Reconstructing Loch Lomond Stadial Glaciers and Climate in the south-west English Lake District

Abstract

The most recent glaciation of the English Lake District occurred during the Loch Lomond Stadial (Younger Dryas) when full glacial conditions returned to the British Isles. The largest ice mass formed over the Western Scottish Highlands with smaller ice masses developing throughout the British uplands.

In the Lake District, our understanding of the extent and timing of the Loch Lomond Stadial glaciation is patchy and poorly constrained by geochronology. Sissons (1980) proposed the development of 64 independent alpine-style ice masses in the district during the Loch Lomond Stadial. The location and geometry of these ice masses showed some agreement to the earlier, but coarser scale, map of ice masses produced Manley (1959) for the same period, however some significant differences were also apparent. More recently, McDougall (1998: 2001) has proposed the development of plateau icefields in the Lake District centred over High Raise, Grey Knotts/Dale Head, Brandreth and Kirk Fell. This much more extensive style of glaciation involved 40-50 m of cold based non-erosive ice occupying the plateau summits and feeding down into warm-based geomorphologically active outlet glaciers in the valleys. Further Loch Lomond Stadial sites have also been identified in the Lake District by Wilson (2002: 2004) and Wilson and Clark (1998: 1999).

The geomorphology of the south-west Lake District is identified and presented here and glaciers are then reconstructed based upon this evidence. Palaeoclimatic inferences made based upon the reconstructed glacial extent vary greatly depending on the style of glaciation that occurred during Stadial (alpine or plateau icefield). Of particular note, plateau icefields have the potential to significantly raise the equilibrium line altitude (ELA) across a region. This lowers the temperature at the ELA and therefore increases the reconstructed palaeoprecipitation at the ELA. In order to test the viability of the reconstructed glaciers in the Lake District, a 2D velocity-mass balance model is applied to the glaciers (adapted from Carr and Coleman,2007). This model assumes that where a glacier is glaciologically viable under the parameters used to drive the model, the basal velocity (Ub) accounts for < 90 % of the surface velocity in the centre of the channel (Us).

Further mass contributions to the glaciers via mechanisms such as snowblow are quantified using a revised definition of potential snowblow areas. The significance of these areas is then assessed with respect to the ELA of the glaciers. Digitisations of the work of Sissons (1980), McDougall (1998), Wilson and Clark (1998: 1999) in the Lake District are then presented and compiled with the work of the current author to illustrate the extent of the Loch Lomond Stadial throughout the whole district.