HR: 0800h
AN: H31A-1269    [Abstracts]
TI: Styles and rates of knickpoint migration from cosmogenic Be-10 in an extensional landscape
AU: * Commins, D C
EM: dcommins@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, PO Box 1000 61 Route 9W , Palisades, NY 10964-1000 United States
AU: Gupta, S
EM: s.gupta@imperial.ac.uk
AF: Imperial College, Prince Consort Road, London, SW7 2BP United Kingdom
AU: Phillips, W
EM: phillips@uidaho.edu
AF: University of Idaho, PO Box 443014 , Moscow, ID 83844-3014 United States
AU: Schaefer, J
EM: schaefer@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, PO Box 1000 61 Route 9W , Palisades, NY 10964-1000 United States
AB: Knickpoints are important elements in transient landscapes as they represent disequilibrium in the hydrologic system. The upstream retreat of knickpoints is a primary mechanism for communication of base level fall through the landscape, and ultimately controls landscape response to changes in the system. Despite the importance of these features, little quantitative information is known on the style or rates of knickpoint migration. We present data from tectonically-controlled knickpoints in the Canyonlands Graben, Utah, to constrain rates and styles of bedrock erosion in this semi-arid landscape. Our results show that knickpoints migrate upstream by processes of groundwater sapping that cause undercutting and eventual collapse of beds with thickness of greater than 1m; this process resets the cosmogenic isotope system allowing us to estimate knickpoint migration rates of approximately 10m/ka. Bedrock erosion rates show that knickpoint zones are fundamentally transient features through which bedrock incision is accomplished.
DE: 1130 Geomorphological geochronology
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 1815 Erosion
DE: 1824 Geomorphology: general (1625)
DE: 1825 Geomorphology: fluvial (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005