At around 07:17am on the 30th of June 1908 near the Podkamennaya Tunguska
river in Siberia, Russia a gigantic explosion took place. The force of the
blast flattened around 18 million trees and cleared an area more than 2,100
square kilometers (800 square miles) in size. For many years after this
devastating impact the true cause of the blast remained entirely unknown. The
part of Siberia where the event took place was incredibly sparsely populated.
Thus, fortunately, only three people were killed.
Unfortunately eyewitnesses to the event were also similarly few and far between.
Generally their stories were all quite similar. Many reported having seen a
column of bluish light nearly as bright as the sun moving across the sky just
before the event. Others noted a bright flash and a sound similar to artillery
fire when the event occurred. Those closer to the explosion were knocked off
their feet by a shock wave that broke windows and damaged buildings hundreds
of kilometers away. One eyewitness gave the following testimony to a Russian
meteorologist in the years after the event:
"At breakfast time I was sitting by the house at Vannavara trading post facing
"north. I suddenly saw that directly to the north over and Onkoul's Tunguska Road
"the sky split in two and fire appeared high and wide over the forest. The split
"in the sky grew larger and the entire northern side was covered with fire. At
"that moment I became so hot that I couldn't bear it - as if my shirt was on
"fire. From the northern side where the fire
"was came strong heat. I wanted to tear off my shirt and throw it down but then
"the sky shut closed and a strong thump sounded and I was thrown a few meters. I
"lost my senses for a moment but then my wife ran out and led me to the house.
"after that such noise came as if rocks were falling or cannons were firing. The
"earth shook and when I was on the ground I had pressed my head down fearing rocks
"would smash it. When the sky opened up hot wind raced between the houses like
"from cannons which left traces in the ground like pathways, and it damaged some
"crops. Later we saw that many windows were shattered and in the barn a part of
"an iron lock had snapped."
This eyewitness was around 65 kilometers (40 miles) away from the explosion when it
took place, but the effects were felt much further afield than that. Indeed
tremors from the explosion were recorded by seismic stations across Eurasia and
airwaves from the blast were detected in Germany, Denmark, Croatia, the United
Kingdom, and even in Washington DC in America. In some places the shockwave
was equivalent to an earthquake measuring 5.0 on the Richter Scale. In
the days following the explosion the night skies over Asia and Europe glowed,
in some cases almost as bright as day. As bizarre as this incident was the utter
remoteness of Siberia made it difficult to investigate. With only three
casualties and a handful of eyewitnesses the world had other priorities.
More than a decade passed before any serious attempt was made to determine
what exactly had happened. Several expeditions were eventually mounted to
the area with one expedition leader noting with some surprise that there was
no impact crater at ground zero of the blast. Instead, while trees for miles
around had been toppled and scorched, the trees directly under the epicenter of
the blast were still standing upright, although burned and stripped of their
branches.
By the 1960s - 50 years after the event - it had been established that the blast area
was shaped like a gigantic butterfly approximately 70 kilometers (or 43 miles)
across and with a body 55 kilometers (or 34 miles) in length. Within this blast
zone several mysterious holes and pothole bogs were located, some of which
expedition leaders suspected might be meteorite craters. The laborious and
expensive excavation of one such bog, however, revealed an intact tree stump at
the bottom and thus temporarily negated this theory. Expeditions in the 1950s and
1960s discovered microscopic spheres scattered throughout the area with many
buried in the ground or in the resin of felled trees. These spheres contained
high concentrations of a nickel iron alloy often found in meteorites,
along with numerous other metals that were unusual for the surrounding
environment. Additionally, the spheres were distributed in a manner consistent
with the air burst of an incoming asteroid. A meteorite strike then became
the leading theory. The stripped trees, the distribution of the spheres, and
other scientific analysis all indicated that an asteroid had entered the
atmosphere and exploded several kilometers above the surface with an
energy roughly 1,000 times greater than the bomb that fell on Hiroshima. Even the
glow in the sky could be explained as ice particles shed by the incoming rock.
As this theory emerged it was challenged by many. Some insisted that a fragment of
the meteorite must have survived and that it should be found. Some proposed
that the explosion had not been caused by an incoming asteroid at all but by a
weapons test or a crashing spaceship. Some insisted that it had been a comet
rather than an asteroid. These theories, however, fell by the wayside as we came
to understand more about the universe beyond our planet. We know now that the
air burst of incoming asteroids far above the surface of the earth is a
routine occurrence. Usually these cause so little harm as
to be entirely unremarkable, but it is inevitable that an air burst
similar to the Tunguska Event will reoccur one day. Indeed such events have
occurred throughout history with an average frequency of around 300 years.
The Tunguska Event was shrouded in mystery for many years in part due to
the remoteness of the area in which it took place. Let us hope that the next air
burst of the same or greater magnitude takes place somewhere similarly remote.