Conditions in the deeper parts of the hot spring systems of Yellowstone National Park, Wyoming

Yellowstone thermal areas are scattered over an area of nearly 50 x 60 kilometers (Fig. 1) and contain waters of diverse compositions. This has lead to the implicit assumption that Yellowstone consisted of discrete hydrothermal systems (e.g., Fournier and Truesdell, 1970). It is the purpose of this paper to suggest that these systems may be separate only near the surface and that there may exist at depth a large, relatively homogeneous body of water at 340 to 370°C containing about 1,000 ppm NaCl. This deep thermal water flows upwards losing steam into the near-surface geyser and hot spring systems where it undergoes variable amounts of dilution with cold meteoric water, reaction with rocks, and further steam loss to produce all of the hot spring waters of the Park. The evidence for these conclusions is from the application of chemical and isotopic geothermometers, from relationships between the chloride concentrations and subsurface heat contents of thermal waters, from the chemical and isotopic compositions of the waters, and from geophysical evidence.