Slope instability of Arctic Trough Mouth Fans: An example off Storfjorden, NW Barents Sea.

Submarine slope instability plays a major role in the development of Arctic Trough Mouth Fans (TMFs). TMFs consist of an alternation of rapidly deposited glacigenic debris flows and a sequence of well-layered plumites and hemipelagic sediments. In this sedimentary context, shallow geophysical data and core samples indicate that there is a specific timing (i.e. shortly after the deglaciation phase) for the occurrence of slope failures. High mean sedimentation rates during glacial maxima of up to 18 kg m-2 yr-1 likely allow excess pore pressure to develop in the water rich plumites and hemipelagic sediments deposited in the previous deglacial period, particularly where such plumites attain a significant thickness. To test this hypothesis, we conduct basin numerical modeling considering the effect of ice stream sediment dispersal patterns and polar margin architecture on resulting stresses, fluid flow focusing and slope failure initiation. The 2D finite element model is based on geophysical, sedimentological and geotechnical data of the Storfjorden Trough Mouth Fan, NW Barents Sea. We find that, during glacial maxima, ice streams and rapid accumulation of glacigenic debris flows on the slope induce pore pressure build-up in continental shelf/upper slope sediments . The overpressure developed during glacial maxima remains during the deglacial phase. This overpressure combined with downslope stratification of high water content and low shear strength deglacial/interglacial sediments results in a significant decrease in the factor of safety of the upper slope sediments. The position of the submarine landslides in the stratigraphic record suggest, however, that such excess pore pressure is not enough to trigger the slope failures and indicate that earthquakes related to isostatic rebound are likely involved in the final activation.