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The Afen Slide

Wilson, C.K.; Bulat, J.; Long, D.. 2005 The Afen Slide. British Geological Survey, 121pp. (CR/05/003N) (Unpublished)

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Abstract/Summary

Summary Identified in 1996, as part of an environmental survey for the Atlantic Frontiers Environment Network (Graham et al 1996, Masson et al 1996), the Afen Slide lies around 95 km northwest off the Shetland Islands. Using seabed picks from 3D exploration seismics reveals the detailed morphology of the slide (Bulat 2001) enabling interpretations about the phases and nature of movement to be made. The head of the slide is at water depth of 830 mbsl and the debris lobe stretches to over 1120 mbsl along a slope varying from >2o to <1o. The overall length 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 with some certainty although the absolute age of the slide or the various phases is more difficult to confirm. There are two 14C dates from the area, one from the surficial sediments within the slide scar (Holmes et al 1997) and the other from within the debris lobe. These suggest a possible first movement at around 16,000 –13,000 years BP with the later retrogressive phases occurring after 5,800 years BP. These are highly speculative, as the exact relationship of the dated material to the post slide stratigraphy is not known. The seismic data combined with information from previous studies indicates that sedimentation in the area is controlled by along slope processes; mounded elongate contourites can be traced through the surrounding area. The seismic record suggests that the depositional environment has remained remarkably consistent since the onset of the last glacial. This may have contributed to the conditions that combined to produce slope failure in this particular area. An abundance of contouritic sands predisposed to liquefaction interspersed with fine-grained low permeability muds would provide a plane of weakness along which failure could propagate. However, the seismicity, necessary to cause liquefaction, during the period in question is not known although threshold values for failure have been calculated to be within the 10,000 yr return period (Hobbs et al 1997).

Item Type: Publication - Report (UNSPECIFIED)
Programmes: BGS Programmes > Marine, Coastal and Hydrocarbons
Funders/Sponsors: Western Frontiers Association, EU 5th Framework
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
Additional Keywords: Faroe Shetland Channel, submarine landslide
NORA Subject Terms: Earth Sciences
Marine Sciences
Date made live: 14 Jan 2015 12:50 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/508870

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