The Tunguska event was a large explosion that occurred near the Stony Tunguska River, in Yeniseysk Governorate (now Krasnoyarsk Krai), Russian Empire, on the morning of 30 June 1908 (N.S.). The explosion over the sparsely populated Eastern Siberian Taiga flattened 2,000 km2 (770 sq mi) of forest (it caused no known human casualties).

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At around 7:17 a.m. local time, Evenki natives and Russian settlers in the hills north-west ofLake Baikal observed a column of bluish light, nearly as bright as the Sun, moving across the sky. About ten minutes later, there was a flash and a sound similar to artillery fire. Eyewitnesses closer to the explosion reported that the source of the sound moved from the east to the north of them. The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away. The majority of witnesses reported only the sounds and the tremors, and did not report seeing the explosion. Eyewitness accounts vary regarding the sequence and duration of the events.

The explosion registered at seismic stations across Eurasia. It is estimated that, in some places, the resulting shock wave was equivalent to an earthquake measuring 5.0 on theRichter magnitude scale. It also produced fluctuations in atmospheric pressure strong enough to be detected in Great Britain. Over the next few days, night skies in Asia and Europe were aglow; it has been theorized that this was due to light passing through high-altitude ice particles that had formed at extremely low temperatures—a phenomenon that many years later would be produced by space shuttles.

In the United States, the Smithsonian Astrophysical Observatory and the Mount Wilson Observatory observed a months-long decrease in atmospheric transparencydue to an increase in suspended dust particles.

The explosion is generally attributed to the disruption in mid-air of a superbolide. It is classified as an impact event, even though no impact crater has been found; the object is thought to have disintegrated at an altitude of 5 to 10 kilometres (3 to 6 miles) rather than hit the surface of the Earth.

Different studies have yielded varying estimates of the superbolide's size, on the order of 60 to 190 metres (200 to 620 feet), depending on whether the body was a comet or a denser asteroid. It is the largest known impact event on Earth inrecorded history.

Since the 1908 event, there have been an estimated 1,000 scholarly papers (mainly in Russian) published on the Tunguska explosion. Many scientists have participated in Tunguska studies, including Leonid Kulik, Yevgeny Krinov, andKirill Florensky. In 2013, a team of researchers led by Victor Kvasnytsya of the National Academy of Sciences of Ukraine published analysis results of micro-samples from a peat bog near the center of the affected area showing fragments that may be of meteoritic origin.

Early estimates of the energy of the air burst range from 10–15 megatons of TNT (42–63 PJ), to 30 megatons of TNT(130 PJ), depending on the exact height of burst estimated when the scaling-laws from the effects of nuclear weapons are employed. However, modern supercomputer calculations that include the effect of the object's momentum estimate that the airburst had an energy range from 3 to 5 megatons of TNT (13 to 21 PJ), and that more of this energy was focused downward than would be the case from a nuclear explosion.

The 15 megaton (Mt) derived estimate is an energy about 1,000 times greater than that of the atomic bomb dropped on Hiroshima, Japan; roughly equal to that of the United States' Castle Bravo (15.2 Mt) ground-based thermonuclear test detonation on 1 March 1954; and about one-third that of the Soviet Union's later Tsar Bomba (at 50 Mt the largest nuclear weapon ever detonated).

It is estimated that the Tunguska explosion knocked down some 80 million trees over an area of 2,150 square kilometres (830 sq mi), and that the shock wave from the blast would have measured 5.0 on the Richter magnitude scale. An explosion of this magnitude would be capable of destroying a large metropolitan area, but due to the remoteness of the location, no fatalities were documented. This event has helped to spark discussion of asteroid impact avoidance.