Something Flattened 800 Square Miles of Siberia in 1908 and Left No Crater

On the morning of June 30, 1908, an enormous fireball passed over central Siberia and detonated above the basin of the Podkamennaya Tunguska River. The blast was loud enough to be felt 800 kilometers away in towns where it broke windows. Air-pressure waves circled the planet and were registered on barometers in Germany, Croatia, the United Kingdom, Indonesia, and Washington, D.C. For weeks afterward, the night sky across northern Europe was bright enough to read by.

What the explosion did locally is the strangest part. It flattened about 2,150 square kilometers of taiga — roughly 80 million trees, knocked outward in a radial pattern — but did not leave an impact crater. Modern reconstructions estimate the object exploded 5 to 10 kilometers above the ground with the force of somewhere between 3 and 50 megatons of TNT, with most current estimates clustering around 10 to 15. The leading hypothesis is that it was a stony asteroid 50 to 80 meters across that fragmented in the atmosphere; alternative reconstructions favor a small comet.

The Soviet mineralogist Leonid Kulik finally led an expedition to the site in 1927, nineteen years after the event. He had expected a crater. Instead he found a zone roughly 8 kilometers across in which the trees were still standing upright but stripped of their bark and limbs, and a wider belt where every tree was on the ground, all pointing the same direction.