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1.
Quantifying river incision into low‐relief surfaces using local and catchment‐wide 10Be denudation rates 
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下载免费PDF全文 Relief generation in non‐glaciated regions is largely controlled by river incision into bedrock but datable fluvial terraces that allow quantifying incision rates are not always present. Here we suggest a new method to determine river incision rates in regions where low‐relief surfaces are dissected by streams. The approach consists of three steps and requires the 10Be concentrations of a stream sediment sample and a regolith sample from the low‐relief surface. In the first step, the spatial distribution of 10Be surface concentrations in the given catchment is modelled by assuming that denudation rates are controlled by the local hillslope angles. The slope–denudation rate relation for this catchment is then quantified by adjusting the relation between slope angle and denudation rate until the average 10Be concentration in the model is equal to the one measured in the stream sediment sample. In the second step, curved swath profiles are used to measure hillslope angles adjacent to the main river channel. Third, the mean slope angle derived from these swath profiles and the slope–denudation relation are used to quantify the river incision rate (assuming that the incision rate equals the denudation rate on adjacent hillslopes). We apply our approach to two study areas in southern Tibet and central Europe (Black Forest). In both regions, local 10Be denudation rates on flat parts of the incised low‐relief surface are lower than catchment‐wide denudation rates. As the latter integrate across the entire landscape, river incision rates must exceed these spatially averaged denudation rates. Our approach yields river incision rates between ~15 and ~30 m/Ma for the Tibetan study area and incision rates of ~70 to ~100 m/Ma in the Black Forest. Taking the lowering of the low‐relief surfaces into account suggests that relief in the two study areas increases at rates of 10–20 and 40–70 m/Ma, respectively. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
2.
Tara L. Metzger James E. Pizzuto Shelia M. Trampush Jonathan M. Friedman Derek M. Schook 《地球表面变化过程与地形》2020,45(2):345-360
Six plains cottonwoods along the axis of a meander were excavated to determine if dendrochronology could identify the year and location of germination and date past overbank sedimentation events. Samples from all excavated trees showed clear anatomical changes associated with burial, including increased vessel size, decreased definition of annual ring boundaries, and decreased ring widths. Some of these burial signatures were created by deposition of only a few centimeters of sediment, and most burial events were detected by multiple samples from the same tree. Four of the trees germinated at or near the upper surfaces of bar deposits, while two germinated within thin overbank deposits draped over bar deposits, indicating that germination is closely associated with bars. Dates and inferred thicknesses of overbank sedimentation events are consistent with repeated topographic surveys and data obtained from cesium-137 (137Cs) analyses. However, the record of overbank sedimentation extracted from the trees does not entirely reflect the history of past peak discharges documented by stream gaging, largely because individual trees are progressively less likely to be flooded through time as the river migrates farther away. Germination dates and locations closely track past positions of the river channel. Germination elevations and the elevations of the tops of point bars appear to be decreasing with time as the bend migrates, implying vertical incision by Powder River at a rate of 7.1 ± 4.3 mm/yr. The rate of floodplain growth determined by elevation changes decreases progressively through time, ultimately reaching an apparent plateau after 0.8–1.3 m of vertical accretion. While similar patterns of vertical accretion have previously been interpreted as resulting from decreasing flood probability with increasing floodplain elevation, distance from the channel is also a first-order control on vertical floodplain growth. © 2019 John Wiley & Sons, Ltd. 相似文献
3.
Rainfall simulators can be a useful research tool for some purposes but are quite unsuitable for others. They have been useful in soil erosion and infiltration studies for over eight decades, but the possibility of using a rainfall simulator in urban nonpoint source pollution involving urban non-erodible surfaces has not been fully explored. In this review, the versatility of different rainfall simulators of varying sizes, configurations and styles used in the past two decades are appraised for possible adaptation to urban sealed surfaces. Recommended criteria for detailed rainfall simulator reporting are also outlined.
EDITOR M.C. AcremanASSOCIATE EDITOR not assigned 相似文献
4.
