Glacially moulded landslide runout debris in the Scottish Highlands

• Published in: Scottish Geographical Journal
• Main Author: Ballantyne, Colin K.
• Other Authors: University of St Andrews. School of Geography & Sustainable Development
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Glacial bedforms; Hummocks; Lateglacial; Loch Lomond Stade; Rock avalanche; Rock-slope failure; G Geography (General); NDAS; G1; Ice Sheet
• Online Access: https://hdl.handle.net/10023/18130; https://doi.org/10.1080/14702541.2018.1501085

A tongue of hummocky terrain ∼1 km long and ∼400 m wide extends downslope from the source area of a rock-slope failure that formed the summit arête of Sgùrr nan Ceathreamhnan in the NW Highlands. The tongue descends from ∼810 m to ∼650 m, crosses a corrie obliquely and laps onto an opposing slope. Individual hummocks are circular to elongate, up to 6 m high and streamlined. A possible origin as recessional or ice-stagnation moraines is inconsistent with hummock morphology and the alignment of the hummock belt, and the streamlining of the hummocks is incompatible with the form of unmodified rock-avalanche runout hummocks. It is proposed that the tongue of hummocky terrain represents rock-slope failure during or after ice-sheet deglaciation, and subsequent modification of runout debris by subglacial erosion during the Loch Lomond Stade (∼12.9–11.7 ka). This interpretation implies (i) that the debris was deposited by an excess-runout rock avalanche; (ii) that the glacier that subsequently occupied the corrie was warm-based; (iii) that Lateglacial landslide runout debris was not invariably evacuated by Loch Lomond Stadial glaciers, as previously suggested; and (iv) that some features interpreted as hummocky moraines elsewhere may have a similar origin. Peer reviewed