2.4.2

Erosional Landforms

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Glacial Erosional Processes

A range of glacial erosional processes have created a variety of distinctive large landforms in many upland glaciated areas around the world.

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Plucking and quarrying

  • If the bedrock beneath a glacier has been weathered in periglacial times, or if the rock is full of joints (well-jointed), a glacier can detach large particles of rock and take them with it. This is called plucking.
  • Quarrying is an extreme form of plucking, creating steep and angular rock cliff faces.
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Abrasion

  • Abrasion happens when sharp rock fragments embed themselves in the base and sides of the ice.
  • These grind down the bedrock as the glacier moves over the rock like sandpaper, making it smooth and wearing it away.
  • This leaves scratches on the rock in the direction of ice movement called striations.
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Crushing and basal melting

  • Crushing is erosion caused by the sheer pressure exerted by rock fragments embedded at the base of a glacier.
  • Basal melting is abrasion by meltwater, acting under great pressure, at the base of the glacier.
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Sub-aerial processes

  • Freeze–thaw weathering on the rock slopes above valley glaciers is a constant source of angular rock fragments that build up to form scree.
  • Mass movement (rock falls and landslides) is a source of rock material which falls onto the surface of ice and is incorporated into it.

Corrie Formation

A corrie is an armchair-shaped, steep-sided hollow at the head of a glaciated valley.

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Features

  • Corries are armchair-shaped and often N or NE facing in the northern hemisphere as this direction will receive the least sunlight.
  • They are in the lee of prevailing winds, causing the snow to accumulate for longer.
  • Size varies but they are often around 0.5km in diameter with a back wall up to 1000m in height.
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Process 1

  • The hollow is deepened initially by nivation.
  • As the ice accumulates it is deepened more by rotational slide, enhancing the abrasion process due to increased compression in the base of the hollow.
  • Ice pulls away from the back wall, plucking rocks already loosened by freeze-thaw weathering.
  • This creates a crevasse (bergschrund) which forms where the ice starts to pull away from the back wall of the corrie.
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Process 2

  • Material falls down this crack and is embedded in the base of the ice.
  • This then causes more abrasion and deepens the hollow
  • Where the pressure and erosion are lower (at the front edge of the hollow) there is deposition of moraine.
    • This is called the lip of the corrie, which often allows water to accumulate behind it in a post-glacial period, forming a tarn.

Jump to other topics

1Tectonic Processes & Hazards

2Option 2A: Glaciated Landscapes & Change

3Option 2B: Coastal Landscapes & Change

4Globalisation

5Option 4A: Regenerating Places

6Option 4B: Diverse Places

7The Water Cycle & Water Insecurity (A2 only)

8The Carbon Cycle & Energy Security (A2 only)

9Superpowers (A2 only)

10Option 8A: Health & Human Rights (A2 only)

11Option 8B: Migration & Identity (A2 only)

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