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From: pamp@bcsaic.UUCP (pam pincha)
Newsgroups: net.space
Subject: Re: Timing of comet showers
Message-ID: <432@bcsaic.UUCP>
Date: Tue, 14-Jan-86 17:11:00 EST
Article-I.D.: bcsaic.432
Posted: Tue Jan 14 17:11:00 1986
Date-Received: Sat, 18-Jan-86 07:50:09 EST
References: <8601102258.AA02103@s1-b.arpa> <6282@utzoo.UUCP>
Reply-To: pamp@bcsaic.UUCP (pam pincha)
Organization: Boeing Computer Services AI Center, Seattle
Lines: 38

In article <6282@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>
>> ... probably much smaller than
>> the ruckus raised by (for example) the massive erruptions that occurred
>> in what is now Yellowstone...
>
>Actually, massive volcanic activity is one of the "dark horse" theories of
>massive extinctions.  There is one province of India that mostly sits on
>a layer of lava *hundreds of meters* thick; that must have been one #@$%&@
>of an eruption, and it has been cited as a possible cause for the Cretaceous-
>Tertiary event that wiped out the dinosaurs.
>
This Indian example would not be a very good example either, since it is
a classic example of a series of flood basalts -- which are very mild in
nature, as opposed to andesitic lavas found at Yellowstone, St.Helens,
Tambor, Karakatoa, El Chichon, Mt. Mazama(now known as Crater
Lake),etc.etc.etc. Basalts are what make up the Hawaiin Islands. They
are characterized as very fluid, high magnesium/iron lavas that
rarely have significant ash falls associated with them. They tend to
form long lava flows eminating from fissures,cracks, and holes that
sometimes form impresive fire fountains. Very little atmospheric
influence. The deposits in India (and the Columbia Plateau of eastern
Washington state that seems to be comprised of flood basalt deposits
(basalt lava flood of great quantites from long fissures int the ground)
are around 10,000 feet thick) would have little atmospheric components
despite their size.

Now there are some very massive ash eruption deposits of the much
more explosive andesite lavas, that would be prime candidates for
mass extinction episodes. The Mt. Mazama explosion put out a massive
amount that spread ash all over the US and beyond. Next to its
remains (Crater Lake) there are fields  of pumice that are 200-500
feet thick. (And as these sort of eruptions go, this was only  a
moderate sized one.)

P.M.Pincha-Wagener
 
volcanic type m