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Re: Chicxulub's Antipode (Re: cause of death at KT)

Phillip Bigelow wrote:

As an aside:
I read a paper some years ago about how tsunamis would interact with
different geometries of land masses. The paper was mostly theoretical,
but very revealing. It turns out that if a tsunami in deep water hits a
hypothetical vertical wall of land (i.e., a wall extending from
bathyal/abyssal depth to the surface), the surface expression of this
collision will be a plume of water traveling a thousand+ feet *straight
upward*. Not the usual slosh-over-land scenario seen on typical
coastlines. Vertical walls also reflect a substantial percentage of the
tsunami (think of a standing wave). In nature, no such geometry exists
on that scale, the closest being undersea volcanos with 70-80 degree
slopes (but they don't form walls of rock).

There are huge near vertical cliffs off the coast of western Tasmania - I remember seeing the images a few years ago when they were first mapped, and they are spectacular. I found a reference to them at http://www.agu.org/sci_soc/exon.html#figure1, but unfortunately the images won't load into my browser. The text is still of interest, though:

"The South Tasman Rise, a submerged continental block larger than Tasmania, extends from 44° to 50°S. About three-quarters of it, or 150,000 km², was mapped (Figure 1 <http://www.agu.org/sci_soc/exon.html#figure1>). The rise only sank completely below the ocean in the last 40 m.y., and parts of it are less than 1000 m deep. Spectacular faults and giant fault blocks were seen in water depths of 2500-4500 m on its western and eastern sides. The submarine cliffs dwarf anything on Australia, reaching 2300 m high in one place, and have slopes averaging 20° (Figure 3 <http://www.agu.org/sci_soc/exon.html#figure3>). The rise is current-swept, so Neogene sediment cover is thin or absent. It consists of about 20% outcropping rock and 80% sedimentary cover and has outcrops of ancient basement rocks like schist, gneiss, granite, and Paleozoic sediments, as well as younger Mesozoic sediments and Tertiary basalts."


-- ***************** Colin McHenry School of Environmental and Life Sciences (Geology) University of Newcastle Callaghan NSW 2308 Australia Tel: +61 2 4921 5404 Fax: + 61 2 4921 6925