Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Michael Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory.

In 2022, the Yellowstone Volcano Observatory released a monitoring plan that laid out a strategy for better understanding and tracking Yellowstone’s volcanic, hydrothermal, and tectonic activity.  The plan pointed out that regional monitoring was well covered, allowing for the detection of small earthquakes and subtle ground motion, but that there was little monitoring within Yellowstone’s famous hydrothermal basins.  The lack of such data prevents scientists from tracking activity that may lead to hydrothermal explosions—essentially steam bursts—which are an underappreciated hazard in Yellowstone National Park.

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The monitoring plan proposed installing multi-component monitoring stations in hydrothermal basins to better track subtle geyser and hot spring activity that the regional network might miss, and that Norris Geyser Basin would be a logical starting point for such work.  The YNM seismometer, located in the Norris Museum, was the only seismic station in Yellowstone that is located in a geyser basin, and it has proven outstanding for detecting eruptions of Steamboat Geyser.  Adding more monitoring stations to the Norris area would build on this excellent start.

In August and September 2023, scientists from the University of Utah, EarthScope Consortium, and USGS collaborated to install a new monitoring site in the Ragged Hills, at the center of Norris Geyser Basin.  The Ragged Hills are a thermal kame, formed when melting glaciers dropped sediment in the basin that was then cemented together by silica deposited by circulating hydrothermal fluids.

The new station incudes four monitoring instruments.  First, a broadband seismometer, designated YNB, will detect subtle shaking of the Earth across a variety of frequencies.  This can include shaking due to local earthquakes, tremors associated with geyser activity, and even the signature of strong earthquakes located elsewhere on the planet.  One of the first signals this seismometer recorded upon becoming operational was the M6.8 that devastated Morocco on September 8, 2023.

Second, a GPS station, designated NBWY, will detect subtle changes in ground motion at the site.  Based on evidence from satellite data and temporary GPS deployments, this site might show changes related to local accumulation and withdrawal of water but which are not picked up by the nearby site NRWY, located on a hill outside, and a few kilometers away from, Norris Geyser Basin.

Largely new to Yellowstone is the third instrument—an array of sensors that are designed to measure low-frequency sound waves that are inaudible to humans, called infrasound.  At the site, three sensors are deployed in a triangle-shaped pattern, which allows the data to be used to calculate the direction of any sources of infrasound, as well as the signal strength.  When a geyser in the Norris area erupts, the sound of the geyser will be detected by the infrasound sensors, and the direction to the sound will be automatically calculated so that it is possible to tell which geyser is the source of the noise, even when no one is present in the basin to observe the activity.  The station has already detected several eruptions of Steamboat Geyser—clearly the loudest feature in the Norris area!

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Finally, a weather station will record wind speed and direction, temperature, humidity, pressure, and other parameters.  This information can be helpful in understanding the sources of any seismic, deformation, or infrasound signals that might be caused by environmental conditions.

This Ragged Hills station is the first such site installed in Yellowstone, with multiple types of measurements collected in a geyser basin for the specific purpose of monitoring hydrothermal activity.  YVO scientists will be closely observing the data from this site over the coming months.  If the deployment proves to be useful at detecting changes within the geyser basin, new sites could be installed in the coming years.  Ideally, multiple such sites will ultimately be established in Norris Geyser Basin and other thermal areas so that the sources of even subtle deformation, seimsicity, and infrasound can be triangulated.

Interested in seeing the new measurements for yourself?  Good news—all of the data from the new site are public!  You can see data plots on the Yellowstone monitoring map on the YVO website and at the University of Utah Seismograph Stations webicorder for station YNB.  Follow along as we continue to learn more about Yellowstone’s spectacular hydrothermal activity!