Post: #1

Look at maps on link!


http://phys.org/news/2012-05-team-eviden...mpact.html




(Phys.org) -- Early on the morning of June 30th, 1908, a huge explosion occurred in a remote part of Siberia near the Podkamennaya Tunguska River. So great was the blast that trees were knocked down in neat rows for nearly a thousand square miles and the sky lit up from parts of Asia to Great Britain. What caused that explosion has never been firmly settled. Most researchers agree that it was the result of either a comet or meteoroid, with most leaning towards the former due to the lack of both an impact crater and meteoroid fragments. Now however, a research team from Italy says that they have found proof that it was in fact a meteorite that struck the Earth and that a nearby lake is the impact crater. They have published the results of their findings in Geochemistry, Geophysics, Geosystems.


For years, amateurs and professionals alike have debated the cause of the Tunguska Event, as it’s come to be known as. Some suggest it was the work of extraterrestrials while others say it was god’s way of getting our attention. Serious scientists, on the other hand, have suggested its most likely cause was a comet melting and then vaporizing as it hit, leaving no real evidence behind. Unfortunately, that theory doesn’t hold up very well in light of the fact that scientists have found differences in the levels of carbon, nitrogen and isotopes of hydrogen and iridium, from the surrounding area which are similar in some respects to those found with certain asteroids. Also, tiny particles that sort of resemble meteorite components have been found in the wood of the fallen trees. None of this evidence can rule anything out however as it could mean there was a comet that had some rocks in it or a meteorite that vaporized due to a soft composition.

The Italian teams says it was a meteorite and claim they have proof of their assertion in the form of an as yet uncovered piece of something tangible beneath the sediment at the bottom of Lake Cheko; a shallow funnel shaped lake approximately five miles from where most believe was ground zero for the explosion.

The team came to this conclusion after performing seismic measurements on the lake bottom in 1999 which showed that sentiment had been building for just about a hundred years, which would of course put it close to the Tunguska Event and also gave evidence of something dense near the middle of the lake.

Further evidence came to light they say in 2009 when they returned to the lake and performed a magnetic survey, which they say showed an anomaly in the same location as their seismic measurements had detected. Now, after three more years of studying evidence they collected from the site, they’ve concluded that Lake Cheko is indeed an impact crater and that the dense object beneath the lakebed is the smoking gun.

Others of course aren’t so sure, and likely will remain pessimistic until someone digs up the object and studies it, proving it to be nothing more than a regular rock, or an object from space that left an impact crater as it struck over a century ago, finally solving the mystery.

More information: Magnetic and seismic reflection study of Lake Cheko, a possible impact crater for the 1908 Tunguska Event, Geochemistry, Geophysics, Geosystems, VOL. 13, Q05008, 12 PP., 2012. doi:10.1029/2012GC004054
Abstract

A major explosion occurred on 30 June 1908 in the Tunguska region of Siberia, causing the destruction of over 2,000 km2 of taiga; pressure and seismic waves detected as far as 1,000 km away; bright luminescence in the night skies of Northern Europe and Central Asia; and other unusual phenomena. This “Tunguska Event” is probably related to the impact with the Earth of a cosmic body that exploded about 5–10 km above ground, releasing in the atmosphere 10–15 Mton of energy. Fragments of the impacting body have never been found, and its nature (comet or asteroid) is still a matter of debate. We report here results from a magnetic and seismic reflection study of a small (∼500 m diameter) lake, Lake Cheko, located about 8 km NW of the inferred explosion epicenter, that was proposed to be an impact crater left by a fragment of the Tunguska Cosmic Body. Seismic reflection and magnetic data revealed a P wave velocity/magnetic anomaly close to the lake center, about 10 m below the lake floor; this anomaly is compatible with the presence of a buried stony object and supports the impact crater origin for Lake Cheko.

Post: #2

http://www.geotimes.org/feb08/article.ht...rater.html

At that link there's a marvelous photo of the lake!!! It looks like a crater.







Long-lost Siberian crater found?


Courtesy of Luca Gasperini, Bologna University

New research suggests Lake Cheko in Siberia may be the long-missing crater from the 1908 impact.

On June 30, 1908, a ball of fire streaked across the sky in Siberia, then exploded between five and 10 kilometers above Earth. The explosion was so bright that it lit up the night sky across Europe and Central Asia. The resulting shockwaves stripped all of the branches from the trees directly below and flattened trees in a 2,000-square-kilometer area around the epicenter. The explosion, now called the Tunguska Event after the region where it occurred, resulted from the collision of a cosmic object with Earth. When the object exploded, debris should have rained down and an impact crater should have formed. Yet no scientifically reliable evidence of this explosion has been found — until now. A team from Italy has found what they think is a crater formed by a piece of the Tunguska Event. The crater, they say, is now the basin of Lake Cheko, about eight kilometers northwest of ground zero.

