Yellowstone’s Hydrothermal System
As described below, scientists can quantify heat and volatile
fluxes by monitoring the volume and composition of emitted
hydrothermal fluids (i.e. hot waters and gases). At
Yellowstone, soluble magmatic volatiles emerge at the
ground surface dissolved in hot spring waters. Neutral to
alkaline, Cl--rich waters generally issue at lower elevations,
where they create terraces of amorphous silica (sinter) along
the outflow of geysers and springs (Fournier 1989). These
waters originate from subsurface, high-temperature
(>200°C) hydrothermal reservoirs, and cool and boil as they
rise. Isotopic data show the water to be dominantly meteoric
in origin, having traveled decades (or more) prior to
discharge (Rye and Truesdell 1993). Far different are the
low-Cl-, acid waters of Yellowstone, emitted principally at
higher elevations (FIG. 1), often in the eastern part of the
caldera. These waters form when gases (mainly steam, CO2,