According to a Russian scientist, Andrei Plekhanov, air near the bottom of these craters contained extremely high concentrations of methane. Methane usually composes just .000179% percent of air. At the bottom of one particular craters the methane concentration was 9.6%. The operating theory is that due to global warming the permafrost is melting and starting to collapse. The hard packed ice that used to form a solid containment barrier to the methane collapses, allowing the methane to push out the melting ice in a violent ejection which formed the crater.
Seven craters have been found so far, with dozens more likely existing across the trackless wastes of northern siberia. The gas escaping in these explosions is highly flammable, and can ignite. This had lead to concerns regard increasing amounts of natural gas production taking place in Siberia and possible risk of a methane explosions harming people. One of the craters is just a few kilometers away from a natural gas production facility. While as of yet no one has been harmed by these craters or methane explosions, the risk is there. Researchers are wary of going into the craters to study them, worried about the chance that there could be secondary methane geysers. Methane continues to leak from these craters, visible to the naked eye, rising up through the new crater lakes that form in them.
Researchers have called for more research in to this phenomenon. New expeditions are already planned, and soon more information will be available.
Source: Washington Post