'Ice covering the shallow straits and bays begins to form by the end of November, while the rest of Baikal freezes by the middle of January. 'This kind of ice, the purest, can only be seen in some areas of the lake in November and December', said Stanislav Tolstev, 46, photographer and tour guide from Irkutsk. 'The first time I paid attention to these bubbles was about four years ago, then I learned to distinguish methane from air bubbles."
Baikal is located in a rift zone which is a deep - in fact the largest on the planet - crack in the Earth's crust which narrows at depths of several dozen kilometres. It does not have a solid bottom: instead there is a cushion of bottom sediments that has been filling the most narrow lower part of the crack for millions of years. These bottom sediments are similar to bogs in that they contain a lot of gas, including methane.
In deep winter, there are roads over the ice, but the larger methane bubbles pose a threat. 'There are areas of the lake where bubbles grow so big that cars fall through the ice,' he said. 'The location may vary from year to year, and usually the large bubbles appear starting from February and can be seen through March and April.'
Scientists monitor methane rising from the floor of Baikal, and while it is said to be increasing, they have disputed this is due to global warming.
More on this at : https://www.sott.net/article/444866-Beauty-of-frozen-methane-bubbles-on-the-worlds-deepest-lake-shown-in-stunning-video