Campus Units

Geological and Atmospheric Sciences

Document Type

Article

Publication Version

Published Version

Publication Date

1-2008

Journal or Book Title

Journal of Glaciology

Volume

54

Issue

184

First Page

169

Last Page

181

DOI

10.3189/002214308784409008

Abstract

If basal-water discharge and pressure are sufficiently high, a soft-bedded glacier will slip over its bed by ploughing, the process in which particles that span the ice–bed interface are dragged across the bed surface. Results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity (velocity weakening). During ploughing at various velocities (15–400 m a−1), till was compacted in front of idealized particles, causing pore pressures there that were orders of magnitude higher than the ambient value. This excess pore pressure locally weakened the till in shear, thereby decreasing ploughing resistance by a factor of 3.0–6.6 with a six-fold increase in ploughing velocity. Characteristic timescales of pore-pressure diffusion and compaction down-glacier from ploughing particles depend on till diffusivity, ploughing velocity and sizes of ploughing particles. These timescales accurately predict the ranges of these variables over which excess pore pressure and velocity weakening occurred. Existing ploughing models do not account for velocity weakening. A new ploughing model with no adjustable parameters predicts ploughing resistance to no worse than 38% but requires that excess pore pressures be measured. Velocity weakening by this mechanism may affect fast glacier flow, sediment transport by bed deformation and basal seismicity.

Comments

This article is from Journal of Glaciology 54 (2008): 169, doi:10.3189/002214308784409008. Posted with permission.

Rights

Creative Commons Attribution license.

Copyright Owner

International Glaciological Society

Language

en

File Format

application/pdf

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