Glaciation

2004 Q6 b ii Explain the formation of a corrie (6 marks)

Snow accumulates in a hollow in the cold northern or eastern side of a mountain. The weight of the snow compacts the bottom layers to form ice and slowly the glacier begins to form and moves downhill due to gravity. As the glacier moves it removes rocks from the back wall due to plucking. Plucking is a process of glacial erosion where ice freezes to the rock and pulls material away as it moves. The rocks may already be shattered due to freeze thaw weathering. Some rock debris gets trapped at the base of the ice and this scours away the underlying rock due to abrasion and so the floor of the corrie is deepened. The rotational movement of the ice means that the ice is moving upwards near the mouth of the corrie which forms a rock lip where there has been less erosion.

2007 SC Q1. Explain the formation of a ribbon lake. (6marks)
The glacier moves down the valley eroding away less resistant rocks. This is done by the ice plucking the first shattered rocks from the valley floor, and abrasing forming a glacial trough. The eroded material is pushed in front of the glacier and is deposited at the furthest part the glacier reaches, forming the terminal moraine. This traps the water when the ice melts to form a ribbon lake.