glaciation Flashcards
How does a glacier form?
Forms when snow accumulates in hollows facing north. Accumulation is lots of snow falling in winter compared to melting in summer. Under the weight/pressure of the overlying snow, its compressed into ice.
What is plucking?
Ice freezes into bedrock, pulling loose rocks away from the back wall, making it steeper.
What is abriason?
Angular rock embedded into the ice grinds the hollow bedrock making it deeper.
What is Frost shattering (freeze thaw action)
When the temp fluctuates above/below 0, water in cracks in rocks freezes, expands and contracts, making the rock weaker until fragments break off.
How is a corrie formed?
Formed when the weight of the ice causes the glacier to slide downhill. A crevasse, Bergschrund, opens up behind the hollow, allowing meltwater and rock fragments to get to the base of the glacier. Through rotational sliding and abrasion, the hollow is deepened. Friction causes the ice to slow down and the front of the corrie allowing a rock lip to form as less erosion takes place. When the glacier melts water is trapped leaving a lochan or tarn (EG Red Tarn in the Lake District)
How is an arete formed?
Formed when 2 corries form back to back, creating a narrow ridge between them. Further Freeze thaw will make the ridge narrower and scree slopes may form. EG Striding Edge in the Lake District
How are U-shaped valleys/hanging valleys formed?
The weight of the glaciers causes them to flow downhill, following existing V-shaped valleys. Former interlocking spurs may be cut off by the glacier as it flows downhill, leaving truncated spurs and steep valet sides. The width/shape of the resulting glacial trough will depend on the nature of the rock type, intensity, weight of glacier, and its erosion. Tributary valleys have smaller, less powerful, glaciers which result in less deep U-shaped valleys ‘hanging’ about the main valley.
How is a ribbon lake formed?
Is a narrow lake occupying a U-shaped valley. It’s made when a glacier has more deeply eroded, less resistant, rock creating a hollow which fills up with water. It may also form when moraine across a valley traps water behind it. EG Windermere in the Lake District.
