
Russian scientists say mystery giant holes suddenly appearing in northern Siberia were caused by dramatic gas eruptions, a process previously 'never observed'.

A new expedition this week to several craters dotting the energy-rich Yamalo-Nenets reindeer region region found evidence they were previously pingos, mounds with an inner ice core common in Arctic and sub-Arctic regions.

Warming over a number of years triggered melting and the resulting empty space inside the ice humps became filled with natural gas, mainly methane, which eventually triggered eruptions.

Scroll down for video

Russian scientists have spent months examining enormous craters which have appeared in the Yamal region of Siberia. The one shown above is among the most famous - known as B1 - and has been found to be 60 metres deep. The reserachers say

Professor Vasily Bogoyavlensky, who led the latest expedition, examined the most famous crater - known as B-1 - which is 18 miles from Bovanenkovo gas field.

It was first noticed last year, causing a flurry of interest around the world and speculation on how this phenomenon was caused, ranging from meteorites, to stray missiles, to UFOs from outer space.

HOW THE CRATERS WERE FORMED After months of research, scientists believe the giant holes were originally a phenomenon known as a pingo. This is a subsurface accumulation of ice that has been covered by land. When the ice melts it can leave behind a gaping hole. The melting of the permafrost caused natural gas trapped in the soil to be released and accumulate in the void, causing the pressure to build and eventually erupt from the ground. Rising temperatures in the soil would have increased the pressure, leading to an eruption. Advertisement

Scientists were this week surprised to find that echo-sounding equipment showed the crater to be more than 200 feet (60 metres) deep, significantly more than previously believed, and large enough 'to fit a multistorey building'.

The hole is already almost full of water after the melting of the winter snow cover. When it was visited last year, its base was far shallower - essentially a lake is beginning to form.

'We can now [explain] more confidently about the process that led to the formation of the famous Yamal crater B-1,' he told The Siberian Times. 'Initially it was a pingo.'

A pingo is a mound of earth-covered ice found in the Arctic that can reach up to 230 ft (70m) in height and up to 2,000 ft (600m) in diameter.

In this case warming from geothermal heat caused this pingo to 'thaw and its half melted ice core [became] filled with gas that originates from the depth through cracks and faults in the ground.

'We know for sure that there is a fissure in the ground on this spot, probably even two intersecting cracks.

'Gullies around the spot confirm this. Through the cracks, deep natural gas got into the melting ice core.

'[Gas] filled it and the pingo erupted.

'It was also heated by a stream of warmth coming from the bowels of the earth through the cracks.'

The process is different than usual because normally pingos thaw and collapse, forming craters and then lakes.'

With the B-1 crater and others known as B-3 and B-4 'we see that the pingo erupts due to the gas, which fills its core.

Researchers have been studying the craters, which show no signs of charring or burning around the edge, and are already forming into lakes. The image above shows scientists and journalists on the edge of the crater B1 in the Yamal region of Russia

This map shows the location of the craters discovered so far in the Yamal region of Russian Siberia. The crater labelled B1 has been found to be nearly 200 feet deep while crater B2, which is 13 miles from B1, is already forming into a lake

'It is very interesting process and we have never observed it before.'

He explained: 'I think that next year it will be full of water and it will turn completely into the lake. After 10-20 years it will be difficult to say what happened here.

'The parapet will be washed away with rains and melting snow, the banks will be covered with grass.

Another of the craters, known as B2 (shown above) is surrounded by several smaller craters, all of which have filled with water. This is thought to have been caused by a mud volcano combined with the melting of ice beneath a pingo

Scientists believe the craters formed as a result of ice beneath the surface melting and releasing gas into the void left behind. As temperatures have warmed and gas levels have increased, the natural gas erupted out of the ground with violent results

Vasily Bogoyavlensky, shown above visiting crater B2, said some of the craters seem to have formed in a complex way with gas erupting out of side channels to form smaller craters around the main one, which appears to have been a mud volcano

'So this large crater fills with water rather quickly - in just two years, so we need to examine such objects very fast when they appear on the landscape.'

Another crater - which has already formed into a lake, known as B-2, some 13 miles from B-1 - may have been caused in a slightly different way, he explained.

B-2 is ringed by 30 'baby' or 'satellite' craters.

'It was the first time scientists - or anyone - had seen crater B-2 up close. It was initially spotted from analysis of satellite images,' reported The Siberian Times.

While it was a pingo, its underground structure appears to be different, and it may have been caused by a combination of the kind of eruption that created B-1, and an entirely different phenomenon known as a mud volcano.

Some scientists have expressed concern at the holes erupting close to major gas extraction plants in the Yamal region. However, Professor Vasily Bogoyavlensky (shown above being interviewed in front of crater B1, who has been leading the research, insists there is no reason to panic. While he warns there are likely to be more craters appearing, they are unlikely to pose a serious threat

This picture of crater B1 shows how it looked last year shortly after it formed. It has since begun filling with water and is turning into a lake

'We could not find a 'mouth' - or 'throat' - in it, though we used different types of echo-sounders,' he said.

'Still, the mouth can be there, but filled with mud, preventing us from detecting it. We will try to do it using other equipment.'

Further research is to be carried out on this crater.

Scientists have spent the past few months visiting the craters in an attempt to learn more about how they formed. The image above shows researchers in the depths of crater B1 after it had been frozen and stabilised by the harsh Siberian winter

For now his preliminary theory is that 'it is a combination of the process that was on B-1 - and that of a mud volcano.

'Initially it was definitely a pingo too. We saw the hillock on the space images and now, when we managed to examine it, we saw the remains of the ice core - the walls of very clean and transparent ice.

'The presence of the small craters around the big one - we can see more than 30 of them - can also indicate that the mouth of this crater had side channels, so the structure of this object can be compared to a tree.

'Gases went through the channels, forming many small craters, but not a big one.'

Scientists were concerned that the erupting holes could pose a threat to Russia's gas extraction in Yamal, the name of which means the 'end of the Earth'.

The craters are thought to have originally been pingos - an accumulation of ice under a mound of earth that have erupted as gas has been released by the melting ice. The image above shows a pingo near Tuktoyaktuk in north west Canada

While the craters were 'quite shocking' to see, the professor said: 'At the moment we do not see any reason for panic.'

More such craters are likely to appear, he said, and they should be monitored closely.

'Last year we passed to officials the information about a big pingo near a gas pipeline,' he said. 'The pingo even began to lift the pipe like a jack-screw.

'Still the officials have not yet taken any measures to move the pipe. But we will continue to research and inform on possible dangers to infrastructure.'

A research team from the Trofimuk Petroleum-Gas Geology and Geophysics Institute had suggested the craters could be linked to the Bermuda Triangle.