Italian scientists from the University of Bologna have investigated the consequences of the explosion of the Tunguska meteorite several times. They hypothesized that the taiga Lake Checo was formed in an impact crater that appeared after the fall of a part of a celestial body that disintegrated in the air. They were led to such conclusions by the study of the geological features of the lake, which has an unusual funnel shape for the reservoirs of these marshy places.
Although 99 years have passed since the disaster on the banks of the Podkamennaya Tunguska River, this event is still shrouded in mystery. There is still no clear answer to the main question: what caused the most powerful explosion in one of the most remote corners of Siberia? The existence of an impact crater could at least knock the ground out from under the feet of supporters of the most sinister and gloomy hypotheses about the origin of the explosion.
In any case, it was one of the largest natural disasters that people have observed throughout the history of mankind. On June 30, 1908, a huge flaming ball appeared in the sky over Siberia. He was moving from the southeast. Then the whole sky burst into flames. An explosion of monstrous force thundered out, which knocked out doors and smashed windows in the houses of the village of Vanavara, lying 65 kilometers from the epicenter, on the gentle shore of the Podkamennaya Tunguska. The shock wave knocked down, and the fiery shaft burned down more than 60 million trees in the taiga on an area of about two thousand square kilometers.
Eyewitnesses who were a hundred kilometers from the fire tornado said that they saw a burning ball and glowing silvery clouds. In different countries in all parts of the world, instruments at seismic stations registered the effects of the explosion.
Scientists now proceed from objective data that on the day of June 30, 1908, an explosion equivalent to 10 to 15 megatons of trinitrotoluene occurred at an altitude of five to ten kilometers. This corresponds to the explosion force of about 700-1000 bombs that destroyed Hiroshima. The strength and localization of the explosion is almost beyond anyone’s doubt, which cannot be said about its cause – the cause is unknown, since neither the impact crater nor other traces and remnants of the burned-out celestial body have been found.
Most scientists believe that a comet or a solid asteroid exploded above the earth’s surface, which disintegrated into small parts under the influence of the atmosphere. In addition, there is a hypothesis about the explosion of underground gas accumulations, as well as dizzying theories about tiny black holes and antimatter particles. There are also rumors that the disaster was provoked by aliens, the wreckage of their spaceship was allegedly discovered in 2004.
Italian researchers believe they have put an end to exotic hypotheses. They are sure that they found an impact crater eight kilometers from the epicenter of the explosion over Tunguska. The water-filled sinkhole is called Lake Checo. The Italians are sure that the deep lake was formed exactly in the place where a large fragment of an asteroid fell, which caused a mysterious powerful explosion in 1908. This is what is stated in the article published in the special scientific journal Terra Nova.
– We believe that the fragment fell at a relatively low speed on a swampy area and knocked out this crater, – says the head of the study Luca Gasperini, an employee of the Institute of Marine Geology in Bologna. – Most likely, a fragment of an asteroid consisting of rocks collapsed on the earth’s surface here, it is unlikely that it could be a comet.
The researcher emphasizes that they do not have absolute confidence yet, of course. The most important necessary evidence is still missing, that is, the fallen asteroid or its fragments. In the images constructed on the basis of the results of research using sonars and echo sounders, a “suspicious” area was formed at a depth of 10 meters under the bottom of the lake.
In this place, the density of the soil is much higher, Gasperini and his colleagues suggest that these may be deposits that have become very dense due to an impact, or even a large piece of an asteroid.
-Unfortunately, we didn’t have the opportunity to drill a well deep enough to take a sample,- Luca Gasperini said. – To continue the research, it is necessary to find sponsors to finance an expensive expedition.
The absence of the main evidence allowed other experts to treat the hypothesis of the Italians very skeptically.
-In my opinion, there is no serious reason to consider this lake an impact crater,- said Gareth Collins of Imperial College London. – A narrow circle of impact crater specialists does not recognize any structures as craters unless there are signs of high temperatures or high pressure. For final conclusions, it is necessary to find melted or scattered stones on impact.
German impact crater expert Cord Ernstsson called Collins’ arguments typical for studying impacts, or impact events, as meteorite impacts on the earth’s surface are sometimes called. He refers to theoretical calculations, models and available data and comes to the conclusion that it cannot be an impact crater. A hitherto unknown process could create new, unknown forms and consequences as a result. It is very important to understand this, but it is far from enough.
-In the end, measurements are more important than theoretical calculations,- Ernstson says. The scientific environment, which Collins defined as “a narrow circle of specialists in impact craters,” is characterized by a rather conservative approach.
In fact, Gasperini and his colleagues see the reason for the absence of the usual “meteorite crater shaft formed by uplifted layers of underlying rocks in the special geological conditions of the Podkamennaya Tunguska basin. The area is covered with swamps located on a 25-meter layer of permafrost. Due to the high temperature during the explosion of the meteorite, presumably, a large amount of water and water vapor was formed, which melted the permafrost and released methane contained in the soil. The ring shaft of the crater sank into the softened and limp permafrost.
The researchers considered different possibilities of occurrence in the swampy taiga of Lake Cheko. Volcanic processes have to be excluded – there are no signs that speak in their favor. The same applies to the so-called thermokarst, the subsidence of the earth’s surface, formed during the thawing of icy frozen rocks and the pulling out of underground ice.
As a result of thermokarst, lakes with an almost flat flat bottom and steep steep banks are formed. Lake Checo has the shape of a funnel or a bell, the Talian scientists recognized the extremely small probability that the Kimchu River feeding Lake Checo, as a result of normal processes of erosion and redistribution of soil, made a funnel 50 meters deep. The depth, diameter and shape of the lake are much more consistent with the impact of a meteorite into soft, pliable soil.
The elliptical shape of the lake indicates the relatively low speed of the fallen object. Experts estimated that the asteroid or its fragment had a diameter of about 10 meters, weighed about 1,500 tons, flew at a speed of 3,600 to 36,000 kilometers per hour and crashed into the Earth at an angle of 45 degrees.
The main confirmation of the hypothesis can be soil samples from under the bottom of the lake. Nothing was found in the 1.8-meter-long core that would indicate the Tunguska disaster. But the Italians did not manage to drill the ground deep enough. Perhaps new research will bring Italian scientists complete success.