Erosion

Glaciers

A mountain glacier and its featuresA mountain glacier and its features A glacier is a moving mass of ice. Some glaciers snake down mountain valleys, while others such as the ice sheets of Greenland or Antarctica are so huge and thick they almost totally cover the land. Although it is solid, ice can flow down slopes and around bends, although much more slowly than a river—often less than a metre (3 ft 3 inches) per day. Glaciers occur in very cold regions, high in mountains and in the far north and south polar regions.


The head of a glacierThe head of a glacier

How glaciers form

A glacier is fed by snow. Over many years, the snow piles up at the head of a high valley and compacts into ice. It collects in a cirque, a bowl-shaped feature. Being thick and heavy, the ice moves under the pressure of its own weight, flowing downhill as a glacier.



The Gornergletscher glacier, SwitzerlandThe Gornergletscher glacier, Switzerland

Moraines

Most glaciers move very slowly—just a few metres a day—but they are a powerful force.The ice carries pieces of rock loosened by frost weathering and scrapes against the valley sides. It carries this loose rock along in long bands called lateral moraines, or underneath the glacier as subglacial moraine. As two glaciers merge their lateral moraines combine into a medial moraine. Where the ice runs over a steeper slope, it develops cracks known as crevasses. Lower down, the glacier melts at its snout. If it moves forward less than it melts, the snout retreats over time, leaving a pile of the rocks that it has carried as a terminal moraine.


A glacier and its morainesA glacier and its moraines

Other glacial features

About 10% of the Earth's land area is covered with ice, including glaciers, ice caps, and the ice sheets of Greenland and Antarctica.

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