐mantled landscapes, hillslopes typically have a characteristic pro?le that has a convex upper hillslope pro?le with a concave pro?le lower down the slope. In this paper hillslope characteristic form is derived using the area–slope relationship from pre‐mining topography at two sites in Western Australia. Using this relationship, concave hillslope pro?les are constructed and compared to linear hillslopes in terms of sediment loss using the SIBERIA erosion model. It is found that concave hillslopes can reduce sediment loss by up to ?ve times that of linear slopes. Concave slopes can therefore provide an alternative method for the construction of post‐mining landscapes. An understanding of landscape geomorphological properties and the use of erosion models can greatly assist in the design of post‐mining landscapes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

19.
This paper presents a case study of mapping basement structures in the northwestern offshore of Abu Dhabi using high‐resolution aeromagnetic data. Lineament analysis was carried out on the derivatives of the reduced‐to‐the‐pole magnetic data, along with supporting information from published geologic data. The lineament analysis suggests three well‐defined basement trends in the north–south, northeast–southwest, and northwest–southeast directions. The reduced‐to‐the‐pole magnetic data reveal high positive magnetic anomalies hypothesized to be related to intra‐basement bodies in the deep seated Arabian Shield. Depth to basement was estimated using spectral analysis and Source Parameter Imaging techniques. The spectral analysis suggests that the intruded basement blocks are at the same average depth level (around 8.5 km). The estimated Source Parameter Imaging depths from gridded reduced‐to‐the‐pole data are ranged between 4 km and 12 km with a large depth variation within small distances. These estimated depths prevent a reliable interpretation of the nature of the basement relief. However, low‐pass filtering of the horizontal local wavenumber data across two profiles shows that the basement terrain is characterized by a basin‐like structure trending in the northeast–southwest direction with a maximum depth of 10 km. Two‐dimensional forward magnetic modelling across the two profiles suggests that the high positive magnetic anomalies over the basin could be produced by intrusion of mafic igneous rocks with high susceptibility values (0.008 to 0.016 SI.  相似文献   

20.
This study presents a semi-empirical model for quantifying the reduction in the mechanical strength of bedrock beneath actively eroding soil-mantled hillslopes. The strength reduction of bedrock controls the rate of physical disintegration of saprolite, which supplies fresh minerals that are then exposed to intense chemical weathering in soil sections. To determine the values of parameters employed in the model requires knowledge of the denudation rate of the hillslope, the thickness of the soil and saprolite layers, the strength of fresh bedrock, and the threshold strength for physical erosion at the uppermost face of the saprolite. These parameters can be obtained from cosmogenic nuclide analyses for quartz samples from the soil–saprolite boundary and basic field- and laboratory-based investigations. Further testing of the model within a diverse range of climatic, tectonic, and lithologic environments is likely to provide clues to the mechanisms responsible for local and regional variations in the rates of soil production and chemical weathering upon hillslopes.  相似文献   

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