Degassing thermal features at Yellowstone National Park include spectacular geysers, roiling hot springs, bubbling mud pots, fumaroles, frying pans, and areas of passive degassing characterized by steaming ground. Most of these features are readily identified by visible clouds of steam that are occasionally accompanied by a strong “rotten egg” odor from emissions of hydrogen sulfide gas. Gas compositions typically are greater than 90% carbon dioxide with lesser amounts of helium, hydrogen, hydrogen sulfide, methane, nitrogen and other trace components. The composition of the gas and relative amounts of gas and steam relate both to the type of feature as well as the geographic location within the park. In 2003 we began a long-term field study of Yellowstone gases with a goal of obtaining complete chemical analyses from a variety of features from all areas of the park. Results from samples collected through 2012 are published in numerous journal articles and reports (Bergfeld et al., 2012, 2014; Chiodini et al., 2012; Evans et al., 2010; Lowenstern et al., 2012, 2014, 2015; and Werner et al., 2008). Synthesis of these data allow us to delineate areas within Yellowstone that are dominated by magmatic versus crustal gas sources and to tease out additional information regarding sedimentary and metamorphic sources for crustal gas. This report compiles our published gas and water data with new gas data from samples collected through September, 2018 and includes some previously unpublished carbon isotope data from waters collected during 2011. Some of the analyses represent replicate samples collected in different bottles on the same day, others are samples collected from the same location in different years, and some sites were only sampled once. A companion data release focused on water chemistry and discharge for 2017-18 waters is planned be published in a separate report. The data herein are organized by sample type: Tables 1 and 2 include bulk chemistry and isotope data for 199 gas samples collected in evacuated bottles containing sodium hydroxide and 41 gas samples collected in dry evacuated bottles, respectively; Table 3 presents chemical and isotope data for 62 water samples from thermal and non-thermal features; Table 4 contains helium and carbon isotope data for 10 water samples and 1 gas sample. Each sample is assigned a group number linked to a particular area within the park (figure 1). Samples in groups 2 through 10 and 12 through 22 tend to be in close proximity. Group 11 includes samples from general locations across Eastern Yellowstone. Samples keyed to group 1 (miscellaneous) are not co-located. The analytical results include major and trace element chemistry for the gases and waters, and isotope values for carbon dioxide (d13C-CO2), dissolved inorganic carbon (d13C-DIC), helium (3He/4He), steam (d18O, dD), neon (20Ne/22Ne and 21Ne/22Ne), and argon (38Ar/36Ar and 40Ar/36Ar). All data in this report supersede previously published analyses. The reader is directed to early publications for details on sampling and analytical methods and for in depth discussions regarding interpretations of the gas data.

There are over 10,000 hydrothermal features in Yellowstone National Park (YNP), where waters have pH values ranging from about 1 to 10 and surface temperatures up to 95 °C. Active hydrothermal areas in YNP provide insight into a variety of processes occurring at depth, such as water-rock and oxidation-reduction (redox) reactions, the formation of alteration minerals, and microbial (thermophile) metabolism in extreme environments, and possible indications of volcanic unrest. Investigations into the water chemistry of hydrothermal features, streams, and rivers in YNP have been conducted by the U.S. Geological Survey (USGS) and other earth-science organizations and academic institutions since 1883 (Gooch and Whitfield, 1888; Price and others, 2024). More recently, USGS researchers have sampled hydrothermal features in YNP at least annually since 1994 (McCleskey and others, 2014, and references within). In this Data Release, the chemical and isotopic analyses of 845 water samples collected beginning in 2009 are reported for numerous thermal and non-thermal features in YNP. This report combines water chemistry data presented in McCleskey and others (2014) with data collected after 2014. These water samples were collected and analyzed as part of research investigations in YNP on and as part of the Yellowstone Volcano Observatory monitoring plans (Yellowstone Volcano Observatory, 2006); arsenic, iron, nitrogen, and sulfur redox species in hot springs and overflow drainages; the occurrence and distribution of dissolved mercury and arsenic; and general hydrogeochemistry of hot springs throughout YNP. For most samples, data includes water temperature, pH, specific conductance, dissolved oxygen, and concentrations of major cations, anions, trace metals, alkalinity, sulfur redox species (hydrogen sulfide and thiosulfate), nutrients, silica, boron, arsenic and iron redox species, acidity, dissolved organic carbon, and hydrogen and oxygen isotope ratios. For select samples, tritium (3H), stable carbon isotopes of the dissolved inorganic carbon, and sulfur isotopes of sulfate are presented. In addition, chemical data for river, stream, and lake waters were obtained to determine input of different solutes from thermal areas throughout YNP. References Cited Gooch, F.A., and Whitfield, J.E., 1888, Analyses of waters of the Yellowstone National Park with an account of the methods of analysis employed: Bulletin 47, p. 84. McCleskey, R.B., Chiu, R.B., Nordstrom, D.K., Campbell, K.M., Roth, D.A., Ball, J.W., and Plowman, T.I., 2014, Water-Chemistry Data for Selected Springs, Geysers, and Streams in Yellowstone National Park, Wyoming, Beginning 2009: doi:10.5066/F7M043FS. Price, M.B., McCleskey, R.B., Oaks, A., Hurwitz, S., and Nordstrom, D.K., 2024, Historic Water Chemistry Data for Thermal Features, Streams, and Rivers in the Yellowstone National Park Area, 1883-2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KSEVI1. Yellowstone Volcano Observatory, 2006, Volcano and earthquake monitoring plan for the Yellowstone Volcano Observatory, 2006-2015: U.S. Geological Survey Scientific Investigations Report 2006-5276, http://pubs.usgs.gov/sir/2006/5276/. First posted - September 19, 2022 (available from author) Revised - March 4, 2025 (version 2.0) NOTE: While previous versions are available from the author, all the records in previous versions can be found in version 2.0.

