Document Type

Article

Publication Version

Published Version

Publication Date

6-2005

Journal or Book Title

Journal of Geophysical Research: Earth Surface

Volume

110

Issue

F2

First Page

1

Last Page

15

DOI

10.1029/2004JF000228

Abstract

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.

Comments

This article is from Journal of Geophysical Research: Earth Surface 110 (2005): no. F02007, doi:10.1029/2004JF000228. Posted with permission.

Copyright Owner

American Geophysical Union

Language

en

File Format

application/pdf

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