Details Emerging On Tunguska Impact Crater

#space_on_irc.freenode.net (Dusty) writes "Lake Cheko in Siberia has been noted as the probable crater of the 1908 Siberian Tunguska event. This news was discussed here in December, but details on the crater were scant. Now a new paper written by Luca Gasperini, Enrico Bonatti, and Giuseppe Longo (the same team in Bologna, Italy that made news in December) has a horde of new details on the supposed crater. The team visited Lake Cheko complete with their own catamaran and completed ground-penetrating radar maps, side-scanning sonar images, aerial images, and some sample collection of Lake Cheko. Intriguingly, they also imaged an object under the sediment that may be a fragment of the impacting body. Their paper (PDF) includes a lot more details including images, side-scanning sonar image, a 3-D view of the lake, a morphobathymetric map. It's an interesting read, these dudes are good. They plan to return this summer and drill the core if weather permits, hopefully answering the question once and for all." The same team also has a more discursive article in the current Scientific American that includes some detail on the working conditions in the Siberian summer. Think: mosquitos.

Comments

Evidence against

[Anonymous Coward]

"The various samplings from the bottom of Lake Cheko (P'yavchenko, Kozlovskaya) revealed extensive development of silt up to 7 meters deep, indicating an ancient origin for the lake (tentatively estimated at 5000 to 10,000 years), thus completely contradicting the hypothesis of the formation of the lake as a result of the Tunguska meteorite fall (V. Koshelev, 1960)."

http://abob.libs.uga.edu/bobk/tungmet.html

Re:Evidence against

[Anonymous Coward]

Yes, which, if you had read the paper linked to, you would see that they tackle said claim directly.

However, as our study progressed, we began to question the old age of the lake for the following reasons:
1 Our sub-bottom acoustic reïection data show that, of a 10 m thick sediment pile, only the top
1 ± 0.5 m is laminated, ïne-grained, normal lacustrine sediments (Gasperini et al., 2007). The
lower chaotic material appears not to be deposited by normal lacustrine sedimentation.
2 210 Pb and 137 Cs datings on sediment cores from the lake suggest sedimentation rates of roughly 1cm/yr)1(Gasperini et al., 2001). Assuming this rate is mostly due to ïne-grained material transported into the lake from the Kimchu
River, the thin lacustrine sequence is compatible with a young (100 years) age for the lake.

Re:Evidence against

[Anonymous Coward]

from TFA:

"we started our work at
Lake Cheko on the assumption that
it was older than the TE: our objective
was to find markers of the TE in the
lake's sediments. However, as our
study progressed, we began to question
the old age of the lake for the
following reasons:
1 Our sub-bottom acoustic reflection
data show that, of a 10 m thick
sediment pile, only the top 1 ± 0.5 m is laminated, finegrained,
"normal" lacustrine sediments
(Gasperini et al., 2007). The
lower chaotic material appears not
to be deposited by normal lacustrine
sedimentation."

they also give 2 more reasons: the sedementation rate for the above sediment gives an age of ~100years, and numerous personal accounts that never mention or map a lake at the location, only a swamp.

For those that can't seem to find it

[the_arrow]

According to Wikipedia, the lake is at 60.964 N and 101.86 E. Might make it easier to find in Google earth.

Re:For those that can't seem to find it

[meatspray]

Or Google Maps Even

http://maps.google.com/maps?f=q&hl=en&geocode=&q=60.964,+101.86&ie=UTF8&ll=60.963631,101.859055&spn=0.010102,0.016522&t=h&z=16

Not the original paper ...

[Anonymous Coward]

The paper in the posting is a reply to a comment with the contrary interpretation (i.e. that Lake Cheko isn't an impact) [Same paper as PDF]. The critical comment should be cited too.

The original paper by Gasperini et al. (2007) is also available as PDF and HTML.

I'm not particularly convinced by the evidence they present. It's quite circumstantial. What they need to find and sample is an ejecta-related layer in the lake stratigraphy or in a lake nearby, and you'd think that if such a large impactor hit the ground there would be plenty of micrometeorite debris in the sediments of the surrounding area. Geomorphological evidence and age just isn't enough.

Re:Not the original paper ...

[aslagle]

That would be why they're planning to return and make core samples....

Re:Semen Semenov? Ouch.

[21mhz]

Sorry to be a bore, but it's a lossy transliteration.
The name actually sounds more like Semyon Semyonov, pretty ordinary (except I wouldn't give my son a surname echo for a first name; matter of taste).

Could have been a comet

[Solr_Flare]

Well, there is little doubt by any reputable scientist that it was some form of extra-terrestrial impact, what has remained in contention for a long time was what exactly impacted at Tunguska.

One side insists it was an Asteroid, but the material that would normally be present at an asteroid impact just isn't there. Others argue it was a comet, but analysis of comets in the last decade or so has put some real doubt into that theory as well.

At this point they pretty much have almost everything else worked out, from the velocity whatever it was had, where it traveled, where it likely went kaboom. They just don't know what the make-up of the object was. This report goes a long way towards proving exactly what the celestial object was.

Re:Very interesting article

[Doc Ruby]

No, the timing of that event was as close as it was going to get to causing any damage to the Earth:

However, since the Earth also travels around the Sun with an average orbital speed of 107,218 km/h, 3 hours earlier the Earth would have been about 300,000 km away from the intersection of its orbit with the projectile's orbit at the time that the South Asian region was rotated towards the projectile's path. So the projectile would have missed the Earth entirely by over 114 times the Earth's radius, about the distance to the Moon, and probably never even noticed by anyone but a few astronomers. Nice try, though.

Re: Mosquitos ++

[mev]

Not married, no kids. Own a duplex, have tenants to take care of it when I'm gone. Work in tech which pays fine and have had an employer that has been willing to allow an occasional LOA. Live frugally and save money rather than rely on sponsors.

Russia is a relatively expensive country, but bicycle travel and camping is not that expensive. It is also a good way to experience a country since it brings you in out of the way places without as many tourists.