Glacial Processes

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Glacial Processes

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.

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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.

Glaciers carry a huge amount of material. These rocks are called moraine and can be carried great distances by a glacier.

The rocks are mainly carried once they have been plucked away from the valley surface by the glacier. Most of the material is carried nearer to the base of the glacier. The glacier also carries however frost shattered material from the valley sides once it has fallen onto the ice surface. This material is called lateral moraine, and is carried at the sides of the glacier. When two valley glaciers meet and merge the two lateral moraines will form a medial moraine, running down the centre of the new, larger glacier.

Glaciers will always reach a point when they will start to melt, mainly due to the rise in temperature as they descend in height down the valley. As the ice melts it cannot carry as much material and so this is deposited. The main depositional feature of a glacier is its terminal moraine, but it will also create recessional moraines and eventually also leave behind lateral, medial and ground moraines.

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