The Explosion Without a Crater

At 7:17 AM on June 30, 1908, something exploded above the Tunguska River in central Siberia. The blast flattened an estimated 80 million trees across 830 square miles. Witnesses hundreds of miles away saw a fireball brighter than the sun. The pressure wave circled the globe twice. For nights afterward, European skies glowed so brightly people could read outdoors at midnight.

No one investigated for nearly twenty years. In 1927, Soviet scientist Leonid Kulik found a bizarre scene. Trees at the center stood stripped and carbonized but upright. Beyond, trees were flattened radially. No crater. No meteorite. The explosion equaled 3 to 15 megatons of TNT -- hundreds of times more powerful than Hiroshima.

the tunguska region, siberia, photographed in 2014 -- the remote area where an estimated 50-meter asteroid or comet fragment exploded in the atmosphere in 1908. source: wikimedia commons

The lack of crater was the key clue. Current consensus: a rocky asteroid roughly 50 to 60 meters wide entered the atmosphere and exploded at 3 to 6 miles altitude due to intense heat and compression. It never reached the ground. The location was fortunate -- Tunguska is among Earth's most sparsely populated areas. A few hours later, rotation would have placed a major city in the path.

The Tunguska event remains the largest impact event in recorded history. It spurred interest in near-Earth object detection. Today, astronomers track thousands of asteroids crossing Earth's orbit. There is no memorial at the site. Just trees. On June 30, 1908, something from space reminded us the planet is part of a dynamic system. The warning was delivered to an empty forest. Next time, we may not be so lucky.