GEOGRAPHIC TRENDS IN THE HYDROTHERMAL WATERS OF YELLOWSTONE

Investigations into the hydrothermal system in the caldera above the Yellowstone hotpot have been ongoing since 1888, primarily by the United States Geological Survey (USGS), and comprehensive geochemical studies have been conducted since 1935. By compiling the geochemical data from the USGS that was collected from 1996 through 2013, GIS maps were created to examine trends in water chemistry (i.e. Ca²⁺, Mg²⁺, SO₄^2-, pH) and stable isotope ratios. Park-wide data trends were determined by creating “Natural Neighbor” rasters. From those rasters, contour layers were created in order to be able to visually analyze multiple trends simultaneously.

A visual analysis of the layered contours and rasters throughout the system revealed significant (relative) enrichment in δ²H values and δ¹⁸O values. On average, however, δ¹⁸O values were more enriched than the δ²H counterparts and fall outside of the range for meteoric waters in the area, as would be expected in hydrothermal waters at or near boiling. The samples collected in 1996-98 and 2001 by the USGS in Brimstone Basin, which is located outside of the caldera in a “fossil” hydrothermal area and are among the coldest samples in the system (~ 4-10°C), have stable isotope values that show depletion of δ¹⁸O without corresponding δ²H depletion. Previous models to explain this δ¹⁸O depletion have suggested that it is due to either CO₂-H₂O oxygen exchange or anhydrite dissolution.

In addition to previously collected data on the hydrothermal system, several surface water samples were collected during July 2016 from the areas surrounding the park. These samples were analyzed for stable isotope values with the Los Gatos Research Liquid Water Isotope Analyzer at the Sacramento State WAGS Lab. Stable isotope ratios for these surface water samples fall within the normal range of meteoric waters in the region and fit the Global Meteoric Water Line developed by Craig (1961).