122 From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change

This session explores how methods such as cosmogenic nuclides, apatite (U-Th)/He thermochronometry, U-series geochemistry, luminescence, and chemical mass balances quantify relationships between climate, tectonics, and erosion.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 212AB

Untangling Climate and Lithologic Controls on Rocky Hillslope Evolution in Steep Landscapes of Eastern California

Paper number: 122-4
Program: Technical Sessions
Time: 2:30 PM – 2:50 PM

Authors

Abstract

In steep mountain regions, hillslopes often display a patchwork of soil and bare bedrock. While the morphology of soil-mantled hillslopes depends largely on rock uplift and erosional efficiency, patchy soil and bedrock hillslopes may also be sensitive to factors such as bedrock strength. Developing and testing models for patchy hillslope evolution is limited by few combined erosion rate, morphology, and bedrock exposure data. Here, we present 41 new 10Be erosion rates combined with morphologic analyses and bedrock mapping from the Eastern Sierra Nevada and Inyo Mountains in California. These steep, rocky catchments have mean slopes between 28º to 48º, and cosmogenic 10Be erosion rates from 0.03 to 0.6 mm/yr. Erosion rates increase monotonically with slope, even at slopes beyond soil critical slopes, presenting a challenge for transport models from soil-mantled regions. We apply these data to a bedrock hillslope model that accounts for patchy hillslopes by isolating soil-mantled and bedrock regions and using only soil-mantled slopes to calibrate a non-linear soil transport model. The bedrock hillslope model effectively models erosion rates and reveals deviations from the non-linear model at slopes above and below soil critical slopes. Model calibration provides additional information about these landscapes including estimates of bedrock strength, reflected as the critical bedrock slope, and erosional efficiency. The modeled critical bedrock slopes correspond well with independent measures of bedrock strength from cliff mapping. When our results are compared with data from the San Gabriel and San Jacinto Mountains to the south, they reveal a limited influence of bedrock strength. While stronger rock produces more extensive bedrock exposure and steeper, taller cliffs, there is no significant relationship between rock strength and erosional efficiency. Climate, however, does appear to influence erosion processes between regions, with higher rainfall correlating with more efficient erosion. While analyses in additional landscapes may help to clarify the relationships between climate, lithology and erosion, this methodology provides a promising tool for incorporating the complex morphology of patchy hillslopes into soil transport models to advance our understanding of how these landscapes evolve and persist over time.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-414674

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