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A laboratory study of particle ploughing and pore-pressure feedback: A velocity-weakening mechanism for soft glacier beds

Journal of Glaciology

By:
,
DOI: 10.3189/002214308784409008

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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 ma-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.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
A laboratory study of particle ploughing and pore-pressure feedback: A velocity-weakening mechanism for soft glacier beds
Series title:
Journal of Glaciology
DOI:
10.3189/002214308784409008
Volume
54
Issue:
184
Year Published:
2008
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
169
Last page:
181
Number of Pages:
13