The significance of contourites for submarine slope stability

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Laberg, Jan Sverre۱; Camerlenghi, Angelo۲
Holding Date 29 September 2008

Slope instabilities in areas of contouritic deposits have been identified on continental slopes, rises and in ocean gateways, including some of the largest submarine landslides known as the Storegga and Trænadjupet Slides offshore Norway. Contouritic sediments are prone to failure because: (1) their composition, geometry and location; well sorted muddy or sandy sediments forming sediment mounds on the continental slope and rise that may experience liquefaction in response to cyclic loading; (2) they are often characterised by high sedimentation rates implying high water content and under-consolidation and thus low shear strength; (3) they could, due to their location on continental slopes, be subjected to rapid loading; on high-latitude margins as offshore Norway excess pore pressure may develop within contourites sandwiched between glacigenic sediments; (4) excess pore pressure could also develop from gas migration and gas-hydrate dissociation due to a relatively high organic-carbon content from often productive water masses along continental margins. When failing, the area affected by mass wasting can be large because the contourites may have a very large areal distribution due to the intrabasinal extent of the thermohaline and geostrophic current systems. Their weakness and resulting low shear strength may also, at least partly, explain why some of the large landslides involving contouritic sediments also show a very long run-out (up to hundreds of kilometers) on gentle slopes.
Acknowledgement This work is a contribution to IGCP 511 (Submarine Mass Movements and Their Consequences).