If all of the valleys in a mountain range become filled with glaciers, and the glaciers cover then entire mountain range, they are called ice caps . They cover large areas of the land surface, including mountain areas. Modern ice sheets cover Greenland and Antarctica. They have an estimated volume of about 24 million km 3 . Antarctica is covered by two large ice sheets that meet in the central part along the Transantarctic Mountains.
Ice shelves are sheets of ice floating on water and attached to land.
They usually occupy coastal embayments, may extend hundreds of km from land and reach thicknesses of 1000 m. Glaciers can also be classified by their internal temperature. Polar glaciers - Ice in a polar glacier always maintains a temperature well below its melting point. The Formation of Glacial Ice Glaciers can only form at latitudes or elevations above the snowline , which is the elevation above which snow can form and remain present year round. The snowline, at present, lies at sea level in polar latitudes and rises up to 6000 m in tropical areas.