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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