Aeolian deposits on a Scottish mountain summit: characteristics, provenance, history and significance.

The summit plateau of The Storr (719 m) in northern Skye is mantled by a sheet of aeolian sediment up to 2.9m thick, covering an area of 33 000 m(2) with a volume of 41 000 m(3). The deposits are of massive, poorly sorted sand with significant components of silt and fine gravel, and contain clasts up to 109mm in length. The thickness and coarseness of the deposits decline westwards and northwards away from the highest cliffs, implying that the sediment comprises particles dislodged from rockwalls and blown upwards in an accelerating vertical or near-vertical airflow, settling through a lower-velocity flow onto.the plateau surface where they are trapped by vegetation. Radiocarbon dating of soils buried under and within the deposits suggests that accumulation began after 7.2-6.9 calendar ka sp but before 5.6-5.3 calendar ka sp, and was probably initiated by exposure of the present rockwall by a massive landslide at c. 6.5 +/- 0.5 calendar ka sp. Pollen analyses of buried organic horizons suggest that a vegetation mat dominated by grasses and sedges was present throughout the period of sediment deposition. Sediment accumulation over much of the plateau averaged 10-20mm per century throughout the late Holocene, but reached c. 60mm per century in the area of the thickest deposits. the volume of the deposits implies the removal of 420-480mm of rock (averaged over the face) during the late Holocene, and suggests that small-scale granular disaggregation and release of small clasts constitute a major component of rockwall retreat under present conditions. The origin of the Storr deposits suggests that plateau-top aeolian sediments on other Scottish mountains accumulated in a similar way, but have been eroded and redeposited on lee slopes following breakage of vegetation cover. (C) 1998 John Wiley & Sons, Ltd.