Glaciers

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Definitions 1

Snout - the lower end of the glacier.

Ablation - The melting of the ice, mainly during summer months, and usually at the snout end of the glacier.

Accumulation - The build up of the glacier due to snow being compacted into ice.

Calving - The splitting of the end of the glacier into smaller sections. These could become icebergs, if the glacier snout ended in the sea. .


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Definitions 2

Glaciation - The effect of large masses of ice on the landscape. Compressed snow accumulates to eventually form ice and create a glacier.

Ice Sheets - These are large masses of ice which cover an entire land surface. Antarctica is the best example as the ice sheet covers the entire continent.

Valley Glaciers - The most common of the two types of glacier. These are confined by the valley sides that have already been carved out by a river. Valley glaciers can be found in all the main mountain ranges of the world, such as the Franz Josef Glacier in the Southern Alps of New Zealand, and the Rhone Glacier in Switzerland

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Formation

Glaciers originate from heavy snowfalls over a prolonged period of time. The snow initially has many air or pore spaces between the flakes. Over time the weight of new snow above it compacts it all, squeezing the air out of the pore spaces, similar to what you might do when making a snowball.

This compaction causes some of the snow to become freezing water that binds the compacted snow together even more, creating ice. As the sir is squeezed out of the ice it will turn a slight shade of blue.

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Glacial Erosion

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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Glacial Transportation

Glaciers carry a huge amount of material. Rocks called moraine can be carried great distances

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.

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Glacial Deposition

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 itterminal moraine, but it will also create recessional moraines and eventually also leave behind lateral, medial and ground moraines.

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