Rock-slope failure following Late Pleistocene deglaciation on tectonically stable mountainous terrain

• Published in: Quaternary Science Reviews
• Main Authors: Ballantyne, Colin, Sandeman, Graeme, Stone, John, Wilson, Peter
• Other Authors: University of St Andrews. Geography & Sustainable Development
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Rock-slope failure; Paraglacial; Stress-release; Palaeoseismicity; Cosmogenic isotopes; GB Physical geography; BDC; SDG 13 - Climate Action; GB; Ice; Ice Sheet; permafrost
• Online Access: http://hdl.handle.net/10023/5169; https://doi.org/10.1016/j.quascirev.2013.12.021

This work is supported by the Carnegie Trust for the Universities of Scotland and the UK Natural Environment Research Council Cosmogenic Isotope Facility (NERC-CIAF project 9046-0308) The ages of 31 postglacial rock-slope failures (RSFs) in Scotland and NW Ireland, derived from 89 cosmogenic isotope exposure ages, are employed to analyse the temporal pattern of failure and its relationship to the timing of deglaciation, rates of glacio-isostatic crustal uplift and periods of rapid climate change. RSF ages span almost the whole period since ice-sheet retreat, from 18.2 ± 1.2 ka to 1.7 ± 0.2 ka, or from 17.1 ± 1.0 ka to 1.5 ± 0.1 ka, depending on the production rate used in 10Be age calculation, but catastrophic failure of rock slopes was ∼4.6 times more frequent prior to ∼11.7 ka than during the Holocene. 95% of dated RSFs at sites deglaciated during retreat of the last ice sheet occurred within ∼5400 years after deglaciation, with peak RSF activity 1600–1700 years after deglaciation. This time lag is inferred to represent (1) stress release initiated by deglacial unloading, leading to (2) time-dependent rock mass strength degradation through progressive failure plane development, and ultimately (3) to either spontaneous kinematic release or failure triggered by some extrinsic mechanism. By contrast, 11 dated RSFs at sites reoccupied by glacier ice during the Younger Dryas Stade (YDS) of ∼12.9–11.7 ka exhibit no clear temporal pattern, suggesting that glacial reoccupance during the YDS was ineffective in preconditioning a renewed cycle of enhanced RSF activity. Comparison of timing of individual RSFs with that of deglaciation and rapid warming events at ∼14.7 ka and ∼11.7 ka suggests that glacial debuttressing, enhanced joint water pressures during deglaciation and thaw of permafrost ice in rock joints could have triggered failure in only a small number of cases. Conversely, the timing of maximum RSF activity following ice-sheet deglaciation corresponds broadly with maximum rates of glacio-isostatic crustal ...