[Nmcaver] Volcanoes and the MemDay Regional

[Duke McMullan N5GAX]

This year's Late Spring Regional takes place in the heart of NM's volcano
country, at the intersection of the Jemez Lineament and the Rio Grande Rift.
The Jemez Mountains, of course, are our biggest example of recent vulcanism
(Or has that word been replaced by volcanism?), but we'll also be on the
edge of the Cerros del Rio field, across the river from our campsite.  I
think.

Those approaching Santa Fe from Albuquerque will pass the San Felipe field,
with the S. Felipe Volcano showing a classic shield profile from the top of
the Santa Ana / San Felipe Mesa as you pass Bernalillo.

Immediately north of Bernalillo, look for the oddly-shaped Canjilon Hill
just beyond the river -- it's the mesa with the basalt plug sticking up at
its northeast "corner".  In addition to intrusions, the mesa contains the
remnants of a maar.  You can see the strata dipping down and back up where
the river has chopped a slice through the side of the mesa.

Online, the Cascades Volcano Observatory says the following about New
Mexico:
                                       ##########################
It seems that each of the Southwestern states has an apparent geologic
specialty. If so, and Arizona is the big Canyon state, Utah is the Mesozoic
fauna state, and Colorado is the big snow-capped Rocky Mountains state, then
what is New Mexico? New Mexicans need only look out their windows for the
answer: New Mexico is the Volcano state. New Mexico has one of the greatest
concentrations of young, well-exposed, and uneroded volcanoes on the
continent. And as a bonus, it is also the Rift Valley state; it has one of
only four or five big continental rifts in the world, East Africa being one
of the other ones. The fact is, New Mexico is one of the best places to
study the natural history of volcanoes. Twenty percent of the U.S. National
Parks and Monuments based on volcanic themes are in New Mexico. There are
more here than Arizona, Idaho, Oregon, and Washington combined.
Volcanism in New Mexico is not "extinct," but is dormant. The record of
volcanism in New Mexico is continuous over tens of millions of years, and
there is no reason to think it stopped magically 3000 years ago with the
eruption of several cubic kilometers of basalt (McCartys lava flow, El
Malpais). New Mexico has one of only three large mid-crustal active magma
bodies (Socorro) in the continent. (The others are Long Valley, California
and Yellowstone, Wyoming.) The Socorro area is one of the few areas where
there is a dearth of young volcanoes, so perhaps the Rift is working on
filling out its volcano landscaping.

Every major type of volcanic landform (composite volcano, shield volcano,
volcanic caldera, major ash-flows, pahoehoe and aa lava, maar crater,
fissure eruptions, cinder cones) occurs in New Mexico.
                                       ##########################

That's found at:

http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_new_mexico.html)

But, enough.  If this sort of thing interests you, hie your browser over to
the above site and start snooping around.  The New Mexico Museum of Natural
History (NMMNH -- how do they pronounce that?) has a lot of great stuff.
Find them at:
http://www.nmmnh-abq.mus.nm.us/nmmnh/sci_volcanoes.html

That page contains a great deal of information, but probably the best item
is found near the bottom of the page where a shortcut is found to "A guide
to volcanoes in New Mexico, which is subtitled "An Abbreviated Guide for
Non-Specialists."  It's a 1.1 MB pdf document, so download may take a while.
You should be able to examine or download it directly with the following
url:
http://www.nmmnh-abq.mus.nm.us/nmmnh/pdf_files/NMvolcanoes.pdf

For a lot more, just goog <"New Mexico" volcanism> or something similar.
You'll get enough back to keep you busy for quite a while.

See you all a White Rock,

                    d
--
As with bad breath, ideology is always what the other person has.
                                   -- Terry Eagleton
Duke McMullan n5gax nss13429rl(fe) (505)255-4642 mtmduke at qwest.net