Paraglacial rock-slope failures in Wasdale, western Lake District, England: morphology, styles and significance

Five sites of rock-slope failure are described from glaciated hill slopes in Wasdale, western Lake District. There are some distinct morphological variations and clear differences in failure styles among the sites but none of them appears to have been modified by glacier ice. It is inferred that they post-date the Last Glacial Maximum (c. 21±3 cal. ka BP) and, in one case, possibly the Loch Lomond Stade glaciation (12.9-11.5 cal. ka BP). More precise dates for the failures are unavailable and they might be of different ages. The failures are regarded as paraglacial (glacially-conditioned), that is, resulting from readjustments to rock-slope stress fields following loss of ice. It is possible that stress release and seismic activity combined to trigger failure. Three of the failures have scarp-edge locations and these are probably residual components of greater failures of unknown size and style that provided substantial amounts of coarse rock debris to the Wast Water screes and also contributed to the widening of Wasdale. Based on these sites, a preliminary conceptual model of talus slope development is proposed. The morphology and aspect of the other two sites suggest they could become sites of cirque initiation following removal of their failed materials. All five failures have led to reductions in the mass of their respective mountain blocks, suggesting that paraglacial rock-slope failures may have played a greater role than previously appreciated in the evolution of the Lake District landscape.