Ice sheet
large mass of glacier ice From Wikipedia, the free encyclopedia
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In glaciology, an ice sheet (Danish: Indlandsis, meaning "inland ice"), usually called continental glacier and sometimes ice shell or ice layer, is a large mass of glacier ice that has an average thickness of over 2 km and covers a large continental area in the polar regions of the Earth. It is located at extreme latitudes and has a conventional area of more than 50,000 km2 (19,000 sq mi).[1][2] In other geologic time spans, there were many of them, which covered an larger area, but they now cover only Antarctica and Greenland.
Theyy are sometimes confused with the sea ice (the floating layer of ice of variant extension that forms in the polar seas), the ice shelf (barrier of ice of glacier origin that spans from the coast to the inner of the ocean), or the polar cap.
Ice sheets are larger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are called ice caps, which usually feed a series of glaciers around its periphery.
Although the surface of an ice shhet is cold, its base is generally warmer because of geothermal heat. In some places, melting occurs, which lubricates the ice sheet so that it flows it rapidly. The process produces fast flowing-channels inside the ice sheet, which are called ice streams.
The two current ice sheets are relatively young in geological terms. The Antarctic ice sheet first formed in the early Oligocene. It retreated and advanced 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, when it apparently developed very quickly. That 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.
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Earth's current two ice sheets
Antarctic ice sheet
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. If all of it were to melt, sea levels would rise by 58 m.[3]
The ice sheet first formed in the early Oligocene. It retreated and advanced many times until the Pliocene, when it came to occupy almost all of Antarctica.
Greenland ice sheet
The Greenland ice sheet covers about 82% of the surface of Greenland, part of Denmark. Satellite images from NASA show that it is melting at a rate of about 239 km3 a year.[4][5] If all of it melted, isea levels would rise by 7.2 m.[3]
The ice sheet did not develop at all until the late Pliocene, when it apparently developed very quickly. That 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.
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References
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