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Ice stream

 
Sci-Tech Dictionary: ice stream
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(′īs ′strēm)

(hydrology) A current of ice flowing in an ice sheet or ice cap; usually moves toward an ocean or to an ice shelf.

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Geography Dictionary: ice stream
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Within a glacier or ice sheet, a stream of ice moving more quickly than, and not necessarily in the same direction as, most of the ice. The physical controls on the motion and areal extent of ice streams are: buttressing by ice shelves, ice stream width, discharge and mass balance; basal sliding; deformation of subsole till; and the extent of drag at the ice-stream margins.

Wikipedia: Ice stream
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Velocity map of Antarctica. Ice streams can be seen with increasing speeds (blue-yellow-white) flowing toward the coast.[1]
Radarsat image of ice streams flowing into the Filchner-Ronne Ice Shelf

An ice stream is a region of an ice sheet that moves significantly faster than the surrounding ice. Ice streams are a type of glacier.[2] They are significant features of the Antarctic where they account for 10% of the volume of the ice. They are up to 50 km wide, 2 km thick, can stretch for hundreds of kilometres, and account for most of the ice leaving the ice sheet.

The speed of an ice stream can be over 1,000 meters per year, an order of magnitude faster than the surrounding ice. The shear forces at the edge of the ice stream cause deformation and recrystallization of the ice, making it softer, and concentrating the deformation in narrow bands or shear margins. Crevasses form, particularly around the shear margins.

Most ice streams have some water at their bases, which lubricates the flow. The type of bedrock also is significant. Soft, deformable sediments result in faster flow than hard rock.[3]


Antarctica

See also: List of Antarctic ice streams

The Antarctic Ice Sheet is drained to the sea by several ice streams. The largest in East Antarctica is Lambert Glacier. In West Antarctica the large Pine Island and Thwaites Glaciers are currently the most out of balance, with a total net mass loss between them of 85 gigatonnes per year measured in 2006.[4]

It has been suggested that the Antarctic ice sheet is losing mass. The past and ongoing acceleration of ice streams and outlet glaciers is considered to be a significant, if not the dominant cause of this recent imbalance.[4]

Greenland

Ice streams that drain the Greenland ice sheet into the sea include Helheim Glacier, Jakobshavn Isbræ and Kangerdlugssuaq Glacier.

References

  1. ^ Bamber J.L., Vaughan D.G., Joughin I. (2000). "Widespread complex flow in the interior of the Antarctic Ice Sheet". Science 287: 1248–1250. doi:10.1126/science.287.5456.1248. PMID 10678828. 
  2. ^ * National Snow and Ice Data Center. "Types of Glacier". http://www.nsidc.org/glaciers/questions/types.html. 
  3. ^ British Antarctic Survey. "Description of Ice Streams". http://www.antarctica.ac.uk//about_antarctica/geography/ice/streams.php. Retrieved 2009-01-26. 
  4. ^ a b Rignot E., Bamber J.L., van den Broeke, M.R., Davis C., Li Y., van de Berg W.J., van Meijgaard E. (2008). "Recent Antarctic ice mass loss from radar interferometry and regional climate modelling". Nature Geoscience 1: 106–110. doi:10.1038/ngeo102. 

Further reading


This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

 
 

 

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Sci-Tech Dictionary. McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved.  Read more
Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Ice stream".  Read more