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Ice sheet

2007 Schools Wikipedia Selection. Related subjects: General Geography

   An Ice sheet is a mass of glacier ice that covers surrounding terrain
   and is greater than 50,000 km² (19,305 mile²). The only current ice
   sheets are Antarctic and Greenland; during the last ice age at Last
   Glacial Maximum ( LGM) the Laurentide ice sheet covered much of Canada
   and North America, the Weichselian ice sheet covered northern Europe
   and the Patagonian Ice Sheet covered southern South America.

   Ice sheets are bigger than ice shelves or glaciers. Masses of ice
   covering less than 50,000 km² are termed an ice cap. An ice cap will
   typically feed a series of glaciers around its periphery.

   Although the surface is cold, the base of an ice sheet is generally
   warmer, in places it melts and the melt-water lubricates the ice sheet
   so that it flows more rapidly. This process produces fast-flowing
   channels in the ice sheet — these are ice streams.

   The present-day polar ice sheets are relatively young in geological
   terms. The Antarctic Ice Sheet first formed as a small ice cap (maybe
   several) in the early Oligocene, but retreating and advancing many
   times until the Pliocene, when it came to occupy almost all of
   Antarctica. The Greenland ice sheet did not develop at all until the
   late Pliocene, but apparently developed very rapidly with the first
   continental glaciation. This had the unusual effect of allowing fossils
   of plants that once grew on present-day Greenland to be much better
   preserved than with the slowly forming Antarctic ice sheet.

Antarctic ice sheet

   A satellite composite image of Antarctica
   Enlarge
   A satellite composite image of Antarctica

   The Antarctic ice sheet is the largest single mass of ice on Earth. It
   covers an area of almost 14 million km² and contains 30 million km³ of
   ice. Around 90% of the fresh water on the Earth's surface is held in
   the ice sheet, and, if melted, would cause sea levels to rise by 61.1
   metres. In East Antarctica the ice sheet rests on a major land mass,
   but in West Antarctica the bed is in places more than 2500 m below sea
   level. It would be seabed if the ice sheet were not there. However, if
   the ice sheet were actually removed, isostatic rebound would occur and
   Antarctica would rise to an average height of 800m above sea level.

Greenland ice sheet

   Map of Greenland
   Enlarge
   Map of Greenland

   The Greenland ice sheet occupies about 82% of the surface of Greenland,
   and if melted would cause sea levels to rise by 7.2 metres. Estimated
   changes in the mass of Greenland's ice sheet suggest it is melting at a
   rate of about 239 cubic kilometres (57.3 cubic miles) per year . These
   measurements came from the US space agency's Grace ( Gravity Recovery
   and Climate Experiment) satellite, launched in 2002, as reported by BBC
   News, 11 August 2006.

Predicted effects of global warming

   Both the Antartic and Greenland ice sheets are predicted to lose mass
   through melting , according to the British Antartic Survey,
   contradicting early predictions by the IPCC that increased
   precipitation would occur over the Antarctic. See: sea level rise.
   Retrieved from " http://en.wikipedia.org/wiki/Ice_sheet"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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