Glacial Erosion Landforms

Glaciers make a huge impacts on landscapes, they exert vast amount of forces on the land. This causes dramatic changes caused by erosion.

Corries or Cirques

Corries are often the starting point of a Glacier. I'm adding a diagram here, so my explanation hopefully will make more sense. The diagram is from BBC Bitesize revision site



http://www.bbc.co.uk/schools/gcsebitesize/geography/glaciation/glacial_erosionrev1.shtml



Snow is captured in a hollow, and over a certain of amount of time this will turn into Glacier ice. As the ice is trapped in a hollow, it is unable to move downhill but gravity will still make the Glacier move. This circular motion within the ice is known as rotational slip and can cause the ice to pull away from the back wall and causing a crevasse.

Plucked debris from the back wall causes further erosion and which deepens the corrie and causes the hollow to get bigger and bigger. Some of this debris is deposited at the end of the Glacier and builds up a lip.

These processes create a rounded shaped hollow with a steep back wall, looks like a armchair. When the ice in a corrie melts, a lake is created within the hollow. This is known as a Tarn. An example of a Tarn is shown in this picture, its an image of Red Tarn on the eastern flank of Helvellyn in the Lake District.

http://www.bbc.co.uk/schools/gcsebitesize/geography/glaciation/glacial_erosionrev1.shtml.

Glacial Troughs

Glaciers cut out distinctive U-Shaped valleys  into the Landscape, this valleys are probably the most remembered landforms made by Glaciers, as it is a very common sight around the world. U-shape valleys are characterised by having a flat floor and very steep sides, This is caused by Glaciers moving through an already existing V-shaped valley caused by a river. The Glaciers force will erode the valley so it becomes wider, steeper, deeper and smooths down the sides. Below is an image of U- shape valleys, again found from the website bbc bitesize.

Great Langdale Valley, Lake District

Like Rivers, Glaciers have tributaries. As the main Glacier erodes deeper into the valley, the tributary is left higher up the steep sides of a Glacier. These tributaries still cause a used U-shape valley ending with a water fall at the cliff face are called Hanging Valleys. Below is an image of a Hanging Valley

http://www.scalloway.org.uk/phyl12.htm

Unlike a river, which erodes softer rock to make an easier route, which causes interlocking spurs. As the Glacier has so much weight and pressure, the Glacier will erode the valley which causes Truncated Spurs. The sloping edges from a interlocking spurs are cut off, as the Glacier tends to move straighter.

These U-Shape Valleys flow all the way to the coastline, when the Glacier melts the valley becomes flooded with sea water. This is known as a Fjord, Fjord's are common along Norway, Alaska, New Zealand, Greenland and Scotland. Below is an impressive image of Fjords in Norway


http://www.fjords.com/

Aretes and Pyramidal Peaks

Arete:- Is a knife edge ridge. It is formed when two Glaciers Corries run back to back or side by side. As each Glacier erodes either side of the the ridge, the ridge becomes steeper and the edge becomes narrower. E.g Striding Edge found in Helvellyn in the Lake District.

Pyramidal Peak:- Is formed with 3 or more corries and Aretes meet. The Glaciers have carved away at the top of a mountain, creating a sharp pointed summit. E.g Mont Blanc and Mount Everest.

Valley Floor Landforms

As the Glacier flows over land, it will meet harder and softer types of rock. Where the rock type is softer, the Glacier will erode a deeper trough than the harder, more resistant rock. When the Glacier melts, water will be left in this deeper troughs and form thin lakes called Ribbon Lakes. The areas of harder rock are called Rock Steps.

If a Glacier hits a particular resistant rock, it will flow over and around the rock. This leaves a smoothed rock mount, this comes in two types:-

Roches Moutonnee:- Often have steep, jagged faces created by plucking on the far side and a gradual incline which is smoothed by abrasion on the other side. Below is an illustration on how a Roches Moutonnee occurs

http://www.bbc.co.uk/schools/gcsebitesize/geography/glaciation/glacial_erosionrev4.shtml

Crag and Tail:- This is typically larger than a Roches Moutonnee. This works opposite to a Roches Moutonnee, as it hits the more resistant rock first and protects that rock behind it. Edinburgh is a perfect example of a Crag and Tail. Below is an illustration of how Crag and Tail occurs, again from the BBC Bitesize website.

http://www.bbc.co.uk/schools/gcsebitesize/geography/glaciation/glacial_erosionrev4.shtml