Snow cover, permafrost and the formation of skin flows on a high-mountain scree slope (Corral de veleta, Sierra Nevada, Spain)

Abstract

. This study examines the origin of a series of mass movements called skin flows occurring on a scree slope located at the foot on the north wall of Pico del Veleta in Sierra Nevada, Spain (3398 m, 37º03'21''N, 3º 21' 57''W). The genesis of these flows is contrasted to the geomorphologic action of snow and the degradation of buried ice masses or permafrost. Oblique photography was used during late summer, yearly monitoring of snow cover duration and surface area from 1998-2008 and the variations of talus morphology. The results show a recent trend in reduced snow cover duration in late summer. The talus is free of snow cover during this season and permafrost degradation in some sections of the talus has accelerated. The contrast between snow cover evolution and skin flows formation indicates when and where the processes occurred. Skin flows are most apt to form on the downslope side of long-lasted snow patches when snow melts rapidly. The sedimentologic characteristics of the detritus material containing large amounts of fine sediment is often responsible for triggering superficial talus destabilization and subsequent detachment and displacement of a thin layer of materials that drags fine sediment, stones and small boulders with it.