Erosional Landforms
Geography: Edexcel A Level, topic 2.4.2
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.
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.
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.
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.
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.
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.
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.
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.
Test yourself on Erosional Landforms
What do we call the sandpaper-like eroding of bedrock by rock fragments embedded in a glacier?
Which of the following is NOT a glacial erosional process?
Which direction do corries normally face?