Whatever the cause, the event resulted in a massive rockfall which has blocked the nearby Bureya river, and left several villages at risk of flooding. So much rock was shifted it would fill 13,600 Olympic-sized swimming pools, say experts. Meanwhile, the falling 34 million cubic metres of debris left a gash in a mountain which could swallow up all the water used if every American showered at the same time.
The Russian army has been dispatched to the scene to try and find out what caused the catastrophic event and move a 525ft-high mound of rock, which has substantially blocked the Bureya, with village in the Khabarovsk and Amur regions at risk of flooding.
The military has being tasked with “moving the mountain”, using explosives and equipment to allow the water to flow again.
But experts have warned nearby rock is fractured and a second gargantuan landslide is not ruled out.
A defence ministry source said a group of specialists is en route “to conduct reconnaissance work” at the site, where the rocks fell some 1,280 ft on to the valley floor.
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There have been claims the mountain collapse was the result of a UFO crash-landing (Image: GETTY)
The source added: “Given the significant size of the landslide, units of engineers and railway forces with special equipment, as well as army and transport aviation, will be involved in clearing the rock.”
Plans are being drawn up for the evacuation of 400 people from the villages of Chekunda, Ust-Urgal and Elga .
Flooding could also disrupt the 2,700-mile long Baikal-Amur Mainline rail link, which is a vital link between the Siberian interior and Russia’s east coast, unless the army can unblock the river quickly.
To complicate matters still further, a hydro-electricity station is also threatened because water is drying up in Bureyskaya hydro power reservoir located downstream.
The mountain collapse happened in a region of eastern Siberia (Image: Google)
The collapse has blocked the Bureya river (Image: Google)
We are trying to find the explanation for this incident
Russia has also sent in teams of geomorphologists, geologists, hydrologists and land-surveyors to assess the carnage, which seems to have happened on December 11, reported The Siberian Times.
Alexey Maslov, head of Verkhnebureinsky district where the incident happened, said: “We are trying to find the explanation for this incident.
“I insist that it was a meteorite.”
However, a local poll in eastern Russian suggested the while 27 per cent agreed with his assessment, more – 33 per cent believed a UFO – was the cause.
Professor Dave Petley, Vice-President for Research and Innovation at the University of Sheffield and an expert in the science of landslides, dismissed both ideas, explaining the mountain slope above the Bureya had a “pre-existing tension crack or depression” at an altitude of around 1,900 ft.
He said: “We can say that this is certainly a rock slope failure, and that it is highly unlikely to be associated with a meteor impact event.”
Prof. Petley admitted it was “slightly” surprising that the fall occurred in winter when the ground was frozen, rather than at a warmer time of year.
He warned local conditions showed “there may be a larger failure yet to come”, creating the potential for an even bigger landslide.
The Tunguska event of 1908 flattened more than 700 square miles of forest (Image: GETTY)
Hunters who first reached the scene – alerted by a sudden and inexplicable change in the flow of the river – reported ‘hot rocks’ on which they could warm their hands.
Their initial guess was that the mayhem had been caused by a meteorite strike – even though there were no reports at the time of a space rock hitting the Russian Far East in December.
Siberia has been the site of a number of meteor strikes over the years.
In 2013, a meteor was famously pictured over the city of Chelyabinsk in western Siberia, lighting up the sky as it exploded at an altitude of 20 miles.
Decades before this, in 1908, the so-called Tunguska event flattened 770 square miles of forest in a remote part of central Siberia.
Theories about the cause of the explosion have ranged from a meteor, comet and, once again, a UFO crash-landing, with the mystery compounded by the lack of any visible impact crater.
Meanwhile, an 269-foot wide asteroid is predicted to narrowly miss the Earth tomorrow.
(Additional reporting by Will Stewart)