Moraine-mound formation by englacial thrusting: the Younger Dryas moraines of Cwm Idwal, North Wales
Published:January 01, 2000
David J. Graham, Nicholas G. Midgley, 2000. "Moraine-mound formation by englacial thrusting: the Younger Dryas moraines of Cwm Idwal, North Wales", Deformation of Glacial Materials, Alex J. Maltman, Bryn Hubbard, Michael J. Hambrey
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The Younger Dryas (c. 11–10 ka BP) moraine-mound complex (‘hummocky moraine’) in the historically important site of Cwm Idwal, North Wales, has previously been interpreted using periglacial, subglacial, ice-marginal and englacial models. In this paper the morphology and sedimentology of these landforms is described and the competing hypotheses tested against this evidence. It is demonstrated that an englacial thrusting model, developed for polythermal glaciers in Svalbard, best fits the available evidence. Thrusting probably resulted from longitudinal compression against a reverse bedrock slope, although a frozen snout, downglacier of sliding ice, may also have been a trigger. It is suggested that the role of ice-deformation, especially thrusting, in landform development has been underestimated, and that the englacial thrusting model may find application in the interpretation of other sites in the palaeo-landform record.
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Deformation of Glacial Materials
The flow of glacier ice can produce structures that are striking and beautiful. Associated sediments, too, can develop spectacular deformation structures, and examples are remarkbly well preserved in Quaternary deposits. Although such features have long been recognized, they are now the subject of new attention from glaciologists and glacial geologists.
This collection of papers addresses how the methods for unravelling deformation structures evolved in recent years by structural geologists can be used for glacial materials, and the opportunities offered to structural geologists by glacial materials for studying deformation in rocks.