A decade ago, a mysterious crater appeared in the Russian Arctic, forming a huge jagged hole hundreds of feet wide, plunging down into an inky abyss. It was surrounded by enormous chunks of soil and ice, testament to the violent forces that created it.
Since 2014, more than 20 such craters have exploded, pockmarking the remote landscape of northwestern Siberia’s Yamal and Gydan Peninsulas — the most recent of which was discovered in August.
The craters have both intrigued and baffled scientists, who have spent years trying to unravel how they erupted into existence. A series of hypotheses have emerged, including wilder theories like a meteor strike or even aliens.
Now, a team of engineers, physicists and computer scientists say they have found a new explanation. Their findings, set out in a study published last month, suggest it’s a mix of human-caused climate change and the region’s unusual geology.
Scientists were already in general agreement the craters form when gases trapped beneath the tundra — including planet-heating methane — build up underground, causing a mound to appear on the surface. When the pressure below exceeds the strength of the ground above, the mound explodes, belching out gases.
What’s still up for debate are the more specific mechanisms of how the pressure builds, and exactly where the gas comes from.
The team behind the new research decided to approach the questions like detective work, said Ana Morgado, a study author and chemical engineer at the University of Cambridge.
They first considered whether the explosions might be chemical reactions, but this was quickly ruled out. “There was no reporting of anything related to chemical combustion,” Morgado said.
It had to be physical then, she told CNN, “like pumping up a tire.”
What the researchers found revolves around the complex geology of this specific slice of Siberia.
It goes like this: beneath the ground is thick permafrost — a jumble of soil, rocks and sediment held together by ice. Underneath this sits a layer of “methane hydrates,” a solid form of methane.
Sandwiched between the two are unusual pockets, about 3-feet thick, of salty, unfrozen water called “cryopegs.”
As climate change drives warmer temperatures, the top layer of soil is melting, causing water to trickle down through the permafrost and into the cryopeg, seeping into this salty layer, according to the research.
The problem is, there’s not enough space for the extra water, so the cryopeg swells, pressure builds and the ground fractures, sending cracks to the surface. These cracks cause a swift drop in pressure in the depths, damaging the methane hydrates and causing an explosive release of gas.
This complex dance between melting permafrost and methane can last decades before an explosion happens, the study found.
The process “is very specific to the region,” Morgado said, so while she believes they have solved the puzzle in this part of the Arctic, if similar explosive craters appear in places with different geology, “there might be another mystery to solve.”
Other scientists are less sure the puzzle has been cracked.
Evgeny Chuvilin, lead research scientist at the Skolkovo Institute of Science and Technology in Moscow, who has spent years studying the craters up close, said the study’s idea is “novel” but pushes back on the idea it fits with the region’s geology.
The permafrost in northwestern Siberia is unusual for its very high amounts of both ice and methane, he told CNN. It would be hard for water from the top layer of soil to push through this thick, ice-dense layer to reach the cryopegs deep beneath the ground.
The findings are “still too general” and don’t account for the complexities of the region, he told CNN.
His own research focuses on methane building up in cavities in the upper levels of the permafrost, before the pressure gets so high it explodes.
There is still more to be done to help solve the mysteries of exactly how this process unfolds, he said.
His caution is echoed by Lauren Schurmeier, a geophysicist at the University of Hawaii. She said while the research made sense in theory, there were still “many potential gas sources for these craters.”
Morgado said she was confident in the theory but “it can always be enriched by considering additional factors,” she added.
What most scientists do agree on, however, is that climate change is playing a role, and may lead to an increase in these explosive craters in the future.
Global warming “affects the strength of frozen rock overlying the underground ice with gas-saturated cavities,’ Chuvilin said, making it easier for the gas to burst out from below. As climate change accelerates, he added, it may lead to more permafrost degradation, powerful gas blowouts and new craters.
Schurmeier goes further. “Climate change is likely a primary driver,” she said. Many of the craters appeared after unusually warm summers and we should expect more of them as the Arctic warms, she added.
Not only are the craters affected by climate change, they also contribute to it. Each explosion belches out methane that was previously locked away, deep in the earth, a gas up to 80 times more effective at trapping heat in the atmosphere than carbon dioxide in the short term.
While the methane produced by each individual crater is not hugely significant in terms of its impact on global warming, Schurmeier said, “they are a terrifying sign that the Arctic is changing.”
Scientists will carry on investigating these explosive phenomena, not least because better understanding them could help predict where they are likely to appear next. Most happen in remote parts, but there are fears they could affect residential areas or oil and gas operations in the region.
Experts already monitor some of region’s many mounds, said Vasily Bogoyavlensky, of the Oil and Gas Research Institute of the Russian Academy of Sciences, who has studied the craters. “It doesn’t mean that we can say that tomorrow will be a new explosion here,” he told CNN, but it allows them to keep tabs on the most critical areas.
For Morgado, these craters are evidence of humans changing the climate and destabilizing the Earth in new ways. “And it’s very fast,” she added, “it’s not millennia anymore; it happens in a couple of decades.”
