Information Page: Glacier Surge
Variegated Glacier Surge in Alaska
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|Where:||Variegated Glacier, Alaska|
Grade level: Under graduate (13-16)
Statement: Surge at the Glacier Snout
Abstract: This movie shows the snout of Variegated Glacier in Alaska. This glacier is about 20 km length and ends in Russell Fjord, a tributary fjord to Yakutat Bay. The Variegated glacier surged over about 2 yrs, in 1982-1983. The glacier is know to surge every 16-26 years! Normal speeds are about 0.1-1 m/day. During this surge this speeded up to ~50m/day. The movie shows a period of relative quiescence, and then a rapid speed up towards the end of the time lapse. The thickening can be observed to; a total of 110 m of thichening resulted from the surge.
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 found in only a few areas: Svalbard, Canadian Arctic islands, and Alaska. Glacial surges can take place at regular, periodic intervals. In some glaciers, surges can occur in fairly regular cycles with 15 to 100 or more surge events per year. In other glaciers, surging is unpredictable. In some glaciers, the period of stagnation and build-up between two surges typically lasts 10-200 years and is called the quiescent phase. During this period the velocities of the glacier are significantly lower, and during those periods the glaciers can retreat substantially.
Glaciers in Alaska exhibit surges with a sudden onset, extremely high (tens of meters/day) maximum flow rate and a sudden termination, often with a discharge of stored water. These are called Alaskan-type surges and it is suspected that these surges are hydrologically controlled. Outburst flows are often associated with these events.
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 may play a key role in surge cycles.
In contrast, surging glaciers in Svalbard appear to have a much slower surging cycle. Monaconbreen in Svalbard surged over several years, and maximum speeds were much less high than measured in Alaska.
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