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Definition: cirque from Philip's Encyclopedia

(corrie, cwm) Bowl-shaped, steep-sided hollow in a mountainous region formed by glaciation. A hollow is scoured out of the rock by ice and freeze-thaw activity. When the ice melts, a lake may form at the base of the cirque. Such lakes are often fed by the retreating glacier.


Summary Article: CIRQUES from Encyclopedia of Earth Sciences Series: Encyclopedia of Paleoclimatology and Ancient Environments

Cirques are glacially eroded features characteristic of mountain glaciation, and are also known as corries or cwms. They have been widely studied, and useful summaries of previous research are provided by Benn and Evans (1998) and Bennett and Glasser (1996).

Cirques are mountainside hollows, open on the downslope side but characteristically bounded on the upslope side by a steep slope or cliff (the headwall) that is arcuate in plan around the more gently sloping or over-deepened floor of the hollow. Glacial cirques are created by the erosional action of localized snow and ice patches, and during glaciation they contain “cirque glaciers” which may feed ice downstream into valley glaciers. Cirques evolve through time under continuing glacial activity by a combination of deepening of the base and headward erosion of the back wall. Early in the glaciation, nivation beneath snow accumulating in a mountainside hollow may be the chief process leading to the development of the cirque. As more snow and ice accumulates in the hollow, glacial erosion of the base and of the lower part of the headwall, combined with subaerial weathering and erosion of the upper parts of the headwall exposed above the ice, lead to the characteristic steep-walled basin of a mature cirque. Cirques tend to become more enclosed, and deeper, with longer glacial occupation. Long-term evolution of cirques can occur over several glacial cycles, and cirques may be altered by ice-sheet processes if glaciation increases beyond local cirque and valley glaciation. Cirque morphology is therefore often complex, and several small cirques may grow together to form one large, complex feature. Typically cirques are of the order of 102-103 m in diameter.

Cirque elevation and orientation can provide paleoclimatic information. The minimum elevation of cirques reflects the regional snowline at the time of their formation. The predominant orientation of cirques within a region can also indicate dominant wind direction, as snow may initially accumulate, and cirques form, on sheltered lee-side slopes, especially where these have a pole-ward aspect sheltered from insolation. Where precipitation shadows occur, on larger mountain masses, cirques are likely to develop with an aspect facing the dominant source of precipitation.

In postglacial environments cirques often contain lakes in their closed basins, and these lakes may drain by overspill across the lip or sill that marks the down-slope limit of the basin. In many locations the lip or sill is erosional in origin, marking the downstream limit of glacial over-deepening of the basin. However, the feature may be created or accentuated by the deposition of moraines marking the maximum extent of corrie glaciation.

Cross-reference

Glacial Geomorphology

Bibliography
  • Benn, D.I.; Evans, D.J.A. 1998. Glaciers and Glaciation. Arnold London UK 734pp.
  • Bennett, M.R.; Glasser, N.F. 1996. Glacial Geology. Wiley Chichester UK 364pp.
  • Peter G. Knight
    © 2009 Springer Science + Business Media B.V.

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