HR: 0800h
AN: H31A-1268    [Abstracts]
TI: Channel Incision in the Inyo Mountains, CA: Transient response to non-steady slip on a Basin and Range normal fault
AU: * Goldstein, E
EM: egoldste@geosc.psu.edu
AF: The Pennsylvania State University, Deike Building, University Park, PA 16802 United States
AU: Kirby, E
EM: ekirby@geosc.psu.edu
AF: The Pennsylvania State University, Deike Building, University Park, PA 16802 United States
AB: Deciphering the landscape record of tectonic forcing requires understanding the rates and processes by which changes in base level are communicated throughout the fluvial network. Progress toward this goal has been hampered in part by a lack of field sites where we can observe a transient response to a known change in boundary conditions. Here we present preliminary observations of channel profile form in the Inyo Mountains, CA. This range is bound on its eastern side by an active normal fault in Saline Valley, which links strike-slip displacement on the Hunter Mountain fault to extension in northern Saline and Eureka Valleys. Channels draining across the fault system exhibit strongly convex, non-equilibrium profiles, characterized by steep lower reaches and low-gradient upper reaches. In contrast, channels developed in similar lithology north and south of the fault tips exhibit smoothly concave profiles. Channels are developed in relatively uniform granitic bedrock and under similar climatic regimes. Upstream reaches of all channels display uniform steepness indices, consistent with a previous quasi-equilibrium form. Knickpoints separating upper and lower reaches, however, show systematic variations in elevation and upstream drainage area along strike of the range, suggesting non-uniform propagation rates. Overall, we conclude that the channels are responding to an increase in slip rate on the bounding fault. Previous structural mapping in the region suggests an increase in extension rate at ca. 1.4 Ma (Sternlof, 1988). We are undertaking a preliminary test of fluvial incision models to assess to what degree the observed differences in knickpoint position can be explained as a consequence of along-strike variations in slip rate.
DE: 1825 Geomorphology: fluvial (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005