The Mechanics of Drumlin Formation with Particular Reference to the Change in Pore-Water Content of the Till

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Abstract
Most drumlins are composed of till that appears similar in all characteristics to non-drumlin till. Evidence, however, in the form of till layer sequences and from palaeomagnetic Koenigsberger ratios indicate that drumlin till may have a slightly higher pore-water content at the time of lodgement than nondrumlin till. In order that deposited till remains at the ice-glacier-bed interface to initiate drumlin formation, it must undergo rapid geotechnical changes whereby its pore-water content is dissipated thereby increasing the shear strength of the till. Two mechanisms of pore-water removal are possible. Firstly, pore water may be removed from localized patches within a mobile layer of till at the ice-glacier-bed interface, thus creating nuclei of higher-strength till around which deforming till may adhere. Secondly, removal of water initially from the thin water film at the base of a glacier may result in increased pressure melting of the ice leading to till melt-out and subsequent loss of pore water from the deposited till. The loss of water at the glacier bed may be either via permeable subglacial deposits or bedrock, or within subglacial depressions.

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