Glaciation Flashcards
erosional features
corrie formation
firstly a glacier forms. Snow accumulates on the north facing hollows when more snow falls in the winter than melts in summer. North and Northeast facing slopes are more shaded, so snow lies longer, with accumulated snow compressed into neve and then eventually ice. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall, steepening it. Abrasion is when angular rock embedded in the ice grinds the hollow, which deepens the hollow. Freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off. The glacier moves downhill due to gravity. The Bergschrund crevasse opens at the back of the hollow. This 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 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 rainwater. An example of a corrie is Easedale corrie and tarn in the Lake District.
arete formation
firstly a glacier forms. Snow accumulates on the north facing hollows when more snow falls in the winter than melts in summer. North and Northeast facing slopes are more shaded, so snow lies longer, with accumulated snow compressed into neve and then eventually ice. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall, steepening it. Abrasion is when angular rock embedded in the ice grinds the hollow, which deepens the hollow. Freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off. The glacier moves downhill due to gravity. Aretes will only form when two corries have formed back to back. Post-glacial freeze thaw continues to attack the steep back walls of the corries after the glacier has melted. This can cause scree slopes to form. This causes the back walls to retreat towards each other creating a sharp ridge between corries. An example of an arete is striding edge in the Lake District.
pyramidal peak
firstly a glacier forms. Snow accumulates on the north facing hollows when more snow falls in the winter than melts in summer. North and Northeast facing slopes are more shaded, so snow lies longer, with accumulated snow compressed into neve and then eventually ice. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall, steepening it. Abrasion is when angular rock embedded in the ice grinds the hollow, which deepens the hollow. Freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off. The glacier moves downhill due to gravity. Pyramidal peaks will only form when 3 or more corries have formed back to back. This causes the back walls to retreat towards each other. A sharp point forms as a result. An example of a pyramidal peak is Helvellyn in the Lake District
U-shaped valley
firstly a glacier forms. Snow accumulates on the north facing hollows when more snow falls in the winter than melts in summer. North and Northeast facing slopes are more shaded, so snow lies longer, with accumulated snow compressed into neve and then eventually ice. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall, steepening it. Abrasion is when angular rock embedded in the ice grinds the hollow, which deepens the hollow. Freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off. The glacier moves downhill due to gravity. gravity causes the glaciers to flow downhill following the existing V- shaped valleys. 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 nature of the rock type and the intensity and weight of the glacier and its erosion. The valley becomes wider and straighter, often with a misfit stream which no longer fits the valley floor, for example Glencoe.
Hanging valley
firstly a glacier forms. Snow accumulates on the north facing hollows when more snow falls in the winter than melts in summer. North and Northeast facing slopes are more shaded, so snow lies longer, with accumulated snow compressed into neve and then eventually ice. Plucking is when ice freezes onto bedrock, pulling loose rocks away from the back wall, steepening it. Abrasion is when angular rock embedded in the ice grinds the hollow, which deepens the hollow. Freeze thaw weathering is when water in cracks in the rock freezes, expands and contracts weakening the rock until fragments break off. The glacier moves downhill due to gravity. hanging valleys are so called because they are located high up on the sides of the glacial through. Hanging valleys usually approach the main glacial trough at a perpendicular angle. A hanging valley is a small u- shaped valley that joins the main u-shaped valley at a perpendicular angle and high above the main valley floor. These smaller valleys were originally tributary river valleys to a much larger v- shaped valley. Hanging valleys filled with glacial ice in the same way as the main u-shaped valley. However the glaciers are much smaller, meaning that the rate of erosion is smaller. Once the glacier has melted it leaves a smaller valley high up from the side. A misfit stream flowing through a hanging valley will create a waterfall as the water has nowhere else to go then down.
Ribbon lakes
The glacier moves downhill due to gravity. gravity causes the glaciers to flow downhill following the existing V- shaped valleys. 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 nature of the rock type and the intensity and weight of the glacier and its erosion. The valley becomes wider and straighter, often with a misfit stream which no longer fits the valley floor. Ribbon lakes can form where softer bedrock is eroded more deeply than the surrounding area. Ribbon lakes can form where a terminal moraine or recessional moraine creates a dam. An example of a ribbon lake is Lake Windermere.
