By Aaron Paget
There is/are three main types of glacial erosion – plucking, abrasion and freeze thaw.
Plucking is when melt water from a glacier freezes around lumps of cracked and broken rock. When the ice moves downhill, rock is plucked from the back wall. Abrasion is when rock frozen to the base and the back of the glacier scrapes the bed rock. Freeze-thaw is when melt water or rain gets into cracks in the bed rock, usually the back wall. At night the water freezes, expands and causes the crack to get larger. Eventually the rock will break away.
Freeze thaw, also called frost shattering, occurs when rocks break up due to continues freezing and thawing of ice in upland areas. Its mainly upland areas such as mountains which tend to receive more rainfall than lowland areas. Some of the water gathers in the joint of the rock. When the temperature falls below freezing the water in the joint freezes, the frozen water can expand up to 11% and this puts pressure on the rocks joint. When this process occurs a lot and often it creates a weakness in the joint and the rock splits.