Formation of a Corrie

Transcription

1 Formation of a Corrie A corrie looks rather like a armchair has been cut out of the rock face When a hill has been heavily eroded with 3 or 4 corries the jagged hill that is left is known as a pyramidal peak. Large crevasse Formation of the Corrie Plucking occurs when the ice begins to stick to the rock Abrasion occurs when the rocks are scraped along the base of the rock Often two or more corries are formed leaving a narrow ridge between them. This narrow ridge is called an arête Freeze thaw affects the back wall, so here rocks that become loose from cracking begin to break off. This ice that is also stuck to the back wall begins to pluck off rock when it moves At the bottom of the hollow piece of rock abrasion starts to occur. So the hollow gets worn down by the sandpaper effect making it deeper. When the glacier leaves the hollow you are left with a corrie.

2 Formation of a Ribbon Lake A ribbon lake is a long and narrow, finger-shaped lake Formation of a Ribbon Lake When the glacier picks up rocks when moving the process of abrasion begins to occur The ribbon lake is usually found in a glacial trough This sandpaper effect starts to wear away the softer rock faster than the hard rock This creates a hollow in the rock called a rock basin Over time as the ice melts and from rainwater the basin starts to fill with water Creating a Ribbon Lake For a ribbon lake to form there needs to be an area of soft rock, usually between hard rock

3 Formation of a Tarn A Tarn is a lake that is formed when a glacier is excavated (moves from) a corrie. The water left behind is called a Tarn. So without the formation of a corrie a tarn would not be formed Formation of the Tarn Freeze thaw affects the back wall, so here rocks that become loose from cracking begin to break off. Tarn This ice that is also stuck to the back wall begins to pluck off rock when it moves At the bottom of the hollow piece of rock abrasion starts to occur. So the hollow gets worn down by the sandpaper effect making it deeper. When the glacier leaves the hollow you are left with a corrie. Water that is left by the glacier forms a lake called a tarn in the hollow rock

4 They occur at the mountain top Formation of an Arête An arête is a thin, almost knifelike, ridge of rock An arête can be formed in two separate ways.. Formation can occur when two u shaped valleys are parallel to one another (side by side) and they have both been eroded by the path of glaciers As the glaciers move they create a deep U shaped valley with steep sides. The ridge between the two valleys is very thin and sharp and is named an arête. The second way an arête can be formed is when two corries are eroding back to back towards each other. The steep back walls meet creating a steep and sharp ridge. This is called an arête.

5 Formation of a Pyramidal Peak A Pyramidal Peak is the peak of a mountain shaped like a pyramid formed this way by glacial erosion Imagine the pyramids of Egypt only with armchair shapes cut into them When three corries occur in the same place in a back to back arrangement a Pyramidal Peak can be formed When there are three or more of these corrie back walls and arêtes joined together to form a single peak it creates a pyramid shape with very steep walls, this is called a pyramidal peak They are a common shape for mountain tops in glaciated areas.

6 Formation of a Hanging Valley Formation of a hanging valley Water once flowed down the mountain sides in small tributaries/streams and joined the river in the main valley The stream falls from a smaller valley into the main valley, this is how it got the name hanging valley Over time a glacier erodes the valley making the valley deeper and deeper until the smaller valleys joining the main valley are much higher This means that when the water from the streams comes down the smaller valleys it has to drop from one valley into the river below This is described as a hanging valley

7 A glacial trough is a steep U shaped valley left behind by the erosion of a glacier Formation of Glacial Trough As we know glaciers follow the paths of rivers We also know that a very large piece of ice called a glacier is very, very strong So your river would look like this and after glacial erosion look like the picture on the right So if we had a river which had many turns and bends in the power of the glacier would in time over ride this. What is meant by this is that the glacier will plough through the rock making the river straighter and wider, shall we say taking the easiest route by using sheer force