Rock slope failure in the British mountains

Abstract

In this first full review of extant Quaternary Rock Slope Failure (RSF) in the British mountains, we provide a near-complete inventory of 1082 sites, 40% being rock slope deformations, 40% arrested rockslides, and 20% rock avalanches. Current RSF activity is negligible, and this relict population is predominantly paraglacial, with a parafluvial minority. Its spatial distribution is perplexing, with RSF density varying greatly, both regionally and locally. In the Scottish Highlands, eight main clusters account for 76% of RSF area in 15% of the montane area. Local concentrations occur in all the British ranges, across high and low relief, in core and peripheral locations, and on varied geological and glaciological domains; as conversely do extensive areas of sparsity, even in similar lithologies. Generic interpretations are thus precluded. Geology is only a secondary control. An association with Concentrated Erosion of Bedrock (CEB) is proposed, as a driver of intensified slope stresses. CEB is most evident at those glacial breaches of main divides where the most vigorous recent incision is inferred, and also in some trough-heads. A clear association between RSFs and these ‘late-developing’ breaches is demonstrated in the Highlands, in 42 localities, with sparsity away from them. It is also seen in seven Lake District localities. Glaciological models identify ice sheet volatility capable of driving breach ramification. High-magnitude paleoseismic events are generally unlikely to have provoked RSF clusters; a few candidates are considered. RSF has been underrated as an agent of mountain landscape evolution in Britain; its spatio-temporal incidence may assist in calibrating regional ice sheet models, and in assessing climate change impacts. We argue that the CEB:RSF association has global relevance in identifying primary drivers of mass movement in bedrock.