There are over 10,000 hydrothermal features in Yellowstone National Park (YNP), where waters have pH values ranging from about 1 to 10 and surface temperatures up to 95 °C. Active hydrothermal areas in YNP provide insight into a variety of processes occurring at depth, such as water-rock and oxidation-reduction (redox) reactions, the formation of alteration minerals, and microbial (thermophile) metabolism in extreme environments, and possible indications of volcanic unrest. Investigations into the water chemistry of hydrothermal features, streams, and rivers in YNP have been conducted by the U.S. Geological Survey (USGS) and other earth-science organizations and academic institutions since 1883 (Gooch and Whitfield, 1888; Price and others, 2024). More recently, USGS researchers have sampled hydrothermal features in YNP at least annually since 1994 (McCleskey and others, 2014, and references within). In this Data Release, the chemical and isotopic analyses of 845 water samples collected beginning in 2009 are reported for numerous thermal and non-thermal features in YNP. This report combines water chemistry data presented in McCleskey and others (2014) with data collected after 2014. These water samples were collected and analyzed as part of research investigations in YNP on and as part of the Yellowstone Volcano Observatory monitoring plans (Yellowstone Volcano Observatory, 2006); arsenic, iron, nitrogen, and sulfur redox species in hot springs and overflow drainages; the occurrence and distribution of dissolved mercury and arsenic; and general hydrogeochemistry of hot springs throughout YNP. For most samples, data includes water temperature, pH, specific conductance, dissolved oxygen, and concentrations of major cations, anions, trace metals, alkalinity, sulfur redox species (hydrogen sulfide and thiosulfate), nutrients, silica, boron, arsenic and iron redox species, acidity, dissolved organic carbon, and hydrogen and oxygen isotope ratios. For select samples, tritium (3H), stable carbon isotopes of the dissolved inorganic carbon, and sulfur isotopes of sulfate are presented. In addition, chemical data for river, stream, and lake waters were obtained to determine input of different solutes from thermal areas throughout YNP. References Cited Gooch, F.A., and Whitfield, J.E., 1888, Analyses of waters of the Yellowstone National Park with an account of the methods of analysis employed: Bulletin 47, p. 84. McCleskey, R.B., Chiu, R.B., Nordstrom, D.K., Campbell, K.M., Roth, D.A., Ball, J.W., and Plowman, T.I., 2014, Water-Chemistry Data for Selected Springs, Geysers, and Streams in Yellowstone National Park, Wyoming, Beginning 2009: doi:10.5066/F7M043FS. Price, M.B., McCleskey, R.B., Oaks, A., Hurwitz, S., and Nordstrom, D.K., 2024, Historic Water Chemistry Data for Thermal Features, Streams, and Rivers in the Yellowstone National Park Area, 1883-2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KSEVI1. Yellowstone Volcano Observatory, 2006, Volcano and earthquake monitoring plan for the Yellowstone Volcano Observatory, 2006-2015: U.S. Geological Survey Scientific Investigations Report 2006-5276, http://pubs.usgs.gov/sir/2006/5276/. First posted - September 19, 2022 (available from author) Revised - March 4, 2025 (version 2.0) NOTE: While previous versions are available from the author, all the records in previous versions can be found in version 2.0.