The Colorado River system in southern Utah and northern Arizona is continuing to adjust to the baselevel fall responsible for the carving of the Grand Canyon. Estimates of bedrock incision rates in this area vary widely, hinting at the transient state of the Colorado and its tributaries. In conjunction with these data, we use longitudinal profiles of the Colorado and tributaries between Marble Canyon and Cataract Canyon to investigate the incision history of the Colorado in this region. We find that almost all of the tributaries in this region steepen as they enter the Colorado River. The consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels, and their coincidence within a corridor of high local relief along the Colorado, suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem. This analysis makes testable predictions about spatial variations in incision rates; these predictions are consistent with existing rate estimates and can be used to guide further studies. We also present cosmogenic nuclide data from the Henry Mountains of southern Utah. We measured in situ 10Be concentrations on four gravel‐covered strath surfaces elevated from 1 m to 110 m above Trachyte Creek. The surfaces yield exposure ages that range from approximately 2·5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m/my. These incision rates are similar to other rates determined within the high‐relief corridor. Available data thus support the interpretation that tributaries of the Colorado River upstream of the Grand Canyon are responding to a recent pulse of rapid incision on the Colorado. Numerical modeling of detachment‐limited bedrock incision suggests that this incision pulse is likely related to the upstream‐dipping lithologic boundary at the northern edge of the Kaibab upwarp. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
5.
Channels on the north‐facing piedmont of the Sierra Madre range in Cuyama Valley, California have alternated between three process regimes during the late Quaternary: (1) vertical incision into piedmont alluvium and older sedimentary deposits; (2) lateral erosion; and (3) sediment accumulation. The state of the piedmont system at a given time has been controlled by upstream sediment flux, regional tectonic uplift and incision of the axial Cuyama River. To better understand the timing and to attempt to interpret causes of past geomorphological processes on the Sierra Madre piedmont, we mapped the surficial geology and dated alluvial deposits using radiocarbon, cosmogenic and optical dating methods. Four primary episodes of sedimentation have occurred since ca. 100 ka, culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka. Fill terraces in Cuyama Valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces. Their vertical spatial arrangement is a record of progressive regional tectonic uplift and concomitant axial Cuyama River channel incision migrating up tributary piedmont channels. Subparallel longitudinal terrace profiles which have a linear age–elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints ～1 m kyr?1 of regional uplift affecting the Cuyama River and its tributaries. Sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments. It is possible that increased precipitation during the Last Glacial Maximum was caused by both continental‐scale circulation pattern reorganization and increased Pacific storm frequency and intensity caused by ‘early warming’ of nearby Pacific Ocean surface waters. Older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes, but may correlate with previous periods of increased precipitation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
WANG Yi-zhou ZHANG Hui-ping ZHENG De-wen YU Jing-xing LI Chao-peng XIAO Lin 《地震地质》2017,39(6):1111-1126
The topography and geomorphology of active orogens result from the interaction of tectonics and climate. In most orogens, a fluvial channel is most sensitive to the coupling between tectonics, lithology, and climate. Meanwhile, the related signals have been recorded by both the drainage geometry and channel longitudinal profile. Thus, how to extract tectonic information from fluvial channels has been a focused issue in geologic and geomorphologic studies.
The well known stream-power river incision model bridges the gap between tectonic uplift, river incision and channel profile change, making it possible to retrieve rock uplift pattern from river profiles. In this model, the river incision rate depends on the rock erodibility, contributing drainage area and river gradient. The steady-state form of the river incision model predicts a power-law scaling between the drainage area and channel gradient. Via a linear regression to the log-transformed slope-area data, the slope and intercept are channel concavity and steepness indices, respectively. The concavity relates to lithology, climatic setting and incision process while the channel steepness can be used to map the spatial pattern of rock uplift. For its simple calculation process, the slope-area analysis has been widely used in the study of tectonic geomorphology during past decades.
However, to calculate river slope, the coarse channel elevation data must be smoothed, re-sampled, and differentiated without any reasonable smooth window or rigid mathematical fundamentals. One may lose important information and derive stream-power parameters with high uncertainties. In this paper, we introduce the integral approach, a procedure that has been widely used in the latest four years and demonstrated to be a better method for river profile analysis than the traditional slope-area analysis. Via the integration to the steady-state form of the stream-power river incision equation, the river longitudinal profile can be converted into a straight line of which the independent variable is the integral quantity χ with the unit of distance and the dependent variable is the relative channel elevation. We can calculate the linear correlation coefficient between elevation and χ based on a series of concavity values and find the best linear fit to be the reasonable channel concavity index. The slope of the linear fit to the χ value and elevation is simply related to the ratio of the uplift rate to the erodibility.
