June 30, 2015

It Happened on June 30th

The Tunguska Event, 1908

Location of Tunguska Event.   © Bobby D. Bryant/Wikimedia Commons
Imagine yourself in Siberia on June 30, 1908. You sit on the porch outside a trading post, eating your breakfast, and looking at the view to the north. It's a little after seven o'clock in the morning. Suddenly, the sky splits open and a wall of fire appears in the split. The split opens, the fire spreads. The whole northern sky appears to be on fire.

You feel like you're on fire, too. Your shirt is so hot that you go to tear it off, fearing it will ignite. But then, just as suddenly, the sky snaps shut. You hear a loud boom as you're thrown from your chair and land a few yards away. Briefly, you black out, and when you regain consciousness, you feel the earth shaking, and a continuous barrage of noise, as though rocks are falling or cannons are being fired, repeatedly.

When the noise ends, you look around, gingerly. You see a wide swath has been cut through the grass between the houses, as though it was burned when the hot air rushed through. Some of your crops have been damaged. The iron lock on your barn snapped. Many of the windows have shattered.

The Event

This is exactly what happened to S. Semenov on the day of the Tunguska Event. He reported it, in 1921, to an expedition led by Leonid Kulik. Mr. Semenov was about 25 miles away from the center of the blast.

Others reported similar stories. The noise was intense. The light was blinding. The heat was incredible, and swept over them in intense winds coming from the north.

The Kulik Expedition

Leonid Kulik
You may be wondering why the first major expedition to investigate the event took place 13 years after the explosion. It's possible, or course, that it wasn't the first expedition. What we do know, however, is that there is no documentation of any investigation before Kulik's. Remember, though, that Russia underwent some turbulent times in those years. The Second World War, the Russian Revolution, and the Russian Civil war all took place during that era. That's a lot of turmoil -- and a lot of chances to lose paperwork.

Leonid Kulik got the Soviet government to fund his expedition, based partly on the chance that there would be a lot of meteoric iron that could contribute to the economy. It wasn't easy to get there. Local guides would only go so far -- they were afraid of the site. When Kulik finally arrived at the site, he was astounded to find, not only no meteor, but not even a crater. Instead, the area around the epicenter was covered with blasted trees, devoid of branches and standing straight up. The area extended about five miles in diameter.

Farther away than that, the trees were still burned, but had fallen, away from the center. The entire area comprised a rough "butterfly" shape, with a wingspan of 43 miles and a body length of 34 miles. The whole area covered about 830 square miles.

Kulik made multiple expeditions to the area over the next decade, and even took aerial photographs. The aerial photographs were burned in 1975 by the Chairman of the Committee on Meteorites. He claimed that they created a fire hazard, but a more likely explanation is that the scientists disliked anything that presented an unexplainable phenomenon. After all, they might be held responsible for not explaining it.

What Caused It?

Photograph from the Kulik Expedition, May 1929.
What is generally believed today is that the event was caused by a meteoroid that exploded about five miles above the earth's surface. It is classified as an impact, even though it didn't touch the earth's surface except as debris. The explosion created was most likely in the neighborhood of 10 to 15 megatons. That's about the same as the United States' hydrogen bomb, Castle Bravo, that was tested on the Bikini Atoll in 1954, or about 1,000 times as powerful as the bomb dropped on Hiroshima. It's also about one-third the power of the most powerful nuclear weapon ever detonated, the Tsar Bomba, detonated on Novaya Zemlya archipelago in 1961.

As far as we know, it's the largest meteor impact that's taken place on land in recorded history. Of course, if a similar impact had taken place over certain ocean regions, we might not have known about it.

It's not unusual for meteoroids to enter the Earth's atmosphere and explode. In fact, it happens every day. Larger explosions are more rare, but even so, the U. S. Air Force estimates that meteoroids as large as 30 feet in diameter -- creating an explosion about equivalent to the bomb dropped on Nagasaki -- explode in the upper atmosphere at least once a year. Explosions like Tunguska take place perhaps every 300 years.

Alternate Theories

Kulik Expedition photograph, 1927.
Of course, there are other theories as to what caused the event. The most common -- and most rational -- is that it was a comet, not a meteoroid. (The chief difference is that a comet is made largely out of ice.) It is also speculation that it could have been a piece of a larger comet, such as Comet 2005NB56, which bounced off the Earth's atmosphere and then back into space. If that is the case, it's due to return in 2045.

Another theory surmises that it could have been a comet containing a large pocket of deuterium, which had a nuclear fusion reaction and exploded, creating a natural H-bomb. It's also been posited that the event could have been caused by a black hole, a chunk of antimatter, or an explosion of natural gas within the Earth's crust.

It's even been suggested that the explosion could have been caused by Nikola Tesla, experimenting with the Wardenclyffe Tower, an early telecommunications project. And of course, there are always the aliens. The explosion could have been a spaceship accident, or a weapon going off, either as a threat, or to save us from a natural disaster.

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