Plucking occurs when a glacier stops moving, meaning that any meltwater at the base of the glacier refreezes, sticking onto the rock. Once the glacier begins to move again, it plucks pieces of this rock away with it, eventually transporting it to another area to be deposited.
Abrasion occurs when previously plucked rocks carried by the glacier scrape the surface of the rock they are travelling across. This wears away the surface of the rock, creating scratches known as 'striae'.
Features formed by glacial erosion:
1) Cirque: A cirque is a large hollow surrounded by 3 steep sides, which may also contain a lake (in which case it is known as a 'tarn'). It was formed when ice in mountain hollows plucked rocks and deepened the hollow itself. Eventually, the ice built up,overflowed and began to move downhill as a glacier. Here it melted and remained as lakewater in the hollow created.
2) Arete: An arete is a narrow, steep-sided ridge which occurs when two cirques form back-to-back or beside each other. Sometimes, three will form around a peak, leaving just one steep side called a 'pyramidal peak'.
3) Glaciated Valley: This is a former valley which was widened, and straightened when a glacier went through it.
4) Ribbon Lake: Ribbon lakes are scooped out of the floor of a glaciated valley, usually in areas of softer rock. These hollows later filled with meltwater, and are also called paternoster lakes if they are linked together by a stream.
5) Hanging Valley: A hanging valley is a small glaciated valley high above the main one. This was formed by a much smaller glacier with less power to erode than the other, meaning when it melted, the valley was left almost 'hanging' above the main valley.
6) Fjords: A fjord is a narrow, deep inlet which were once glaciated valleys but were flooded when the sea level rose due to excess meltwater.
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