Younger Dryas moraines in the NW Highlands of Scotland : genesis, significance and potential modern analogues
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The Younger Dryas was the last period during which glaciers shaped large parts of the Scottish landscape. Reconstructing the palaeoclimate and glacial processes that operated during this time is crucial for the understanding of past atmosphere-cryosphere interactions and predicting future climate change. This thesis presents results from geomorphological and geological mapping in the NW Highlands of Scotland that have resulted in the reconstruction of a Younger Dryas ice cap. Reconstruction of equilibrium-line altitudes and palaeo-precipitation values suggest that the Scottish west coast was wetter than at present. Detailed sedimentological analyses of "hummocky moraines" allow the modes of moraine formation to be reconstructed in great detail and existing models to be tested. "Hummocky moraines" largely represent terrestrial ice-contact fans consisting of supraglacial debris flows and intercalated glaciofluvial units indicating an ice-marginal mode of formation. Different stages of deformation in these fans indicate highly dynamic glaciers that oscillated during retreat, partly or completely overriding previously formed landforms during readvances. Clast shape analyses reveal that debris was mostly subglacially derived and transported. The evidence is incompatible with a morphological model according to which the moraines could be formed by englacial thrusting. Comparison with modem glacial landsystems indicates the following similarities with Scottish Younger Dryas glaciers. Low winter temperatures are similar to those on Svalbard, the marginal response of Younger Dryas glaciers to temperate environments and the modes of deposition to less responsive debris-covered glaciers. High precipitation along the Scottish west coast probably suppressed continuous permafrost development and caused high mass turnover and very dynamic, dominantly temperate Younger Dryas glaciers. Only a narrow zone around the margins appears to have been frozen to the ground, aiding elevation of basal debris and rapid deposition near the snout. The specific climatic and glaciological conditions during the Younger Dryas appear not to have a single modem analogue.
Thesis, PhD Doctor of Philosophy
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