Submarine landslides, Gulf of Mexico continental slope: insights into transport processes from fabrics and geotechnical data

Ursa Basin on the Gulf of Mexico continental slope is a site of extremely fast sedimentation, building thick sequences of underconsolidated and overpressured muds and clays. Frequent sliding created mass transport deposits (MTD). In a study of strength, frictional behaviour, and fabrics of IODP Expedition 308 drillcores we find that mass transport is governed by very low friction coefficients and peak shear strengths of the sediments. The majority of the samples shows velocity weakening, enabling runaway instabilities in the sediment once deformation has started. While sediments at the bases of MTD seem to strengthen by the sliding, those below the bases remain weak, constraining a hazard for slide reactivation. Submarine sediment sliding leaves a strong and irreversible imprint, changing fabric geometries, and reducing the pore space. This is a transport phenomenon leading to expulsion of large amounts of pore fluids during sliding. MTD transport is probably as cohesive bodies, defining a considerable geohazard potential