A laboratory study of particle ploughing and pore-pressure feedback: a velocity-weakening mechanism for soft glacier beds
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The Department of Geological and Atmospheric Sciences offers majors in three areas: Geology (traditional, environmental, or hydrogeology, for work as a surveyor or in mineral exploration), Meteorology (studies in global atmosphere, weather technology, and modeling for work as a meteorologist), and Earth Sciences (interdisciplinary mixture of geology, meteorology, and other natural sciences, with option of teacher-licensure).
History
The Department of Geology and Mining was founded in 1898. In 1902 its name changed to the Department of Geology. In 1965 its name changed to the Department of Earth Science. In 1977 its name changed to the Department of Earth Sciences. In 1989 its name changed to the Department of Geological and Atmospheric Sciences.
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1898-present
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- Department of Geology and Mining (1898-1902)
- Department of Geology (1902-1965)
- Department of Earth Science (1965-1977)
- Department of Earth Sciences (1977-1989)
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- College of Liberal Arts and Sciences (parent college)
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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 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.
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This article is from Journal of Glaciology 54 (2008): 169, doi:10.3189/002214308784409008. Posted with permission.