The distribution and origin of shallow gas seeps in the vicinity of the Posolsky Bank in Lake Baikal were studied based on the integration of detailed seismic, multibeam, and hydro-acoustic water-column investigations. In all, 65 acoustic flares have been detected on the Posolsky Fault scarp near the crest of the bank and in a similar, nearby setting at water depths of -43 to -332 m. The seismic data reveal BSRs (bottom-simulating reflectors) occurring up to water depths of -300 m. Calculations involving hydrate stability, heat flow, and topographic modulation based on BSR occurrence and multibeam bathymetry enabled prediction of a methane-ethane gas mixture and heat-flow values that would account for gas hydrate stability in the lake sediments under prevailing ambient conditions. These predictions are supported by ground truth data. The findings suggest that seeps concentrated along the crest of the Posolsky Bank are fed mainly by gas coming from below the base of the gas hydrate stability zone, which would migrate updip via permeable stratigraphic pathways beneath the bank. Gas would ultimately be released into the water column where these pathways are cut off by faults
The article outlines the main approaches to studying the bottom topography of Lake Baikal and interpretation of bathymetric data. Measurement equipment and experimental data processing algorithms are described. A measuring complex is based on using the Kongsberg EM710S multibeam echosounder which allows one to take a detailed digital elevation model of the bottom. The paper demonstrates experimental results obtained during a series of expeditions to the Baikal in 2015 – 2019. Currently an area of about 12117 km2 (∼38%) of Lake Baikal bottom has been explored. Examples of a digital model of the Baikal bottom are also presented. The paper demonstrates 3D models of detected water columns showing intense of a gas bubbles emanation near the mouth of Selenga river, acoustic images of the Baikal Gigaton Volume Detector (Baikal-GVD), and a bathymetric map of Academician Ridge that was previously examined with the Mir 1 and Mir 2 in July 2009.
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