Yellowstone Volcano Observatory 2021 annual report

The Yellowstone Volcano Observatory (YVO) monitors volcanic and hydrothermal activity associated with the Yellowstone magmatic system, carries out research into magmatic processes occurring beneath Yellowstone Caldera, and issues timely warnings and guidance related to potential future geologic hazards. This report summarizes the activities and findings of YVO during the year 2021, focusing on the Yellowstone volcanic system. Highlights of YVO research and related activities during 2021 include deployments of seismometers in Norris Geyser Basin and Upper Geyser Basin to investigate geyser plumbing systems, semipermanent Global Positioning System array deployment from May to October, geological studies of post-glacial hydrothermal activity, refining the ages of Yellowstone volcanic units and updating existing maps of geologic deposits, installation of a new continuous gas monitoring station near Mud Volcano, sampling of thermal waters around Yellowstone National Park to monitor water chemistry over space and time, and assessment of thermal output based on satellite imagery and chloride flux in rivers.

Steamboat Geyser, in Norris Geyser Basin, continued the pattern of frequent eruptions that began in 2018 with 20 water eruptions in 2021—a significant decrease from the 48 eruptions that occurred in both 2019 and 2020. Total seismicity—2,773 located earthquakes—was elevated compared to the 1,722 earthquakes located in 2020, but not significantly outside the historical average of about 1,500–2,500 earthquakes per year. Overall subsidence of the caldera floor, ongoing since late 2015 or early 2016, continued at rates of a few centimeters (1–2 inches) per year, whereas deformation in the Norris Geyser Basin area was below detection levels. Satellite deformation measurements indicate the possibility of slight uplift amounting to about 1 centimeter (less than 1 inch) along the north caldera rim, south of Norris Geyser Basin. The deformation is similar to that which occurred in the late 1990s. Throughout 2021, the aviation color code for Yellowstone Caldera remained at “green” and the volcano alert level remained at “normal.”