Glacial Erosion
A glacier can only erode if it is has a continuous supply of material.
The main source of material for a glacier results from the process of freeze-thaw weathering. This occurs in rocks which have many joints and cracks in them and where temperatures are frequently around freezing point. Water gets into cracks during the day and freezes at night. As it freezes it expands and puts pressure on the surrounding rock. When the ice melts, pressure is released. Repeated freezing and thawing widens the cracks and causes jagged pieces of rock to break off. The glacier uses this material, called moraine, to widen and deepen the valley. |
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There are two main processes of glacial erosion:
Abrasion: This is where the material carried by a glacier rubs against and wears away the sides and floor of the valley, like sandpaper would.
Plucking: This results from glacial ice freezing onto solid rock. As the glacier moves away it pulls with it large pieces of rock.
Glacial erosion creates upland features. As the ice erodes it moves in a circular motion known as rotational slip. This deepens hollows in the land to form bowl shapes called corries, these are sometimes also known as cwms or cirques. Corries began to form at the beginning of the ice age when snow accumulated in hollows facing away from the sun. The snow then turned to ice and moved downhill.
Freeze thaw weathering and plucking loosened material from the back of the hollow, which created a steep back wall as can be seen in the picture.
| The valley floor was also deepened due to moraine being scraped along the bottom. As ice melted the rock basin created could be seen, melt water often lay in the base of the corrie and known as a tarn. |  |
If two corries form next to one another a ridge is formed between them called an arête, as seen in the picture below. Several corries and arêtes around a mountain summit form a pyramidal peak, an example of a pyramidal peak is Mount Snowdon in Wales.
