Landforms from glacial erosion

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  • Created by: Isla S
  • Created on: 10-04-14 11:00

Aretes and Pyramidal Peaks

Arete

  • When two corries occur back to back, they can erode backwards.
  • As they do this, they steepen the back wall in both corries.
  • Eventually leaves a steep knife-edged ridge called an Arete
  • Striding Edge

Pyramidal Peak

  • When three of more corries erode backwards towards one another, this can create a PP.
  • A steep sided pointed mountain.
  • Matterhorn
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Corrie

  • Form in hollows where snow can accumulate - in N. Hemisphere, tends to be in NW to SE facing slopes (protected from the sun therefore snow can lie longer on the ground and accumulate - accumulation highest, ablation lowest).
  • Snow compacts into ice and accumulates over many years to form Neve.
  • Hollow deepened by Nivation (combined effects of repeated freezing and thawing and removal of material by melting snow) by the snow & Neve and it grows into a corrie.
  • Moves downhill because of gravity, its mass, meltwater and the slope.
  • Rotational movement 
  • Ice freezes to the back wall - plucking - steepens the back wall
  • Freeze thaw and frost shatter on exposed rocks creates scree on top of the ice, within it and under it.
  • This material from frost shattering and plucking is moved along under the ice - abrading the hollow by scratching the surface rock - also aided by the PMP is often surpassed, allowing melt water to exist at the base - basal sliding.
  • Creates a steep back wall and the corrie.
  • At the front edge of the corrie, the ice thins out as it speeds up down valley, so this area is eroded less and crevasses form - leaves a rock lip.
  • When the ice melts, a corrie lake can form.(Grisedale Tarn)
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U-Shaped Valley

  • As the glacier moves down valley it plucks the rock from beneath it - rub against the bed of the valley, eroding it further.
  • Deepens and widens the valley.
  • The front end of the glacier acts like a bulldozer, shifting & removing soil, plucking rock from interlocking spurs & truncating them. 
  • Lateral moraines & ground moraines abrade the valley sides and floor further.
  • Melt water at the glacier base contributes. 
  • Also where PMP is exceeded, the glacier can basally slide - more erosion.
  • Extending and compressing flow & basal material can cause differential erosion - some parts of the valley floor are over deepened - ribbon lakes (collect from meltwater and rain water after the glacier has melted)
  • Glacier erodes some parts of floor more - varying strengths of the bedrock, thicker ice in one region of the glacier than another, or there is more moraine abrading the ground in one area than another.
  • Found in areas where the ice has been subjected to compressing flow.
  • Glacier melts, water fills the depressions where the valley floor eroded the most.
  • Lakes form as melt water from receeding moraine is trapped behind moraine
  • Where extending flow occurs, more resistant, less eroded rock steps can be left.
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Hanging Valley

  • Within glacial valleys, there are main glaciers and smaller tributary glaciers.
  • Main glacier can erode its valley to a much greater extent because they are wider, deeper, have more mass and more moraines to use as erosive tools. 
  • Tributary valley glaciers are smaller, have less mass and moraine hence erode their valley less.
  • This means that the main valley is deeper, wider and steeper and this becomes evident post glaciation, when the tributary glacier is left hanging high above the main valley.
  • When rivers return, they often form waterfalls in these hanging valleys.
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