Depositional glacial features are created when glaciers retreat and leave behind their freight of crushed rock and sand (glacial drift), they created characteristic depositional landforms.
Moraines
When a river loses it energy, it deposits its sediment load. Similarly when glacial ice melts, the rocks and sediment that have been carried along are laid down. Piles of these deposits are called moraines.
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Drumlin
Drumlins are elongated hills of glacial deposits. They can be 1 km long and 500 metres wide, often occurring in groups. These would have been part of the debris that was carried along and then accumulated under the ancient glacier. The long axis of the drumlin indicates the direction in which the glacier was moving. The drumlin would have been deposited when the glacier became overloaded with sediment, however glaciologists still disagree as to exactly how they were formed.
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Erratics
River deposits are sorted into different sizes, due to the relationship between the velocity of the river and the size of the sediment load. However, since glacial deposits are carried within the glacial ice the deposits are mixed (unsorted) and angular.
The extreme of this can be seen in erratics. These are large rocks or boulders that are often found on their own, rather than in piles. They are unusual shapes, unusually large and of a rock type uncommon to the area they have been deposited, eg the Norber erratic. |
Kettle Hole
A kettle hole is formed by blocks of ice that are separated from the main glacier - for example ice blocks left after a glacial retreat or during a glacial flood (jökulhaup). The ice blocks may then be buried in the outwash sediment. On melting of these ice blocks, they leave behind depressions that fill with water to become kettle hole lakes.
Many kettles have been infilled with sediments, especially peat, during the Holocene. |
Esker
An esker is a long, narrow, winding ridge composed of stratified sand and gravel deposited by a subglacial or englacial meltwater stream. Eskers range in size from a few meters to a many miles. They may occur unbroken or as detached segments. The sediment is sorted according to grain size, and cross-laminations that show only one flow direction commonly occur. Esker formation presumably takes place after a glacier stagnates, because movement of the ice would likely spread the material and produce ground moraine. Notable areas of eskers are found in Maine, U.S.; Canada; Ireland; and Sweden.
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Till
Till is unsorted material deposited directly by glacial ice. It shows no stratification and is composed of clay and/or boulders of intermediate sizes. The rock fragments are usually angular and sharp rather than rounded, because they are deposited from the ice and have undergone little water transport. Although difficult to distinguish by appearance, there are two types of till, basal and ablation. Basal till was carried in the base of the glacier and commonly laid down under it. Ablation till was carried on or near the surface of the glacier and was let down as the glacier melted.
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Outwash Plain
The large quantities of water that flowed from the melting ice deposited various kinds of materials, the most important of which is called glacial outwash. Outwash plains are made up of outwash deposits are characteristically flat. They consist of layers of sand and other fine sediments, which are especially good for agriculture.
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