An Ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 square kilometers (19,305 square miles).
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.
The Antarctic ice sheet
is the largest single mass of ice on Earth
t covers an area of almost 14 million square km and contains 30 million cubic km of ice.
Around 90 percent of the fresh water on the Earth's surface is held in the ice sheet, an amount equivalent to 70 m of water in the world's oceans.
In East Antarctica, the ice sheet rests on a major land mass, but in West Antarctica the bed can extend to more than 2500m below sea level.
The land would be seabed if the ice sheet were not there. Ice enters the sheet through snow and frost and leaves by calving of icebergs and melting, usually at the base but also sometimes at the surface at warm sites..
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.
The ice sheet is almost 2,400 kilometres long in a north-south direction, and its greatest width is 1,100 kilometres at a latitude of 77° N, near its northern margin.
The Greenland Ice Sheet has experienced record melting in recent years and is likely to contribute substantially to sea level rise as well as to possible changes in ocean circulation in the future.
Ice sheets are bigger than ice shelves or glaciers.
Ice shelf :
An ice shelf is a thick, floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface, typically in Antarctica or Greenland.
The boundary between floating ice shelf and the grounded (resting on bedrock) ice that feeds it is called the grounding line.
When the grounding line retreats inland, water is added to the ocean and sea level rises.
Ice cap :
Masses of ice covering less than 50,000 square kilometers are termed an ice cap.An ice cap will typically feed a series of glaciers around its periphery.