HR: 13:40h
AN: H53E-01    [Abstracts]
TI: The Response of Fluvial Landscapes to Glaciation
AU: * Brocklehurst, S H
EM: shb@man.ac.uk
AF: Department of Earth Sciences, University of Manchester, Manchester, M13 9PL United Kingdom
AU: Whipple, K X
EM: kxw@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, M.I.T., Cambridge, MA 02139 United States
AB: A major consequence of climate cooling is the growth of glaciers in mountain ranges previously sculpted by fluvial and hillslope processes. Climate change and the tectonics of mountain ranges are linked if glacial erosion either alters the relief structure, or exhumes material in a different fashion from rivers. Glacial erosion carves cirques and U-shaped valleys, and cooler climates also affect hillslope processes, as freeze-thaw, rockfall, landsliding and debris flows start to dominate. The signature of glacial erosion on the landscape is readily identified from digital elevation model (DEM) analyses, including hypsometry and longitudinal profiles, and comparison with the evolution of fluvial landscapes can be made using a landscape evolution model. These techniques demonstrate that the evolution of glaciated landscapes is not a simple function of regional climate change. In smaller drainage basins in the eastern Sierra Nevada, California, glaciers have generated modest relief, and have incised the valley floor at higher elevations. In larger drainage basins, where accumulation areas are greater and the rainshadow effect is less, glaciers have carved a strikingly different morphology. There is more relief, and valley floor incision occurs at much lower elevations. The Sangre de Cristo Range, Colorado, has evolved similarly, although with pronounced asymmetry, caused by the prevailing winds from the west. Accumulation of wind-blown snow on the eastern side of the range causes much more substantial erosion and deposition of spectacular moraines. In more tectonically active regions, such as the Southern Alps of New Zealand, and the Nanga Parbat region of Pakistan, smaller glacial valley floors steepen in response to rapid rock uplift, whereas larger glaciers maintain shallow gradients despite rapid rock uplift. Hillslope processes are apparently slower than valley floor incision, at least for some period, allowing dramatic relief production and decoupling of valley floor and hillslope processes. Potential causes of the nonlinear response of basins of different sizes to regional climate cooling include the increased longevity and discharge of larger glaciers, and their more complex subglacial hydrology.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1827 Glaciology (1863)
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting