[Geysers] Dating Geysers Techniques and Results

[Jack Ashe]

There is an extraordinarliy great variation in estimates of  geyser age available on the internet (1000- 40,000 yrs) even  for the same structure (Castle Geyser).  I am assuming that there are NPS Visitor Center workers on this list. 
What do you tell visitors about the ages of the geyser basin features?
Is the info pasted below the best recent information on geyser dating?

 
Castle Geyser and Bobby Sox Trees: Pulses and Pauses in the Development of Hydrothermal Features in the Upper Geyser Basin, Yellowstone National Park, Wyoming
Foley, Duncan 
American Geophysical Union, Fall Meeting 2007, abstract #V53B-1334 
Preliminary 14-C dating of Castle Geyser, combined with observations of living and dead trees in hydrothermal areas, suggests that hydrothermal systems in Yellowstone have pulses of activity interspersed with pauses of little or no activity. Between the time scale of volcanic activity, with pulses and pauses over thousands to hundreds of thousands of years, and geyser eruptions, with pulses and pauses over minutes to decades, lies the time scale for pulses and pauses in the development of individual hydrothermal systems and large thermal basins. Castle Geyser has long been noted as being among the largest, and therefore probably oldest, geysers in Yellowstone. Watson (1961) proposed an age of 8000 years for the geyser cone, and Bryan (2001) suggested that it is 5000 to 15000 years old. Recent dating, accompanied by 3-D laser mapping, suggests a complex, multi- stage development of the geyser. AMS 14C dating of microbial and pollen carbon trapped in
 siliceous sinter that forms a broad, gently-sloping shield at the base of the geyser cone yields ages of 8787 +/- 60 years BP and 10472 +/- 70 years BP. Carbon from sinter on the cone of the geyser yields ages equal to or younger than 1038 +/- 35 years BP. No samples dated so far have ages between 8787 and 1038 years BP. The morphology of the geyser suggests that the pause after shield formation was followed at least one stage of terrace formation (from either hot spring or pool-type geyser activity), which in turn has been followed by the construction and partial destruction of a massive cone. Where thermal waters are high in silica, thermally killed trees may develop white lower trunks, informally known as "bobby sox." Forest growth implies a time of no thermal activity; forest death, where clear evidence of thermal activity exists, implies inception or rejuvenation of hydrothermal activity. Many thermal features, such as Castle and Old Faithful
 geysers, have evidence of trees that are now encrusted by silica. The duration from initial tree kill to complete desiccation may be long enough to provide a useful chronometer for thermal activity. The 14C date of a small bobby sox tree near Gem Pool in the Upper Geyser Basin yielded an age of 190 years BP. The pulses and pauses documented by 14C dating of Castle Geyser, and observed in the nature of tree growth and subsequent hydrothermal kill, may be combined to develop a chronology of hydrothermal activity which, when combined with other data sets, may help provide clues to deeper processes in the Yellowstone caldera. 
Jack



      
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