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How does frost action help form the headwalls of cirques?

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esker: Nunavut — glacial landform Eskers, or narrow ridges of gravel and sand left by a retreating glacier, wind through western Nunavut, Canada, near the Thelon River.

Frost action, specifically through processes like frost shattering and ice wedging, is a primary driver in the formation and retreat of cirque headwalls.1

The process typically occurs near the bergschrund, a large crevasse that separates moving glacier ice from the stationary rock wall. During early summer, this crevasse opens, exposing the base of the rock wall to diurnal temperature fluctuations. As water enters cracks in the bedrock and freezes, the resulting pressure exceeds the rock's tensional strength, causing it to shatter.213

This rapid disintegration of the lower rock causes the upper sections to avalanche, which helps maintain the steep, nearly vertical profile of the headwall. The resulting rock debris is then incorporated into the glacier, where it serves as an abrasive tool that further scours the base of the headwall and the floor of the cirque.21