ETYM French, from Latin circus.
A steep-walled semicircular basin in a mountain; may contain a lake; SYN. corrie, cwm.
Steep-sided hollow in a mountainside of a glaciated area. The weight and movement of the ice has ground out the bottom and worn back the sides. A cirque is open at the front, and its sides and back are formed of arętes. There may be a lake in the bottom, called a tarn.
A cirque is formed as follows: (1) snow accumulates in a hillside hollow (enlarging the hollow by nivation), and turns to ice ; (2) the hollow is deepened by abrasion and plucking; (3) the ice in the cirque rotates under the influence of gravity, deepening the hollow still further; (4) since the ice is thinner and moves more slowly at the foot of the hollow, a rock lip forms; (5) when the ice melts, a lake or tarn may be formed in the cirque. The steep back wall may be severely weathered by freeze-thaw, weathering providing material for further abrasion.