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This forwarded (with permission) from Jim Cunningham:
----- Original Message -----
From: James R. Cunningham <firstname.lastname@example.org>
Sent: Wednesday, November 24, 1999 7:56 PM
Subject: 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?
Nowhere near the critical energy for disruption -- even a far more massive
five mile diameter asteroid wouldn't be close. The impact that appears to
have split the moon off from the earth was the 'big one'.
> 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.
You're quite correct. You can't. It's been suggested that the Chicxulub
impact ionized all the ocean within a 100-200 mile radius of the impact,
converting it and the underlying rock to a plasma, so that it wasn't
available for the tsunami.
So you get an initial outbound tsunami beginning a hundred miles or so
outside that radius, then a secondary outbound tsunami created by the
reflection of the inbound tsunami which fills the void left by the original
impact (less the seawater which is boiled off into the atmosphere). But it
really isn't initially like a wave; it's more like a tidal bore.