Glaciers are usually classified according to their shape and their relationship with the surrounding and underlying topography, but some are described on the basis of the temperature distribution within the ice. However, we need to bear in mind that these distinctions are not strict and that transitions exist between all these types of glacier.
Glaciers classified according to topographic setting
Ice sheets and ice caps
The largest glaciers are the ice sheets of Antarctica and Greenland. Covering a continent twice the size of Australia, the Antarctic Ice Sheet contains 91 per cent of the world's freshwater ice. This ice sheet is more than 4000 metres thick in some places, inundating entire mountain ranges. In much of West Antarctica, ice rests on bedrock that is many hundreds of metres below present sea level. Consequently, if the West Antarctic Ice Sheet were to melt, a sea with numerous island archipelagos would emerge. In contrast, the ice sheet over East Antarctica rests on ground that is mainly above sea level, but drains radially via a number of valleys, some of which are below sea level. Apart from the Transantarctic Mountains and the mountainous backbone of the Antarctic Peninsula, which are high enough in places to project above the level of the ice sheet, rock outcrops are few and far between. Isolated rocky mountains surrounded by ice are known as nunataks, a word from the Inuit language.