Quantifying the roles of bedrock damage and microclimate on potential soil production rates, erosion rates, and topographic steepness: A case study of the San Gabriel Mountains, California
Jon D. Pelletier
Department of Geosciences, University of Arizona, Gould-Simpson Building, 1040 East Fourth Street, Tucson, Arizona 85721-0077, USA
Received: 08 Jul 2016 – Accepted for review: 06 Aug 2016 – Discussion started: 16 Aug 2016
Abstract. Discerning how tectonic uplift rates, climate, soil production rates, erosion rates, and topography interact is essential for understanding the geomorphic evolution of mountain ranges. Perhaps the key independent variable in this interaction is the potential soil production rate, i.e., the upper limit at which bedrock can be converted into transportable material. In this paper I document the controls on potential soil production rates using the San Gabriel Mountains (SGM) of California as a case study. The prevailing conceptual model for the geomorphic evolution of the SGM is that tectonic uplift rates control topographic steepness, erosion rates, and potential soil production rates. I test the alternative hypothesis that bedrock damage and microclimate also exert first-order controls on landscape evolution in the SGM via their influence on potential soil production rates. I develop an empirical equation that relates potential soil production rates in the SGM to a bedrock damage index that depends on the local density of faults and a microclimatic index that relates to aspect-driven variations in vegetation cover and wildfire severity and frequency. Assuming a balance between soil production and erosion rates at the hillslope scale, I further show that observed trends in topographic steepness can be reproduced using the empirical equation for potential soil production rates. The results suggest that tectonic uplift rates, bedrock damage, and microclimate play co-equal and interacting roles in controlling landscape evolution in the SGM and perhaps other tectonically active mountain ranges.
Pelletier, J. D.: Quantifying the roles of bedrock damage and microclimate on potential soil production rates, erosion rates, and topographic steepness: A case study of the San Gabriel Mountains, California, Earth Surf. Dynam. Discuss., doi:10.5194/esurf-2016-37, in review, 2016.