Britannica
Sources used in this answer
How do cirques form at the heads of glacial valleys?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
glacial landform
Eskers,
or narrow
ridges of
gravel and sand left by a retreating glacier,
wind through western
Nunavut, Canada, near the Thelon River.
Cirques are amphitheatre-shaped basins located at the head of a glacial valley. Their formation is primarily driven by erosion occurring beneath a bergschrundâa large crevasse that separates stationary ice from the moving glacier.12
The process generally involves the following stages:
- Frost Shattering: During early summer, the bergschrund opens, exposing the rock at the base of the headwall to diurnal temperature fluctuations. This leads to rapid disintegration of the rock through frost action and ice wedging.12
- Headwall Retreat: The resulting rock debris avalanches down, creating a steep, often vertical headwall.1
- Glacial Abrasion: This rock material is incorporated into the glacier. Due to the downward velocity of ice in the accumulation zone, these rocks are transported to the base of the glacier, where they act as tools that scour and deepen the cirque floor.12
- Basin Formation: The persistent action of a cirque glacier often creates an over-deepened basin, which may form a tarn if the ice melts.12