Haakon Mosby Mud Volcano: Terrain model and multibeam backscatter analyses

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Beyer, A. , Rathlau, R. and Schenke, H. W. (2004): Haakon Mosby Mud Volcano: Terrain model and multibeam backscatter analyses , EGU General Assembly 2004, Nice, FranceApril 2004. .
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During a recent cruise of the German R/V Polarstern detailed investigations of the Haakon Mosby Mud Volcano (HMMV) have been carried out. Prior to the biological, geophysical and geochemical data acquisition, a high resolution multibeam survey was accomplished. The obtained precise bathymetric data served as basis for the subsequent sampling.HMMV is located at the continental slope of the western Barents Sea between Norway and Svalbard in a water depth of 1270m. We were able to map the height variations of HMMV very precisely, although the accuracy of the deployed multibeam echo sounder Hydrosweep DS-2 is between 0.5 and 1% of the water depth. Due to the slow ship speed (5knots) and the dense line spacing (approx. 200m) with a corresponding multiple overlap, typical multibeam artefacts are avoided around the center of HMMV.The area of HMMV can be characterized by three zones. The central structure of the volcano has a diameter of about 950m and its rim shows a maximum height of only 12m with respect to the surroundings. Around the central elevation of HMMV a circular dyke exists with 2m height and 100m width. The diameter is approx. 1350m. This structure is most pronounced in the north. The zone of the surrounding slope that seems to be influenced by the HMMV activity, indicated by a change in surface slope, has a diameter of 2500m.The echo intensity of the acoustic pulse has been analysed as well. Multibeam backscatter analyses of HMMV revealed three different acoustic provinces. The flattish center of HMMV shows highest reflectivity values (-37.0dB). The rim of the central structure of the volcano has a variable micro topography and moderate backscatter values (-40.4dB). Whereas the normalised backscatter of the area in between this rim and the circular dyke is lowest (-43.5dB). These results imply a clear change of seafloor properties within a very small area. The shape of the angular backscatter curve also varies between different segments of HMMV. We think that the backscatter variations are due to different micro topography and may also be influenced by subsurface gas hydrate occurrence. The backscatter data of the surrounding sediments show homogenous seafloor properties north and east of HMMV. The western side however, indicates mud flows which originate from the center of HMMV. Their flow direction is focused downslope. The combination of bathymetry and backscatter data points to a good correlation at the center of HMMV. However, the mud flow at the western side is only visible in the angular backscatter data.

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