Comparison of Mass Wasting Processes on the Slopes of the Rockall Trough, Northeast Atlantic

The deep-water, sediment-starved Rockall Trough separates the western Irish shelf from the Rockall Bank. Both margins have narrow, steep slopes that connect the continental shelf with the deeper basin but differ in their underlying geological controls and sediment transport processes. We compare and contrast the opposing margins of the Rockall Trough and review the size, depth distribution and degree of mass wasting processes and associated geohazard risk on each margin.Rapid contourite buildup, shallow underlying abrupt basement topography and slope oversteepening due to erosion at the base of the western margin have led to large slope failures such as the Rockall Bank Slide Complex. In contrast, the eastern margin of the Rockall Trough marked the westernmost extent of the British Irish Ice Sheet, reflected on the shelf by the presence of end moraines. Sediment was delivered by meltwater discharged from the ice sheet which locally reached the shelf edge. In conjunction with the effect of erosion from bottom currents and localised slope failures, the waning of the ice sheet led to the formation of numerous canyons incising this slope. Slope failures on the eastern margin were relatively small and sediment was progressively evacuated towards the deeper basin through canyons. In contrast, mass wasting on the western margin involved larger sediment volumes. Processes resulting in mass wasting on the western margin are likely to be still active.In contrast, the eastern margin that was glacially nourished is likely to be less active with only minor mass wasting resulting from contour current scour and local canyon margin collapse.