Maximum altitude of Late Devensian glaciation on South Uist, Outer Hebrides, Scotland

Mountains on South Uist support a high-level weathering limit that separates an upper zone of shattered bedrock, blockfields and tors from a lower zone of glacially moulded bedrock. This weathering limit descends gently SE from a maximum altitude of c. 470 m, following the direction of regional ice movement. Analyses of joint depths and clay-fraction mineralogy indicate that the weathering limit represents the upper limit of Late Devensian glacial erosion. The limit is therefore interpreted as a periglacial trimline cut around palaeonunataks, and thus as representing the maximum altitude of the Outer Hebrides Ice Cap. The former ice divide probably lay along the west coast of the Uists at an altitude of slightly over 500 m. This evidence is combined with ice altitude data for adjacent land areas and the results of offshore research to reconstruct the surface configuration of the last ice sheet across western Scotland and the adjacent shelf. The reconstruction suggests that The Minch was occupied by a broad ice saddle over 400 m in altitude, with a major ice stream flowing southwestwards across the Sea of the Hebrides. No unequivocal evidence was found in the South Uist hills for glacial readvances after the last glacial maximum.