HR: 0800h
AN: H51C-0384    [Abstracts]
TI: Degradation of Terrace Risers: Analysis of Hillslope Diffusion due to Physical, Biological and Climatic Processes
AU: * Clarke, B A
EM: brian@crustal.ucsb.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, CA 93106 United States
AU: * Clarke, B A
EM: brian@crustal.ucsb.edu
AF: Department of Earth Science, University of California, Santa Barbara, CA 93106 United States
AU: Burbank, D A
EM: burbank@crustal.edu
AF: Institute for Crustal Studies, University of California, Santa Barbara, CA 93106 United States
AU: Burbank, D A
EM: burbank@crustal.edu
AF: Department of Earth Science, University of California, Santa Barbara, CA 93106 United States
AB: River-cut terrace risers form at a known initial geometry. Their subsequent degradation, from down-slope transport of sediment, is an aggregate of hillslope processes, mainly attributed to particle-by-particle gravitational unraveling and biological disturbances. This study examines the ability of linear, non-linear, and geometric models to quantify terrace degradation through time and accurately depict the resulting geomorphic form. In addition to the physical processes, the effects of microclimate, due to slope aspect and inclination, strongly affect local degradation rates. By comparing terraces risers from the Ohau River in the McKenzie Basin, New Zealand, where there are no native burrowing mammals, to terraces from Grand Teton National Park, North America, we can compare factors affecting hillslope diffusion and perhaps isolate localized effects on degradation rates and terrace profile form due to burrowing mammals and microclimate. Preliminary analysis of terrace profiles in both regions reveals asymmetric slope and curvature profiles between the upper and lower portion of the terrace risers, as well as correlations between diffusion rates and terrace height. Analysis of profile slope and curvature suggests a non-linear relation between sediment flux and gradient, and imply a heterogeneous diffusion coefficient over the length of individual profiles, caused by varying intensities of dominant transport processes. Initial results suggest that increases in sediment transport rates due to burrowing mammals are minimal. Increases in sediment flux due to burrowing mammals are masked by more dominant gravitational unraveling processes and the effect of terrace height and microclimate. Additionally, the diffusion coefficient, which controls the efficiency of degradation, may vary over the length of the profile, thus creating distinct asymmetries in slope and curvature. Through the analysis of terraces of known age, the results of this study are used to back-calculate local diffusion coefficients, which in turn are used with the best fit sediment transport model to determine the approximate time of formation of previously undated scarps in the area.
DE: 1824 Geomorphology: general (1625)
DE: 1826 Geomorphology: hillslope (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005