Depositional features
Moraine
As glaciers move down hill, they push material with them. When the glacier eventually melts, the material left behind is known as the terminal moraine. There are several types of moraine: - Terminal moraine indicates the furthest point the glacier reached before melting. - Lateral moraine is the material left at the sides of the glacial trough. - Medial moraine a ridge of material left behind where two glaciers once met. - Ground Moraines (till) – A range of materials including boulders, stones and clay that are deposited across a valley floor as a glacier melts. |
Ribbon lakes
Ribbon lakes can be formed when water accumulates behind the terminal moraine in the glacial trough. Ribbon lake formation also occurs when weaker rock in the valley floor is eroded away quicker than other areas of harder rock forming a hollow that gradually collects meltwater. |
Drumlins
These are formed when a glacier moves too slow to transport material or erode the landscape. In effect, the glacier tends to shape those landscapes made of clay, creating smooth hills. These hills are elongated downhill as a consequence of the glaciers movement. Drumlins can stretch up to 1km in length and can be up to ½km wide. |
Erratics These are pieces of rock that have been transported very far distances. Some rocks will have been moved many miles from where they started, for example a rock type usually found in Scotland may have been pushed all the way down towards Southern England. |
Eskers These are long, winding ridges that the glacier has deposited as it moves down hill. They can sometimes be many kilometres in length. |
Kames These are the small mounds of sand and gravel deposited at the front of a melting glacier. As the glacier retreats, the mounds are left unsupported and tend to collapse. |
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Extension (A level): Fluvioglacial processes
Fluvioglacial processes are a result of the release of large amounts of meltwater through ablation. It is fluvioglacial processes that create Eskers, Kames and outwash plains (sandurs).
Outwash plains, also known as sandurs, are made up of deposited sediments carried by meltwater streams beyond the snout of a glacier. The sediment on the plains is normally presented in size order, with the largest rocks being located nearer the ice front and the smaller rocks, clay and silt being carried further away. The deposits tend to form vertical layers which can be used to indicate the year or season of their deposition.
Kettle holes can be found on outwash plains. These are formed when large ice blocks, washed out onto the plain by the meltwater, eventually melt resulting in the formation of lakes. Occasionally these lakes will establish aquatic plants resulting in the development of marshes.
Meltwater streams that cross the outwash plain become braided. This occurs when coarser rocks block a stream sending the stream off route.
In the lakes, located around glaciers, a distinct layering can be found among their deposits. These layers consist of a layer of silt sitting on top of a layer of sand which represents 1 year’s deposition in the lake. These layers are known as varves. The layer of sand is usually thicker than the layer of silt; sand is deposited when meltwater is at its peak and carrying its maximum load. The layer of silt is deposited when the stream discharge decreases. The thickness of each layer indicates the trend of the climate and its past warmer and colder periods.