Data in this data release were obtained for water samples collected under Yellowstone National Park Research Permit YELL-05194 in 2017 through the Integrated Yellowstone Studies Project funded by the Mineral Resources Program. Isotope-spiked incubations were carried out to determine methylation and demethylation potential for Frying Pan spring, Crystal Sister East, Crystal Sister West, and Turbulent Pool, which were selected based on existing data on total mercury and methylmercury concentrations (see companion data release (https://doi.org/10.5066/P9IUY03O). The data represent the experimental conditions of incubation experiments (temperature, time, and experimental spikes) and concentration data associated with each condition.

Data in this data release were obtained for water samples collected under Yellowstone National Park Research Permit YELL-05194 in 2017 through the Integrated Yellowstone Studies Project funded by the Mineral Resources Program. Isotope-spiked incubations were carried out to determine methylation and demethylation potential for Frying Pan spring, Crystal Sister East, Crystal Sister West, and Turbulent Pool, which were selected based on existing data on total mercury and methylmercury concentrations (see companion data release (https://doi.org/10.5066/P9IUY03O). The data represent the experimental conditions of incubation experiments (temperature, time, and experimental spikes) and concentration data associated with each condition.

Yellowstone National Park (YNP; Wyoming, Montana, and Idaho, USA) contains more than 10,000 hydrothermal features, several lakes, and four major watersheds. For more than 140 years, researchers at the U.S. Geological Survey and other scientific institutions have investigated the chemical compositions of hot springs, geysers, fumaroles, mud pots, streams, rivers, and lakes in YNP and surrounding areas. Water chemistry studies have revealed a range of compositions including waters with pH values ranging from about 1 to 10, surface temperatures from ambient to superheated values of 95°C, and elevated concentrations of silica, lithium, boron, fluoride, mercury, and arsenic. Hydrogeochemical data from YNP research have led to insights on subsurface conditions of temperature and chemistry, water-rock-gas interactions and processes of high-temperature mineral alteration with dissolution and precipitation, redox processes, thermophilic microbial metabolism under extreme conditions and effects of thermal water chemistry on river systems. In this Data Release, water chemistry data for 4,918 water samples are reported for numerous thermal features, rivers, streams, lakes, drillholes, and precipitation in and around YNP. The data for these samples were originally located in 38 reports published between 1888 and 2022 and in multiple unpublished documents. Spanning more than 600 unique sampling sites throughout the YNP region, this dataset includes samples collected as early as 1883 (Gooch & Whitfield, 1888) and as recently as 2021 (McCleskey, et al, 2022). The thermal features sampled most frequently include Cistern Spring (180 samples) and Echinus Geyser (73 samples) in Norris Geyser Basin and Ojo Caliente Spring (143 samples) in the Lower Geyser Basin, while more than 500 sites have 5 samples or fewer. Water chemistry data from thermal features, rivers, and streams are most represented, comprising 75% (thermal) and 17% (rivers/streams) of the dataset. Across all major areas of the park, Norris Geyser Basin has been sampled more than any other basin, with more than 1,100 samples reported in this dataset.

Yellowstone National Park (YNP; Wyoming, Montana, and Idaho, USA) contains more than 10,000 hydrothermal features, several lakes, and four major watersheds. For more than 140 years, researchers at the U.S. Geological Survey and other scientific institutions have investigated the chemical compositions of hot springs, geysers, fumaroles, mud pots, streams, rivers, and lakes in YNP and surrounding areas. Water chemistry studies have revealed a range of compositions including waters with pH values ranging from about 1 to 10, surface temperatures from ambient to superheated values of 95°C, and elevated concentrations of silica, lithium, boron, fluoride, mercury, and arsenic. Hydrogeochemical data from YNP research have led to insights on subsurface conditions of temperature and chemistry, water-rock-gas interactions and processes of high-temperature mineral alteration with dissolution and precipitation, redox processes, thermophilic microbial metabolism under extreme conditions and effects of thermal water chemistry on river systems. In this Data Release, water chemistry data for 4,918 water samples are reported for numerous thermal features, rivers, streams, lakes, drillholes, and precipitation in and around YNP. The data for these samples were originally located in 38 reports published between 1888 and 2022 and in multiple unpublished documents. Spanning more than 600 unique sampling sites throughout the YNP region, this dataset includes samples collected as early as 1883 (Gooch & Whitfield, 1888) and as recently as 2021 (McCleskey, et al, 2022). The thermal features sampled most frequently include Cistern Spring (180 samples) and Echinus Geyser (73 samples) in Norris Geyser Basin and Ojo Caliente Spring (143 samples) in the Lower Geyser Basin, while more than 500 sites have 5 samples or fewer. Water chemistry data from thermal features, rivers, and streams are most represented, comprising 75% (thermal) and 17% (rivers/streams) of the dataset. Across all major areas of the park, Norris Geyser Basin has been sampled more than any other basin, with more than 1,100 samples reported in this dataset.

