Friday, 9 May 2008

Glaciation model answers from Mr Nailor

1. Name two processes that contribute to glacial erosion and describe how each one takes place.

1. ABRASION. As a glacier moves, the rocks frozen into its base and sides scratch the valley bottom and sides and wear (erode) it. It has a sandpaper effect so the eroded rock looks smooth.
2. PLUCKING. When a glacier is not moving it tends to freeze itself to the valley sides. If the glacier then starts to move it will tear lumps of rock out of the valley sides. This happens a lot at the backwall (headwall) of the glacier.

3. Ribbon lakes(finger lakes) are often found on the floor of a U-shaped valley (glacial trough). Describe three ways in which a ribbon lake is formed.

1. If a valley floor contains both hard and soft rocks the glacier will erode deeper into the softer rock. This eroded hollow may the fill with water to create a lake.
2. Where a tributary glacier joins a main valley glacier the extra weight of ice will erode downwards more at this point. This deeper hollow may then fill with water to create a lake.
3. When a glacier reaches lower ground it will start to melt in the higher temperatures. As it melts it deposits rock debris contained in the ice. This deposited rock forms a bank of rock called a terminal moraine across the valley floor. This can act as a dam and a lake can form behind it.

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