DiBiase,R.A., Whipple,K.X., Heimsath,A.M. and Ouimet,W.B.(2010): Landscape form and millennial erosion rates in the San Gabriel Mountains, CA. Earth and Planetary Science Letters, 289, 134-144.

『カリフォルニア州サンガブリエル山脈の地形と千年期間の浸食速度』


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


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