Erosional Features Flashcards
Corrie
A corrie is formed when snow accumulates in north facing hollows when more snow falls in winter than melts in the summer. North/north-east facing slopes are more shaded so snow lies longer with accumulated snow compressed into neve and eventually ice. Corries are formed by 3 processes: plucking, abrasion and freeze-thaw weathering. Plucking is when ice freezes on to bedrock, pulling loose rocks away from the back wall. Abrasion is when the angular rock embedded in the ice grinds the hollow. Frost shattering/freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off.Glacier moves downhill due to gravity. Bergschrund crevasse opens up at the back of the hollow which allows melt water and rock fragments to get to the base of the glacier increasing erosive power. The weight of the glacier pushes down causing rotational sliding, which over deepens the hollow. Friction causes the ice to slow down at the front edge of the corrie, allowing a rock lip to form which traps rain water.
Arete
A corrie is formed when snow accumulates in north facing hollows when more snow falls in winter than melts in the summer. North/north-east facing slopes are more shaded so snow lies longer with accumulated snow compressed into neve and eventually ice. Corries are formed by 3 processes: plucking, abrasion and freeze-thaw weathering. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall. Abrasion is when the angular rock embedded in the ice grinds the hollow. Frost shattering/freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off.Glacier moves downhill due to gravity. Bergschrund crevasse opens up at the back of the hollow which allows meltwater and rock fragments to get to the base of the glacier increasing erosive power. The weight of the glacier pushes down causing rotational sliding, which over deepens the hollow. Friction causes the ice to slow down at the front edge of the corrie, allowing a rock lip to form which traps rain water. An arête is formed when two corries erode back towards each other and create a knife shaped ridge in the middle. Freeze-thaw weathering can make the ridge more pronounced and can cause scree slopes to develop.
Pyramidal Peak
A corrie is formed when snow accumulates in north facing hollows when more snow falls in winter than melts in the summer. North/north-east facing slopes are more shaded so snow lies longer with accumulated snow compressed into neve and eventually ice. Corries are formed by 3 processes: plucking, abrasion and freeze-thaw weathering. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall. Abrasion is when the angular rock embedded in the ice grinds the hollow. Frost shattering/freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off.Glacier moves downhill due to gravity. Bergschrund crevasse opens up at the back of the hollow which allows meltwater and rock fragments to get to the base of the glacier increasing erosive power. The weight of the glacier pushes down causing rotational sliding, which over deepens the hollow. Friction causes the ice to slow down at the front edge of the corrie, allowing a rock lip to form which traps rain water. An arête is formed when two corries erode back towards each other and create a knife shaped ridge in the middle. Freeze-thaw weathering can make the ridge more pronounced and can cause scree slopes to develop. A pyramidal peak is formed where three or more corries and arêtes meet. Glaciers erode backwards towards each other, carving out the rocks by plucking and abrasion. Freeze thaw weathers the top of the mountain, creating a sharply pointed summit. A pyramidal peak has steep, triangular faces divided bysharp ridges or arêtes.
U-Shaped Valley
U-shaped valleys are created through glaciation.
Gravity and the weight of the glaciers causes them to flow downhill, following existing V-shaped valleys.
The glacier freezes onto bedrock and, as it moves downhill due to gravity, it pulls away large chunks of rock from the back wall - a process known as plucking.
Abrasion, when the angular rock embedded in the ice grinds the hollow, making it deeper.
Frost shatters when water in cracks in the rock freezes, expands and contracts, weakening the rock until fragments break off.
As glaciers move through a landscape, the processes of plucking and abrasion widen, steepen, deepen and smooth valleys into a ‘U’ shape.
Former interlocking spurs may be cut off by the glacier as it flows downhill leaving truncated spurs and steep valley sides.
The width and shape of the resulting glacial trough will depend on the rock type and the intensity and weight of the glacier.
Tributary valleys have smaller less powerful glaciers which result in less deep U-shaped valleys ‘hanging’ about the main valley.
After glaciation, freeze-thaw action continues with the warming and cooling of temperatures, as well as other agents of weathering. This causes rocks to weaken and fall to the valley floor as scree.
Hanging Valley
Hanging valleys are created through glaciation.
Gravity and the weight of the glaciers causes them to flow downhill, following existing V-shaped valleys.
The glacier freezes onto bedrock and, as it moves downhill due to gravity, it pulls away large chunks of rock from the back wall - a process known as plucking.
Abrasion, when the angular rock embedded in the ice grinds the hollow, makes the valley deeper.
Frost shatters when water in cracks in the rock freezes, expands and contracts, weakening the rock until fragments break off.
The degree to which glaciers can erode down into the landscape is dictated by their size: the larger the glacier, the deeper the valley it can erode.
Small glaciers can erode only shallow valleys while large glaciers can erode much deeper valleys.
A hanging valley is a shallow valley carved by a small glacier and thus the elevation of the valley floor is ‘hanging’ high above the elevation of the valley floor carved out by the larger glacier.
Ribbon Lake
As a glacier flows over the land, it flows over hard rock and softer rock.
Softer rock is less resistant, so a glacier will carve a deeper trough
When the glacier has retreated, (melted) water will collect in the deeper area and create a long, thin lake called a ribbon lake.
A ribbon lake is a long and deep, finger-shaped lake, usually found in a U-shaped valley.
A ribbon forms in a hollow when a glacier has more deeply eroded less resistant rock or it may fill up a valley behind a wall of moraine across the valley.
Many of the lakes in the English Lake District are ribbon lakes, e.g. Windermere.
The areas of harder rock left behind are called rock steps.
