A blast flattened 80 million trees — and left behind no trace of what caused it

On June 30, 1908, a powerful explosion occurred over the Podkamennaya Tunguska River in Siberia, with an estimated force of over ten megatons of TNT — hundreds of times stronger than the atomic bomb dropped on Hiroshima.

The shockwave flattened around 80 million trees across an area of more than 2,000 square kilometers. And yet, despite such a massive explosion, no crater or clear fragments of the object that caused it were ever found.

The most widely accepted explanation is an airburst from a small asteroid or comet fragment, which broke apart several kilometers above the surface before it could hit the ground — which explains the lack of a crater despite the catastrophic surface damage.

The significance: Tunguska remains the most commonly cited example of how real the threat from space objects is — and how little separates "nothing happened" from a regional-scale catastrophe.