From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 26 Dec 2007 21:01:30 -0600
Message-ID: <08de01c84834$c8b280e0$b64fe146_at_ATARIENGINE>


    With all this talk about Canyon Diablo, I thought
it would be fun to try to model it with LPL Impact
Calculator, While I thought it would be fun, it was
actually exasperating. I started off with all the usual
things about the impactor that one has read in the
literature for decades. First, everybody says a 100
meter or bigger impactor. Well, the Calculator always
returns a crater way too big, no matter what the angle
or speed, for an impactor that big.

    So, you find that you need a much smaller impactor
than that 100 meter job they're always talking about.
Another truism is that it was a low-angle, low velocity
object. Angle doesn't change things much, but speeds
make a big difference. For all the impactors under 25 km/s,
the Calculator says "No Fireball, No Vaporization."
And we know that there was a lot of vaporization... The
Famous Spherules. So I tried a 75-meter impactor at
27 km/s and got roughtly the right size of crater. Smaller
ones wouldn't vaporize and larger ones made bigger
craters than the real crater.

    I was calculating for a distance of 50 km (thinking
of EP's and Mike's 30 miles away), and I got the
following at 50 km: A Richter force 5.8. The fireball is
about 1000 meters in diameter, 5 times brighter than the
Sun, puts out 2.2 times as much heat as the Sun and lasts
for 16 seconds.

    The blast overpressure at 50 km is 0.85 psi, the wind
of the blast is 30 mph, and the sound as loud as heavy
traffic. There is a light dusting of powdered ejecta less
than a millimeter deep, but there will also be a buncha
chunks with an average size of 3 inches. Ouch! It's about
a 5 Megaton impact.

    I moved in to 20 km from the impact, and I was in big
trouble! The fireball appeared 14 times bigger than the Sun,
and the heat flux was 16.4 times that of the Sun -- first degree
burns over most of the body. The blast overpressure is
3.5 psi; the wind is 120 mph; the ejecta blanket is under a
half-inch thick, but the average tossed "chunk" is about
a yard across! Still 5 Megaton...

    Out at 33 km (20 miles) is where things got survivable.
No burns, only a 50 mph wind, no burst eardrums, and all you
have to do is dodge 9 inch chunks of hot iron. Still 5 Megaton...

    I tried smaller but faster impactors (but with the same
kinetic energy) and with this one small change, suddenly,
there was no crater: the iron impactor airburst! Frankly,
I always figured irons were more resistent. It fragmented
at a height 94,000 feet. There's a small crater field of
numerous small pits, but no crater at all. No fireball. No
vaporization, 2 psi overpressure, a 75 mph gust of wind,
windows shatter, and no one gets hurt. Still a 5 Megaton
blast, but 20 miles up as well as 20 miles away.

    If Canyon Diablo had been this kind of an airburst,
there would have been some big house-sized chucks sitting
on the desert floor here and there, a dozen or two shallow
pits, and millions of tons of small Diablo-ites scattered for
many miles -- they'd sell for a penny a piece. It would be...
Campo del Cielo! (which must have formed just that way).

    Fiddle as I might, I could never get a vaporization event
out of an airburst; it takes a ground impact, and the greater
the vaporization, the bigger the crater. From this I surmise
that an iron-vapor event would leave a heck of a mark.

    Unless... it's on the surface of a 3000 meter ice cap, of

Sterling K. Webb
----- Original Message -----
From: "E.P. Grondine" <epgrondine at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Wednesday, December 26, 2007 6:22 PM
Subject: Re: [meteorite-list] ARCTIC IRON

Hi Mike -

One problem here is that we don't know where in Alaska
or Siberia these fossils come from. (Firestone's team
or the Calgary shop owners might know where the
Alaskan tusks were found.) The straight between Alaska
and Siberia is not that wide. I'm thinking that this
thing has to range about maybe 300-500 miles, but who

I don't know what the spread pattern was for shperules
from the Barringer imapact as Nininger measured it
was, and I don't know if Nininger managed to find the
whole field. Ballistic re-entry of irons over a fairly
large range is still a possibility, if not a

We had freezing sleet blowing horizontal here the
other day in Illinois, and my guess is its going to be
several months before Alaska becomes accessible...

good hunting,
E.P. Grondine
Man and Impact in the Americas

PS - I don't remember exactly the 1.8 psi range of
death by blast from Barringer, but for sure the rain
of molten iron and succeeding fires would have been
fatal out to a considerable range. I suppose I should
remember all of this dead on, but since my stroke that
has not been possible.

>Why would a crater the size of Canyon Diablo pepper
>Mammoths in both Siberia and Alaska?
>Meteor crater is big, but my god, you would not have
>been killed if you were 30 or 40 miles away, and you
>think it would shower iron with enough force to
>things thousands of miles away? I am confused here.
>Michael Farmer

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Received on Wed 26 Dec 2007 10:01:30 PM PST

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