These solid compounds, formed at certain pressure and temperature from methane and water, are mainly found in oceans (in layers located several hundred meters under seabed) and in permafrost areas. It is much more seldom that they are found close to the bottom (several meters below only) within the boundaries of gas-emitting structures which are similar to mud volcanoes. They can be found in the Black, Caspian, Mediterranean and Okhotsk seas and even in fresh water bodies.
It was back in 1992 that experts spoke for the first time of the possible presence of such compounds in sedimentary rock on the bottom of Lake Baikal. The information came from a Russian-American deep-water seismic expedition which investigated the Southern and Central trenches of the lake. A seismic signal known as BSR (Bottom Simulating Reflector) traced deep within the lake several hundred meters of sedimentary rock. This made it possible to anticipate the presence of gas-hydrates in this area.
The year 1998 saw the beginning of Russian-Belgian studies on the Baikal aimed at a detailed assessment of its near-bottom structures. These studies were later described by Prof. Jan Clarx of the Royal Museum of Central Africa (Belgium). In the summer of 1999 the expedition organized by the Institute of Lymnology of the Siberian Branch of the Russian Academy of Sciences, and led by Prof. Mark de Batiste of the University of Ghent (Belgium), investigated the bottom of the lake and sedimentary strata in a trench south of the Selenga delta.
Seismic recordings helped to identify all of the BSR peculiarities and obtain clear outlines of the zone of disintegration of the layer of gas-hydrates along the rifts. Also found at that time were vertical channels through which gas travels along the rifts and reaches the bottom.
At the same time researchers from the All-Russia Institute of Oceanography at St. Petersburg, using a hydro-sounding station of lateral coverage, obtained profiles over the gas emission zone wherein these structures are clearly outlined. Clearly visible on these diagrams are clusters of mud volcanoes in three separate areas of gas discharge, with craters of some 2 km in diameter. Taking part in that expedition were also the Royal Museum of Central Africa (Belgium), the Joint Institute of Geology, Geophysics and Mineralogy, and the Institute of Chemical Kinetics and Combustion (both of the RAS Siberian Branch).
The next expedition for the studies of gas-hydrates in the bottom sediments of Lake Baikal was conducted in the winter of the year 2000. Its main task was to add up to the collection of bottom probes obtained during the summer, and, despite the bitter cold and gales and snowstorms, the winch operator lifted up bottom core samples one after the other. On March 21 the man responsible for drilling operations, O. Khiystov, spotted bubbles of gas streaming up towards the surface of the lake. The drilling bit was hoisted up from the water and the researchers found, after the usual 40 cm of sediments, large crystals of gas-hydrates some 7 cm in size in a layer of about 10 cm thick. Gas- hydrates were discovered in subsequent cope samples too.
The data obtained by echo sounding through ice made it possible to draw up a detailed topographical bottom map of this area. It shows a zone with gas- hydrates being located in a crater stretching from east to west.
The discovery of these compounds in the bottom sediments of Lake Baikal is of special importance because this was the first time that gas-hydrates have been found at a shallow depth and in fresh water. The first and foremost task facing the researchers now is to draw up a topographical map of the whole bottom of the lake. This will help trace the distribution patterns of all such important compounds and assess their connection with tectonic processes which are still in progress in this basin. Another task is to study the chemical characteristics of the local gas-hydrates.
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