Tunguska Event

The Tunguska Event was an event on Earth, also known as the Tunguska blast, (TV: In the Forest of the Night) the Tunguska disaster (COMIC: The Hyperion Empire) or the Tunguska Incident. (AUDIO: Kaleidoscope)

Explosion
It was believed to have been caused by a meteor impact in the Tunguska province of Russia on 30 June 1908. The "meteor" was, in actuality, half of the TARDIS. It had split in half, then time rammed itself. The energy released by the impact caused the Great Divide to open in Russia, allowing some of the Charrl to enter that time period from 22,000. (PROSE: Birthright)

Another account put that, whilst tracking the Monk's TARDIS, the Doctor's TARDIS, carrying the Seventh Doctor and the Sleeze Brothers touched down in Tunguska. Finding themselves in a forest, El Ape used a phosphorous grenade to clear a path, which the Doctor saw as endangering the continuum. However, his warning came too late as the time travellers made a hastily retreat into the TARDIS as a massive explosion occured, wiping out the surrounding forest. Determining that the Monk was not present, the Doctor dematerialised the TARDIS soon after. Unbeknownst to the Doctor, the whole incident was witnessed by two bystanders who survived the blast, albeit without their hair and clothing. (COMIC: Follow That TARDIS!)

According to the Twelfth Doctor, the Tunguska blast should have blown the Earth off its axis, but instead, it simply knocked "a few tens of thousands of trees" over. The trees in the region protected the Earth from the impact by "filling the atmosphere with oxygen, pumping it up, like a massive, inflammable airbag", and the impact burnt off the excess oxygen. (TV: In the Forest of the Night)

Aftermath and legacy
After the Tunguska Event, Nicholas II set up the KVI. (PROSE: Trace Memory)

The Third Doctor attempted to take Liz Shaw and Jo Grant to witness the meteor impact but the TARDIS instead materialised in St Petersburg in December 1916. (PROSE: The Wages of Sin)

After her defection from the Soviet Union to the United Kingdom in 1958, the Czech scientist Dr Nadia Červenka provided the Sen-Gen Facility with a neuro-chemical hallucinogen developed using a yellow fungus which was discovered in the crater. It was believed to be extraterrestial in origin. (AUDIO: Artificial Intelligence)

The Tunguska Event was covered in the book Unexplained Mysteries and Disasters by Smedley B. Clarke, which was published by the 21st century. Deadbeat was reading a copy when he met the Seventh Doctor, which incidentally led to him being embroiled in the book's events. (COMIC: Follow That TARDIS!)

In 2015, Kate Stewart equated the Tunguska disaster with the Windermere incident. (COMIC: The Hyperion Empire)

The Twelfth Doctor and Bernice Summerfield both knew the truth of the Tunguska Event. (PROSE: Big Bang Generation)