The Late Devensian periglaciation of upland Scotland

Abstract

A wide variety of Late Devensian periglacial landforms developed on Scottish mountains both before ca. 13,000 BP and during the Loch Lomond Stadial of ca. 11,000-10,000 BP. Nearly all such features are now inactive. Late Devensian periglacial weathering produced three types of regolith mantle (openwork block deposits, sandy diamicts and silt-rich frost-susceptible diamicts), each of which supports a characteristic assemblage of relict landforms. On upper slopes these include large-scale sorted circles and stripes, earth hummocks and nonsorted relief stripes, sorted and nonsorted solifluction features, massive boulder sheets and lobes, and nivation benches. Talus, protalus ramparts, rock glaciers and alluvial fans also developed at the base of mountain slopes. The distribution of Late Devensian periglacial features on Scottish mountains is locally controlled by topography, the response of underlying rocks to periglacial weathering and the limits of former glaciers. Regional variations in the altitude of certain forms of Loch Lomond Stadial age (particularly protalus ramparts and rock glaciers) indicate a decrease in former snowfall eastwards across the Scottish Highlands and northwards from the Highland Boundary Fault. Several upland periglacial features are also diagnostic of former permafrost, and complement palaeotemperature reconstructions based on ice-wedge casts and the equilibrium firn line altitudes of stadial glaciers. These suggest that under stadial conditions mean January temperatures at 600 m and 1000 m on mountains in the Western Grampians must have been no higher than −20°C and −23°C respectively, and possibly several degrees lower.