<html><head><style type="text/css"></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif"> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">I've thought about this problem before.  The post below is well written, but it never specifically includes the radioactive decay into the calcification.  1 TU now presumes 16 TU input if the water is about 50 years old.  There is a lot of accounting to be done.</DIV> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif"> </DIV> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">But the real problem is with low concentrations of tritium, which is the case.  This could be from young (~50 years) water, or mixing of very old water with some proportion of brand new water near the surface.  Both would give the same result.</DIV> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif"> </DIV> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">The 500 year old figure has often puzzled me, because that's 41 half lives of tritium, after which there's no way you could detect tritium in any predicitive way.  That figure must have been derived from some other method.  Anyone know?</DIV> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif"> </DIV> <DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif"><BR>-----------------<BR>Ralph,<BR><BR><BR>Here is something for the geyser mailing list:<BR><BR>Dating water is tricky, particularly in geysers where waters are boiling. <BR>One method scientists use to date water involves measuring the <BR>concentration of tritium (3H), which is a short-lived radioactive isotope <BR>of hydrogen with a half-life of 12.32 years.  Some tritium forms naturally <BR>as cosmic radiation interacts with the upper atmosphere, but during the <BR>1950s and early 1960s, testing of nuclear weapons raised atmospheric <BR>concentrations hundreds of times above the normal background <BR>concentration.  Tritium concentrations in the atmosphere have decreased <BR>following the signing of the Nuclear Test Ban Treaty in the early 1960s <BR>and have since approached natural levels.<BR><BR>By measuring tritium concentrations in spring (or geyser) waters, what is <BR>actually being dated is the last interaction between a water molecule and <BR>the atmosphere.  However, when precipitation (with a known tritium <BR>concentration) enters the subsurface (groundwater) system, mixing of the <BR>water molecules occurs, so that at any given location along the flow path <BR>from recharge to a geyser, a finite volume of water would represent  some <BR>integration of water molecules from many years.  It is not realistic to <BR>assume that the entire volume erupting from a geyser percolated into the <BR>subsurface at the same time.  More likely, the erupted volume is a mixture <BR>of water molecules that fell as precipitation over a rather long time <BR>period.  To illustrate this point of mixing my USGS colleague (emeritus) <BR>Bob Fournier reported in a 1969 paper in the journal Science that more <BR>than 24 consecutive eruptions were required to clear Old Faithful of a <BR>tracer (rhodamine B) in a 1963 experiment.<BR><BR>Nevertheless, some inferences can be made by using tritium.  For example, <BR>this year's precipitation in Yellowstone has a concentration of 10 Tritium <BR>Units.  (One tritium unit equals 1 tritium atom in 1018 hydrogen atoms). <BR>If for example the tritium concentration of a geyser is 5 TU, we calculate <BR>that the water could represent a 50:50 mixture of this year's <BR>precipitation and pre-bomb (more than 50-year-old) precipitation (0 TU). <BR>However, this is not a unique solution, both because of subsurface mixing <BR>and the time-variance of the tritium input.  (The most straightforward <BR>interpretation of tritium occurs when its concentration is 0 TU, and we <BR>can confidently infer that none of the water has interacted with the <BR>atmosphere for 50 years.)<BR><BR>In the past year, our group at the USGS, in collaboration with the <BR>National Park Service, has sampled the waters of five geysers (Old <BR>Faithful, Daisy, Grand, Oblong, and Aurum) six times.  We are still in the <BR>process of analyzing the data, but so far we have found some detectable <BR>tritium in all five geysers (though always less than 1 TU).  This implies <BR>that some recent water molecules are part of the total volume erupted.<BR><BR>Other methods used by scientists for dating "young" water include <BR>measuring the concentrations of chloro-fluorocarbons (CFCs) and noble-gas <BR>(mainly argon) isotopes dissolved in water.  As with tritium, the data <BR>require considerable interpretation.  "Older" waters are often dated using <BR>radiocarbon methods, but this is problematic in volcanic areas such as <BR>Yellowstone because of the input of magmatic carbon.<BR><BR>The short answer to Lucille Reilly's question following what she heard <BR>during a geyser walk "OF's water supply is about 500 years old" - I don't <BR>know how that info came about....<BR><BR>I hope the discussion group finds this helpful and not confusing!<BR><BR>P.S.  There was some more press coverage of the geyser paper; here are two <BR>of them:<BR><BR><A href="http://livescience.com/" target=_blank>LiveScience.com</A> - <BR><A href="http://www.livescience.com/environment/080603-old-faithful.html" target=_blank>http://www.livescience.com/environment/080603-old-faithful.html</A><BR><BR>Casper Star Tribune - <BR><A href="http://www.trib.com/articles/2008/06/04/news/wyoming/doc48469fcdaa2b65920643" target=_blank>http://www.trib.com/articles/2008/06/04/news/wyoming/doc48469fcdaa2b65920643</A><BR>77.txt<BR><BR><BR>Cheers,<BR><BR>----------------------------------------------------<BR>Shaul Hurwitz<BR>U.S. Geological Survey MS #439<BR>345 Middlefield Rd.<BR>Menlo Park, CA 94025<BR>Tel: (650) 329-4441<BR><A href="mailto:shaulh@usgs.gov" ymailto="mailto:shaulh@usgs.gov">shaulh@usgs.gov</A><BR><A href="http://wwwrcamnl.wr.usgs.gov/hydrotherm/" target=_blank>http://wwwrcamnl.wr.usgs.gov/hydrotherm/</A><BR>-----------------------------------------------------<BR><BR><BR>_______________________________________________<BR>Geysers mailing list<BR><A href="mailto:Geysers@lists.wallawalla.edu" ymailto="mailto:Geysers@lists.wallawalla.edu">Geysers@lists.wallawalla.edu</A><BR><A href="https://lists.wallawalla.edu/mailman/listinfo/geysers" target=_blank>https://lists.wallawalla.edu/mailman/listinfo/geysers</A><BR></DIV></DIV></div></body></html>