1 EQ2 Erosional Glacial Landforms

OCR Specification

Corrries

Armchair shaped hollows with a steep back wall, deep basin and corrie lip at the front. Formed through nivation in a hollow in which snow collects. At a critical depth, the ice acquires rotational movement and deepens the hollow further. Plucking also steepens the back wall. Debris from plucking and weathering falls into the corrie which then deepens the hollow through abrasion. Post glaciation, the hollow may be filled with water, forming a tarn e.g. Easedale, Lake District.

Arêtes

A narrow, steep sided ridge round between two carries. They form due to erosion such as plucking in corries which are back to back e.g. Striding Edge in the Lake District which has steep slopes of 200-300m on either side.

Roches moutonnées

A small bare outcrop of rock shaped by glacial erosion, with one side smooth and gently sloping and the other steep, rough, and irregular. As ice moves over them, pressure causes the ice to melt as it ascends, so the first side is smoothed by abrasion. On the down-valley side, pressure is reduced and meltwater refreezes, causing plucking. They are an indication of the direction of ice movement e.g. Coniston area of the Lake District typically 1-5m high and 5-20m long.

Glacial striations

Scratches and grooves on bedrock caused by glacial abrasion e.g. Easedale Valley

Ellipsoidal basins

Major erosional landforms created by ice sheets. Ellipsoidal basins can be huge e.g. Great Lakes in the North East of the USA. Lake Superior is over 80,000km2.

Pyramidal peaks

Occurs when three or more corries develop on a single hill, with retreating back walls, steepening to form a pyramidal peak. Weathering may further sharpen it e.g. The Matterhorn in the Swiss Alps at over 1200m high.

Glacial Troughs

A deep U shaped valley with steep valley walls formed as a result of glacial erosion. Glaciers usually develop in established V shaped river valleys, and then erodes the bedrock beneath through abrasion, plucking and frost shattering to form a glacial trough e.g. Glen Avon in Scotland