Glacial Transportation and Deposition

Aim: To be able to understand the way Glaciers are able to transport material and then deposit it further along.

A glacier can not only shape valleys and create fjords, a valley glacier is also capable of transporting a variety of material - all things great and small ! Some of this debris may be derived from previous rockfalls from the valley and the surrounding area. This is then transported on the surface of the glacier which is named supraglacial debris. Otherwise the debris may be buried within the glacial ice - named englacial. 

Figure 1: Image illustrating some of the debris carried by glaciers (Source:Reference)

Subglacial is the material found at the base of a glacier, which may include fragments of rock and eroded material at the base of the glacier. Another term for describing this type of debris is a more popular noun of Moraine. (See figure 2)

Figure 2: Diagram illustrating a glacier in terms of debris and moraine (Source: Reference)

The large amounts of debris that is transported by a glacier is eventually deposited further along the path. The majority of this will be the material released by the melting of the ice at the glacier snout or where the glacier changes between compressing and extending flow. The debris that is directly deposited by the glacier ice is known as boulder clay or till. (See figure 3)

Figure 3: Diagram illustrating where the boulder clay is layed down (Source:Reference)

Till: This is an unsorted mixture of rocks, clays and sands that has been transported as supraglacial or englacial debris and deposited when the ice melted. The stones tend to be angular or in some cases sub-angular (unlike river and beach material which is smooth and round). Till can sometimes be transported across the country - for example some from south Lancashire has be sfound in the Lake District and souther scotland. 

Sometimes a large boulder that has been moved from one area and deposited in another which has a very different geology is known as erratic.

Types of glacial deposit:

Lodgement till - subglacial material that was deposited by the moving glacier. (A drumlin is a typical feature of this).

Ablation till - is formed at the snout of the glacier where the ice has melted. Terminal end, push and recessional moraines are typical features.