As a kid, I was fascinated by the mysterious explosion that occurred over Siberia. Basically, in the morning of 30 June 1908, a few native peoples in Siberia reported seeing a blue light in the sky that was as bright as the sun and hearing a series of loud explosions, accompanied by fierce winds and fire. These explosions, which flattened the pristine Siberian Taiga for 770 miles (2,000 kilometers) around, are estimated to have had the power of 2000 Hiroshima atomic bombs. However, this area is so remote and Russia was experiencing so much political turmoil that no one was able to investigate the scene until 1927, when the accompanying black-and-white images first recorded the devastation.
Scientists have carefully explored the area but have never found an impact crater. But based on the size of the devastation and the direction that the flattened trees point, they hypothesized that either a meteor or comet exploded approximately 6 miles (10 kilometers) above the surface of the Earth. Even though an unknown number of native peoples died, this event could have been much worse: if the explosion had occurred approximately 4 hours and 47 minutes later, it would have completely devastated the city of St. Petersburg.
A team of Italian scientists led by Luca Gasperini, a geologist with the Marine Science Institute in Bologna, just published a paper describing their 1999 study where they used acoustic imagery to investigate the bottom of Lake Cheko, located five miles (eight kilometers) north of the explosion's suspected epicenter (see map, below);
They found that the basin of Lake Cheko is not deep, steep and round like a typical impact crater, but instead, it's elongated and shallow, measuring about 1,640 feet (500 meters) long tapering down to a maximum depth of 165 feet (50 meters). (see bathymetry data, below);
Gasperini's team says their data suggest that a 10 meter (33 foot) wide fragment of the celestial object was blasted free by the explosion and continued traveling in the same direction that the original object was moving in. This fragment traveled slowly, about 1 kilometer a second (0.6 mile) per second. When the fragment plowed into the marshy terrain five miles north of the explosion epicenter, it created a long, trenchlike depression.
"It splashed on the soft, swampy soil and melted the underlying permafrost layer, releasing CO2 [carbon dioxide], water vapor, and methane that broadened the hole, hence the shape and size of the basin, unusual for an impact crater," argues Gasperini, adding that "our hypothesis is the only one that accounts for the funnel-like morphology of Lake Cheko's bottom." (See comparison between the morphologies of Lake Nikolaji, which is not an impact lake, to Lake Cheko, and to a known impact crater, below);
But Russian scientists previously concluded that Lake Cheko had formed before 1908, and therefore, could not possibly have been caused by the Tunguska event. Yet, based on their 1999 data, Gasperini's team argues that the older deposits found by the Russians were already there when the explosion took place.
"The funnel-like shape of the basin and samples from its sedimentary deposits suggest that the lake fills an impact crater," Gasperini asserted.
Not that I am an expert, but I wonder about the lack of other, smaller, fragments that should also have been blasted free and impacted the earth along the main fragment's trajectory. Don't you find this lack of other fragments odd? Or perhaps they just haven't been found yet.
Nevertheless, Gasparini's team is planning to return to the area to search for more fragments.
"If the body was an asteroid, a surviving fragment may be buried beneath the lake. If it was a comet, its chemical signature should be found in the deepest layers of sediments."
This study was published in the journal, Terra Nova.
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