Newest Volcano Notice Including Yellowstone

Yellowstone Caldera activity remains at background levels, with 77 located earthquakes in September (largest = M3.4). Deformation measurements indicate no significant uplift or subsidence of the caldera or north caldera rim for the past several months. A small hydrothermal explosion occurred at Biscuit Basin on September 27.

Recent Work and News

Yellowstone Volcano Observatory scientists spent September in the park conducting geological research, setting up new monitoring stations, and maintaining existing monitoring equipment.  This work included studies of Lower Geyser Basin hydrothermal activity and lakes, recovery of temporary GPS stations, microgravity measurements, maintenance of temperature monitoring stations, establishing a new hydrothermal monitoring station in Upper Geyser Basin, and reestablishing a camera with a view of Yellowstone Lake.

Although there were only sporadic minor eruptions from Steamboat Geyser, in Norris Geyser Basin, during the month (and only 1 major eruption so far in 2026), nearby Echinus Geyser had an eruption on September 15, continuing a trend of occasional eruptions that has persisted throughout most of the year.  In Upper Geyser Basin, Giant Geyser (the second tallest geyser in Yellowstone National Park) erupted on September 10 and 22, its fourth and fifth eruptions of the year.  The geyser appears to be in a new stage of frequent activity for the first time since 2018–2019.

Thermal features in Biscuit Basin, in the Upper Geyser Basin not far from Old Faithful Geyser, remained active in September.  Black Diamond Pool, which was the site of a hydrothermal explosion on July 23, 2024, had several eruptions during the latter half of the month, including one large event that sent water and mud tens of feet (many meters) into the air on the night of September 23.  In addition, the small pool of hot water that formed via collapse after the June 13, 2026, hydrothermal explosion erupted multiple times on September 24 and 27.  Just after 8:12 PM MDT on September 27, the pool was the source of a hydrothermal explosion that threw boiling water, steam, mud, and rocks at least 100 feet (30 meters) into the air—the first such significant explosion from this feature.  The event was well recorded by a nearby seismic, acoustic, and camera monitoring station.

Seismicity

During September 2026, the University of Utah Seismograph Stations, responsible for the operation and analysis of the Yellowstone Seismic Network, located 77 earthquakes in the Yellowstone National Park region. The largest event of the month was a minor earthquake of magnitude 3.4 located about 20 miles northeast of Moran, WY, on September 6 at 10:25 p.m. MDT.

September seismicity in Yellowstone was marked by a small swarm of 24 earthquakes located about 7 miles north-northwest of West Yellowstone, MT, on September 8. The magnitudes ranged from -0.1 to 2.8.

Earthquake activity in Yellowstone is at background levels.

Ground Deformation

Data from continuous GPS stations indicate little net deformation of the caldera or north caldera regions over the past several months.  Subtle variations in ground motion are probably caused by seasonal variations associated with groundwater conditions as summer transitions to fall.

An example of GPS data can be found at http://www.unavco.org/instrumentation/networks/status/pbo/data/NRWY (click on Static Plots / Cleaned)