An enormous 260ft hole in Siberia has baffled scientists - because they have no idea how it got there.
The gigantic puncture in the earth was spotted by helicopters in the remote gas-rich region of the Yamal Peninsula, close to the Arctic Circle.
The unmissable hole is thought to be up to 80 metres (260ft) wide, but experts have no idea how far it goes down.
Russian scientists said a team has been sent to investigate the hole and is due to arrive at the scene on Wednesday.
The cause of its sudden appearance in Yamal - which means the 'end of the world' - is not yet known, though one scientific claim is that global warming may be to blame.
Others believe it may have been caused by a meteorite striking earth, but noone seems certain on a definite cause.
The giant hole appeared close to a forest some 30 kilometres from Yamal's biggest gas field Bovanenkovo.
Experts are confident that a scientific explanation will be found for it and that it is not - as one web claim suggested - evidence 'of the arrival of a UFO craft' to the planet.
A report and footage highlighted by Zvezda TV said the dark colour of the crater indicates 'some temperature processes'.
The Siberian Times said others claim that the darkening around the inner rim indicates its formation was accompanied by severe burning scorching the edges.
Some observers believe water or dry soil is seen falling into the cavity.
Initial reports and images were suspected to be fakes, but the hole is a real phenomenon and it is believed to have been formed around two years ago.
An expedition organised by the Yamal authorities includes two experts from the Centre for the Study of the Arctic and one from Cryosphere Institute of the Russian Academy of Sciences. They plan to take samples of soil, air and water from the scene.
They will be accompanied by a specialist from the Emergencies Ministry.
A spokesman for the ministry's Yamal branch ruled out a meteorite but said it was too early to say what cause the gigantic hole in the earth.
He told The Siberian Times: 'We can definitely say that it is not a meteorite. No details yet'
The Yamal Peninsula in the Yamalo-Nenets Autonomous Okrug is a strategic oil and gas bearing region of Russia.
It is Russia's main production area for gas and the Bovanenkovo field is of central importance to gas supplies from Siberia to the world.
The gas field was discovered in 1972 and developed by Gazprom starting production in 2012.