Physical Geography

Erosional features formed by glaciation range from small scratch marks to vast corries and U shaped valleys. They are all created by the erosive power of ice, armed with angular rock fragments which are scraped along the valley floor, grinding down the underlying rocks.

Three main erosional processes are at work within glaciers; Plucking, Abrasion, and Freeze Thaw. Before we look at the types of features they produce, lets find out how each of these processes erode.

You should be familiar with the process of freeze thaw, but if you're not, don't worry because we will cover it again now.

Read the article about How Glaciers Erode before you progress any further with this lesson, so that you will be familiar with the words and ideas used in the activities.
 

Activity  After you have read the article about how glaciers erode and transport sediment, make some brief notes under the following headings... 1. What is Freeze-Thaw? 2. What is Plucking, and where abouts would it occur in a glacier? 3. What is abrasion and why is it an important cause of glacial erosion? 4. What are the main sources of rock debris found on, in and under a glacier? 5. What role do crevasses play in the erosional process? 6. What are shear plains and what can they do to englacial sediment?

Activity  The surface of a glacier is often littered with rock debris of all shapes and sizes. In a river you might expect some of this material to become rounded as it moves down stream, but in a glacier most of the material is rough and angular. Why do you think that the surface debris is both angular and of such a wide range of sizes?

 
 

Further Activities You will now have to carry out some research of your own... a) We haven't yet looked at how sediment is transported away from the glacier by water. Read about valley glaciers to discover the name geographers use to describe this type of material b) How do you think you might be able to differentiate between sediments transported by water over short and long distances, and material transported only by the glacial ice? What evidence would you look for in terms of particle size, sorting and roundness?