Stratigraphy and Morphology of Drumlins within the Múlajökull Active Drumlin Field, Iceland
Friday, 19 December 2014
Our current understanding of drumlin formation is largely based on investigations of individual drumlins either within Pleistocene drumlin fields or within the forefields of contemporary glaciers, showing variable composition and structure resulting in different models for drumlin genesis. The stratigraphy and morphology of drumlins within the active drumlin field at the Múlajökull surge-type piedmont glacier, Iceland, have been studied in order to shed light on their formation. A total of 110 drumlins where mapped and measured and their internal stratigraphy and composition were documented in three exposures. The exposures all revealed several till units where the youngest till truncates the older ones on the flanks of the drumlins and at the proximal side. A geomorphological study shows that drumlins within the 1992 surge end moraine are relatively long and narrow whilst drumlins further away from the current ice margin are wider and slightly shorter. Three models are proposed to explain the stratigraphy and morphological evolution of the drumlins within the Múlajökull drumlin field. Firstly, we suggest that radial crevasses in the glacier terminus lead to spatial differences in normal pressure at the base so that deposition is favoured beneath and erosion in between the crevasses and, consequently, the crevasse pattern of the glacier controls the location of the drumlins. Secondly, sediment accumulating beneath the crevasses acts as an obstacle to the ice, which decreases the ice flow and facilitates sedimentation. Simultaneously and subsequently, the accumulation of sediments is shaped by the ice flow into a drumlin. Thirdly we conclude that the drumlins are evolving from being wide and low to in the distal part to narrow and high in the proximal part. The drumlins are then maintained and their relief increases as the glacier erodes the sides and the proximal end of the drumlin and drapes new till layer over the landform.