[Rockhounds] Something going on in Yellowstone

[Tim Fisher]

It has happened many times with the same hotspot. Google McDermitt caldera.

-----Original Message-----
From: rockhounds-bounces at lists.drizzle.com
[mailto:rockhounds-bounces at lists.drizzle.com] On Behalf Of Dora Smith
Sent: Thursday, January 01, 2009 6:28 AM
To: J Bryan Kramer; Rockhounds at drizzle.com: A mailing list for rock and gem
collectors
Subject: Re: [Rockhounds] Something going on in Yellowstone

I'm the original not expert.  I learn something totally new about it every
five minutes.   I did learn in teh course of reading through some of that
stuff that apparently the basalt flows predate the hot spot eruptions, some
ancient - shield volcano?   

I've no idea when such a thing happened in North America.    And to be more
confusing I got the impression that there were more ordinary eruptions
before that happened.   Not Earth didn't have an entire history before teh
end-Permian extinction, and there was a smaller flood basalt eruption in
India at the end of the Cretaceous, but I keep thinking that a flood basalt
eruption in North America must coincide with the development of the crust
itself if I never heard of it before.   

But it sounds like you're not familiar with the Yellowstone caldera at all.
This is a very different type of volcano, and they only came to understand
it since I graduated from college 30 years ago.    VERY recent.  Hah, hah,
hah.    Santorini, the volcano that may be associated with the Exodus
phonemena, was of this sort, and so was the eruption of Toba in the
Phillippines 75,000 years ago that brought the human race to the brink of
extinction.   Not a flood basalt, but the next biggest monster.    Sometimes
very thick magma builds up in a huge, abscess-like crater underground under
such conditions that it can't easily erupt to the surface.    When it does
that's a problem enough - you get pyroclastic flows and ash clouds that
travel some little distance.   Like in Pompeii, and Mt. St. Helen's.
But large caldera volcanoes erupt rarely and alter Earth's history when they
happen.    If Yellowstone blew it would kill all life on half the North
American continent and the climate changes would  starve nearly everyone
else on the planet.    Problem is it's due to blow and pressure is building
up, and noone knows how much pressure has to build up or what it all means.
The cycle of that volcano is in hundreds of thousands of years - not our
time scale.    Confusing the issue is that the volcano is caused by a hole
in the Earth's crust that moves over time, relative to I think the North
American plate.  Unfortunately it hasn't at this time moved out from under
the last caldera, but it does appear to have moved in a direction consistent
with its previous movement.   If the volcano significantly changed its
geology it could conceivably begin to erupt less violently.  Though part of
the violence is due to the nature of the magma rather than the hard cap
formed by the previous eruption.   

Several years ago I got interested and put together a web page.
http://www.tiggernut24.com/catastrophes.html   There's an associated page on
teh geology of Sumatra and subduction faults that isn't relevant to much
that goes on in North America (except in teh Cascades).
http://www.tiggernut24.com/earthquake.html   I begin with a link to the web
pages of a PBS special a few years ago.   And the Wikipedia article, and
some general geology of hot spots and caldera volcanos.

One thing that complicates the issue is that between the monster eruptions
every 600,000 to 700,000 years, Yellowstone does have smaller and more
normal eruptions, and these have left more routine lava flows in the area.
I'm not yet up on what kinds of volcano flows leave what kinds of lava
deposits, and it's very relevant to understanding Yellowstone.   I thought
people here would know that.   On my web site I also have links to some new
technical papers that ought to include that information.    

Yours,
Dora Smith
Austin, TX
tiggernut24 at yahoo.com