Crater From 1908 Tunguska Blast Found

MaineCoasts writes "A team of scientists from the Marine Science Institute in Bologna claims to have found the crater left by the aerial blast of a comet or asteroid in 1908 in the Tunguska region of Siberia. The blast flattened 770 square miles (2,000 square kilometers) of forest, but to date no remains or crater have been found. This has left open the question of what kind of object made the impact. The team believes that, contrary to previous studies, nearby Lake Cheko is only one century old and '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.' The team's findings are based on a 1999 expedition to Tunguska and appeared in the August issue of the journal Terra Nova."

Snore

[Mr. Underbridge]

Old, dupey, probably hokey news.

http://science.slashdot.org/article.pl?sid=07/06/26/1917259

This was discussed in June

[SecuritySimian]

http://science.slashdot.org/article.pl?sid=07/06/26/1917259 [slashdot.org]

Re:I've always wondered

[eldavojohn]

At the time I wondered, after seeing all those flattened trees, how they failed to find the crater. Wouldn't it just be a case of going to several spots, drawing a parallel line to the flattened trees, then looking on a map for the point where the lines intersect? Presumably all the trees fell "away" from the blast area.

No, the explosion was above ground level, see our prior discussion on this [slashdot.org].

Also, my post on this [slashdot.org] has a link to a PDF with a sketch of the breaking apart and trajectories.

Also, remember how long ago this happened. There was an expedition there but they didn't have the technology we did. I'm not sure if the tree patterns would help you 100 years later.

Airburst

[wiredog]

An airburst wouldn't leave a crater. Drawing lines would lead to the hypocenter, directly under the burst.

Googlink

[PhilHibbs]

Google map [google.co.uk] of the point that the National Geographic map link goes to

Uni. Bologna homepage on Tunguska

[Paul Jakma]

Uni of Bologna have a site on Tunguska [bo.infn.it], including a whole section on this new, possible crater [bo.infn.it] - with pictures.

Re: Tesla connection?

[Black Parrot]

I watched a google movie about Nikola Tesla the other night and there was speculation that the blast may have had something to do with the "death ray" that he was fooling around with at the time.

And of course, everything you hear about Tesla is true.

Tesla built his "death ray" at Wardencliffe on Long Island, and it is a possible that he tested it one night in 1908.

Who can argue with unsourced speculation like that?

Re:The lake already existed

[EnderGT]

Something to remember about that "witness account":

L. V. Dzhenkoul was born in 1904, so his personal memories of the 1908 Tunguska Event are minimal. Here he is recounting what he was told by his father V[asilii?] I[l'ich] Dzhenkoul and uncle I[van] I[l'ich] Dzhenkoul (both long dead by the time of Kolobkova's 1960 interview.

It seems highly likely to me that this individual is using "the mouth of the Cheko" as a landmark that is known to him, and is not necessarily indicating that this feature was present prior to the incident.

Re:Uni. Bologna homepage on Tunguska

[kc8jhs]

Google maps view [google.co.uk] of the area equivalent to this map from the Univeristy site.

Re:I've always wondered

[mikael]

The trees that were directly below the air explosion were still upright. The trees at some distance were flattened. A large explosion all around Europe was heard on that night, along with a glow in the sky. But it took several months for the expedition to find out what had caused the explosion/light. By that time, the crater would have filled with water and appeared to be a lake to the expedition team.

If it had been a loosely packed asteroid or a comet, it would have disintegrated into lots of small chunks and vaporised before reaching the ground.

The eyewitness reports are interesting:

"Kezhemskoe village. On the 17th an unusual atmospheric event was observed. At 7:43 the noise akin to a strong wind was heard. Immediately afterwards a horrific thump sounded, followed by an earthquake which literally shook the buildings, as if they were hit by a large log or a heavy rock. The first thump was followed by a second, and then a third.

We have friends who own a house next to quarry. Whenever there is a major explosion there always seems to two explosions heard; the first seems to be the shockwave travelling through the ground (a large dull sound thump) while the second is the shockwave through the air which sounds like a shotgun being fired. Then there is the all clear. So maybe the lake is the crater.

Re:Googlink

[Oizoken]

and a google map link [google.co.uk] to the actual place of the crater

Re:I don't get it... what is EXPLODING?

[Chibi Merrow]

At a high enough velocity/pressure or at the right time scale, everything is a fluid, including the atmosphere. If you fall 100 stories into a lake you'll still die. When you're moving at solar orbital velocities and you slam into a thick atmosphere (like Earth's), you'll explode.

Re:Airburst

[SETIGuy]

An airburst should leave multiple craters. After all, the pieces have to go someplace. Whether or not we can find those smaller craters after a century is another issue...

It did go somewhere. You're breathing it now.

I think you may have a misconception as to why an airburst occurs. A meteor (or comet) enters the atmosphere and is decelerated by interacting with the air. To first order the rate of deceleration (and therefore the stress on the meteor) is related to the ratio of the surface area of the object to its mass. If the deceleration stress exceeds the tensile strength of the material it will fragment. If you break an object into multiple pieces, you've increased the surface area but left the total mass the same. The net effect that fragmenting increases the stress and results in more fragmentation and more rapid deceleration. Once fragmentation starts it doesn't like to stop. It progresses very rapidly and all of the kinetic energy gets turned into heat in a few microseconds.

Another way of thinking about it is that it would be hard to get solid pieces surviving after a 15 megaton airburst. Pick your favorite 60 meter diameter piece of rock. Put a 15 Mton H-bomb on it and set if off. Tell me home much of your rock is left.