Debris flows in settings that have experienced net glacial erosion within the UK's Ice-scoured Quaternary domain are the result of a complex interaction of a range of geological and geomorphological factors. On the 11^th of August 2016 a rainfall-triggered debris flow deposited 100 t of sediment onto local road and rail infrastructure blocking transport between town of Fort William and port of Mallaig in north-west Scotland. The debris flow occurred in an ice-scoured setting, where current 1:50,000-scale geological maps suggest that little or no sediment is expected on the valley slopes. In this study, we show how weathering and mass-wasting processes have interacted with bedrock structures to fill localised depressions with sediment on the upper parts of the slope. The intense rainfall event of August 2016 caused the destabilisation of this localised sediment, with eventual failure along bedrock joint surfaces resulting in two debris flows. This study demonstrates the combination of processes that can result in thick accumulations of sediment on slopes that are otherwise generally lacking in superficial sediment cover. These sediment accumulations have the potential to pose a significant landslide hazard in areas that might previously have been thought of as lower susceptibility. The research illustrates a need to improve understanding and representation of sediment thickness and distribution on hill slopes – particularly those that show an absence of superficial deposits at the scale of currently available geological maps.

英国第四纪冰域内经历过净冰川侵蚀的环境中的碎屑流是一系列地质和地貌因素复杂相互作用的结果。11^日2016 年 8 月，一场降雨引发的泥石流将 100 吨泥沙沉积在当地公路和铁路基础设施上，阻碍了威廉堡镇和苏格兰西北部马莱格港之间的交通。泥石流发生在冰层冲刷的环境中，目前的 1:50,000 比例尺地质图表明，预计山谷斜坡上几乎没有沉积物。在这项研究中，我们展示了风化和质量消耗过程如何与基岩结构相互作用，从而用斜坡上部的沉积物填充局部凹陷。2016 年 8 月的强降雨事件导致这种局部沉积物不稳定，最终沿基岩节理面发生破坏，导致两次泥石流。这项研究表明，这些过程的组合可能导致斜坡上沉积厚厚的沉积物，否则通常缺乏表层沉积物覆盖。这些沉积物堆积有可能在以前被认为是低敏感性的地区造成严重的滑坡灾害。该研究表明，需要提高对山坡上沉积物厚度和分布的理解和表示，特别是那些在当前可用地质图的尺度上显示没有表层沉积物的山坡。