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

Where a glacier melts and "retreats" up its valley, it leaves behind some distinctive glacial features besides moraines. These include drumlins, small hills of gravel, and roche moutonnées, tear-shaped mounds of rock. Both features have been shaped and smoothed by the heavy mass of flowing ice. Eskers are winding ridges of gravel that were laid down by meltwater streams flowing beneath the glacier.


A U-shaped valley created by glacial erosionA U-shaped valley created by glacial erosion

Glacial valleys

In mountainous regions, valleys have been gouged out by glaciers. They have a characteristic U-shape, making them quite distinct from river valleys, which have a V-shape. In some parts of the world, most notably Norway and New Zealand, U-shaped valleys near the coast have been “drowned” by rising sea levels. These deep inlets, known as fjords, have very steep sides. Some fjords snake inland from the sea for many kilometres.



A Norwegian fjordA Norwegian fjord


Consultant:
 Ian Fairchild
 

See also in Earth

See also in Prehistoric

See also in Geography

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

About 75% of the world's fresh water is stored in glaciers, ice caps and ice sheets.

If all the world's land ice melted, sea levels would rise approximately 70 m (230 ft) worldwide.

In 1953, the Kutiah Glacier in Pakistan moved more than 12 km (7.5 miles) in three months, averaging about 112 m (367 ft) per day. It was the fastest glacial surge ever recorded.

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