New footage from inside the mysterious crater that appeared in Siberia recently has been released.

No one is sure how the crater formed, but guesses made by commenters on YouTube videos and articles posted by media outlets around the world included a meteorite crash, UFO landing site, global warming, a gas explosion, or a sinkhole caused by collapsing rock.

The most logical theory is that the crater was a "build-up of excessive pressure underground, due to the region's changing temperatures," according to Daily Mail.

Scientists recently returned from their first expedition to get a look inside the hole, which was first spotted via helicopter.

They collected samples of soil, air, and water from the scene of the enormous crater to try figuring out where the hole came from.

"They found the crater, around up to 300 feet deep, has an icy lake at its bottom, and water is cascading down its eroding permafrost walls," said The Siberian Times. "It is not as wide as aerial estimates which earlier suggested between 164 feet and 328 feet."

Satellite mapping imagery is being used to figure out when the hole formed. Most researchers believe that it formed within the last year or two.

The structure is fragile, meaning scientists can't climb down it themselves, and have to send a camera down instead.

Dr. Chris Fogwill of the University of New South Wales said 80 percent of the crater seemed to be made up of ice and that there were no traces of an explosion. This eliminates the possibility that it was caused by a meteorite.

"Could it be linked to the global warming? Well, we have to continue our research to answer this question," said Andrey Plekhanov, senior researcher at the Russian Scientific Centre of Arctic Research, according to The Daily Mail.

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