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.'"

Comments

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.

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

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 and here http://dx.doi.org/10.1016/S0025-3227(03)00086-0 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 and http://www.lpl.arizona.edu/~jmelosh/ImpactTsunami. pdf , but also http://www.spaceref.com/news/viewpr.html?pid=10986 ).

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) 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.