The Tunguska Event

Summary

Something exploded over Siberia in 1908 with enough force to flatten roughly 2,150 square kilometres of forest and fell an estimated eighty million trees, all of them pointing away from a single centre. When the first scientist reached the site nineteen years later, he found no crater and no meteorite. That absence is the most famous fact about Tunguska, and it is usually presented as the mystery. It is the explanation.

What is documented

The morning. On 30 June 1908, at about a quarter past seven in the morning, a fireball crossed the sky above the basin of the Podkamennaya Tunguska River in central Siberia and exploded. The region was, and largely remains, empty. There were no instruments, no towns, and almost no witnesses.

The witnesses there were. S. B. Semenov, roughly sixty-five kilometres from the centre, described the sky splitting and fire appearing over the forest, and heat so intense that it felt to him as though his shirt were burning. He was thrown from where he sat. Others hundreds of kilometres away reported a blast that knocked them down and rattled or broke windows.

The instrumental record. The event was not observed, but it was measured. Seismic waves from the explosion were recorded across Eurasia, as far as Western Europe. In the days that followed, unusually bright nights were reported across Europe, with sky glow sufficient to read by.

The forest. Roughly 2,150 square kilometres of taiga were flattened, an area larger than Greater London. An estimated eighty million trees were felled. They lay radially, in a pattern that pointed outward from one place.

The nineteen-year gap. No scientist reached the site until 1927. The region was extraordinarily remote, and the intervening years brought the First World War, the Revolution and the Civil War. The first expedition was led by Leonid Kulik, a mineralogist, who returned repeatedly over the following decade; his last visit was in 1938 to 1939. He died in 1942.

What Kulik found. Kulik expected a crater and meteorite fragments. He found neither. He found felled, splintered, scorched trees lying radially for fifteen to thirty kilometres, with little regrowth two decades on. The epicentre was trivial to locate, because every trunk pointed away from it. And at that centre, the trees were still standing: stripped of their branches and bark, scorched, but rooted, like a forest of telegraph poles. Beneath them was a marshy bog.

What was found later. No large fragment of the object has ever been recovered. Microscopic material has: iron and silicate spherules, and traces of nickel and other meteoritic elements, in the soil and peat of the region.

Leading explanations

Airburst of a small asteroid (established). The consensus, and the one that accounts for the evidence without remainder: an object tens of metres across entered the atmosphere at high speed, compressed the air ahead of it, heated, and came apart. It converted its kinetic energy into an explosion several kilometres up rather than on the ground.

This explains the flattened forest (a downward-propagating shockwave from a point above), the radial pattern (the wave spread outward in every direction from that point), the scorching, the standing trees at the centre (directly beneath the burst, the shockwave arrived vertically and had no lateral force to topple them), and the absence of a crater and of fragments (the object never reached the ground).

The burst altitude is generally placed between about five and ten kilometres. Britannica describes a stony or carbonaceous asteroid roughly fifty to a hundred metres across.

The energy figure, and how firm it is. Tunguska is routinely reported at fifteen megatons of TNT, or ten to fifteen. That number is not a measurement. There were no instruments at the site, and the energy has been reconstructed from indirect evidence: the extent of the flattened forest, the seismic record, and modelling of how airbursts behave. Published estimates run wider than the commonly quoted range in both directions. "Hundreds of times the Hiroshima bomb" is a defensible statement. A single precise multiplier is not.

Comet rather than asteroid (contested). Some researchers have argued for a cometary body, largely ice and volatiles, pointing to the bright nights over Europe afterwards as consistent with vaporised cometary material high in the atmosphere. This would also account for the absence of substantial fragments. The airburst mechanism is the same either way; what is unsettled is what the object was made of.

Chelyabinsk, 2013. The airburst model stopped being theoretical. An object roughly twenty metres across broke up over Chelyabinsk at high altitude in a blast of several hundred kilotons. It left no crater. The shockwave alone shattered windows across the city and injured roughly 1,500 people. It was recorded on hundreds of cameras. Tunguska is the same phenomenon, larger.

Explanations that were never needed. Antimatter, a passing microscopic black hole, a crashed spacecraft, an experiment by Nikola Tesla. Each was proposed to account for the missing crater. None was necessary, because the missing crater was never anomalous.

Current status

Later explained. The registry keeps Tunguska because it was genuinely anomalous in 1908 and remained so for decades: an explosion of continental significance, with no crater, no fragment, and no mechanism anyone could name. The explanation, when it came, was more interesting than the mystery, and it carries a live consequence.

An object too small to see coming flattened an area the size of a major city without ever touching the ground. That is not a historical curiosity. It is the reason the near-Earth object surveys exist.

Last reviewed: July 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.