Without calculating channel slope, the integral approach makes up for the drawback of the slope-area analysis. Meanwhile, via the integral approach, a steady-state river profile can be expressed as a continuous function, which can provide theoretical principle for some geomorphic parameters (e.g., slope-length index, hypsometric integral). In addition, we can determine the drainage network migration direction using this method. Therefore, the integral approach can be used as a better method for tectonogeomorphic research. 相似文献
7.
Mineral magnetic analysis of B‐horizons of soils developing upon the surfaces of alluvial fans was undertaken in order to: (i) differentiate and rank discrete fan surfaces by order of formation; (ii) establish whether fan surfaces formed simultaneously in adjacent fan systems; and (iii) deduce probable patterns of fan development. The results of the analysis indicate that the greatest concentration of ferrimagnetic and anti‐ferromagnetic minerals occurs within soils which have developed upon the proximal fan surfaces with a progressive reduction in magnetic minerals in soils associated with medial and distal surfaces. The build‐up of magnetic minerals in the proximal fan soils suggests that these surfaces formed first followed by the medial and distal surfaces. With the exception of the Kalivia Sokas fan, the majority of depositional events responsible for fan surface formation occurred simultaneously, suggesting that adjacent fan systems share broadly similar depositional histories. Although the precise timing of depositional events is uncertain, it is probable that by the end of the late Pleistocene, small, largely undissected fans comprising two to three surfaces had formed. At the start of the Holocene, fan systems experienced significant fanhead incision. A net distal extension of the fan trench coupled with a progressive basinward shift of the locus of deposition during the middle and late Holocene resulted in formation of medial and distal fan surfaces. Changes in climate are deemed to be the major control of fanhead incision, fan trenching and fan surface formation. However, the likely effects of long‐term tectonic activity and approximately five thousand years of human occupation upon fan development in the Sparta Basin remain unclear. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
8.
《国际泥沙研究》2023,38(5):662-672
The evaluation of the trend of flood stage changes in alluvial rivers downstream of dams is important for flood management. However, the flood stage associated with a given discharge generally is nonstationary in river reaches with multiple tributaries. This is not only because of the dam-induced shifting in the cross-sectional area and/or channel roughness but also because of the backwater induced by high flows from the tributaries. To determine the total trend of the flood stage and quantify the separate contributions of hydrological and geomorphic effects, the current study proposed a framework approach consisting of hydrological analysis and multiscenario numerical modeling. By this means, the trend in the flood stage could be distinguished from the stage oscillation driven by varying factors, including extreme hydrologic events. The effects of chronic changes, including channel incision and flow resistance increase, also were quantitatively separated. This framework was applied to the Chenglingji–Datong (CD) reach downstream of the Three Gorges Dam (TGD) in the Yangtze River, China. The results indicated that the effect of the roughness increase counterbalanced the effect of channel incision when the flow discharge was beyond the bankfull level. The backwater effect induced by tributary inflow was the major cause of the flood stage rise in recent years. The method presented in the current study provides a useful tool for managers and engineers to obtain better insight into the driving mechanisms of flood stage changes in river reaches that are downstream of dams. These findings indicate that the flood stage may not decline or may even occasionally increase, although the cross-sectional area was enlarged by channel incision. Special attention should be given to the flood risk situation in the study reach after the TGD began operation. 相似文献
9.
