Maximum altitude of Devensian glaciation on the Isle of Skye

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Abstract
Synopsis: A high-level periglacial trimline occurs on the mountains of Skye at altitudes of 750–870 m in the Cuillins, c. 850 m on Blà Bheinn, c. 760 m on Glamaig, 440–610 m on Trotternish and at c. 480 m on Macleod’s Tables in Duirinish. Widespread survival of gibbsite in soils above the trimline indicates significantly more advanced weathering than in soils at lower altitudes, implying that the trimline marks the upper level of Devensian glacial erosion and thus defines the maximum altitude of the ice dome that developed on Skye during the Devensian glacial maximum. Three-dimensional reconstruction of the form of the ice surface suggests that glaciers descended steeply from west-facing corries in the Cuillins, whilst east-facing corries nourished an ice mass that escaped north via Glen Sligachan and SE over cols and around the southern end of the Cuillin ridge. Across central and northern Skye the ice surface descended more gently at gradients of 7.5–9.0 m km −1 , declining to an altitude of c. 450 m across Duirinish, Waternish and the northern tip of Trotternish. Implied basal shear stresses are consistent with those of an ice mass moving across a rigid bed, and the dimensions of the former ice dome indicate confluence of Skye ice and Outer Hebridean ice in the Minches.