Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.h33c1398o&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #H33C-1398
Mathematics
Logic
1150 Cosmogenic-Nuclide Exposure Dating (4918), 1625 Geomorphology And Weathering (0790, 1824, 1825, 1826, 1886), 1826 Geomorphology: Hillslope (1625), 9360 South America
Scientific paper
The nature of hillslope processes under abiotic, hyperarid conditions is poorly constrained, limiting our ability to understand how these landscapes form and respond to changes in climate and base level. This is particularly important as more data is collected at the Columbia Hills and other hillslopes on Mars. To address this problem, we selected two hillslopes with contrasting boundary conditions in the hyperarid core of the Atacama Desert, Chile, where biological processes relevant to hillslope evolution are absent. Despite precipitation of about 1mm/yr, one hillslope is bounded by small, actively incising channels (``active hillslope'') while the other is bounded by a stable alluvial fan of possible Pliocene age (``stable hillslope''). From the first, we can constrain the rate of bedrock erosion driven by base level lowering under hyperarid conditions, and from the second, the rate and mechanisms by which hillslopes ``relax'' in the absence of active dissection. On both hillslopes, we have measured curvature and soil thickness and are calculating bedrock erosion rates based on cosmogenic isotope analyses. These data are then interpreted using a soil mass-balance model in which soil depth is a function of soil production from physical erosion of bedrock, physical transport downslope, atmospheric deposition of salts and silicate dust, and chemical erosion. We are testing the hypotheses that: (1) active hillslope channel incision increases hillslope curvature, thins soils, and increases the bedrock erosion rate; and (2) the blanketing of stable hillslopes by atmospheric deposition of salts and silicate dust decreases curvature and thickens soils which decreases bedrock erosion rates. Our results confirm these hypotheses: preliminary calculations show bedrock erosion rates on the shoulderslope of the active hillslope of 1 m/Myr vs. 0.3 m/Myr on the stable hillslope, greater convexity on the active hillslope compared to the stable one, and consistently thicker soils on the stable hillslope than on the active one. This work is part of a larger study of hillslope pairs along a precipitation gradient in the Atacama Desert, research undertaken to both quantify hillslope soil geomorphology in the driest places on Earth and provide guidance to Mars research.
Amundson Ron
Dietrich William
Finkel Rebecca
Nishiizumi Kuni
Owen Jacqueline
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