A decade ago, a mysterious crater appeared in the Russian Arctic, forming a huge jagged hole hundreds of feet wide, that sank into an inky abyss. It was surrounded by huge chunks of dirt and ice, evidence of the violent forces that created it.

Since 2014, more than 20 such craters have erupted, dotting the remote landscape of north-west Siberia’s Yamal and Gydan peninsulas – the latest of which was discovered last August.

The craters have caused a “headache” for scientists, who have spent years trying to uncover how they formed. A number of theories were created such as by a meteorite strike or even by aliens.

Now, a team of scientists says they’ve come up with a new explanation that may explain their creation, according to CNN. Their findings, presented in a study published last month, suggest that it is a mixture of climate change caused by humans in combination with unusual geology of the area.

Scientists used to agree that the craters form when gases trapped beneath the tundra – including planet-warming methane – build up underground, causing a mound to appear on the surface. When the pressure below exceeds the force of the ground above, the dike explodes, spewing gases.

What is still debated are the more specific mechanisms, namely how the pressure is created and where exactly the gas comes from.

The team that launched the new research first looked at whether the explosions might have been chemical reactions, but this was quickly ruled out. “There were no reports of anything related to chemical combustion,” said Ana Morgado, study author and chemical engineer at the University of Cambridge.

What the researchers found revolves around the complex geology of this particular part of Siberia. Under the ground there is thick permafrost – a jumble of soil, rock and sediment held together by ice. Beneath this is a layer of “methane hydrate”, a solid form of methane. Between the two are unusual pits, about 3 feet thick, of salty, unfrozen water called “cryopegs.”

As climate change leads to warmer temperatures, the top layer of soil is melting, causing water to flow through the permafrost and seep into this salty layer, according to the research.

The problem is that there is not enough room for the extra water, so the “cryopeg” swells, the pressure increases and the soil breaks, creating cracks in the surface. These cracks cause a rapid pressure drop at depth, destroying the methane hydrates and causing an explosive release of gas. This complex dance between melting permafrost and methane can take decades before an eruption occurs, the study found.

The process “is very region-specific,” Morgado said, so while she believes they’ve solved the puzzle in this part of the Arctic, if similar craters show up in places with different geology, “maybe there’s another mystery to solve.”

Other scientists aren’t so sure the puzzle has been solved

Evgeny Chuvilin, chief scientist at the Skolkovo Institute of Science and Technology in Moscow, who has spent years studying the craters up close, said the idea of ​​the study is “novel” but brings back the idea that it fits the geology of the area.

Permafrost in northwestern Siberia is unusual for very high amounts of ice and methane, he told CNN. It would be difficult for water from the upper layer of the soil to pass through this thick, dense layer of ice to reach the “cryopegs” deep underground.

The findings are “still very general” and do not reflect the complexity of the region, he told CNN.

His own research focuses on in the accumulation of methane in cavities in the upper levels of the permafrost, before the pressure becomes high enough to explode.

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. He said that while the research made sense in theory, there were still “many possible sources of gas for these craters.”

Morgado said she was confident in her theory, but as she says “it can always be fleshed out by considering additional factors.”

What most scientists 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 the frozen rocks that overlay the subsurface ice with gas-saturated cavities,” Chuvilin said, making it easier for the gas to erupt from below. As climate change accelerates, he added, it could lead to greater permafrost degradation, powerful gas eruptions and new craters.

Schurmeier goes further to say that “climate change is probably a primary factor,” she said. Many of the craters appeared after unusually warm summers, and we should expect more of them as the Arctic warms, he added.

Not only are craters affected by climate change, they also contribute to it. Each eruption spews previously locked methane deep into 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 isn’t very significant in terms of its impact on global warming, Schurmeier said, “it’s a scary sign that the Arctic is changing.”

Scientists will continue to investigate these explosive phenomena, mainly because a better understanding of them could help in prediction. Most occur in remote places, but there are fears they could affect residential areas or oil and gas operations in the area.

For Morgado, these craters are proof that humans are changing the climate and destabilizing the Earth in new ways. “And it’s very fast,” he added, “it’s not millennia anymore, it’s happening in a few decades.”