Genesis of hummocky moraine in the Bolmen area, southwestern Sweden |
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| Authors: | GUNNAR ANDERSSON |
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| Institution: | Department of Quaternary Geology, Lund University, Sölvegatan 13, S-223 62 Lund, Sweden |
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| Abstract: | During the late Weichselian deglaciation of southern Scandinavia vast areas of hummocky moraine were formed. The genesis of this landform was studied by geomorphological and sedimentological methods in an area in southwestern Sweden. Four exposures in moraine hummocks were investigated using sedimentological methods. They were found to be composed of stratified diamictons with frost-shattered boulders and deformed intrabeds of sorted sediments. The diamictons were interpreted as sediment-flow deposits, with the hummocks formed in stagnant ice by flowage of supraglacial glacial debris into depressions and subsequent inversion of the landscape due to ice melt. With the exception of hummocky moraine, the study area contains low relief moraine, which like the hummocky moraine was supraglacially formed. A new model is presented where the distribution of hummocky and low relief moraine is dependent on the vertical distribution of glacial debris in the ice sheet, which in turn is related to the flow regime of the ice sheet prior to stagnation. A compressive flow before stagnation favoured development of the hummocky moraine, while low relief moraine formation occurred where the ice flow was extending or at steady state. |
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