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Scientists can now “sniff” Yellowstone gases in real time

September 13, 2021

Much is known about how the chemical compositions of gases vary across the Yellowstone volcanic system, but how they vary in time has remained largely a mystery.  Our understanding should greatly improve with a recent installation of a station that continuously monitors gases and communicates those data in real time.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Jennifer Lewicki, research geologist with the U.S. Geological Survey in Menlo Park, CA.

SNIF multi-GAS station on Mount St. Helens, Washington
USGS scientist Laura Clor performing maintenance on the SNIF multi-GAS station on Mount St. Helens, Washington.

Over the past several decades, scientists have sampled gases from all of the major thermal areas of Yellowstone in an effort to better understand the types and quantities of gases that are emitted, and the state of Yellowstone’s volcanic activity.  This work has required very careful preparation of sampling equipment before going to the field, collection of gases within areas that may be hazardous, and detailed chemical analysis in the laboratory.  Because this work is so time-consuming, knowledge of how the compositions of Yellowstone’s gases are changing, and how that might relate to volcanic or hydrothermal activity, has been elusive.  To improve monitoring efforts, scientists have been working to build and deploy instruments that can measure continuous real-time gas compositions from Yellowstone’s famous expanses of hissing fumaroles, bubbling pools, and burping mud pots.

The multi-GAS (multicomponent Gas Analyzer System) is an instrument that continuously measures the concentrations of the four gases most commonly emitted by volcanoes: H2O, CO2, H2S, and SO2.   Measuring how the relative amounts of these gases change over time can provide important clues as to when magma enters the Earth’s deep crust and migrates upwards towards the surface, especially when combined with other real-time data, such as seismic and ground deformation.  Monitoring these variations, along with wind and atmospheric temperature, pressure, and humidity also allows us to better understand the levels to which gases build up near the ground surface, the weather conditions controlling build up, and potential gas-related hazards

Interior of SNIF multi-GAS enclosure on Mount St. Helens, Washington
Interior of the SNIF multi-GAS enclosure on Mount St. Helens, Washington

Over the past several years, USGS scientists have been building and testing multi-GAS capabilities at volcanoes in the Cascades, Alaska, Hawai’i, and in different Yellowstone thermal areas.  Deployments in Yellowstone are especially challenging because all the equipment must be small enough to be backpacked into remote thermal areas and sufficiently rugged to survive the Park’s long, dark, snowy winters.  This contrasts to other high-mountain multi-GAS sites where helicopters are used to deliver batteries and other site infrastructure.  For example, just the batteries at the ‘SNIF’ multi-GAS site at Mount St. Helens in Washington weigh over 700 pounds!  Consequently, initial deployments in Norris Geyser Basin and Solfatara Thermal Area in Yellowstone were restricted the summertime.  Furthermore, the lack of cellular network coverage or radio links for telemetry meant that access to data relied on in-person downloads by field technicians.  However, with major upgrades to the multi-GAS that included satellite telemetry, an improved solar power system, and an innovative lightweight equipment enclosure, a new station (“MUD”) was installed in July 2021 at Mud Volcano thermal area for what is planned to be a year-round, multi-year deployment. 

Emissions from the thermal area smell strongly of rotten eggs, but the initial monitoring data show that they are comprised of only ~0.02% H2S and contain no SO2—consistent with results from other areas of Yellowstone.  Instead, the emissions are dominated by water vapor (~92-93%) and CO2 (~7-8%).  Ambient CO2 levels at the station average around 800–900 ppm, or about twice the level of clean air.  This is not surprising, since the Mud Volcano area is known to be a copious emitter of CO2. Over the long term, having the capability to collect real-time, continuous data is expected to greatly improve our understanding of how Yellowstone gas compositions change over time, and also to rapidly detect changes in the Yellowstone volcanic system, should any occur. 

The real-time data from the MUD multi-GAS station are available on the YVO monitoring page (  Just click on the small cloud symbol (which represents a gas-monitoring instrument) on the map near Mud Volcano and enjoy the brand-new data stream!

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