Cold environments Case Studies

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Corrie and Tarn (GLACIAL)

What is it: An armchair shaped hollow with steep jagged backwall and bergschrund crevasse. They often contain a lake held in by rock lip.

Example: Cwn Idwal, Snowdonia

What processes are used?: Nivation, rotational flow, plucking and abrasion

How is it formed? 

  • Snow collects in hollows
  • Snow compacts as ice
  • Ice moves under gravity and lubricted by meltwater
  • Ice rotates to lip
  • Abrasion deepens corrie
  • Plucking steepns back and sides
  • Corrie lochan (tarn) may fill hollow
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U Shaped Valley (GLACIAL)

What is it: A wide flat valley with steep cliff like valley sides.

Example: Nant Ffrancon Valley, Snowdonia

What processes are used?: Plucking and abrasion

How is it formed? 

  • Glacier flows along earier "V" shaped valley
  • Glacier will abrade sides and floor of river valley
  • Valley is widened, deepened and straightened by plucking and abrasion.
  • When ice melts valley is "U" shaped
  • It has very steep sides and a fairly flat floor
  • Any later rier are called misfit streams because they are too small to have carved out the valley
  • Very straight because of the inflexibility and power of glacier that gorged them out
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Ribbon Lake (GLACIAL)

What is it?: A finger shaped thin lake on floor of U shaped valley

Example: Lake District

What processes are used?: Abrasion and compressing flow

How is it formed?

When a glacier moves along its valley some parts are deepened more. When the glacier retreates the deepened sections are filled with meltwater and become lakes.

They can also be formed when a glacier deposits near anatural barrier across a glacial trough.

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Fjord (GLACIAL)

What is it: A drowned U shaped valley at sea level

Example: Milform Sound, New Zealand

What processes are used?: Sea level rise and ice retreat

How is it formed? 

When a glacial valley is formed the glacier then retreats away. Once the U shaped valley has been carved out eventually the sea fills the valley left behind.

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Hanging Valley (GLACIAL)

What is it: A smaller tributary glacier valley left hanging above the main valley, often marked by a waterfall

Example: Southern Alps in New Zealand

What processes are used?: Plucking, abrasion and freezethaw

How is it formed? 

Vertical erosion appears more in the main glacier than in the smaller one. This is becuase there is less ice, mass and erosion so it is not affected as much as the main valley. As the glacier retreats the river flows down the smaller valley and into the main one in the form of a waterfall. This gives the appearance of the smaller valley "hanging" above the main valley.

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Roche Moutonnee (GLACIAL)

What is it: A mass of resistant rock with a smooth rounded stoss end and a jagged lee slope marked with striations.

Example: Nant Ffrancon Valley, Snowdonia

What processes are used?: Plucking and abrasion

How is it formed? 

The pressure of the glacier over obstacles causes the ice to melt. As it pasts over the meltwater refreezes and plucking occurs. However, the main rock cannot be picketd up so the glacier continues to retreat over it. The stoss end has more abrasion and the lee slope has more plucking.

Striations are formed wjn large rocks under the ice scratch the bedrock and are found on the lee side.

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Arete and Pyramidal Peak (GLACIAL)

What is it: An arete is a steep knife edged ridge and a pyramidal peak is a steep sided pointed mountain peak

Example: The Matterhorn, Alps (Pyramidal peak)

What processes are used?: Plucking and abrasion

How is it formed? 

  • Arete: When two corries from back to back
  • Pyramidal Peak: When 3 or more arete form back to back
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Esker (FLUVIOGLACIAL)

What is it: A winding sinuous ridge of course sand and gravel, rounded, stratified and sorted

Example: 

What processes are used?: Deposition of material carried under hydrostatic pressure

How is it formed? 

They are formed by streams that deposited minerals that flowed on top of glaciers, inside the cracks of glaciers, and in tunnels below glaciers. As the ice melted away they carved out a crevasse in the glacier which became filled with debirs and material, creating an esker

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