Ancient Crash, Epic Wave

avtchillsboro writes "A NY Times article says that scientists have discovered evidence a massive impact crater 18 miles in diameter and 12,500 feet under the Indian Ocean. The evidence, they say, consists of four massive chevron-shaped sediment deposits on the island of Madagascar. 'Each covers twice the area of Manhattan with sediment as deep as the Chrysler Building is high. On close inspection, the chevron deposits contain deep ocean microfossils that are fused with a medley of metals typically formed by cosmic impacts. And all of them point in the same direction — toward the middle of the Indian Ocean where a newly discovered crater, 18 miles in diameter, lies 12,500 feet below the surface.' Interestingly, the scientists say that the currently accepted notion that there have been no major impacts in the last 10,000 years is wrong; and that major impacts occur on average every 1,000 years, rather than the currently accepted 500,000 to 1,000,000 year interval. '(T)he self-described "band of misfits" that make up the two-year-old Holocene Impact Working Group say that astronomers simply have not known how or where to look for evidence of such impacts along the world's shorelines and in the deep ocean.'"

See it in context thanks to Google Maps

[Anonymous Coward]

If you're interested in looking at the Google Earth view of the features mentioned in the article, look here [google.com].

Be sure to look up and down the coast on either side of this particular feature.

Re:Lots of water

[Remus Shepherd]

Most researchers never bothered looking for deep ocean impact craters because they assumed the craters would be covered in sediment. In fact, they probably *are* covered in sediment, and it's only because of the new gravimetric technology that we can see them at all.

Another picture of the chevrons is here. [usgs.gov] Features like this are visible all over the world, as the graphic accompanying the NYT article shows. Pretty spooky...I just never realized before how much scar tissue the Earth has on her.

Tsunami "expert" Ted Bryant

[Spalti]

After RTFA, I found out Ted Bryant is the Tsunami expert in this group of researchers. While researching for my thesis, I was confronted with his book, "Tsunami: the underrated hazard". This work, while being quite easy to understand, can hardly be called scientific based on his way of making citations (grouping all references at the beginning of a chapter which leaves you without the possibility to look up where he drew his conclusions from).

Reviews of his book can be found here: http://hol.sagepub.com/cgi/reprint/12/5/637 [sagepub.com] and here http://dx.doi.org/10.1016/S0025-3227(03)00086-0 [doi.org] and here: Synolakis, C.E., and G.J. Fryer, 2001. Book Review: Tsunami: the underrated hazard by Edward Bryant, Eos, Trans. Am. Geophys. Union, 82, 588 (can't find a quick link right now).

The existence of so-called megatsunamis is hardly scientifically proven, especially not by the work of Bryant (he classified sedimentary features embedded in sandstone somewhere in Australia as relics of an ancient megatsunami when in a nearby graveyard the same sandstone wouldn't resist local climate and erosion for more than a few centuries).

The propagation of tsunamis with huge waveheights seems to be limited due to dispersion effects and the so-called "Van-Dorn-Effect" should cause these huge waves to break as soon as they reach the continental shelf (http://www.agu.org/pubs/crossref/2005/2004GL02191 8.shtml [agu.org] and http://www.lpl.arizona.edu/~jmelosh/ImpactTsunami. pdf [arizona.edu] , but also http://www.spaceref.com/news/viewpr.html?pid=10986 [spaceref.com]).

After working some time in the field of megatsunamis (my thesis concentrated on the Cumbre Vieja Scenario postulated by Ward&Day back in 2001 (http://www.es.ucsc.edu/~ward/papers/La_Palma_grl. pdf [ucsc.edu]) and, based on scientific grounds, I had to "debunk" it as several researchers have done before me), I have learned to take these reports with a grain (or better, a big portion) of salt.

Re:Interesting methods, troubling results

[Dunbal]

Of the dozens of films, none come from areas where the waves were 20 feet or higher,

      Don't think of a tsunami as a traditional wave - it's not. It's a wave with an EXTREMELY long wavelength, in the km range. So from your perspective it will just look like the ocean decides to come inland. The water level rises suddenly, and keeps rising. Don't look for a "crest", there won't be one. Just water coming inland constantly, and knocking everything down. Then the "wave" recedes, because once the energy is spent, well, we all know water likes to flow downhill...