Lateglacial Rock-Slope Failures in the Scottish Highlands

Abstract

Recent dating of catastrophic rock-slope failures (RSFs) in the Scottish Highlands has confirmed that many occurred in the millennium following deglaciation. This implies that numerous Lateglacial RSFs occurred in the interval between ice-sheet deglaciation (˜15–14 ka) and the final retreat of glacier ice (12.5–11.5 ka) at the end of the Loch Lomond Stade (LLS), but have not been recorded because RSF runout debris was removed by LLS glaciers. The morphology of postglacial RSFs is used as a guide to identification of the failure sites of such Lateglacial RSFs. Key elements are a steep (>55°) headscarp separated by a pronounced break of slope from a subjacent quasi-rectilinear or stepped failure plane inclined at 35–45°; flank scarps, headscarp tension cracks and detached blocks may also be present. Inferred Lateglacial RSF sites occur on trough walls, spur ends and within cirques. Many small valley-side scarps lacking runout debris are inferred to represent sites of minor Lateglacial RSFs. The implications of these findings for trough development, mountain summit morphology and cirque evolution are discussed. Future research questions relating to RSF sites that predate the Last Glacial Maximum and the contribution of Lateglacial RSFs to the sediment budget of LLS glaciers are outlined.