June 30, 1908: The Tunguska impact

Today in the history of astronomy, an asteroid flattens 830 square miles of Siberian forest.
By | Published: June 30, 2025 | Last updated on July 1, 2025

The Tunguska impact flattened hundreds of miles of forest and devastated local wildlife, but the remoteness of the region kept it from being a mass casuality event. Credit: Leonid Kulik/Wikimedia

Key Takeaways:

  • The Tunguska Event, occurring on June 30, 1908, involved an airburst of an asteroid approximately 3 to 6 miles above the Tunguska River in Siberia.
  • The explosion released energy equivalent to up to 15 megatons of TNT, resulting in a shockwave that flattened trees across an area of approximately 830 square miles.
  • Despite the immense power of the explosion, human casualties were minimal due to the event's remote location.
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An enormous explosion occurred approximately 3 to 6 miles (3.8 to 9.7 kilometers) above the Tunguska River area of Siberia on June 30, 1908, when an asteroid entered Earth’s atmosphere and exploded in an airburst. This event, known as the Tunguska Event, unleashed an estimated energy equivalent to up to 15 megatons of TNT, with a powerful shockwave that flattened trees for approximately 830 square miles (2,150 square km) around. Thanks to the remoteness of the area, human fatalities were low (some sources say no people died, while others say two or three), though the event did devastate reindeer populations. Local reindeer herders who were eyewitnesses described a brilliant flash, a fireball, a thunderous explosion, intense ground tremors, a hot wind, and even being thrown into the air. The impact is a touchpoint in discussions of the potential threat of near-Earth objects and the need for planetary defense, and led to the recognition of June 30 as International Asteroid Day.

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