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Hilltop Curvature Increases With the Square Root of Erosion Rate.

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Title: Hilltop Curvature Increases With the Square Root of Erosion Rate.
Authors: Gabet, E. J.1 manny.gabet@sjsu.edu, Mudd, S. M.2, Wood, R. W.1, Grieve, S. W. D.3, Binnie, S. A.4, Dunai, T. J.4
Source: Journal of Geophysical Research. Earth Surface. May2021, Vol. 126 Issue 5, p1-16. 16p.
Subject Terms: *Erosion, *Sediment transport, Slopes (Physical geography), Soil creep, LIDAR
Abstract: The shape of soil‐mantled hillslopes is typically attributed to erosion rate and the transport efficiency of the various processes that contribute to soil creep. While climate is generally hypothesized to have an important influence on soil creep rates, a lack of uniformity in the measurement of transport efficiency has been an obstacle to evaluating the controls on this important landscape parameter. We addressed this problem by compiling a data set in which the transport efficiency has been calculated using a single method, the analysis of hilltop curvatures using 1‐m LiDAR data, and the erosion rates have also been determined via a single method, in‐situ cosmogenic 10Be concentrations. Moreover, to control for lithology, we chose sites that are only underlain by resistant bedrock. The sites span a range of erosion rates (6–922 mm/kyr), mean annual precipitation (39–320 cm/yr), and aridity index (0.08–1.38). Surprisingly, we find that hilltop curvature varies with the square root of erosion rate, whereas previous studies predict a linear relationship. In addition, we find that the inferred transport coefficient also varies with the square root of erosion rate but is insensitive to climate. We explore various mechanisms that might link the transport coefficient to the erosion rate and conclude that present theory regarding soil‐mantled hillslopes is unable to explain our results and is, therefore, incomplete. Finally, we tentatively suggest that processes occurring in the bedrock (e.g., fracture generation) may play a role in the shape of hillslope profiles at our sites. Key Points: Hilltop curvature at our sites does not vary linearly with erosion rate, as predicted by theoryThe inferred transport coefficient appears to be insensitive to climateProcesses affecting the underlying bedrock may control the shape of soil‐mantled hillslopes [ABSTRACT FROM AUTHOR]
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Abstract:The shape of soil‐mantled hillslopes is typically attributed to erosion rate and the transport efficiency of the various processes that contribute to soil creep. While climate is generally hypothesized to have an important influence on soil creep rates, a lack of uniformity in the measurement of transport efficiency has been an obstacle to evaluating the controls on this important landscape parameter. We addressed this problem by compiling a data set in which the transport efficiency has been calculated using a single method, the analysis of hilltop curvatures using 1‐m LiDAR data, and the erosion rates have also been determined via a single method, in‐situ cosmogenic 10Be concentrations. Moreover, to control for lithology, we chose sites that are only underlain by resistant bedrock. The sites span a range of erosion rates (6–922 mm/kyr), mean annual precipitation (39–320 cm/yr), and aridity index (0.08–1.38). Surprisingly, we find that hilltop curvature varies with the square root of erosion rate, whereas previous studies predict a linear relationship. In addition, we find that the inferred transport coefficient also varies with the square root of erosion rate but is insensitive to climate. We explore various mechanisms that might link the transport coefficient to the erosion rate and conclude that present theory regarding soil‐mantled hillslopes is unable to explain our results and is, therefore, incomplete. Finally, we tentatively suggest that processes occurring in the bedrock (e.g., fracture generation) may play a role in the shape of hillslope profiles at our sites. Key Points: Hilltop curvature at our sites does not vary linearly with erosion rate, as predicted by theoryThe inferred transport coefficient appears to be insensitive to climateProcesses affecting the underlying bedrock may control the shape of soil‐mantled hillslopes [ABSTRACT FROM AUTHOR]
ISSN:21699003
DOI:10.1029/2020JF005858