The Tunguska event was caused by a space rock tens of metres across
At 7:17am on 30 June 1908, an immense explosion tore through the forest of central Siberia.
Some 80 million trees were flattened over an area of 2,000 square km (800 square miles) near the Tunguska River.
The blast was 1,000 times more powerful than the atomic bombs dropped on Hiroshima and Nagasaki and generated a shock wave that knocked people to the ground 60km from the epicentre.
The cause was an asteroid or comet just a few tens of metres across which detonated 5-10km above the ground, 100 years ago today.
Eyewitnesses recalled a brilliant fireball resembling a "flying star" ploughing across the cloudless June sky at an oblique angle.
The plume of hot dust trailing the fireball gave rise to descriptions of a "pillar of fire", which was quickly replaced by a giant cloud of black smoke rising over the horizon.
"The sky split in two and fire appeared high and wide over the forest. The split in the sky grew larger, and the entire northern side was covered with fire," one local remembered.
"At that moment I became so hot that I couldn't bear it, as if my shirt was on fire… I wanted to tear off my shirt and throw it down, but then the sky slammed shut. A strong thump sounded, and I was thrown a few yards."
This eyewitness was lucky, but an elderly hunter who was much closer to the explosion died after being flung against a tree by the blast. That the airburst did not cause more casualties was in large part due to the remoteness of the area.
Bright light
To many, this event - the biggest space impact of modern times - serves as a reminder of the continuing threat posed to our planet by objects from space...