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A corrie is an armchair-shaped hollow found on the side of a mountain. This is where a glacier forms. In France corries are called cirques and in Wales they are called cwms.

How does a corrie form?

1. Snow collects in a sheltered hollow on the side of a mountain. This is usually on north-facing slopes in the Northern Hemisphere. The snow doesn't melt in the summer because it is high up, sheltered and cold.
2. Every winter, more snow collects in the hollow. This becomes compacted and the air is squeezed out, leaving ice.
3. The back wall of the corrie gets steeper due to freeze-thaw weathering and plucking.
4. The base of the corrie becomes deeper due to abrasion.
5. As the glacier gets heavier it moves downhill. The glacier moves out of the hollow in a circular motion called rotational slip.
6. Due to less erosion at the front of the glacier a corrie lip is formed.
7. After the glacier has melted a lake forms in the hollow. This is called a corrie lake or tarn.

Corrie features

Corries produce the following erosional features:

• ����ê�ٱ�� - this is a narrow ridge of land that is created when two corries erode back towards each other
• pyramidal peak - if three or more corries erode back towards each other, at the top of a mountain a pointed peak is left behind

Other features of erosion

When a glacier moves downhill it erodes everything in its path through abrasion and plucking. Glaciers usually follow the easiest route down a mountain, which is often an old river valley. Interlocking spurs created by a river are eroded at the ends by the glacier to create truncated spurs. After the glacier has melted it leaves a U-shaped glacial trough. Sometimes the glacial trough fills with water, called a ribbon lake. Old tributaries, which would have once fed into the valley are left suspended and are known as hanging valleys.