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I am certainly no expert at this, but doesn't all
this rather beg the question how much impact the earth can bear before its
structural integrity is compromised? If a 'mere' one-mile diameter projectile
can produce all this maehem (one million Krakatoa explosions is quite
expressive), then where would a five of more-diameter comet leave
us?
On a sidenote, I rather doubt whether you may
indefinitely extrapolate the size of the tidal wave, considering a limited
volume of water (20,000 of wave feet requires VERY much water), the pull of
gravity, and the construction of the Atlantic seabed.
Ilja
----- Original Message -----
Sent: Wednesday, November 24, 1999 3:13
PM
Subject: Vredefort
Robert Dietz,
writing long before the Alvarez/Chicxulub business, described the Vredefort
Ring in the Transvaal region of South Africa as: “a dome of granite 26 miles
in diameter surrounded by an upturned and even partially overturned collar of
Pre-Cambrian rock. A great ring syncline (the trough of a fold in the rocks)
surrounds the collar, making the entire deformation 130 miles in diameter.
Geologists have traditionally attributed this huge structure to a long
sequence of tectonic events.” He continues:
- Upon reconstruction, the event that produced this structure emerges
beyond doubt as the greatest terrestrial explosion of which there is any
clear geological record. Apparently an asteroid a mile or so in diameter
plunged into the earth from the southwest, for the structure is
overturned somewhat in the northeast. The huge object drilled into the
earth and released enormous shock forces, causing a gigantic upheaval.
Strata nine miles thick peeled back like a flower spreading its petals to
the sun, opening a crater 30 miles in diameter and ten miles deep. The shock
must have reached with shattering force down through the entire 30-mile
thickness of the earth’s crust. Shock pressures of many millions of
atmospheres spread around the collar, forming scattered pockets of
pseudotachylite (fused rock) like raisins in raisin bread. Rock that had
lined the cavity was melted and injected into the rock walls as great dikes
of fused rock… Except for these rocks, which remained molten until the shock
had passed, the collar rocks had intensely and wonderfully shattered, and it
is in these that the shatter cones abound.
He writes further
that the energy of “this grand-scale event…. must have been comparable to that
of the impacts that produced the magnificent rayed craters Tycho and
Copernicus on the moon. The Vredefort blast was a million times larger than
the 1883 Krakatoa volcanic explosion in the East Indies, and several thousand
times larger than the greatest possible earthquake. In the terminology of
nuclear explosions, it was at least a 1.5 million megaton event (one megaton
is equivalent to the force exerted by the explosion of a million tons of TNT).
By comparison the meteorite impact that produced Barringer Crater was a mere
five-megaton explosion.” And yes, he does say that “a giant meteorite falling
into the middle of the Atlantic Ocean could generate a wave 20,000 feet high
that would overwhelm vast areas of the continents surrounding the ocean,
sweeping over the entire eastern seaboard of the U.S., and across the
Appalachians.”
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