Seabed morphology and gas venting in the Black Sea mudvolcano area: Observations with the MAK-1 deep-tow sidescan sonar and bottom profiler

Abstract

The central part of the Black Sea was investigated with the MAK-1 deep-tow acoustic system providing sidescan observations and acoustic profiling. Subsequently underwater TV recordings and bottom sampling was done in an area with extensive mudvolcanism. The mud volcanoes can be divided into three types according to their dimensions and morphology. The first type has a seabed diameter of more than 2 km, reaches a height of 100–150 m, has a complex top with a crater-like structure and gentle slopes, and reflects massive mudflows in the crater and at its flanks. The second type has smaller dimensions, is more conical in cross-section almost without relief on its relatively steep slopes, and is characterised by small, radial mudflows. The third type is made up by the only mud volcano with a partially collapsed rim and with massive and liquid mudflows. The first type expectedly is in a mature, relatively passive stage, the latter two types seem to be younger and more active. Various types of low relief slides are found in the area and are related to the presence of shallow subbottom gas (40–100 m below the seafloor) or mudvolcano activity. Evidence for the presence of gas in the mudvolcano area is shown by gas venting, acoustic turbidity (acoustic masking), numerous pockmarks, acoustic voids, and acoustic windows. Gashydrates do occur associated with some of the mudvolcanoes.