Aretes and Pyramidal Peaks
- 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
- When three of more corries erode backwards towards one another, this can create a PP.
- A steep sided pointed mountain.
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- 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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- 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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- 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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