Alluvial channel bed incision and bank widening have been reported in both the south‐western and south‐eastern US throughout the past century. Distinct regional differences in climate and landscape properties likely influence the rate of erosion. This study discusses regional differences in hydraulic driving forces and substrate resistance and tests the hypothesis that regional differences exist in average rates of channel incision, bank erosion, and knickpoint retreat. Specifically, we hypothesize that erosion rates are higher in south‐western US streams and reason that this is because of greater flood magnitudes and limited substrate resistance. A review of the literature documenting incision, bank erosion, and knickpoint retreat, however, indicates that intra‐regional differences are larger than inter‐regional differences and that average rates in the south‐western US are either statistically similar or less than the rates in parts of the south‐eastern US. This could either be a result of strong intra‐regional hydroclimatic and substrate variability or because average erosion rate may not be an appropriate metric for inter‐regional comparisons because of the variability between case studies associated with the field methods to measure erosion, duration of study period, and time since disturbance to the channel. Nevertheless, these findings provide a basis for future evaluations of the relative importance of different controls on driving and resisting forces in these and other landscapes characterized by rapid channel incision and arroyo formation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
What controls the architecture of drainage networks is a fundamental question in geomorphology. Recent work has elucidated the mechanisms of drainage network development in steadily uplifting landscapes, but the controls on drainage‐network morphology in transient landscapes are relatively unknown. In this paper we exploit natural experiments in drainage network development in incised Plio‐Quaternary alluvial fan surfaces in order to understand and quantify drainage network development in highly transient landscapes, i.e. initially unincised low‐relief surfaces that experience a pulse of rapid base‐level drop followed by relative base‐level stasis. Parallel drainage networks formed on incised alluvial‐fan surfaces tend to have a drainage spacing that is approximately proportional to the magnitude of the base‐level drop. Numerical experiments suggest that this observed relationship between the magnitude of base‐level drop and mean drainage spacing is the result of feedbacks among the depth of valley incision, mass wasting and nonlinear increases in the rate of colluvial sediment transport with slope gradient on steep valley side slopes that lead to increasingly wide valleys in cases of larger base‐level drop. We identify a threshold magnitude of base‐level drop above which side slopes lengthen sufficiently to promote increases in contributing area and fluvial incision rates that lead to branching and encourage drainage networks to transition from systems of first‐order valleys to systems of higher‐order, branching valleys. The headward growth of these branching tributaries prevents the development of adjacent, ephemeral drainages and promotes a higher mean valley spacing relative to cases in which tributaries do not form. Model results offer additional insights into the response of initially unincised landscapes to rapid base‐level drop and provide a preliminary basis for understanding how varying amounts of base‐level change influence valley network morphology. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
11.
Geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces. This work is aimed at improving the geostatistical approach used in previous works and developing a method for evaluating the incision rates of rivers in their lower catchments during the Late Quaternary. We chose the major valleys of the Adriatic foothills (central Italy), affected since Late Miocene by a differential tectonic uplift which is still active. In particular, (i) we applied the geostatistical analysis to reconstruct the original top‐surfaces of fluvial‐to‐coastal terrace bodies at the Metauro River and Cesano River mouths; (ii) we performed correlations between the height distribution of the alluvial terrace sequences and the Quaternary climatic curve to estimate the average long‐term fluvial incision rates in the lowermost reaches of the Metauro, Cesano, Misa and Esino Rivers. The obtained averaged incision rates have been interpreted also in the light of the Stream‐Length Gradient Index (SL Index), Steepness Index (Ks), and Concavity Index (θ) as proxies of the stream‐power per unit length. Results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers. In particular, we better delineated the surface geometry and boundaries of well‐developed coastal fans at the mouths of the Metauro and Cesano Rivers, already recognized in previous works through sedimentological, morphostratigraphic, and chronological data. Moreover, we found evidence for cut‐and‐fill phases that took place during and immediately after the river aggradation of the late Quaternary glacial periods. Despite the Slope–Area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration, we observed some space and time variability of averaged incision rates for adjacent valleys, mainly explained by physiographic configuration and dynamics of drainage network. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
12.
Erosion of a high‐altitude,low‐relief area on the Korean Peninsula: implications for its development processes and evolution 下载免费PDF全文
下载免费PDF全文 The processes involved in the development of high‐altitude, low‐relief areas (HLAs) are still poorly understood. Although cosmogenic nuclides have provided insights into the evolution of HLAs interpreted as paleo‐surfaces, most studies focus on estimating how slowly they erode and thereby their relative stability. To understand actual development processes of HLAs, we applied several techniques of cosmogenic nuclides in the Daegwanryeong Plateau, a well‐known HLA in the Korean Peninsula. Our denudation data from strath terraces, riverine sediments, soils, and tors provide the following conclusions: (1) bedrock incision rate in the plateau (~127 m Myr?1) is controlled by the incision rate of the western part of the Korean Peninsula, and is similar to the catchment‐wide denudation rate of the plateau (~93 m Myr?1); (2) the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate; (3) a discrepancy between the soil production and catchment‐wide denudation rates implies morphological disequilibrium in the plateau; (4) the tors once regarded as fossil landforms of the Tertiary do not reflect Tertiary processes; and (5) when compared with those of global paleo‐surfaces (<20 m Myr?1), our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape, and thus is not a paleo‐surface. Our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo‐surfaces around the world. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
13.
