Isotope and chemical compositions of meteoric and thermal waters and snow from the greater Yellowstone National Park region

Abstract

Abstract : An intensive hydrogeologic investigation, mandated by U.S. Congress and centered on the Norris-Mammoth corridor was conducted by USGS and other scientists during 1988-90 to determine the effects of using thermal water from a private well located in the Corwin Springs Known Geothermal Resources Area, Montana, on the thermal springs of Yellowstone National Park (YNP), especially Mammoth Hot Springs. As part of this investigation, we carried out a detailed study of the isotopic and chemical compositions of meteoric water from cold springs and wells, of thermal water, especially from the Norris-Mammoth corridor and of snow. Additional sampling of meteoric and thermal waters from YNP and surrounding region in northwest Wyoming, southwest Montana and southeast Idaho was carried out in 1991-92 to characterize the distribution of water isotopes in this mountainous region and to determine the origin and possible recharge locations of thermal waters in and adjacent to the Park. The deltaD and delta18O values for 40 snow samples range from -88 to -178% and -12.5 to -23.9% respectively, and define a well constrained line given by deltaD = 8.2 delta18O + 14.7 (r2 = 0.99) that is nearly identical to the Global Meteoric Water Line. The deltaD and delta18O values of 173 cold water samples range from -115 to -153% and -15.2 to -20.2%, respectively, and exhibit a similar relationship although with more scatter and with some shift to heavier isotopes, most likely due to evaporation effects. The spatial distribution of cold-water isotopes shows a roughly circular pattern with isotopically lightest waters centered on the mountains and high plateau in the northwest corner of Yellowstone National Park and becoming heavier in all directions.