Glacial Landforms

Following on from the previous post on glacial processes, the next thing to look at are the glacial landforms that occur as a result of these processes. Due to the forceful action of erosion and weathering, the landscape through which the glacier moves is left looking very different to many other landscapes created from erosional and weathering processes.

There are two different types of landform that are created from glaciers: erosional and depositional. 

First of all I will start by looking at erosional landforms.

Corries (also known as cwms or cirques) are found at the top of the mountain where the glacier first begins. They are bowl-shaped hollows which form as a result of plucking, abrasion and freeze-thaw action as the glacier moves further down the mountain or valley. If the ice within a corrie melts, a lake often forms and this is known as a tarn.

U-shaped valleys form as a result of a glacier moving down the valley. Glaciers usually follow the path of old river beds and so the glacier continues to erode the v-shaped river valley, cutting through harder rock that the river could not erode and thus creates a much wider U-shaped valley. Characteristically they have a flat floor with steep sides. Glaciers are also much like rivers in that when they erode through the upper course of the glacier, they leave behind truncated spurs (on a river they are known as interlocking spurs).

Arêtes are sharp, knife edge, ridges of rock which form when two corries form back to back. Each glacier continues to erode either side of the strip between the two corries which eventually leads to the creation of a very steep and narrow ridge.

Pyramidal peaks form as a result of the meeting of 3 or more corries and arêtes. The continued erosion eventually leads to the formation of a pyramidal peak (also known as a horn).

Diagram illustrating the above erosional land forms

Ribbon lakes form as a result of the erosion by the glacier on the valley floor. As it flows 

over this land, softer rock erodes much quicker and easier as opposed to hard rock and so the glacier creates deeper troughs in the soft rock. When the glacier has retreated, water will begin to collect in these deep troughs and can create long, thin, ribbon lakes.

Crag and tail also forms as a result of the differential erosion of the soft and hard rock over which a glacier flows. As the glacier flows over soft rock it eventually hits an area of hard rock and so instead of cutting right through it, it goes over the hard rock. This area of hard rock protects the softer rock behind it, creating a crag and tail. One good example of a crag and tail is Edinburgh castle.

 Diagram illustrating a crag and tail (BBC Bitesize)

Now that I have finished looking at the erosional landforms created by glaciers, I am going to move on to looking at the depositional landforms.

Till, also known as boulder clay, is the debris that is deposited when a glacier has retreated and is made up of a variety of material, including rock, sand, gravel and mud.

Moraines are deposits that have previously been carried by a glacier and dropped as the glacier retreats. There are four different types of moraine:

            Terminal – found at the furthest point that was reached by the glacier

            Lateral – found along the sides of the glacier

            Medial – found at the place where two glaciers have joined together to    create    one, larger, glacier

            Ground – variety of sizes and types of rock found at the bottom of the glacier

Not all material that was once carried by the glacier is deposited as a moraine. Material is sometimes carried by the melt water streams and is deposited as it flows. As a result, after many years of this small, steep mounds of debris accumulates adjacent to the glacier, known as kames.

Erratics are large, unsorted boulders that are deposited once a glacier has retreated. As they are so large they are often found individually, and not in piles and are often of a different rock to that of the surrounding area.

Drumlins are large, long hills which are created as a result of glacial deposits. Although there is much disagreement on how precisely they were formed, it is thought that they were created when subglacial material that had accumulated from various erosive and weathering processes was deposited. As the drumlins are shaped by glacial movement, all of those created by the same glacier face in the same direction; running parallel to the flow of the glacier.

Diagram above illustrates the above depositional landforms

As has been the case with other areas that I have already covered within this glacial topic, I think it is important to incorporate imagery into the teaching. Visual aids help to show pupils what they are learning and it could be easier for them to remember the different terms if they have been able to see it. Another way to help the learning of these terms would be to hand out a diagram of a glacier valley and ask students to add the labels for the different landforms created.

BBC Bitesize as well as National Geographic have been very useful with this area and are filled with useful pictures, diagrams and resources which could prove to be very useful!

Links used:

http://nsidc.org/cryosphere/glaciers/questions/land.html National Snow and Ice Data Centre

http://education.nationalgeographic.com/education/encyclopedia/glacier/?ar_a=1#page=1 National Geographic

http://www.bbc.co.uk/schools/gcsebitesize/geography/glacial_landscapes/glacial_deposition_landforms_rev1.shtml BBC Bitesize