HR: 16:30h
AN: C34A-03    [Abstracts]
TI: Debris-Bed Friction of Hard-Bedded Glaciers
AU: * Cohen, D
EM: dcohen@iastate.edu
AF: Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science I, Ames, IA 50011 United States
AU: Iverson, N R
EM: niverson@iastate.edu
AF: Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science I, Ames, IA 50011 United States
AU: Hooyer, T S
AF: Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 United States
AU: Fischer, U H
AF: Laboratory of Hydraulics Hydrology and Glaciology, Gloriastrasse 37 - 39, Zurich, 8092 Switzerland
AU: Jackson, M
EM: mja@nve.no
AF: Norwegian Water Resources and Energy Directorate, Middelthunsgate 29 P. Box 5091 Majorstua, Oslo, 0301 Norway
AU: Moore, P L
EM: pete@stribmail.com
AF: Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science I, Ames, IA 50011 United States
AB: Field measurements of debris-bed friction on a smooth rock tablet at the bed of Engabreen, a hard-bedded, temperate glacier in northern Norway, indicated that basal ice containing 10% debris by volume exerted local shear traction of up to 500~kPa. The corresponding bulk friction coefficient between the dirty basal ice and the tablet was between 0.05 and 0.08. A model of friction in which non-rotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if ice is Newtonian. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed show that this force can reach values several hundred times that on a sphere isolated from the bed, thus drastically increasing frictional resistance. Various estimates of basal friction are obtained from this model. For example, the shear traction at the bed of a 200~m thick glacier sliding at 20~m$\,$a$^{-1}$ with a geothermally induced melt rate of 0.006~m$\,$a$^{-1}$ can exceed 100~kPa. Debris-bed friction can, therefore, be a major component of sliding resistance, contradicting the common assumption that debris-bed friction is negligible.
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting