[meteorite-list] meteorites and tsunamis

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Tue Dec 28 21:50:38 2004
Message-ID: <41D21B59.6A6416FB_at_bhil.com>

Hi,

    The very large U. of Arizona Press collection
"Hazards Due To Comets and Asteroids" (1994) has in it a
paper "Tsunami Generated by Small Asteroid Impacts" by
Hills, Nemchinov, Popov, and Teterev. The classic
"Effects of Nuclear Weapons" by Glasstone and Dolan is
good too (it has a chapter on tsunamis).
    The figure of a 100 meter stone (or 40 meter iron)
given by Herbert is a significant one. Smaller objects
than these are likely to be slowed down considerably
coming through the atmosphere (or break up altogether)
with a serious loss of energy, but a 100 meter stone or
40 meter iron will reach the ground pretty much at its
celestrial velocity.
    When you talk about a tidal wave's height, there are
two "heights." First, there's the height of the
undisturbed free-travelling ocean wave, and second, the
"runup height" which is the height the wave achieves
when it runs up on the land and is forced higher and
higher. Usually the runup height is 10 or more times
higher than the ocean wave, depending on the
characteristics of the shore and its shallows.
    In Sri Lanka a thousand kilometers or more from the
epicenter, reports are of a 15 to 30 foot runup height.
In Sumatra, the runup height must have been much
greater, but there are few witness reports because
anybody close enough to get a really good look died.
    Reading through these two sources, I get the
impression that the recent tidal wave was somewhat
smaller than that that would have been produced by a 100
meter stone hitting the ocean at the same spot. In
evaluating that statement you should know that I think
the recent disaster was much worse than we realize even
now.
    There is a phenomenon of big disasters, that they so
devastate certain areas that no word gets out at all and
the full scale of the disaster is not appreciated. For
example, on Sunday morning the deaths were given as
14,000 and today (Tuesday) the figure given is 52,000. I
would not be surprised if the actual death toll when it
is fully known were closer to 175,000 +/- 60,000.
    In Banda Atche (capital of the Sumatran province
nearest the epicenter), a London Financial Times
reporter interviewed survivors in neighborhoods where
there were survivors and was told by the residents that
the death toll was 80% of their neighborhoods. Banda
Atche is a city of 100,000 people, so it's quite likely
that there were 52,000 or more deaths in just that one
city.
    A town of 10,000 people ten miles down the coast
from Banda Atche has not yet even been reached by
anybody from the outside, but flyovers have not spotted
any living moving human beings there. Counted deaths in
Sri Lanka are officially up to 22,000 and those figures
do contain any reports from the rebel-controlled north
of the island. And none of the counted death totals
includes the large numbers of people that must have died
when they were swept out to sea. But there are reports
of very large numbers of corpses washing up on the Thai
and Malaysian west coasts.
    At any rate, even this considerable catastrophe is
less than what the smallest asteroid (100 meter) that
could make it through the atmosphere full-tilt would
produce. A 400 meter object like 2004 MN4 striking the
ocean at 20 km/s would produce a tsunami about 100 times
bigger than the recent one. It would achieve runup
heights of about 200 feet even 1000-2000 kilometers
away.
    So it's a really good thing that 2004 MN4 is going
to miss us in 2029. Thanks to those "pre-discovery"
plates, Herbert can get his sleep, none of us have to
start building arks or move to mountain tops!


Sterling K. Webb
-------------------------------------------------------------

harlan trammell wrote:

> i am looking for some definitive information in regard
> to the size of meteorites that could generate
> tsunamis like the big one in the indian ocean. is
> there any info on this? are their any graduate or
> doctoral level papesr published on this?
>
Received on Tue 28 Dec 2004 09:50:01 PM PST