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 occurding in the bedrock (e.g.,
fracture generation) may play a role in the shape of hillslope profiles
at our sites.