Re: [asa] Super volacanos (sic)

On Sunday Randy wrote:

< This past week pbs aired a Nova episode called Mystery of the
< Megavolcano, http://www.pbs.org/wgbh/nova/megavolcano/.

< I noted in particular the comment about the specific chemical
< signature that is unique to each volcano. Volcanic ash carries the
< chemical signature for its unique volcano. I wondered whether
< there has been any attempt by the YEC community to address this?

Randy,

To my limited knowledge, the only attempt by any YEC geologist to use
volcanic ash characteristics and geochemistry to determine a source
volcano was the surprising study report by Steve Austin and Bill Hoesch
that I wrote about last August <
http://www.calvin.edu/archive/asa/200608/0066.html> and <
http://www.calvin.edu/archive/asa/200608/0201.html>. They were looking at
ash in the Jurassic-age Morrison Formation of the Colorado Plateau and
using the chemical proportions of radioactive and daughter elements to
identify an possible ash source area in California. Most people would
call this procedure 'radiometric dating' but in a sense that ratio is
simply another chemical signature of the ash layer.

By the way, if you want to try your own hand at identifying a source
volcano based on converging lines of evidence and chemical composition of
ash, NOVA has produced a great little junior high to high school science
class exercise to accompany the "Mystery of the Megavolcano" program. You
can download the teacher's guide at <
http://www-tc.pbs.org/wgbh/nova/teachers/activities/pdf/3312_megavolc.pdf
>. Print off the last 4 pages of the 11 page guide and then see if you
can identify the source of the volcanic ash that killed hundreds of
animals in what is now Ashfall State Park in Nebraska. This exercise uses
real data from the ash found in Nebraska and from 8 possible
volcanos/megavolcanos in the western U.S. (Don't cheat and look at the
teacher's answers on pages 3, 5, & 6!)

< They simply deny the validity of the determination of the age of the
< volcanic rock but the chemical composition is another matter. The
< flood would have widely dispersed and mixed the ash from all the
< various volcanos. However, the ash/rock is very well contained
< geographically. Do they say all these volcanos happened after the
< flood? Or haven't they discussed it? Perhaps this is another useful
< talking point.

Volcanic ash layers are found mixed throughout the sedimentary rock
sequence. As you get deeper and deeper in the stack (and hence older and
older), the ash layers are more altered and harder to recognize. (Volcanic
glass, a major component of ash, is not stable and eventually
recrystallizes (devitrifies)). Just west of Denver, on Dinosaur Ridge, a
small ash layer was identified in the middle of the Cretaceous Dakota
Formation. For years we have been telling students that the dinosaur
footprints found in the layers just above were approximately 100 million
years (MY) old based on stratigraphic and fossil evidence suggesting an
age of Early to Middle Cretaceous. Zircon crystals were recently removed
from the small ash layer and dated by a uranium-lead radiometric method.
The results came back from the lab at 105.6 (+/- 1.3) MY. Another
convergence of evidence! The chemistry of the ash has not yet been traced
back to a specific volcanic source. I bring this up because the Dakota
Formation that contains this ash layer has been identified as a Flood
deposit by YECs. (See "Dinosaur Ridge on a Young Earth" by Ed Holroyd.)
Therefore, according to YEC literature, distinct volcanos were erupting
during the Flood.

As you note in your initial post, "the flood would have widely dispersed
and mixed the ash from all the various volcanos". This is especially true
since a common large component of volcanic ash is pumice and pumice
(literally rock foam) floats. After the large Krakatoa eruption in the
August of 1883, large rafts of pumice floated around the Indian Ocean for
months to years. Distinct geographically-contained volcanic ash layers
with geochemical fingerprints are very hard to reconcile with deposition
during a single year-long global flood.

Steve
[Opinions herein are my own and not to be attributed to my employer, my
spouse, my church, etc]
_____________
 Steven M. Smith, Geologist, U.S. Geological Survey
 Box 25046, M.S. 973, DFC, Denver, CO 80225
 Office: (303)236-1192, Fax: (303)236-3200
 Email: smsmith@usgs.gov
 -USGS Nat'l Geochem. Database NURE HSSR Web Site-
  http://pubs.usgs.gov/of/1997/ofr-97-0492/

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Received on Tue Oct 3 12:15:07 2006