Tunguska Impact Crater Found?

BigBadBus writes in with a claim by an Italian team that they may have found an impact crater resulting from the 1908 Tunguska explosion over Siberia. The BBC story quotes a number of impact experts who doubt the Italians' claim. "A University of Bologna team says a lake near the epicenter of the blast may be occupying a crater hollowed out by a chunk of rock that hit the ground. Lake Cheko — though shallow — fits the proportions of a small, bowl-shaped impact crater, say the Italy-based scientists. Their investigation of the lake bottom's geology reveals a funnel-like shape not seen in neighboring lakes. In addition, a geophysics survey of the lake bed has turned up an unusual feature about 10m down which could either be compacted lake sediments or a buried fragment of space rock."

Re:Shouldn't this be easy to prove?

[drinkypoo]

If this is in fact the real impact site, shouldn't there be elevated iridium levels in the lake sediments, as is usually found at other impact sites? I guess "prove" is too strong a term, but I'd challenge anyone to find an alternate explanation for elevated iridium, if found.

It's impossible to be scientific based on the material in the article, but a few things jumped out at me. The most telling are that there's no upside-down layer of material around the supposed crater, and then there's the following passage:

"We have no positive proof this is an impact crater, but we were able to exclude some other hypotheses, and this led us to our conclusion," Professor Longo, the research team leader, told BBC News.

so wait, there is no positive proof that this is an impact crater, but you concluded that it is? that sounds like bullshit to me.

But IANAG[eologist] or in any related field, and of course this is just one little article on the beeb which is pretty much known for fucking up the technical details...

Re:Tunguska

[Himring]

Exactly. At some point, the plot has to actually work. X Files rocked, but Carter got caught up in the 'revealing for the sake of revealing' treadmill.... His thematic story shows -- meant to connect and be going some where -- never really went anywhere. I think the stand-alone episodes ended up carrying the series....

Heh, one of my favorite parts is when Skully gives up her baby like she's returning a movie.

The Easy Question Is...

[Nom du Keyboard]

The easy question is, was there any record of this lake before the explosion?

Follow up with, are there other lakes that didn't exist before the explosion, but do since?

any idea how large the region is?

[iHasaFlavour]

Tunguska is big, really big..

And extremely remote. It's not even slightly surprising that this was missed.

The original expidition didn't head to the impact site until years after the event, and still they found a devastated surface, and no-one went back again for a very long time.

Until fairly recently it just wasn't feasable to do any kind of large scale study of the region. I think people sometimes forget just how barking huge our planet is, you'd be amazed at the number of area's that are still effectivelly blanks on the map, or mapped by air/satellite only.

Re:Shouldn't this be easy to prove?

[Ironsides]

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." -- Sir Arthur Conan Doyle

They eliminated pretty much everything but an impact crater. Thus, they think it might be an impact crater.

The easy answer (FTFA) is ...

[benhocking]

No. However, it was a poorly surveyed area, so non-existence of (prior) evidence is not evidence of (prior) non-existence.

Re:Shouldn't this be easy to prove?

[btgreat]

Though he said he didn't have positive evidence, it does sound like they have negative evidence. The way you describe their conclusions makes it seem like there was no other reason for a lake to be there so it must have been a crater. What it sounds like to me is that instead of there being no other theories contradicting his case, they were able to disprove those other theories, and all that was left is impact crater.

I don't think there was absence of evidence, it was just that the evidence applied to other theories rather than the impact crater. Simple deductive reasoning: A lake was formed. It could have been by methods A, B, or C. We have evidence that it wasn't A or B. Thus it was C.

Semantics aside, some of the material presented in the article does make the researchers' conclusion seem somewhat dubious. I'm not arguing that the lake was the crater, just that it is possible that the professor is more justified than the article might make him appear at first glance.

Re:Google Maps

[OverlordQ]

Doesn't seem 'natural' to me for an inlet and outlet to be positioned so close together on a lake--though the topography could indeed make that make sense if I could see a map of it.

Go take a basic geography course. Easiest conclusion is that there was a sharp bend in the river there that eroded away and the stream filled in the low-lying areas.

And using Google for comparing foliage is like using a rubber band to measure distances. Pictures could have been taken at different days, times, seasons, etc.

Re:any idea how large the region is?

[Anonymous Coward]

Finding ground zero in 1908 was easy, I've seen many photos from multiple expeditions from the period. It was hard going getting there, not the actual locating it. There is no impact zone because it never hit the earth.

All the trees were blown down in the same direction, so the explorers simply followed them back in the opposite direction until they reached a central point. The center was determined because all trees were pointing away from them, except a few in the center that remained standing, but stripped of limbs.

This is what tells us the thing exploded above ground, just like Hiroshima. Just like Hiroshima, years later, the new plant life exhibited abnormal growth.

Looking for a crater is pointless. At best, there'll be small fragments scattered around. But such meteor debris is found all over the world.

Re:Impact, eh?

[himi]

I call bullshit simply based on the question of where the hell Tesla would have gotten the ~80 petajoules of energy needed for a 20 megaton explosion, regardless of how wonderful his deathray may have been. Even if he was charging some massive bank of capacitors for a year, that would require 2.5GW for the whole year, which is utterly ridiculous for 1908.

himi

Re:The problem is...

[Anonymous Coward]

Sorry, but I have to go with the GP here. Talking about TV shows is about the lamest past-time ever.