ALBERT

Description: The Hakon Mosby Mud Volcano (HMMV) in 1100 m water depth on the continental slope off Northern Norway was mapped with multibeam microbathymetry systems attached to the scientific ROV Victor 6000 during the ARK XIX 3/b expedition of R/V Polarstern (June-July 2003). Two multibeam systems were used: a Reson SeaBat 8125 (455 kHz, 1°x0.5°, 44 hours diving producing 235 millions of soundings) and a Simrad EM2000 (200kHz, 1.5°x3.5°, 15 hours diving producing 19 millions of soundings). Data were processed with the Ifremer CARAIBES software?, including (1) graphic and interactive ROV navigation adjustment using bathymetry as a reference, (2) roll and pitch calibration and tide correction, (3) ping editing and filtering to de-spike erroneous soundings. A final bathymetric map (grid size of 0.5 meter) has been produced using mainly Reson SeaBat 8125 data, filling the gaps with Simrad EM2000 data.We present the microbathymetric map. The seafloor morphology of the HMMV is characterized by a polygonal central body, up to 1 km across, surrounded by circular moats. The bathymetric map illustrates important seafloor features in considerable detail. The downslope and upslope edges of the central body have a NE/SW direction. This direction is also the dominant direction of a number of fractures and fissures that can be traced across the volcano. Several individual mud flows can be identified Recent mud flows all appear to originate from the central part of the mud volcano. They have formed a large flat area in the southern half of the volcano. Outside this flat area, older flows, characterized by a rough topography and a surface elevation of up to 10 m with respect to the flat area, could have been disrupted and pushed aside by the younger flows emitted at the center.The microbathymetry map provides important clues to the geological functionning of the HMMV. It puts contraints on the relative ages of seafloor compartments. It brings an essential background information for the interpretation of in situ measurements and samples.