The morphology, setting and processes of the Afen Slide

Abstract: Identified in 1996, during an environmental survey for the Atlantic Frontiers Environment Network, the Afen Slide lies around 95 km northwest of the Shetland Islands. The head of the slide is at a water depth of 830 mbsl, and the debris lobe stretches to over 1120 mbsl along a slope varying from around 0.7° to 2.5°. The overall length (head scarp to toe of lobe) of the slide is in excess of 12 km, and the maximum width attained is around 4.5 km. The relative timing of the various phases can be determined from the morphology, imaged using seabed picks from 3D exploration seismics, and high-resolution deep-tow boomer data. These seem to show at least four major phases of failure and several distinct modes of sediment transport, ranging from hydroplaning to block sliding. The most likely trigger for the failure is a seismic event focused on the nearby Victory Transfer Zone. Sensitising factors include the presence of contouritic sands directly beneath the surface of rupture. These would serve as a plane of weakness and, under seismic loading, may further weaken due to liquefaction. Indeed, previous studies have shown that the slope in this area is stable in the absence of external triggers. The processes of sediment transport subsequent to failure are also investigated using sediment cores, as well as the 2D and 3D seismic, and appear to indicate that flow transformation occurred in at least the first phase of mass movement. [Copyright &y& Elsevier]