Pre-Flandrian slope deformation in the Scottish Highlands: examples from Glen Roy and Glen Gloy

Synopsis Slope deformation at localities in Glen Roy and Glen Gloy became essentially inactive prior to the formation of glacial lake shorelines (Parallel Roads) that are related to the maximum of Loch Lomond Readvance glaciers (10 500–10 000 BP). As such it is distinct from, and predates, differential uplift that has been linked with catastrophic lake drainage, landslip and possible seismic activity. The deformation is tentatively ascribed, first, to stress relief during glacial unloading and, second, to high cleft water pressures associated with the retreat of the main Late Devensian (Dimlington Stadial) ice across the area shortly after 13 000 BP and with permafrost, particularly during the Loch Lomond Stadial (11 000–10 000 BP). Such deformed, but almost featureless slopes may be present elsewhere where topography and structure are favourable: their preservation in Glen Gloy suggests that the upper part of this valley was not glaciated during the Loch Lomond Stadial.