Tunguska

2,150 km2 of forest flattened, and no crater

On the morning of 30 June 1908, at about 7:14 local time, something exploded over the taiga of Central Siberia near the Podkamennaya Tunguska, one of the main tributaries of the Yenisei. The shock wave knocked witnesses to the ground, killed at least three people and many animals, and shattered windows within 200 km. Russian and German seismological stations recorded it at close to magnitude 5, atmospheric waves were detected worldwide, and from 30 June to 3 July the nights were strangely bright across western Eurasia. The nearest village, Vanavara, lay about 60 km to the south, in country where the Evenks lived by reindeer herding, hunting and fishing.

The Russian press reported the blast within days, but science took years to arrive. Leonid Kulik led the first expedition in 1921 and only found the epicentre in 1927. He and the researchers after him found nearly 2,150 square kilometres of forest knocked flat in a radial pattern, the mark of an explosion in the air. The scientific consensus is a meteor air burst: an object perhaps 50 to 60 metres across, moving fast from the south-east, blew apart 5 to 10 km up with an energy most often put at 10 to 15 megatons, enough to destroy a major city. No fragment has ever been formally identified, and whether it was an asteroid or a comet is still argued. The Chelyabinsk meteor of 2013 behaved in a similar way.

Lake Cheko, about 8 km northeast of the epicentre and unrecorded before 1908, may be a crater left by a piece that broke away first. A University of Bologna team found an anomaly beneath the lake bed in a geophysics survey and planned to drill down to it, but Cheko lacks the flap of overturned material that rings other impact craters, and several sediment studies argue against it. A 2019 study suggested the blast may have killed most of the breeding population of the Sushkin's goose. Tunguska remains the benchmark for judging the risk from near-Earth objects, and the site is protected within a nature reserve.