thumb|Two cirques with semi-permanent snowpatches near [[Abisko National Park, Sweden]]

thumb|Upper Thornton Lake Cirque in [[North Cascades National Park, U.S.]]

A (; from the Latin word ) is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from , meaning a pot or cauldron) and ; ). A cirque may also be a similarly shaped landform arising from fluvial erosion.

The concave shape of a glacial cirque is open on the downhill side, while the cupped section is generally steep. Cliff-like slopes, down which ice and glaciated debris combine and converge, form the three or more higher sides. The floor of the cirque ends up bowl-shaped, as it is the complex convergence zone of combining ice flows from multiple directions and their accompanying rock burdens. Hence, it experiences somewhat greater erosion forces and is most often overdeepened below the level of the cirque's low-side outlet (stage) and its down-slope valley (backstage). If the cirque is subject to seasonal melting, the floor of the cirque most often forms a tarn (small lake) behind a natural dam, which marks the downstream limit of the glacial overdeepening. The dam itself can be composed of moraine, glacial till, or a lip of the underlying bedrock. the side at which the glacier flowed away from the cirque. Many glacial cirques contain tarns dammed by either till (debris) or a bedrock threshold. When enough snow accumulates, it can flow out the opening of the bowl and form valley glaciers which may be several kilometers long.

Cirques form in conditions which are favorable; in the Northern Hemisphere the conditions include the north-east slope, where they are protected from the majority of the Sun's energy and from the prevailing winds. These areas are sheltered from heat, encouraging the accumulation of snow; if the accumulation of snow increases, the snow turns into glacial ice. The process of nivation follows, whereby a hollow in a slope may be enlarged by ice segregation weathering and glacial erosion. Ice segregation erodes the vertical rock face and causes it to disintegrate, which may result in an avalanche bringing down more snow and rock to add to the growing glacier.]]

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.

Where cirques form one behind the other, a cirque stairway results, as at the Zastler Loch in the Black Forest.

As glaciers can only originate above the snowline, studying the location of present-day cirques provides information on past glaciation patterns and on climate change.

  • Europe (fluvial)
  • Cirque de Navacelles, Grands Causses, France
  • Cirque du Bout du Monde, Grands Causses, France
  • Cirque du Bout du Monde, Burgundy, France
  • North America
  • Cirque of the Towers, Wyoming, United States
  • Iceberg Cirque, Montana, US
  • Summit Lake cirque, and others on Mount Blue Sky, Colorado, US
  • Great Basin and others on Mount Katahdin, Maine, US
  • Great Gulf, New Hampshire, US
  • Tuckerman Ravine, New Hampshire, US

See also

References

Notes

Citations

  • Photographs and case study of corrie glaciers

es:Glaciar#Clasificación