The Process of Glacial Erosion

Glacial erosion is the process undertaken when glaciers erode the landscape, with this being most common in the UK in upland areas such as N. Wales (as noted in a previous posting), the highlands of Scotland and the Lake District.

What Causes Glacial Erosion?

There are three main processes that can work both independently and in relation to each other. These are:

1. Freeze-thaw 
2. Plucking 
3. Abrasion

Freeze-thaw is only one that I have any knowledge of due to having studied it when looking at weathering. This may perhaps be the same for students as well.

 

The title ‘freeze-thaw’ kind of explains the action of erosion, however I will explain it as well for those (including myself) who might be a little bit rusty on the concept.

Put simply, freeze-thaw is the action of water entering a crack (or similar opening) in a rock (for instance), freezing (where the water expands and makes the crack larger), and then melting when the weather permits. This process then reoccurs with the possibility of more water entering the now wider crack, freezing and expanding even further until eventually the rock breaks up. An example of this is shown below. (This example found on the internet would be an ideal image to provide to a class of students to provide them with a step by step example of how freeze-thaw occurs).

 

 

Plucking (like freeze-thaw) has a name which explains its actions. Once again it is a nice simple concept to understand. Plucking occurs when ice from the glacier freezes around rocks, stones and other material that are attached to the ground. This means that the rock, stone and other material is now attached to both the ground and the glacier. In the case of plucking, the rock is more greatly attached to the ice than the ground and as such is pulled (or ‘plucked’) away from the ground and is often carried by the ice to a new location. 

Abrasion basically follows on from plucking as it is where the material that has been picked up by the glacier is rubbed against the bedrock both along the bottom and the sides of the glacier as it moves to provide a smooth surface to the ground. Nevertheless, there is still the possibility of scratch marks in the bedrock due to angular debris. These scratch marks are called striations. 

The following diagram provides a visual aid as to how plucking and abrasion occur.

 

The final diagram briefly shows how the three actions of erosion link together.

 (Please note that all these images come from a variety of internet sources which can be found using google images).