Solute and geothermal flux monitoring using electrical conductivity in the Madison, Firehole, and Gibbon Rivers, Yellowstone National Park R. Blaine McCleskey a,⇑ , Laura E. Clor b , Jacob B. Lowenstern b , William C. Evans c , D. Kirk Nordstrom a , Henry Heasler d , Mark A. Huebner c a U.S. Geological Survey, 3215 Marine St., Suite E. 127, Boulder, CO 80303, USA b U.S. Geological Survey, Mail Stop 910, Menlo Park, CA 94025, USA c U.S. Geological Survey, Mail Stop 434, Menlo Park, CA 94025, USA d National Park Service, Yellowstone National Park, Mammoth, WY 82190, USA article info Article history: Received 10 April 2012 Accepted 23 July 2012 Available online 2 August 2012 Editorial handling by I. Cartwright abstract The thermal output from the Yellowstone magma chamber can be estimated from the Cl flux in the major rivers in Yellowstone National Park; and by utilizing continuous discharge and electrical conductivity measurements the Cl flux can be calculated. The relationship between electrical conductivity and concen- trations of Cl and other geothermal solutes (Na, SO 4 , F, HCO 3 , SiO 2 , K, Li, B, and As) was quantified at mon- itoring sites along the Madison, Gibbon, and Firehole Rivers, which receive discharge from some of the largest and most active geothermal areas in Yellowstone. Except for some trace elements, most solutes behave conservatively and the ratios between geothermal solute concentrations are constant in the Mad- ison, Gibbon, and Firehole Rivers. Hence, dissolved concentrations of Cl, Na, SO 4 , F, HCO 3 , SiO 2 , K, Li, Ca, B and As correlate well with conductivity (R 2 > 0.9 for most solutes) and most exhibit linear trends. The 2011 flux for Cl, SO 4 , F and HCO 3 determined using automated conductivity sensors and discharge data from nearby USGS gaging stations is in good agreement with those of previous years (1983–1994 and 1997–2008) at each of the monitoring sites. Continuous conductivity monitoring provides a cost- and labor-effective alternative to existing protocols whereby flux is estimated through manual collection of numerous water samples and subsequent chemical analysis. Electrical conductivity data also yield insights into a variety of topics of research interest at Yellowstone and elsewhere: (1) Geyser eruptions are easily identified and the solute flux quantified with conductivity data. (2) Short-term heavy rain events can produce conductivity anomalies due to dissolution of efflorescent salts that are temporarily trapped in and around geyser basins during low-flow periods. During a major rain event in October 2010, 180,000 kg of additional solute was measured in the Madison River. (3) The output of thermal water from the Gibbon River appears to have increased by about 0.2%/a in recent years, while the output of thermal water for the Firehole River shows a decrease of about 10% from 1983 to 2011. Confirmation of these trends will require continuing Cl flux monitoring over the coming decades. Published by Elsevier Ltd. 1. Introduction The thermal output from the magma chamber underlying Yel- lowstone National Park (YNP, Fig. 1) manifests itself in the many geysers and hot springs. The thermal flux emanating from the nearly 10,000 features in YNP is difficult to measure directly. How- ever the Cl flux, which is more straightforward to measure, has been used as a surrogate for heat flow in geothermal systems (Ellis and Wilson, 1955). Long-term Cl flux monitoring may be used to assess the adverse impacts on thermal features from development of water, geothermal, oil and gas resources adjacent to the park (Friedman and Norton, 2007). In addition, inflation/deflation of the magma chamber or increased seismic activity may be detected in the Cl flux. Since the 1970s, the U.S. Geological Survey (USGS) and the Na- tional Park Service (NPS) have collaborated on Cl flux monitoring in YNP to assess the rate of heat and fluid release from deep hydro- thermal and magmatic systems (e.g. Norton and Friedman, 1991). The Firehole and the Gibbon Rivers come together to form the Mad- ison River, one of four major rivers (Madison, Yellowstone, Snake and Falls Rivers) that drain most of YNP. The Firehole River receives discharge from some of the largest and most active geothermal areas in the park including the Upper, Midway and Lower Geyser Basins. The majority of the geothermal input into the Gibbon River origi- nates from Norris Geyser Basin (McCleskey et al., 2010a,b). The 0883-2927/$ - see front matter Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.apgeochem.2012.07.019 ⇑ Corresponding author. Tel.: +1 303 541 3079. E-mail address: rbmccles@usgs.gov (R.B. McCleskey). Applied Geochemistry 27 (2012) 2370–2381 Contents lists available at SciVerse ScienceDirect Applied Geochemistry journal homepage: www.elsevier.com/locate/apgeochem