Drumlins

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  • Topic: Glaciology, Glacier, Glacial landforms
  • Pages : 6 (1981 words )
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  • Published : March 15, 2013
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Describe the spatial characteristics of drumlins in Ireland and explain their relationship to the evolution of the last lowland ice sheets in Ireland.

Drumlins are undoubtedly among the most intensively studied of all glacial landforms and have bee particularly widely used as ice-directional indicators. They frequently occur in ‘fields’ or ‘swarms’ in lowland areas where there was little obstruction to the passage of ice, or in piedmont zones where flow was radiative or dispersive. They are also occasionally found on the floors of glacial troughs. Many are ellipsoidal in form, some kilometres in length have been observed (Lemke 1958). Most possess a prominent stoss end with a trailing distal slope. It is generally agreed with the direction of the drumlin long axis reflects local direction of ice movement with the stoss end usually pointing up-glacier. The ice moulded or streamlined form appears to be produced by variations in stress levels at the base of the ice, although the precise mode of formation of the features is far from clear. The Kingscourt drumlins mentioned below gives a detailed account of the spatial characteristics and it’s internal components. ‘In addition to the regional ice flow trends displayed by their long axes, the overall shape of drumlins can provide information on former glacial dynamics, such as indications of basal ice pressure and rate and type of ice flow (Doornkamp and King 1971)’[1].

The recent work on drumlins has tended to concentrate on three aspects: drumlin shape and distribution, stone orientations within drumlins and theoretical considerations of pressure distributions within the ice and the till. Vernon (1966), in a study of drumlins in County Down, noted that they are concentrated in bands both perpendicular and parallel to ice flow but that their spacing is variable. Doornkamp and King (1971) point out that where drumlin density is high, the drumlins themselves were small. This is not as obvious as it seems, because small drumlins, being spread sparsely, could result in low-density values. It also seems likely that conditions that are conducive to regular spaced but few in number are also conducive to large drumlins. ‘In contrast, drumlins are more numerous in those areas where conditions were marginal for their formation and the ice moved less consistently and slowly’[2].

McCabe has helped our understanding of the drumlinising of the landscape substantially, which had been analysed mainly using morphological criteria, and to determine ice direction. Sedimentological analyses have indicated a complex set of depositional units within the drumlins: 1. Forms with a core of older till facies.

2. Subglacial lodgement/ meltout till facies.
3. Subglacial channel stratified facies.
4. Lee-sided stratified facies.
5. Re-mobilised/ superimposed till facies.
6. Overridden ice-marginal subaquatic facies.

‘These facies have led to the conclusion that the large drumlin fields of Ireland are the result of high basal water volumes leading to uncoupling of the glacier from the underlying sediments, resulting in downdraw into the surrounding ocean and a surge of the glacier. Such surging, involving high-pressure water, would streamline the underlying deposits and the large volumes of water and low basal shear stresses would allow the preservation of the resulting drumlins’[3].

This abstract details precisely a drumlin and it’s internal, external and importance to understanding drumlin’s significance in studying their evolution from the last glacial maximum. ‘An exposure in a Late Pleistocene drumlin near Kingscourt, Ireland, provides a good insight into some of the processes that give rise to such subglacial bedforms. The drumlin is located on a ridge, cored by red sandstone of Carboniferous (Namurian) age, which rises to 150 m above m.s.l. The drumlin itself is about 380 m long by 170 m wide and is 20 m in height. It is orientated VVNW-ESE. Ice...
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