GLACIAL EROSION AND LANDFORMS

As mentioned in the previous post, glacial erosion can have a huge influence on the shape of landscapes. This is because they erode at such a fast pace, surprisingly much faster than a river (despite moving much slower) providing they have a continuous supply of material. The main source for this material is from freeze-thaw weathering. Freeze-thaw occurs in rocks that have many cracks and joints in them and where temperatures are around freezing point. The water that gets into these cracks freezes at night and expands putting pressure on the surrounding rocks. The melting of the ice releases the pressure however continuation of this process widens the cracks more and eventually causes jagged pieces of rock to break off. The glacier uses this material, called moraine to widen and deepen its valley. 

There are two main types of glacial erosion: abrasion and plucking. 

Abrasion: is when the material carried by a glacier rubs against the sides and floors of a valley like sandpaper. It is similar to corrasion by a river but on a much larger scale.  

Plucking: occurs when meltwater from a glacier freezes onto solid rock. As the glacier moves forward it extracts pieces from the rock surface.

LANDFORMS

Right so I now know what a glacier is and how one forms, the next step is to look at the landforms they create/leave behind. When glaciers move, they tend to follow the easiest possible route which is usually a river valley. Unlike a river, glaciers can fill the whole valley and therefore have much greater erosive power. There are numerous types of landforms that are created by glacial erosion which I have listed below.

A good source that can be referred to is: http://www.geography.learnontheinternet.co.uk/topics/glaciation2.html.

Glacial trough - These are made by the movement of a glacier downhill eroding into the floors and walls of, usually, old river valleys. The glacier carves through the rock deepening and widening the valley by abrasion and plucking. When the ice melts a glacial trough is left behind, also known as a U-shaped valley.

Corries – A deep semi-circular hollow found near the top of a mountain, formed by plucking and abrasion processes of moving ice downhill. Corries are also known as cirques, they are all names for the same formation. Corries can be found at Helvellyn in the Lake District.

Aretes – This is a knife edge ridge separating two corries. These can be found in the Lake District.

Pyramidal peaks – These are formed when three or more corries form in the side of a mountain, cutting inwards to learn a ‘horn’ or pyramidal peak in the middle. Pyramidal peaks can be found in Mount Snowdon.

Truncated spurs – These are formed by the glacier eroding and cutting off the river valleys interlocking spurs leaving truncated spurs. Truncated is really just another word for ‘cut-off’. Truncated spurs can also be found in the Lake District. 

Hanging valleys – This are old tributaries that are left hanging high up on the valley sides.

DEPOSITIONAL FEATURES

Moraine – A mass or rocks and sediment carried and deposited by a glacier. 

Scree – The accumulation of broken rock.

Ribbon lakes – These sometimes form when the terminal moraine that is deposited by ice melting traps water behind it in the glacial trough. This water forms what is known as a ribbon lake. These can also be found in the Lake District.

Till – The material deposited by a glacier which includes clay, sand, gravel and boulders. 

Drumlins – These are the smooth egg shape hills left behind when a glacier has not had enough energy for erosion and transportation of material to take place. 

Eskers – The material that was being carried in a stream under a glacier that gets left as a long ‘wiggly’ ridge called an esker. 

Kames – Little heaps of material deposited on the ground when a glacier melts. This material would have been trapped in the crevasses of a glacier before it began to melt.

This is a useful video: http://www.bbc.co.uk/schools/gcsebitesize/geography/glacial_landscapes/glaciation_video.shtml, taken from BBC Bitesize, which illustrates the glacial erosion processes. When teaching this, it is important that students have a description of the above landforms/depositional features, a range of definitions can be found online.