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Glacial landforms.

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a) Outline the possible sources of glacial till. As it melts, ice deposits the material it has transported. Such debris varies greatly in size and composition and, in contrast to fluvial deposits, is unsorted as it is all collected from the bottom or sides of the rocks through the process of abrasion. Meltwater will transport ice-deposited debris further and produce fluvioglacial deposits of sorted material. The term drift includes both glacial and fluvioglacial deposits. Glacial deposits are termed till. Lodgement till is laid down beneath moving ice and ablation till beneath relatively static, melting ice. b) Examine the field evidence that could be used to distinguish between landforms of glacial and fluvioglacial deposition. Fluvioglacial deposits are likely to be more rounded than glacial deposits because of the processes of attrition that occurs during water transport. They are also likely to be sorted into layers because as the discharge of meltwater streams drops, large load items will be deposited; medium sized items will be deposited when discharge falls further, and finally small items will be deposited. ...read more.


Or it may be the result of deformation of subglacial ice producing areas of lower pressure that allows till accumulation. Drumlins are often found at confluence of tributary glaciers and where glaciers spread out into plains. Crag and tail are where resistant outcrops of rocks project into the base of the glacier, deposition may occur in the zone of lower pressure downstream of obstruction. This is streamlined by glacier movement to produce a tail for the crag. So these are the features and landforms that will distinguish them from fluvioglacial landforms. These landforms will be much rougher, not very rounded, and will not be sorted into different layers, unlike fluvioglacial landforms. Fluvioglacial deposits are sorted vertically and horizontally and consist of particles that are more rounded than glacial deposits. Material is deposited by meltwater because of a loss of energy, for example when water enters a lake or when there is a sudden drop in discharge. The most important features formed by fluvioglacial erosion are meltwater channels. Such channels may be proglacial, marginal, subglacial or overflow channels. ...read more.


Kame terrace's that are deposited by meltwater between unglaciated higher ground and edge of ice sheet. Kame delta's, delta built into a proglacial lake. Varves are alternate layers of silt and sand deposited in fluvioglacial lakes, the coarser, lighter coloured sand is deposited in spring when meltwater stream discharge is high and load is carried at its maximum. The darker silk sized sediments are deposited in the autumn, and discharge levels are lower, and only small particles can be transported. Kettles are blocks of ice that become detached from a retreating glacier, and will be partially buried by fluvioglacial deposits. When the ice melts, its form of depression will fill with meltwater. Braided streams are fluvioglacial streams that exhibit a high degree of braiding, as seasonal fluctuations in discharge produce periods of depression. To answer the question, the field evidence that would be examined would firstly be the shape of the landform and whether it was rounded or not. Secondly whether the material was sorted or not would give a clear indication as to whether it was glacially deposited or fluvioglacialy deposited. Also, it would seem appropriate to suggest that landforms that are located near lakes or other water features would be formed by fluvioglacial depositions. ...read more.

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