A century ago 2,000 square kilometres of Siberian forest were flattened in an apparent explosion. The event has puzzled scientists ever since and, although theories abound as to the cause of the blast, nobody has managed to find out exactly why 80 million trees toppled over near the Tunguska River in 1908.
One of the more fanciful theories put forward is that an alien spaceship crashed, devastating the area for thousands of kilometres in all directions. But most scientists are inclined to look for more rational causes.
Russian researcher Vitaly Romaiko has led over 20 expeditions to this site.
This place is mysterious. People started speculating that it was an alien spaceship. I agree it was something from outer space but its more likely to be a fragment of a comet, a snowball-like body of ice and gas that exploded when it hit the earth's atmosphere, Vitaly Romeiko said.
A century later, tribesmen in the Tunguska area remain mystified and it still provokes intense debate among scientists.
What is certain is that a celestial body caused an explosion a thousand times more powerful than the bomb dropped on Hiroshima at the end of World War II.
Eighty million trees were flattened by the blast. They toppled over in a radial pattern. But the trees in the epicentre of the explosion remained standing. Their branches were stripped so that they looked like telegraph poles.
This phenomenon was discovered by Soviet scientist Leonid Kulik, who in 1927 led an expedition to the blast's epicentre.
He measured the 2,000 square kilometres of devastation and recorded images of felled trees. He concluded the blast was caused by a meteorite crashing down to earth.
It was a fireball flying in the sky that came down to earth and destroyed everything around. For locals it was forbidden to go there, local gods said don't go there something crashed there and you will die! said Stanislav Krivyakov, National Park Director.
For many in the local Evenki tribe, the catastrophe of 1908 remains taboo. They are scared to set foot in the vicinity of the blast. Instead, theyve chosen to mark the centenary from afar.
My ancestors were very scared something evil had fallen from the sky. And it was considered so bad that people weren't allowed to talk about it. I think I've picked up that influence and I'm scared to go there. We shouldn't venture into the unknown, said Malvina Yastrikova, a member of the Evenki tribe.
However, for others in the area the 100th anniversary is something to commemorate.
