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

On Sat, 02 Sep 2006 04:51:01 -0700 "James R. Cunningham"
<jrccea@bellsouth.net> writes:
> Phillip Bigelow wrote:
> > On Fri, 01 Sep 2006 22:09:18 +0200 David Marjanovic
> > - Tsunamic effects would have been minor, because North and South 
> America
> > would have blocked the waveform from the paleo Pacific

> Why?  If I remember correctly, the isthmus of Panama didn't exist at 
> that
> time, if so, there was a direct connection to the Pacific.

It would depend on whether the submerged area (in this case, proto
Panama) is on continental crust (which would make the water shallow
there) or on deep ocean floor.  A shallow sea can dissipate a tsunami
wave quite effectively (by forcing the bottom half of the waveform
upward, while causing the upper half of the waveform to rise up and curl,
dissipating its energy.  The residual energy of the tsunami is then
transmitted as surface waves (which would no longer be called a tsunami).

But if proto Panama was at bathyal depth or abyssal depth, then yes, the
full force of the Chicxie tsunami would have entered the Pacific Ocean.

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).

I have heard that there are one or two coastlines (islands) where
near-abyssal depths are found only a mile or so offshore, but their
localities escape me.  In any case, they are exceedingly rare.