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The significance of rock structure, lithology and pre-glacial relief for the shape of intermediate-scale glacial erosional landforms
Karlstad University, Faculty of Social and Life Sciences, Centre for Climate and Safety.
2002 (English)In: Earth Surface Processes and Landforms, Vol. 27, 251-268 p.Article in journal (Refereed)
Abstract [en]

The main landforms within the glacially scoured Precambrian rocks of the Swedish west coast are closely connected to the principal structural pattern and have lately been explained as mainly a result of etch processes, probably during the Mesozoic and with a possible second period of etching during the Neogene. To explore the effect of multiple glacial erosion on the rock surfaces, an island with two different lithologies and with striae from different direction was selected for a detailed study, focusing on the shape of roches moutonnées. Air-photo interpretation of bedrock lineaments and roches moutonnées combined with detailed field mapping and striae measurements are used to interpret the structural and lithological control on the resulting shape. The study reveals a significant difference in shape between roche moutonnées in augen-granite and orthogneiss. Low elongated and streamlined roche moutonnées occur in the gneiss area, striated by a Late Weichselian ice flow from the NE. This ice flow is sub-parallel with both the local dominant trend of topographically well expressed joints and the schistosity of the gneiss. Frequently there are no signs of quarrying on the lee-sides of the gneiss roches moutonnées and hence they are resembling the shape of whalebacks, as typically are associated with the exposed basal weathering surface found in tropical areas. The granite roche moutonnées are formed by an older ice flow from ESE, which closely followed the etched WNW-ESE joint system of the granite. The Late Weichselian ice flow from NE caused only minor changes of the landforms. On the contrary, marks of this early ESE ice flow is poorly preserved in the gneiss area, where it probably never had any large effect as the flow was perpendicular to both schistosity and structures, and accordingly also to the pre-glacial relief. The study demonstrates that coincidence between ice flow direction and pre-glacially etched structures are most determining for the effects of glacial erosion

Place, publisher, year, edition, pages
2002. Vol. 27, 251-268 p.
Keyword [en]
roches moutonnées, structures, pre-glacial relief, etching, glacial erosion, Sweden
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:kau:diva-24760OAI: oai:DiVA.org:kau-24760DiVA: diva2:598531
Available from: 2013-01-22 Created: 2013-01-22 Last updated: 2013-01-22

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Johansson, Magnus
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