[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Vredefort

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.
----- 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.”