Scientists may have come a step closer to uncovering the mystery of giant exploding craters in western Siberia.
The craters, called gas emission craters (GECs), were first spotted in the Yamal and Gydan peninsulas in western Siberia in 2014.
The underground gas explosions lead to materials on the surface above, such as mud or soil, being ejected hundreds of metres into the air.
Researchers have spent a decade working on theories for how they were formed.
"GECs have so far only been observed in the Yamal and Gydan peninsulas, suggesting that some specifics in this region can trigger the formation only here and not elsewhere in the vast Arctic belt of permafrost," researchers wrote in a new study published in the journal Science of the Total Environment.
They added: "The recent discovery of GECs in Western Siberia has challenged researchers for the past decade.
"The GECs have only been observed in this limited region."
Many researchers have suggested that the soil's internal processes are responsible for the formation of the GECs.
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Researchers have been working on theories of how they were formed for a decade
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But the new study, published this month, suggests heat and gas below the surface was instead the explanation.
Researchers said: "This study critically reviews the existing models and concludes that focused deep heat and gas from below the permafrost may be the key factor allowing the formation of GECs."
The study said atmospheric heating is also believed to trigger their formation.
The exploding craters appear to form where warmer, unfrozen ground under lakes meets thinner frozen ground, researchers added.
The formation of GECs has also been connected to global climate change.
Researchers made reference to "unusually high temperatures" in the winter and summer prior to the formation of the crater in the Yamal peninsula in 2014.
"Although this was based on a very short time series (2006–2014), it is well known that Western Siberia has experienced unprecedented warming since the Little Ice Age culminated about 200 years ago," the study said.