The 1908 Tunguska Event, thought to have been caused by an asteroid about 50 meters in diameter, flattened 2,150 square kilometers of forest, an area equivalent to that of Tokyo.
Notes on verification
Corroborated by NASA, ESA, and Britannica regarding event date, affected forest area, and estimated impactor size; Tokyo comparison holds when using the metropolis/prefecture area (~2,194 sq km).
Sources
- July 5: the day the world was due to end – Cosmos (cosmos.isas.jaxa.jp)
- https://www.nasa.gov/history/the-tunguska-event/ (nasa.gov)
- https://www.metro.tokyo.lg.jp/english/about/history/index.html (metro.tokyo.lg.jp)