[Geysers] More on dating geyser water

[Ralph Taylor]

I forwarded Scott Bryan's rather negative comments on Dr. Hurwitz's previous
note on dating geyser water.  Shaul was kind enough to elaborate on the
previous note and explain further.  His answer follows:




1. I previously wrote a piece for the group about age dating of water and
described why it is tricky and very much assumption-dependent. To that
extent, here is a paragraph from the abstract of the modified Rye and
Truesdell paper which appears in the new USGS Professional paper
(http://pubs.usgs.gov/pp/1717/downloads/pdf/p1717H.pdf):

 

"Derivation of this deep fluid solely from present-day recharge is
problematical. The designation of source areas depends on assumptions about
the age of the deep water, which in turn depend on assumptions about the
nature of the deep thermal system. Modeling, based on published
chloride-flux studies of thermal waters, suggests that for a 0.5- to
4-km-deep reservoir the residence time of most of the thermal water could be
less than 1,900 years, for a piston-flow model, to more than 10,000 years,
for a well-mixed model.".

Currently several studies are trying to provide some constraint on the
apparent age of the thermal water by using a variety of isotopic techniques.
Nevertheless, each one of these methods depends on many unconstrained
assumptions.  Our hope is that integration of the different techniques will
narrow the assumptions and allow a better estimate.

I also want to emphasize that since Rye and Truesdell have made their
tritium measurements (in the 1970's and 80's) tritium levels in the
atmosphere have decreased significantly, but modern techniques to allow
detection of much lower concentrations of tritium and with a much greater
precision.   In a study carried out in the past year we have detected
measurable tritium in four of the five geysers we sampled (Old faithful,
Aurum, Daisy, and Oblong).  In Grand except for one sample with low tritium
concentrations samples were below detection limit.  So far we have analyzed
24 geyser samples and by August or September we hope to have results from
ten more samples.

 

2. With regards to the filtering approach we used to detect seasonality of
Old Faithful.  In the paper we published in the journal Geology we explained
our filtering approach and applied the same rigorous criteria to all geysers
analyzed.  We note that the detected seasonality and annual variability
could not be random and filtering just enhanced the signal, it did not
create it.

 

3. With regards to George Marler's paper "Seasonal changes in ground water
in relation to hot spring activity" published in American  Journal of
Science in 1964 - indeed the observations documented in that paper (based on
limited observations) indicate that geysers have seasonal characteristics.
We did not cite this (excellent) paper because of space restrictions, but
certainly highly regard it. 


Shaul Hurwitz
U.S. Geological Survey MS #439
345 Middlefield Rd.
Menlo Park, CA 94025
Tel: (650) 329-4441
shaulh at usgs.gov
http://wwwrcamnl.wr.usgs.gov/hydrotherm/

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