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A 'cirque' is an amphitheatre-like valley (or valley head) formed at the head of a glacier by erosion. A cirque is also known as a 'cwm' in Wales, a 'coomb' or coombe in England, and a 'corrie' in Scotland and Ireland, although these terms apply to a specific feature of which several may be found in a cirque .
Cirques can be up to a square kilometre in size, situated high on a mountain side, and are typically partially surrounded on three sides by steep cliffs. The highest cliff is often called a headwall. The fourth side is the "lip" which is the side that the glacier flowed away from the cirque. Many glacial cirques contain tarns dammed by either till or a bedrock threshold.
Cirques form in conditions which are favorable; which in the northern hemisphere includes the north-east slope being in shade and away from prevailing winds. These areas are sheltered from heat, and so, they encourage the accumulation of snow. If the accumulation of snow increases, the snow transforms into glacial ice. The process of nivation follows (where a hollow in a slope may be enlarged by freeze-thaw weathering and glacial erosion). Eventually, this hollow can become big enough so that glacial erosion intensifies. Debris (or till) in the ice may also abrade (glacial abrasion) the bed surface; should ice move down a slope it would have a ‘sandpaper effect’ on the bedrock beneath on which it scrapes.
Eventually, the hollow can become a large bowl shape in the side of the mountain, with the headwall being weathered by constant freezing and thawing, and eroded by plucking. The basin will become deeper if it continues to become eroded by abrasion. Should plucking and abrasion continue, the dimensions of the cirque will increase, but the proportion of the landform would remain roughly the same.
If two adjacent cirques erode toward one another, an arête, or steep sided ridge, forms. When three or more cirques erode toward one another, a pyramidal peak is created. In some cases, this peak will be made accessible by one or more arêtes. The Matterhorn in the European Alps is an example of such a peak.

Contents

Notable cirques

See also

External links

Notable cirques

★ Blue Lake Cirque, NSW, Australia

★ Great Basin, Maine, United States

★ Iceberg Cirque, Montana, United States

★ Cirque de Gavarnie, France

★ Cirque de Navacelles, France

★ Cirque of the Towers, Wyoming, United States

★ Tuckerman Ravine, New Hampshire, United States

★ Śnieżne Kotły, Karkonosze Mountains, Poland

★ Chandra Taal, Himachal Pradesh, India

★ Western Cwm, Nepal

See also

★ Glacial landforms

External links

★ Photographs and case study of corrie glacier