Mysterious Siberian craters linked to explosive methane releases

Since 2014, mysterious craters have started appearing in northwestern Siberia. According to reports, the most recent one formed in August of this year. The issue has drawn the attention of scientists who are trying to explain the mechanism of their formation. One hypothesis links the craters to natural gas deposits. Another suggests that the craters form after methane explosions caused by permafrost thawing.

After studying the craters, a team from the University of Cambridge and the University of Granada reached a slightly different conclusion. "There are very, very specific conditions that allow this phenomenon to occur," explains Ana Morgado, a chemical engineer from the University of Cambridge and one of the study's authors, as quoted by "Advancing Earth and Space Science. "We are talking about a very niche geological space," she added.

To solve the mystery, scientists asked themselves whether chemical or physical processes caused the explosions. As explained by Julyan Cartwright, a geophysicist with the Spanish National Research Council and a participant in the study, there are only "two ways to trigger an explosion". "Either a chemical reaction occurs, resulting in an explosion, like a dynamite blast, or you pump up a bicycle tire until it explodes—that's physics," indicated the scientist.

According to scientists, the mere thawing of permafrost is not enough to cause an explosion, although this process is hugely significant. Researchers have focused on cryopegs, pockets of cold brines, which might be closely related to the formation of craters in Siberia.

Underneath cryopegs lies a layer of crystallized methane hydrates (methane clathrate, methane hydrate). These are kept stable by the high pressure and low temperatures inside these cold brine pockets. The situation changes when water from thawing permafrost starts seeping into the brines.

In short, the entire process resembles a balloon bursting when too much gas fills it. The increasing pressure inside the cryopegs creates fissures in the soil, which travel upward from the cryopeg towards the surface.

The cracked soil then causes a sudden drop in pressure at depth. This change damages the methane hydrates below the cryopeg, causing methane to revert to a gaseous state and leading to a physical explosion.

According to scientists, this process is spread over decades, which means we don't observe these phenomena very often. At the same time, scientists warn that "the amount of methane released may have quite a significant impact on global warming".