The U.S. Geological Survey, in cooperation with the National Park Service, Yellowstone Center for Resources, as part of work for the Yellowstone Volcano Observatory, has compiled a shapefile map of thermal areas and thermal water bodies in Yellowstone National Park. A thermal area is a continuous, or nearly continuous, geologic unit that contains one or more thermal features (e.g., hot springs, mud pots, or fumaroles); hydrothermally altered rocks and/or hydrothermal mineral deposits; heated ground and/or geothermal gas emissions; and is generally barren of vegetation or has stressed / dying vegetation. There are more than 10,000 thermal features in Yellowstone, most of which are clustered together into about 120 distinct thermal areas (e.g., Upper Geyser Basin, Crater Hills Thermal Area, or Roadside Springs). A thermal water body is a body of water, usually a lake, pond, or wetland area, that is thermally emissive because it receives heated water from a nearby thermal area, nearshore thermal springs, or from underwater vents. The shapefile released here is based on a thermal area polygon shapefile that was initially provided by the Spatial Analysis Center at the Yellowstone Center for Resources in Yellowstone National Park. The thermal area polygons were initially based on field mapping (by R. Hutchinson and others, unpublished data, 1997) and digitizing boundaries over high-spatial-resolution (1 m/pixel) visible color orthophotos from the National Agriculture Imagery Program (NAIP) acquired in 2006. Updates to this map are based on more recent field mapping and remote sensing data analysis, including nighttime thermal infrared data (e.g., ASTER and Landsat 8/9), high-spatial-resolution visible data from commercial satellites (e.g., WorldView-3), and NAIP imagery from 2015, 2017, 2019, and 2022. The downloadable shapefile contains a map of these thermal areas and thermal water bodies with information (if available) about their chemistry and thermal activity. The names of the thermal areas are either derived from the USGS Geographic Names Information System (GNIS) or are locally used names, as indicated in the attribute table. Thermal area mapping in Yellowstone is a work in progress, partly because there are still remote areas that have not yet been explored in detail, and partly because changes occur frequently. Thermal areas expand and contract, develop and decay, and migrate – over time scales that range from weeks to years. Thus, this map will be periodically assessed and updated. A note about safety: Thermal areas can be dangerous, with scalding water, mud, or gases that are sometimes hidden beneath unstable ground. Unstable ground sometimes looks solid, but stepping onto unstable ground can result in breaking through a thin crust and being exposed to scalding water, mud, or gases, which can cause severe burns. Since the establishment of the National Park, more than 20 people have died from burns suffered after they entered or fell into a hot spring. For the safety of park visitors and the protection of delicate thermal formations, it is prohibited to enter a thermal area in the back country, and one must stay on the trails or boardwalks when entering front country thermal areas (unless working in a thermal area on an official permit).

From May to September 2017 measurements of gas and heat emissions were made at Solfatara Plateau Thermal Area, an acid-sulfate, vapor-dominated area in Yellowstone National Park, Wyoming. An eddy covariance system measured half-hourly CO2, H2O and sensible and latent heat fluxes, air temperature and pressure, wind speed and direction and soil moisture. A Multi-GAS instrument measured (0.5 Hz frequency) atmospheric H2O, CO2, SO2 and H2S volumetric mixing ratios, air pressure, temperature and relative humidity and wind speed and direction. Soil temperature at 30 cm depth and CO2 flux were also measured on a grid across a 0.11 km2 area using thermocouple probes and the accumulation chamber method, respectively. The eddy covariance, Multi-GAS and soil CO2 flux and temperature data sets are saved in spreadsheets in the *.csv format.

From May to September 2017 measurements of gas and heat emissions were made at Solfatara Plateau Thermal Area, an acid-sulfate, vapor-dominated area in Yellowstone National Park, Wyoming. An eddy covariance system measured half-hourly CO2, H2O and sensible and latent heat fluxes, air temperature and pressure, wind speed and direction and soil moisture. A Multi-GAS instrument measured (0.5 Hz frequency) atmospheric H2O, CO2, SO2 and H2S volumetric mixing ratios, air pressure, temperature and relative humidity and wind speed and direction. Soil temperature at 30 cm depth and CO2 flux were also measured on a grid across a 0.11 km2 area using thermocouple probes and the accumulation chamber method, respectively. The eddy covariance, Multi-GAS and soil CO2 flux and temperature data sets are saved in spreadsheets in the *.csv format.