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

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: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: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