A new 50-metre deep crater has appeared in the Russian Arctic – and it’s not the first to cause astonishment in the region.

When the mysterious holes first appeared in 2014 there was wild speculation that they were caused by Kremlin missile tests, aliens from UFOs, or that they were manmade – as a prank.

The new hole – which is the 17th to appear in six years – was initially spotted by chance from the air by a Vesti Yamal TV crew en route from an unrelated assignment.

A group of scientists then made an expedition to examine the large cylindrical crater estimated at up to 50 metres deep.

It is one of the biggest so far found.

The scientists say the crater was caused by a large explosion, sparked by “a methane gas buildup in the thawing permafrost”.

Blocks of soil and ice were thrown “hundreds of metres” from epicentre by a “colossal force” after a summer of unprecedented heat, the experts say.

Gas is released in soil that has been frozen for thousands of years but is now defrosting.

Scientist Dr Evgeny Chuvilin, a leading researcher at Skolkovo Institute of Science and Technology, said this particular crater was “striking in its size and grandeur”.

Professor Vasily Bogoyavlensky, of the Russian Oil and Gas Research Institute in Moscow, told the TV station: “This object is unique.

“It holds a lot of additional scientific information, which I am not yet ready to disclose. This is a subject for scientific publications.”

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These craters appear because “gas-saturated cavities are formed in the permafrost,” he said.

Bogoyavlensky has previously claimed that drilling for natural gas in Yamal – a key supplier for Europe – may be a factor in the eruptions.

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He is also concerned at the risk of ecological disasters if the explosions occur under gas pipelines, production facilities or residential areas.

The explosion comes after a record hot summer in many Arctic regions across Russia.

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