Debris-bed friction of hard-bedded glaciers

Cohen, D.; Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Jackson, M.; Moore, P. L.

Abstract:

[1] 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 nonrotating spherical rock particles are held in frictional contact with the bed by bed-normal ice flow can account for these measurements if the power law exponent for ice flowing past large clasts is 1. A small exponent (n < 2) is likely because stresses in ice are small and flow is transient. Numerical calculations of the bed-normal drag force on a sphere in contact with a flat bed using n = 1 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 glacier sliding at 20 m a-1 with a geothermally induced melt rate of 0.006 m a-1 and an effective pressure of 300 kPa 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. Copyright 2005 by the American Geophysical Union.

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Article

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70027337

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Cohen, D.; Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Jackson, M.; Moore, P. L.

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English

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Journal of Geophysical Research F: Earth Surface

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Debris-bed friction of hard-bedded glaciers; 2005; Article; Journal; Journal of Geophysical Research F: Earth Surface; Cohen, D.; Iverson, N. R.; Hooyer, T. S.; Fischer, U. H.; Jackson, M.; Moore, P. L.