Also known as a corrie or cwm, this is a circular, armchair-shaped, hollow cut into bedrock during glaciation, up to 2 km across. The steep side and back walls are subject to intense physical weathering (Matsuoka and Sakai (1999) Geomorph. 74, 1–4); the front opens out downslope.

The formation of cirques remains unclear. Haynes (1968) Geografiska A 50, 221–34 concludes that bedrock jointing determines the overall cirque morphology, and Hooke (1991) GSA Bull. 103, 1104–80 finds that periglacial freeze–thaw weathering and glacial quarrying facilitate erosion of the headwall. Turnbull and Davies (2006) ESPL 31, 9 show that cirques can be initiated by large, deep-seated failures of rock slope. Fluvial erosion and large-scale slope failures can be important for the creation of hollows, which are then deepened during glaciations; see Wilson and Smith (2006) Geograf. Annal. A 88, 3.

During glaciation, ice is thought to undergo rotational slipping, perhaps overdeepening the cirque floor (Vilborg (1977) Geografiska A, 59, 3–4), although Hooke ( (1991) GSA Bull. 103) suggests that glaciohydraulic supercooling is central to overdeepening. (See also the classic paper by Lewis (1938) Geol. Mag. 75 on a meltwater hypothesis of cirque formation.) Cirques seem to grow by headward extension, biting back into the mountain mass until only arêtes or pyramidal peaks remain; see Oskin and Burbank (2005) Geology 33, 12 on cirque retreat.

Aspect plays an important role in the orientation of cirques: in the Fuegian Andes, for example, the cirques which are oriented towards the south-east are the most abundant. Glacial ice is preserved in these due to the limited exposure to sunlight, or the effects of humid air masses (Planas et al. (2002) Geomorph. 87, 1). Evans (2006) Geomorph. 80, 3–4 considers the effects of geology, relief, and region on the allometric development of cirques in Wales. Gordon (1977) Geograf. Annal. A 59 shows that, in general, the larger a cirque, the longer the period of glacial occupancy.