Basement-controlled multiple slope collapses, Rockall Bank Slide Complex, NE Atlantic

The eastern flank of the Rockall Bank is dominated by the scarps of a large slide complex with unusual low aspect ratio (120km wide and 150km long). With the use of an extensive 2D seismic dataset, re-processed high-resolution multibeam bathymetry, a TOBI mosaic and one piston core we demonstrate that the headwall of the Rockall Bank Slide Complex (previously referred to as the Rockall Bank Mass Flow) may have occurred as a multiphase slope collapse in at least three episodes of instability since 16ka BP, with each of the events generating a slide with a more typical elongate morphology. Reconstructions of the pre-slide seafloor suggest a volume of collapsed sediments in the range265-765km³. Seismic facies investigation indicates that the slope and failed sediments comprise almost exclusively contourites that are prone to failure due to their well sorted character and high water content. A systematic examination of the slope morphology, seismic facies and sub-seafloor structures demonstrates a direct relationship between the RBSC seafloor scarps and the basement morphology. Focused fluid flow along basement-bounding faults, and/or differential compaction across the scarps, are considered to have had an important role in slope failure. This study highlights the importance of deeply-buried structures in the stability of slopes. It also shows how detailed examination of high-resolution data across large areas of slope instability can reveal smaller-scale multiple events. We believe that where contour-swept slopes are steep, the resulting intensification of near-bottom velocities prevents healing slope processes and as a result steep slope gradients remain steep and thus unstable.