『Abstract
It has been long hypothesized that topography, as well as climate
and rock strength, exert first order controls on erosion rates.
Here we use detrital cosmogenic 10Be from 50 basins,
ranging in size from 1 to 150 km2, to measure millennial
erosion rates across the San Gabriel Mountains in southern California,
where a strong E-W gradient in relief compared to weak variation
in precipitation and lithology allow us to isolate the relationship
between topographic form and erosion rate. Our erosion rates range
from 35 to 1100 m/Ma, and generally agree with both decadal sediment
fluxes and long term exhumation rates inferred from low temperature
thermochronometry. Catchment-mean hillslope angle increases with
erosion rate until 〜300 m/Ma, at which point slopes become invariant
with erosion rate. although this sort of relation has been offered
as support for non-linear models of soil transport, we use 1-D
analytical hillslope profiles derived from existing soil transport
laws to show that a model with soil flux linear in slope, but
including a slope stability threshold, is indistinguishable from
a non-linear law within the scatter of our data. Catchment-mean
normalized channel steepness index increases monotonically, though
non-linearly, with erosion rate throughout the San Gabriel Mountains,
even where catchment-mean hillslope angles have reached a threshold.
This non-linearity can be mostly accounted for by a stochastic
threshold incision model, though additional factors likely contribute
to the observed relationship between channel steepness and erosion
rate. These findings substantiate the claim that the normalized
channel steepness index is an important topographic metric in
active ranges.
Keywords: erosion; landscape evolution; topographic metrics; cosmogenic
radionuclides; San Gabriel Mountains』
1. Introduction
2. Study area
3. Methods
3.1. Cosmogenic erosion rates
3.2. Catchment-mean hillslope angle
3.3. Catchment-mean channel steepness index
3.4. Catchment-mean local relief
4. Results
4.1. Interrelations among topographic metrics
4.2. Spatial distribution of topographic metrics
4.3. Erosion rates and topography
5. Analysis
5.1. Catchment-mean slope and erosion rate
5.2. Catchment-mean channel steepness index and erosion rate
6. Discussion
6.1. Implications for channel incision theory
6.2. Implications for hillslope transport theory
7. Conclusions
Acknowledgements
References