Lake Cheko is almost perfectly circular and has a “funnel-like morphology,” with its deepest point quite close to its center, according to Luca Gasperini, a geologist with the Marine Science Institute in Bologna, Italy, who recently studied the lake. These features resemble a typical impact crater, Gasperini says. And the lake’s location is consistent with the estimated trajectory of the object across the sky before it blew up. However, Lake Cheko’s basin is much shallower than impact craters normally are, and an elongated area that stretches toward the northwest mars its almost perfectly circular shape. These irregularities, Gasperini says, are evidence of a “soft crash”: A large piece of the cosmic object survived the blast, but it hit Earth at an oblique angle and a slower speed, thus causing the lake’s slightly irregular shape.

The region is remote and uninhabited, so no one is sure whether Lake Cheko was there before the crash or not. The lake did not appear on regional maps until 1928, but it’s not certain the area had been previously mapped. Gasperini’s team is studying sediment samples taken from the lake’s floor, and they think that sediment only recently started collecting there, indicating that the lake itself is young. Gasperini and his team published their findings in the journal Terra Nova last August.

But the story doesn’t end there, Gasperini says, as more evidence is needed. If a piece of the cosmic object was big enough to survive the blast and create a lake, then other fragments should have survived the blast too, and they would be scattered along the path from the lake to ground zero, says William Hartmann, senior scientist at the Planetary Science Institute in Tucson, Ariz. Previous expeditions to the site of the explosion have not turned up any fragments, but they did not have any reason to focus on the area leading from ground zero to the lake. Should future studies of that path uncover any fragments, it would certainly support the crater hypothesis, Hartmann says. There would probably be other kinds of evidence as well, he says. The rocks around the lake would show signs of trauma. The energy and heat from a cosmic body impact cause “shock-metamorphic” effects, which include rocks that are shattered, melted or deformed in other ways. So far, nobody has looked for this particular kind of evidence, but finding any of these phenomena would be strong support for the idea that an impact created the lake.

An object the size of the Tunguska object will fall to Earth about once a century, Hartmann says. But most of Earth’s surface is covered with water, so these impacts have gone unwitnessed. “[T]he whole history of our planet is punctuated by these events,” he says. But only rarely do we get to see one, he adds.

Post: #3

http://www.youtube.com/watch?v=mQSwVMBIeKg

Post: #4

Post: #5

Is Lake Cheko an impact crater? Hardly so. This idea was put forward as long ago as 2007 (see: Gasperini, L., et al. “A possible impact crater for the 1908 Tunguska Event.” Terra Nova, 2007, Vol. 19, 245–251). But here is an article, in which this question is discussed in detail and the authors' answer is definite “no”: http://www.univie.ac.at/geochemistry/koe...a-2008.pdf (G. S. Collins et al. “Evidence that Lake Cheko is not an impact crater”). Also, I must add that the problem of the Tunguska explosion is rather complicated. For more information about this problem I would recommend the following books: “The Tungus Event or The Great Siberian Meteorite,” by John Engledew (Algora Publishing, ISSN 9780875867809), “The Tunguska Mystery,” by Vladimir Rubtsov (Springer N.Y., ISSN 9780387765730) and, with some reservations, “The Mystery of the Tunguska Fireball,” by Surendra Verma (Totem Books, ISSN 9781840467284). After reading these books I doubt that the “impactor” will soon be excavated from the lake bottom.

Post: #6

Here's a good thread that touches on this subject including video

http://lunaticoutpost.com/Topic-Tunguska-revisited

Post: #7

The video in #3 suggests that the current theory is that it could have been a huge natural gas eruption, but this wouldn't account for the broken trees at the centre of the devastation unless the gas only ignited once it was sufficiently high enough in the air.

Post: #8

I've seen the evidence that is posted on the Bologne University website concerning this event. I'd have to say that Lake Cheko's bed looks a lot like some of those craters that Spirit and Opportunity had examined on Mars. I also noticed on the topo map clip that is also posted on the website, that there are a whole bunch of smaller lakes scattered around the area that could possibly be other impact craters for smaller fragments. It would be interesting to see the entire topo quadrangle of that area to see if there are more lakes scattered around the blast area.

I haven't looked into this yet, but apparently another Tunguska like event had occurred in 1949 in Poland where a whole bunch of lakes were created from an exploding meteorite. I've only come across references to this event from various sources on the Tunguska Event.

http://www-th.bo.infn.it/tunguska/

Post: #9

They need an impact crater to keep the comet/asteroid theory alive.

Post: #10

absurdious  Wrote:

They need an impact crater to keep the comet/asteroid theory alive.

Not necessarily. If there was indeed a comet/asteroid, presumably with an ice core, that exploded before reaching Earth, that would be perfectly consistent with the resultant damage. Especially when you see the snapped of trees at the epicentre.