Movement of Ice Sheets during the last glacial advance in the UK

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Geography

GLACIATION ESSAY

Distinguish between the erosional processes of abrasion and plucking
(5 marks)

Plucking occurs when melt water leaks into the crack and joints of the rocks in the floor and sides of the valley in which the glacier is present. This water then freezes due to the low temperatures, becoming attached to the rocks and the glacier itself, and as the glacier advances it simply pulls the rock from the valley side or floor and carries it away. Plucking is a process which is particularly effective in eroding well jointed rocks; especially at the base of a glacier due to a process called “pressure melting” where the weight of the ice produces melt water.

This debris which the glacier “plucks” and carries away results in another process known as abrasion.

Abrasion occurs when the rocks and debris which are held in the base and sides of the glacier scrape over and slowly erode the valley floor and sides; in the same way in which sandpaper wears away wood. The coarse material held in the glacier will grove the valley floor and sides, whereas the finer material will smooth and polish the rock. Abrasion will also break down the glacial debris to form fine “rock flour” which results in the glacial melt water having a milky white colouring to it.  

Examine the impact of processes of glaciial erosion on the landscape
(20 marks)

There are two main processes of glacial erosion which take place as the glacier moves forward; and which mainly occur in upland areas. The first of these processes is called plucking and is when melt water freezes between the glacier and the underlying rocks causing the glacier to become attached to the rock. As the glacier advances the rock is then “plucked” from the valley floor or side. The advancing glacier then proceeds down the valley scraping the plucked rocks along the valley floor and sides resulting in the second of the two processes of glacial erosion, know as abrasion.

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These two processes, along with weathering processes can shape the landscape to produce a number of glacial landforms.

The first of these glacial landforms is the armchair shaped Cirques (or Corries) These are hollows which are found on upland mountainsides which have a steep back wall, a deep basin and a lip at the front that is either made of solid rock or deposited moraine. An example of a cirque can be found in Walcott, Antarctica. Cirques begin to form with the Nivation of a small hollow on a mountainside where snow accumulates year after year. This hollow enlarges over ...

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