Glaciation Flashcards
- Explain the conditions and processes involved in the formation of a corrie. You may wish to use an annotated diagram or diagrams.
Snow accumulates in mountain hollows when more snow falls in winter than melts in the summer. (1 mark) North/north-east facing slopes are more shaded so snow lies longer (1 mark), with accumulated snow compressed into neve and eventually ice. (1 mark) Plucking, when ice freezes on to bedrock, pulling loose rocks away from the backwall, making it steeper. (1 mark) Abrasion, when the angular rock embedded in the ice grinds the hollow, making it deeper. (1 mark) Frost shattering continues to steepen the sides of the hollow when water in cracks in the rock turns to ice when temperatures drop below freezing; expansion and contraction weakens the rock until fragments break off. (1 mark) Rotational sliding further deepens the central part of the hollow floor as gravity causes the ice to move. (1 mark) Friction causes the ice to slow down at the front edge of the corrie, allowing a rock lip to form, which traps water as ice melts, leaving a lochan or tarn. (1 mark) During spring/summer, thawing takes place, allowing water to penetrate cracks in the rocks at the base of the hollow. (1 mark) The broken fragments build up over time and are removed by meltwater, further enlarging the hollow. (1 mark) Frost shattering on the backwall supplies further abrasion material as loose scree falls down the bergschrund. (1 mark) This is a large crevasse separating moving ice from the ice still attached to the backwall. (1 mark)
- With the aid of a diagram, explain how terminal moraine is formed.
Moraine is material carried along by the glacier. When the glacier reaches lower altitudes or temperatures rise, the ice melts and deposits moraine at its snout. Terminal moraine marks the furthest extent of the glacier. It forms a jumbled mass of unsorted materials that stretches across the valley floor. Once the ice has retreated, the terminal moraine can often form a natural dam, creating a ribbon lake.
(Diagram for full marks)
- With the aid of a diagram, explain how drumlin is formed.
Drumlins are elongated hills of glacial deposits ad are formed when the ice is still moving. The steep slope faces upstream and the lee slope is gentler, longer axis of the drumlin which indicates the direction in which the glacier was moving. The drumlin would have been deposited when the glacier became overloaded with sediment, and as the glacier lost power due to it melting the material was then deposited. It is possible that there was a small obstacle in the ground which caused the till to build up around it forming a drumlin. It may also have been reshaped by further ice movements after it was deposited.
(Diagram for full marks)
- With the aid of a diagram, explain how esker is formed.
Eskers are mounds of sand and gravel that commonly snake their way across the landscape and are produced as a result of running water in, on or under the glacier. When the glacier retreats, the sediment that had been deposited in the channel is lowered to the land surface where it forms a mound, or hill, that is roughly parallel to the path of original glacial river. The water is unable to escape sideways because of the restricting walls of ice and the stream bed is gradually built up above the level of the ground on which the glacier rests. The ice that formed the sides and roof of the tunnel later disappears, leaving behind sand and gravel deposits in ridges with long and twisting shapes. (Diagram for full marks)
