Ice sheet
In glaciology, an ice sheet (Danish: Indlandsis), called usually in English continental glacier and sometimes ice shell or ice layer, is a large mass of glacier ice that covers a large continental area in the polar regions of the Earth. They're located at extreme latitudes with a conventional area of more than 50,000 square kilometres (19,000 sq mi).[1][2] In other geologic time spans, there was a major number and they were covering an larger area, but currently they only cover Antarctica and Greenland. This concept might not be confused with the sea ice (the floating layer of ice of variant extension that forms in the polar seas), neither the ice shelf (barrier of ice of glacier origin that spans from the coast to the inner of the ocean) nor the polar cap.
Ice sheets are larger than ice shelves or alpine glaciers. Masses of ice covering less than 50,000 km2 are denominated an ice cap. An ice cap will typically feed a series of glaciers around its periphery.
Although the surface is cold, the base of a sheet of ice is generally warmer due to geothermic heat. In some places, melting occurs and the melting water lubricates the ice sheet to flow it rapidly. This process produces fast flowing channels inside the ice sheet: these are ice streams.
The two current ice sheets are relatively young in geological terms. The Antarctic ice sheet formed first as a small layer of ice (various perhaps) since the Oligocene, but come back and advanced many times until the Pliocene, when it come to cover almost all of Antarctica. The Greenland ice sheet wasn't developed in absolute until the finals of the Pliocene, but apparently it developed too rapidly with the first continental glaciation. This got the unusual effect of allowing that the fossils of plants that were once growing in the actual Greenland they'll be conserved much better than the Antarctic ice sheet which forms slowly.
Earth's current two ice sheets[change | change source]
Antarctic ice sheet[change | change source]
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 this ice sheet. If all of it were to melt, it would cause sea levels to rise by 58 metres.[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[change | change source]
The Greenland ice sheet covers about 82% of the surface of Greenland, a part of Denmark. Satellite images from NASA show that it is melting at a rate of about 239 cubic kilometres (57.3 cubic miles) each year.[4][5] If all of it melted, it would cause sea levels to rise by 7.2 metres.[3] The ice sheet did not develop at all until the late Pliocene, but apparently developed very quickly. 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.
Related pages[change | change source]
References[change | change source]
- ↑ "Glossary of Important Terms in Glacial Geology". Archived from the original on 2006-08-29. Retrieved 2006-08-22.
- ↑ "American Meteorological Society, Glossary of Meteorology". Archived from the original on 2012-06-23. Retrieved 2013-10-17.
- ↑ 3.0 3.1 Some physical characteristics of ice on Earth Archived 2007-12-16 at the Wayback Machine, Climate Change 2001: Working Group I: The Scientific Basis. Intergovernmental Panel on Climate Change (IPCC)
- ↑ Rasmus Benestad et al.: The Greenland Ice. Realclimate.org 2006
- ↑ Greenland melt 'speeding up', BBC News, 11 August 2006