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Re: What is a hypervelocity impact?
Jim and list,
I went looking for an answer to this same question several weeks ago, and
found it on p. 123 of Kathleen Mark's book "Meteorite Craters".
She attributes the origin of the term to R.S. Dietz, who studied
shattercones found in the Kentland quarry in Indiana starting in the 1940s.
"Hypervelocities he defined as velocities greater than the speed with which
sound travels through average rock; greater, that is, than about 5
kilometers (3 miles) per second. It is thought that, on average, a giant
meteroite strikes the earth with a velocity of at least 15 kilometers (9
miles) per second. Hypervelocity impact must create an intense,
high-velocity shock (or pressure) wave which spreads out from the impact
point through the surrounding rocks. Therefore, Dietz pointed out,
indications that a large volume of rock has been intensely and naturally
shocked would constitute evidence of meteoritic impact. Perhaps the
presence of shatter cones could provide such evidence."
Mark's book is available from Amazon for about $20, and is recommended
reading for anyone who wants to better understand how terrestrial meteorite
craters came to be recognized as such through the field work and writings
of scientists such as Dietz.
At 08:33 10-06-99 -0700, you wrote:
>Obviously hypervelocity must be pretty fast, but just how fast?
>
>I thought it meant supersonic, but now it is used in relation to a vacuum.
>
>--
>Jim Hurley Freelance graphics artist
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