crag and tail

geology

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June 25, 2026

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A crag and tail is an elongate hill with a steep, ice-smoothed rock face at one end and a gentler slope of rock or glacial drift at the other. This geological feature is formed by glacial erosion. As ice moves over bedrock, it erodes the rock surface. Harder parts of the rock form protruding knobs, while softer rock is eroded away around them. These knobs protect the softer rock on their lee side, creating a tail that points away from the knob towards the glacier's margin. This process is similar to the formation of flutes, where subglacial debris is injected into cavities on the lee side of obstacles, creating elongate tails of till.123

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roche moutonnée
A crag and tail is distinguished from a roche moutonnée by the presence of an elongate, tapered ridge of till extending downstream. Often produced by selective erosion of softer strata, roche moutonnée landscapes are characteristic of glaciated crystalline shield areas.
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A crag and tail is distinguished from a roche moutonnée by the presence of an elongate, tapered ridge of till extending downstream. Often produced by selective erosion of softer strata, roche moutonnée landscapes are characteristic of glaciated crystalline shield areas.
Read More