PLEASE NOTE:


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Subject: Roberto Gorelli article on recent megaton class impacts
To: cambridge-conference@livjm.ac.uk
Date sent: Mon, 26 May 1997 23:31:03 -0500 (CDT)
From: pib@nwu.edu

I came across the following message from George Zay while perusing the
archives of the meteorite mailing list at Meteorite Central. Zay summarizes
an article by Roberto Gorelli which appeared in a recent issue of the
International Meteor Organization journal "WGN." I have not read the
original article myself. Mr. Gorelli presented a paper on this same topic
at last summer's Tunguska '96 conference. I do not believe the proceedings
of that conference are available yet. They are scheduled to appear in a
special issue of the journal "Planetary and Space Science."

-- Phil "Pib" Burns
Northwestern University, Evanston, IL. USA
pib@nwu.edu
http://pibweb.it.nwu.edu/~pib/


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I thought some of you might find this of some interest?
George Zay
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Roberto Gorelli of Italy wrote a short article in the International Meteor
Organizations journal WGN about "Real Frequency of Meteoritical Events of
Megatonic Class".

Paraphrasing the articles conclusion, he calculated that the frequency of a
Megatonic impact somewhere over the earth is at every 10 years and the
frequency of such an event occuring over land would be about every 30-35
years...and this is believed to be an underestimation. He provided a list of
the known 7 megatonic impact events of the last two centuries. They are:

1. April 5, 1800. North America: Fall of a big meteorite with an earthquake
and destruction of a forest. Released Energy unknown. Source: E.Howard in
Transactions Philosoph. Ann; 1802, 23, Chapter 338.

2. November 9 or 19, 1819, Canada and Northern United States: Black rain
accompanied by bolids, shaking as of an earthquake, and obscuration of the
sky, Released energy unknown. Sources: (1) Zurcher, Meteors. p.238; (2)
Edinburgh Philosophical Journal 2-381; (3) F.G. Plummer in U.S. Forest
Service bulletin no. 117.

3. February 24, 1885, Pacific Ocean Long: 170 deg East, Lat: 37 deg North;
Red inflamed sky, blinding mass fell on the ocean and lifted a big mass of
water. Released energy unknown. Source report of Mr. Innerwish transmitted to
the Hydrographic Office in Washington by the San Francisco branch and
published in Science, 5-242.

4. May 3, 1892, Sweden, Norway, Denmark and surrounding locations: Fall of
500 tons of dust. Released energy unknown.

5. June 30, 1908, tunguska, Siberia, Russia; Released energy: 12.5 megatons.

6. August 13, 1930, Rio Curuca, Amazonia, Brazil: Released Energy: 0.1 - 1
megaton.

7. December 11, 1935, West Marudi Mountain, British Guyana, Released Energy:
more than 10 megatons?

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CCCMENU CCC for 1997

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