HR: 1340h
AN: H53C-1378    [Abstracts]
TI: Rock Matters: Lithologic Controls on Landscape Evolution
AU: * Johnson, E R
EM: elizabeth.rose.johnson@gmail.com
AF: Dartmouth College, Department of Earth Sciences 6105 Sherman Fairchild Hall, Hanover, NH 03755, United States
AU: Heimsath, A M
EM: Arjun.Heimsath@ASU.edu
AF: Arizona State University, School of Earth and Space Exploration 550 East Tyler Mall, Tempe, AZ 85287, United States
AU: Dade, W B
EM: William.B.Dade@Dartmouth.edu
AF: Dartmouth College, Department of Earth Sciences 6105 Sherman Fairchild Hall, Hanover, NH 03755, United States
AB: Landscapes are shaped through balances between external forcing (climate, tectonics, humans) on erosion and internal controls like material strength. It is widely held, and commonly assumed, that erosion rates vary directly with tectonic uplift rates. It is, however, still relatively unclear how the balance between tectonic forcing and lithologic properties impacts landscape evolution. We focus this study to explore whether landscapes of different rock types evolve differently under similar tectonic forcing. Our field area is the San Gabriel Mountains in southern California. The entire mountain range falls within a similar climatic zone, and it has both a tectonic and lithologic gradient. Previous work quantified a clear correlation between catchment steepness, erosion rates and inferred uplift rates across the field site. For work presented here we chose three lithologies (anorthosite, granite, and mixed metamorphics) across various erosional-uplift regimes, from low-relief soil mantled hill slopes to high- relief rocky hill slopes. At each site we measured parent material strength with a drop-cone penetrometer and/or a shear vane tester. Preliminary analyses suggest that material strength varies significantly with relative erosion rate. We also show that material strength does not vary significantly between rock types under similar erosional regimes. Because we observe quantitative differences in material strength for a given lithology under different erosion rates, we show support for the hypothesis that erosion rates influence material strength and not the reverse. Keeping in mind that the only other variable considered here is tectonic forcing, we suggest that relative erosion rates are controlled more by tectonic forcing than lithology, but that lithology may still account for the variability within an erosional regime.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
DE: 1859 Rocks: physical properties
SC: Hydrology [H]
MN: 2007 Fall Meeting