From T. E. Groves
Kingston-upon-Thames, Surrey
Dan McKenzie of Cambridge’s earth sciences department has demonstrated that
the basaltic lava produced in the mantle rocks at mid-ocean ridges is released
due to a reduction in pressure on those rocks.
The impact of an asteroid hitting the Earth would have produced not only a
pressure wave from the initial shock but a rarefaction wave when the strata
rebounded, and this rarefaction wave would presumably have followed the same
path as the pressure wave.
Those pressure waves from earthquakes which intersect the Earth’s core can be
shown to be refracted to form a rough focus in the mantle, so I assume that the
same would be true of the rarefaction wave from the impact.
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From all this, I suggest that the impact caused a rarefaction wave so intense
that the focused wave momentarily reduced the local pressure to a level which
brought the basalt melt out of the mantle rocks. This melt, being less dense,
then rose to the surface to create the eruption.
