Rock-slope failure scars on sandstone mountains in NW Scotland
Amongst the most neglected landforms in formerly glaciated mountain environments are the scars of major rock-slope failures where the displaced rock or runout debris has been removed by glacial erosion. The characteristics of 33 such debris-free failure scars (DFFSs) on Torridonian sandstone terrain...
| Published in: | Proceedings of the Geologists' Association |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2024
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| Online Access: | https://research-portal.st-andrews.ac.uk/en/researchoutput/rockslope-failure-scars-on-sandstone-mountains-in-nw-scotland(69941602-2a51-4e84-9e09-d54a3d14d556).html https://doi.org/10.1016/j.pgeola.2024.05.003 |
| Summary: | Amongst the most neglected landforms in formerly glaciated mountain environments are the scars of major rock-slope failures where the displaced rock or runout debris has been removed by glacial erosion. The characteristics of 33 such debris-free failure scars (DFFSs) on Torridonian sandstone terrain were analysed. These range from 0.011 to 0.183 km2 in ground area, and scar volume implies removal of ~0.4–9.9 Mt of rock. Failure planes are planar or stepped at gradients of 37–50°, implying failure as ‘rough’ translational slides; most probably represent former rock avalanches or fragmented rockslides where shear through bedding planes resulted in runout fragmentation. Extension of 85 % to the slope crest is consistent with coseismic triggering during periods of glacio-isostatic crustal uplift. At least ten DFFSs demonstrably pre-date expansion of the last ice sheet at ~35 ka, and at least five probably represent failure that occurred in the Lateglacial interval of ~16–11.7 ka. Fourteen are located within cirques, confirming the importance of RSFs in cirque extension during ice-free interglacials or interstades; others have contributed to trough widening and the formation of arêtes. Older upper-slope cavities in Torridonian mountains are probably also the results of (possibly recurrent) rock-slope failures. It is concluded that the large-scale morphology of the Torridonian sandstone mountains reflects a long-term synergic relationship between alternating episodes of glacial erosion and rock-slope failure: reduction of rock-slope stability during each glacial-deglacial cycle has predisposed slopes to eventual failure, with subsequent glacial removal of displaced blocks and runout debris. |
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