Glacial Systems - Glacial Erosional Landforms

The main types of glacial erosional landforms are summarised below.

Corries (or cirques, or cwms)

These are amphitheatre-shaped mountain-side hollows found where the build-up of snow was greatest (in the northern hemisphere this is typically on north or east facing mountain slopes). They are formed when lying snow accumulates over a number of years and compresses lower layers into ice (firn) in a hollow. Once it has developed a sufficient volume, gravity causes it to move in a rotational manner out of the hollow and down the mountain side, eroding the floor by plucking and abrasion. Corries are the sources of Alpine glaciers.

Arêtes

Where two corries occur back to back and headward recession (cutting back) takes place over time forming a narrow, steep, rocky ridge between the two corries.

Glacial troughs (or U-shaped valleys)

These are valleys formed by the glacial processes of weathering, erosion and transportation. They have steep sides and flat floors. Unlike V-shaped river valleys, glacial troughs are straight as they have truncated any interlocking spurs which existed prior to glacial advance.

Truncated spurs

These are where interlocking spurs (the result of meandering river erosion) which predate the glacier are eroded and amputated by the straight-flowing glacier as it drives a path down a valley.

Hanging valleys

These are formed by tributary glaciers which enter a glacial trough. Unlike in river landscapes they do not cut down to the level of the main valley as the glaciers they carried were considerably smaller, but instead lie suspended above in the valley side at the end of the ice advance. They are often represented by a waterfall emerging from the higher tributary valley in the post-glacial landscape.

Roches moutonnées

These are asymmetrical rocky outcrops in the trough floor. The up-valley side (stoss) gently slopes and is smoothed by abrasion of the glacier. The down-valley side (lee) is steep in gradient, and subject to plucking as ice accelerates past it. They represent significantly more resistant rock on the glacial trough floor that the glacier found more difficult to erode than surrounding rocks.