A vast hole appearing in the frozen ground of Siberia is a head-scratcher; 20 of them blasting through more than 500 feet of permafrost is downright mind-boggling. That’s the puzzle scientists have wrestled with since 2014, when the first 100-foot-wide crater erupted through ground that had been frozen solid for hundreds of thousands of years. Since then, numerous craters have followed in the wake of the first, raising questions about the stability of the region’s permafrost and the mysterious geology that lies beneath.

Covering most of Russia and northern Kazakhstan, Siberia is best known for its climate, which is marked by long, dry winters. Although not always a frozen wilderness, the region experiences sub-freezing temperatures for months at a time, allowing the soil and rock to remain frozen in a state called permafrost. Eight years ago, helicopter pilots flying over Siberia’s Yamal Peninsula discovered a strange sight: a “spectacular” crater that appeared to have swallowed hundreds of square meters of earth and stretched more than 170 feet deep.

More than a dozen similar craters followed, dotting the Siberian landscape as TV crews and satellite images mottled them one by one. These gaping holes didn’t just terrify those who lived and worked throughout the region; they were the manifestation of something strange and potentially dangerous underground. Now, in a paper for Geophysical Research Lettersresearchers from the University of Cambridge in England and the University of Granada in Spain detail how and why these craters formed.

Permafrost crater found on the Yamal Peninsula in 2014. Credit: Morgado, A. et al., Geophysical Research Letters, 2024

Permafrost is not just soil and rock; everything is stuck to the ice. Beneath that ice is a layer of solid methane known as “methane hydrates.” Sometimes a third layer hides between the sediment and its bed of methane: “cryopegs,” or pockets of liquid salty water.

According to scientists, cryopeges form when warmer surface temperatures cause the frozen “glue” of permafrost to melt. This water seeps through the ground and hits methane hydrates, forming pools of liquid. As the basins grow, so does the pressure beneath the permafrost, and eventually cracks form at the surface. On a large enough scale, these cracks produce such a rapid drop in pressure that the methane hydrates break apart, resulting in an explosion of methane gas.

These explosions are believed to be responsible for the sudden appearance of monstrous holes in the ground. And if these researchers are right, Siberia can expect to see more gas developments in the future. Not only has climate change triggered melting permafrost throughout the Arctic, but large bursts of methane gas create a environmental feedback loop which exacerbates the greenhouse effect, which could then trigger more crater explosions. The team calls this phenomenon “osmotic pumping” in their paper.

“We believe that, in addition to being of direct relevance to permafrost researchers, this work will be of interest to a large number of people involved in climate change research,” the team writes, “because the mechanism we uncover of osmotic pumping leading to permafrost . explosions have potentially serious consequences.”