Abrasion - Glaciers carry a large amount of material with them. Some of these sharp boulders are embedded in the bottom of the glacier and act as erosive agents for the glacier. These rocks mean that the glacier acts like sandpaper, scouring along the valley floor. The effects of abrasion are that the rock surface of the valley will be polished and may have deep grooves cut in them. These grooves are called striations.
Plucking - This is the main erosive process of a glacier. As the glacier moves along the valley the ice melts slightly around large boulders, before re-freezing around them. As it then moves on the boulders are literally ripped out of the ground and will often become agents of abrasion.
Freeze-Thaw - Water enters cracks in the rock during the day. Overnight the temperature drops and the water freezes. As it freezes, it expands. The expanded ice places pressure on the rocks around it. Over time this constant pressuring of the rock causes it to crack and split. This process will break of rocks ready to be plucked by the glacier.
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