The following link (see extracts below) leads to a discussion of the Yamal blowholes and includes an interview with Marina Leibman, a scientist at the Russian Academy of Sciences, who lead a team of scientists that visited the site of one of the holes (in mid-July 2014) that was approximately 30 meters in diameter and about 70 meters deep:http://www.eenews.net/stories/1060003940
Extract: ""I have an opinion, but no proof," said Marina Leibman …
In Leibman's view, an unusually warm summer in the Yamal region in 2012 caused extensive permafrost melt, which unleashed methane gas trapped in the ice and sediment. That expanding gas presence unleashed by melt in turn caused the permafrost to pop up like a cork, spraying debris in a visible ring around the created hole, she explained. The presence of the debris likely couldn't have happened without such a popping action, she said.
It was not an explosion, but more of an eruption that sprayed debris far from the hole itself. The visited chasm most likely formed in 2013, according to Leibman. The holes have to be relatively recent, because of vegetation patterns, further indicating that the warm summer of 2012 may have played a role, she said.
Despite concerns about methane release from permafrost generally, the 30-meter-wide (98.4 foot) funnel is not likely to be a constant source of gas after the initial blowout, according to researchers.
"Sure some methane was released as it is a reason for the whole thing ... but when we were there we measured methane content and it was higher than the normal but far from a limit of risk of explosion," Leibman said. When asked about a climate change link, she said she preferred the term "local climate fluctuations."
One possible explanation is that warming helped create a cavity underneath the ground covered by a relativity stable top, said Vladimir Romanovsky, a professor of geophysics at the University of Alaska, Fairbanks, who has spoken to Russian scientists investigating the holes.
In theory, such a cavity could be created underground over a period of years as pure ice deep underground became more vulnerable to melt than a mix of ice and earth material at the surface, which acted like a stabilizing roof. Those dynamics, combined with an underground water source at the spot -- also boosted by warming -- perhaps helped create the underground cavity.
When pressure built up in it from gas, it could have burst the top, he said.
The pressure could have come from methane either from melting surrounding ice or perhaps from a deep underground pathway transferring it from the area's rich gas fields, he said."
edit: this article larges presents the same point of view as the Nature article that ghoti links to in Reply #19 (and could be taken to be in line with Robert Scribbler's article that Colorado Bob linked to [see Reply #18])