The normal fault-bend folding theory uses active axial surfaces, inactive axial surfaces, and growth axial surfaces to describe the geometric relationship between faults and deformation of a hanging wall. The dip of a growth axial surface is related to the fault slip rate and the basin sedimentation rate: higher fault slip rates result in smaller dips of growth axial surfaces, whereas higher basin sedimentation rates produce larger dips of growth axial surfaces. Moreover, the growth axial surface will be a straight line if both the fault slip and sedimentation rates remain relatively unchanged, but will become curved if both rates are variable. Therefore, the characteristics of growth axial surfaces can provide clear information on the evolution of faulting and deposition. By studying the seismic profiles of the Zhangwu fault depression of the southern Songliao Basin, we show that the migration of growth axial surfaces and unconformities can be used as indicators of basin development. Multiphase tectonic activity will not only produce unconformities but also result in migration of growth axial surfaces or inactive axial surfaces. Therefore, the normal fault-bend folding theory, particularly with regard to the evolution of growth axial surfaces, can be applied to the interpretation of geometric and kinematic evolutions of half-grabens and the exploration of related tectono-sedimentary processes. 相似文献
14.
Simulation of the frictional stick-slip instability 总被引：7，自引：0，他引：7
15.
Robert A. Berner 《Earth and Planetary Science Letters》1976,29(2):333-340
A general one-dimensional diagenetic equation is derived which expresses the effect of the following processes upon the depth and time distribution of a dissolved species in a modern subaqueous sediment: adsorptive or ion exchange equilibrium between pore water and grain surfaces; slower chemical or radiogenic reactions in the pore solution and on the grain surfaces; diffusion in solution and on grain surfaces; advection of grains due to depositional burial; and advection of water due both to burial and to flow past the grains. It is shown that the effects of equilibrium adsorption can be expressed in terms of a lowered diffusion coefficient only in the special case where there is negligible flow of water relative to grains, adsorption is described by a simple linear isotherm, and there is nochemical reaction occurring in the sediment (i.e. only radioactive decay or no reaction at all). Consideration of a commonly used special case of the general equation indicates that if equilibrium adsorption is strong, the depositional term in the resulting diagenetic equation may become quantitatively as important as the terms for diffusion and chemical reaction. Thus, when modelling diagenesis, deposition often cannot be ignored. A coupled pair of differential equations are also derived which express the steady state depth distribution for two ions exhibiting equilibrium ion exchange while undergoing chemical reaction, diffusion, and deposition. 相似文献
16.
R. Betti 《地震工程与结构动力学》1997,26(10):1005-1019
A boundary element formulation of the substructure deletion method is presented for the seismic analysis of the dynamic cross-interaction between multiple embedded foundations. This approach is particularly suitable for three-dimensional foundations of any arbitrary geometrical shape and spatial location, since it requires only the discretization of the foundations’ surfaces. The surrounding soil is represented by a homogeneous viscoelastic half-space while the foundations are assumed to be rigid and subjected to incoming SH-, P-, and SV-waves arbitrarily inclined in both the horizontal and vertical planes. The proposed methodology is tested for the case of two identical embedded square foundations for different values of the foundations’ embedment and distance. The effects of the cross-interaction are outlined in the components of the impedance matrix and of the foundation input motion. © 1997 John Wiley & Sons, Ltd. 相似文献
17.
