Surge (glacier)
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Glacial surges are short-lived events where a glacier can move up to velocities 100 times faster than normal, and advance substantially. Surging glaciers are clustered around a few areas. High concentrations of surging glaciers can be found in Svalbard, Canadian Arctic islands, and Alaska. Glacial surges take place at regular, periodic intervals, with the period between two surges called the quiescent phase. During this period the velocities of the glacier are significantly lower, and the glaciers can retreat substantially.
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[edit] Causes
There have been many theories of why glacial surges occur.
[edit] Critical mass
Meier & Post (1969) suggest that once mass accumulates to a critical point, basal melting begins to occur. This provides a buoyancy force, "lifting" the glacier from the bed and reducing the friction force.
[edit] Deformable bed hypothesis
In other cases, the geology of the underlying country rock, may dictate surge frequency. For example, poorly consolidated sedimentary rocks are more prone to failure under stress; a sub-glacial "landslip" may permit the glacier to slide. This explains why surging glaciers tend to cluster in certain areas.
[edit] Supply of freshwater
Surges may also be caused by the supply of meltwater to the base of a glacier. Meltwater is important in reducing frictional restrictions to glacial ice flow. The distribution and pressure of water at the bed modulates the glaciers velocity and therefore mass balance. Meltwater may come from a number of sources, including supraglacial lakes, geothermal heating of the bed, conduction of heat into the glacier and latent heat transfers. There is a positive feedback between velocity and friction at the bed, high velocities will generate more frictional heat and create more meltwater. Crevassing is also enhanced by greater velocity flow which will provide further rapid transmission paths for meltwater flowing towards the bed.
The evolution of the drainage system under the glacier plays a key role in surge cycles.
