It has been nicknamed Gateway of the Underworld.

And not only is the Batagaika crater in Siberia widening each year, but it’s producing dangerous levels of gas, which should ring alarm bells for the world.

That is the view of experts who warn while sinkholes such as these are naturally occurring, the world is beginning to see more of them, particularly in colder areas of the planet.

The crater, which is expanding by around 15m every year, first appeared in the 1960s and captivated locals who were scared of approaching the area after hearing booms from the ravine.

Many local Yakutian people see the ravine as a doorway to the underworld, The Siberian Times reported.

And while the mysterious thuds may seem supernatural they have a more organic explanation.

According to The Times, the thuds which have scared locals are probably the result of falling soil into the deep crater.

Scientists say the crater holds the secret of our planet’s past with soil found at the site dating back 200,000 years as it can reveal environmental changes.

The ravine opened up after a huge chunk of forest was cleared, which caused the land to sink but has been exacerbated by warmer temperatures melting the permafrost.

As more and more permafrost melts, the ravine continues to expand, which has been worsened further by flooding adding to its expansion.

The remote Siberian area some 676km north of Yakutsk is one of the coldest areas in the world with many scientists agreeing the ravine has deepened with climatic changes.

Professor Julian Murton, a geologist at the University of Sussex, told The Independent the melting of the permafrost should be a cause for concern given it contains vast amounts of methane, which in turn can heat up the planet.

“As the climate warms – I think there’s no shadow of a doubt it will warm – we will get increasing thaw of the permafrost and increasingly development of these ‘thermokarst’ features. There will be more slumps and more gullying, more erosion of the land surface,” he said.

Dr Christopher Fogwill, ARC Future Fellow at the University of New South Wales said it was the release of methane gas from the permafrost regions that was the real cause for concern.

He said sinkholes such as these are a type of permafrost sinkhole and he believed it was created after a pingo – an earth-covered mound that forms in Arctic and subarctic regions – collapsed.

While some scientists argue permafrost sinkholes could be related to global warming, Dr Fogwill said such holes were actually naturally occurring.

“There’s actually nothing at all odd or unusual about them,” Dr Fogwill said.

Constantly melting ice, or melting permafrost, helped created such big holes.

“The Arctic is warming, and is one of the warmest rapidly warming areas on Earth,” he said.

“But the big hole is not just the issue. It’s not the hole that’s just releasing the gas, but the whole land around it.”

So should we be scared?

According to Dr Fogwill, yes and no.

“The melting permafrost is certainly an issue because of the increased methane produced in those areas,” he said.

Dr Fogwill also said holes were not unique to Russia with several opening up across the northern hemisphere and Arctic areas.

It wouldn’t be the first such sinkhole to capture the world’s attention.

In 2014 three craters opened up in Siberia – one in Taymyr peninsula and two in Yamal – with locals fearing they were something more sinister.

Some speculated they were caused by missiles or were a man-made hoax while others went as far as claiming they were the result of an alien invasion.

But scientists from the Trofimuk Institute of Petroleum-Gas Geology and Geophysics in Novosibirsk had a far more reasonable explanation and believe that they are the result of large underground gas explosions.

The region is renowned for its enormous gas reserves and craters of this kind are not totally unusual.

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In the former soviet state of Turkmenistan, a massive crater called the Door to Hell has been burning for more than four decades.

The pit, located in a natural gas field some 270km north of the capital also has a perfectly reasonable explanation but wasn’t caused by permafrost.

“Soviet geologists started drilling a borehole to prospect for gas at this spot in 1971,” said Turkmen geologist Anatoly Bushmakin.

“The boring equipment suddenly drilled through into an underground cavern, and a deep sinkhole formed. The equipment tumbled through but fortunately no one was killed.”

“Fearing that the crater would emit poisonous gases, the scientists took the decision to set it alight, thinking that the gas would burn out quickly and this would cause the flames to go out,” Bushmakin said.

But they never did, and now serve as a potent symbol of Turkmenistan’s vast gas reserves, believed to be the fourth largest in the world.

– news.com.au