L. Allan James 《地球表面变化过程与地形》2004,29(7):869-882
Sand and gravel tailings from nineteenth century open‐pit hydraulic gold mines formed large alluvial fans at tributary con?uences in the northwestern Sierra Nevada, California. In the Bear River watershed, several of these fans were so large that they blocked main channels for decades. Some channels not only aggraded deeply, but also moved laterally and cut across the inner bends of valley spurs. Now locked in bedrock channels, these valley‐spur cutoffs impose local controls on geomorphic, hydraulic, and sedimentary processes. One cutoff has incised 25 m into bedrock over the past century (25 cm a?1) with rapid initial incision rates of up to 50 cm a?1 (1884–1890). Recognition of spur cutoffs in the geological record may help to identify large landslides and provide an analogue for a type of natural earth?ll dam spillway not prone to catastrophic failures. Tailing fans, valley‐spur cutoffs, and the sediment they trap are described from contemporary accounts and recent ?eld conditions in the Bear River watershed. These anthropogenic changes represent a major shift in the watershed from supply‐limited to transport‐limited sediment budgets and a change in geomorphic processes away from long‐term drainage evolution dominated by ingrown meanders. The large volumes of mining sediment stored in these landforms will be slowly released over the next millennium and could be signi?cant to contemporary ecological and public health issues due to recent ?ndings of high mercury loadings associated with hydraulic mines. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
18.
In this paper we derive an integral formula that encompasses all linear processes on seismic data. These include migration, demigration and residual migration, as well as data mapping procedures such as transformation to zero offset, inverse transformation to zero offset, residual transformation to zero offset and offset continuation. The derivation of the equation is different from all previous approaches to unification. Here we do not use a cascaded operation between two operators, but rather the superposition principle. In this regard, the derivation is not only more fundamental, but also simpler and more general. We study the kinematics and the dynamics of these processes and show that the signals can be reconstructed asymptotically either by finding the envelope of particular surfaces or by stacking energy along “adjoint” surfaces. For example, in the case of migration, the first set of surfaces are isochrons, while the “adjoint” surfaces are diffraction responses. In practice, the distinction between these two types of surfaces is equivalent to choosing the order of the computational loops with regard to the input and output seismic traces. 相似文献
19.
Larry Syu-Heng Lai Joshua J. Roering Noah J. Finnegan Rebecca J. Dorsey Jiun-Yee Yen 《地球表面变化过程与地形》2021,46(13):2671-2689
The incision rate and steepness of bedrock channels depend on water discharge, uplift rate, substrate lithology, sediment flux, and bedload size. However, the relative role of these factors and the sensitivity of channel steepness to rapid (>1 mm yr−1) uplift rates remain unclear. We conducted field and topographic analyses of fluvial bedrock channels with varying channel bed lithology and sediment source rock along the Coastal Range in eastern Taiwan, where uplift rates vary from 1.8 to 11.8 mm yr−1 and precipitation is relatively consistent (1.5–2.7 m yr−1), to evaluate the controls on bedrock channel steepness. We find that channel steepness is independent of rock uplift rate and annual precipitation but increases monotonically with sediment size and substrate strength. Furthermore, in reaches with uniform substrate lithology (mudstone and flysch), channel steepness systematically varies with sediment source rock but not with channel width. When applied to our data, a mechanistic incision model (saltation-abrasion model) suggests that the steepness of Coastal Range channels is set primarily by coarse-sediment supply. We also observe that larger particles are mainly composed of resistant lithologies derived from volcanic rocks and conglomerates. This result implies that hillslope bedrock properties in the source area exert a dominant control on the steepness of proximal channels through coarse-sediment production in this setting. We propose that channel steepness may be insensitive to uplift rate and flow discharge in fast-uplifting landscapes where incision processes are set by coarse sediment size and supply. Models assuming a proportionality between incision rate and basal shear stress (stream power) may not fully capture controls on fluvial channel profiles in landslide-dominated landscapes. Processes other than channel steepening, such as enhanced bedload impacts and debris-flow scour, may be required to balance rock uplift and incision in these transport-limited systems. 相似文献
20.
The Schmidt hammer is employed by geomorphologists as a convenient field instrument for measuring the hardness of rock surfaces. Field trials indicate that the readings obtained are a function of not only the hardness of the surfaces but also their texture. Smooth planar surfaces give much higher readings than rough or irregular surfaces. This makes interpretation of the results particularly difficult when the hammer is used to measure the hardness of natural rock surfaces that have been roughened by weathering. 相似文献