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The Yellowstone Volcano Observatory 2021 annual report has been published!  Your one-stop shop for the year that was in Yellowstone geological activity and research is now available online.

Cover of Yellowstone Volcano Observatory 2021 Annual Report
Front cover of the Yellowstone Volcano Observatory 2021 annual report, which includes a summary of earthquake, deformation, and geyser activity, as well as research investigations and other information. The report is freely available online at

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

How many earthquakes occurred in the Yellowstone region in 2021?  How many times did Steamboat Geyser erupt?  What geological mapping was completed during the year?

Good questions.  And now, the answers to these questions, and more, are all compiled in one easy-to-navigate source—the Yellowstone Volcano Observatory 2021 Annual Report, which can be accessed at!

In the publication, you can find details about Yellowstone seismicity over the course of 2021.  For example, there were 2,773 earthquakes located by the University of Utah Seismograph Stations, including 10 magnitude 3 earthquakes, 163 magnitude 2 earthquakes, and 2,600 earthquakes with magnitudes less than 2.  Of the total number of earthquakes, 65% occurred as part of swarms (defined as the occurrence of many small earthquakes in the same small area over a relatively short period of time).  The largest swarm of 2021 included 825 events beneath Yellowstone Lake during July 15–25.

Ground deformation in Yellowstone Caldera followed trends that have been ongoing since 2015, with subsidence of a few centimeters (about 1 inch) over the course of the year.  On the north side of the caldera, however, satellite radar measurements suggest a slight amount of uplift—about 1 centimeter (0.4 inches).  This pattern is not unusual, having also occurred in the same area during 1996–2004.

Steamboat Geyser remained active, erupting 20 times during 2021, but the activity was a far cry from the show the geyser put on during 2018–2020, which included 32 eruptions in 2018 and 48 eruptions each in 2019 and 2020.  The time between 2021 eruptions varied from 6.5 days to 65 days—the longest interval between eruptions since the current activity at Steamboat began in March 2018.  Other noteworthy geyser activity included the reawakening of Sawmill Geyser, near Old Faithful, after a 4.5-year slumber.

Map of seismicity in the Yellowstone region during 2021
Map of seismicity (red circles) in the Yellowstone region during 2021. Gray lines are roads, black dashed line shows the caldera boundary, Yellowstone National Park is outlined by black dot-dashed line, and gray dashed lines denote state boundaries.

Yellowstone Volcano Observatory scientists spent quite a bit of time in the field during 2021 researching past and current volcanic activity in the region.  Professors and students from Montana State University mapped a number of geological deposits in places like Mount Everts, near Mammoth Hot Springs and the North Entrance to Yellowstone National Park, and the Sour Creek resurgent dome, on the east side of Yellowstone Caldera.  Their work included the recognition of a new set of rock units associated with the formation of Yellowstone Caldera 631,000 years ago, and suggests that the eruption was far more complex than previously thought.

Gas geochemists installed a new continuous gas-monitoring sensor in the Mud Volcano area.  This instrument, known as a multicomponent gas analyzer system, or multiGAS, can detect a variety of gas types that are often emitted by volcanoes, like CO2, H2O, H2S, and SO2.  The instrument is the first of its kind established to collect these data year-round at Yellowstone—a challenging environment in which to operate gas monitoring equipment during winter months!

There were even studies of explosion deposits in Yellowstone Lake.  Sediment cores collected from the lake bottom have identified a number of hydrothermal explosion deposits and provided insights into thermal areas hidden from sight beneath the waves on the lake floor.

The Yellowstone Volcano Observatory 2021 annual report is part of a series of USGS Circulars that began several years ago and that includes entries for 2017, 2018, 2019, and 2020.  We hope that you find the reports to be informative and enjoyable as windows into geological activity in the Yellowstone area, and research accomplished by Yellowstone Volcano Observatory scientists, in 2021.

Field work and research are already underway in 2022, and we look forward to detailing all of YVO’s accomplishments for the coming season in the 2022 report.  Stay tuned!

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