glacier

A glacier is any large mass of perennial ice that originates on land by the recrystallization of snow or other forms of solid precipitation and shows evidence of past or present flow. One international group has recommended that all persisting snow and ice masses larger than 0.1 square kilometre (about 0.04 square mile) be counted as glaciers.

Glaciers occur in all parts of the world and at almost all latitudes. In Ecuador, Kenya, Uganda, and Irian Jaya (New Guinea), glaciers even occur at or near the Equator, albeit at high altitudes. The two great ice masses, the Antarctic and Greenland ice sheets, contain about 99 percent of the world’s glacier ice.

Glaciers are replenished mainly by snowfall and shrink primarily by melting, runoff, or breaking off of icebergs. For a glacier to remain at a constant size, there must be a balance between income (accumulation) and outgo (ablation). If this mass balance is positive (more gain than loss), the glacier will grow; if negative, it will shrink.

Glacier ice stores about three-fourths of all the fresh water in the world. Glacier ice covers about 11 percent of the world’s land area and would cause a world sea-level rise of about 90 metres (300 feet) if all the existing ice melted.