HR: 0800h
AN: C41A-0053    [Abstracts]
TI: Relief History and Coupling of Glacial Valley and Hillslope Erosion in the Teton Range, Wyoming
AU: * Tranel, L M
EM: lmtranel@vt.edu
AF: Department of Geosciences Virginia Tech, 4044 Derring Hall 0420, Blacksburg, VA 24061, United States
AU: Spotila, J A
EM: spotila@vt.edu
AF: Department of Geosciences Virginia Tech, 4044 Derring Hall 0420, Blacksburg, VA 24061, United States
AU: Dennen, R L
EM: llewie@vt.edu
AF: Department of Geosciences Virginia Tech, 4044 Derring Hall 0420, Blacksburg, VA 24061, United States
AU: Hetland, B R
EM: bhetland@vt.edu
AF: Department of Geosciences Virginia Tech, 4044 Derring Hall 0420, Blacksburg, VA 24061, United States
AU: Morgan, S A
EM: smorga05@vt.edu
AF: Department of Geosciences Virginia Tech, 4044 Derring Hall 0420, Blacksburg, VA 24061, United States
AU: Waller, C M
EM: wallerc@vt.edu
AF: Department of Geosciences Virginia Tech, 4044 Derring Hall 0420, Blacksburg, VA 24061, United States
AB: Alpine landscapes are the product of coupling and competition between erosion and weathering mechanisms. In the Teton Range, Wyoming, a unique, rugged landscape has evolved through a combination of block tilting, fluvial and glacial incision, cirque retreat, and physical weathering and mass wasting of ridges. We are studying the interaction and effectiveness of these processes using field observations and detrital thermochronology, with particular focus on changes associated with Late Cenozoic climate change. The Tetons are an ideal location for this investigation, because the patterns of net rock uplift and incision since onset of normal faulting at 9 Ma are structurally constrained. To investigate the erosion pattern since glacial advances began, we have used apatite (U-Th)/He detrital thermochronology of moraine and modern river sands to identify where sediment is sourced based on an established bedrock age-elevation gradient and basin hypsometry. Preliminary results from modern river sediment in Garnet Canyon are plagued by poor sample quality, but show a disproportionately large component of young ages, presumably sourced from low altitudes. This may reflect glacial incision, consistent with an increase in relief associated with Late Cenozoic global cooling that has been observed in numerous locations. However, evidence of hillslope denudation implies that glacial erosion may have brought the Tetons close to a topographic steady state. Estimates of mass flux based on surveys of talus fans in Garnet Canyon suggest ridges have recently eroded at close to the rate of long term rock uplift, whereas the long term average rate of peak and ridge erosion must have been much slower. We interpret that glacial incision increased relief up to a point, but then over steepened hillslopes, such that the landscape reached a threshold for mass wasting. Observations of densely spaced joints and fractures in the bedrock suggest material properties may have facilitated reaching this threshold. The Teton landscape thus illustrates the complexity of integrated erosional mechanisms through transitional climate conditions.
DE: 0710 Periglacial processes
DE: 0720 Glaciers
DE: 0790 Weathering (1625, 1886)
SC: Cryosphere [C]
MN: 2007 Fall Meeting