Yellowstone Volcano Observatory 2021 Annual Report

Abstract

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 (see sidebar on volcanic hazards on p. 2). YVO is a collaborative consortium made up of the U.S. Geological Survey (USGS), Yellowstone National Park, University of Utah, University of Wyoming, Montana State University, UNAVCO, Wyoming State Geological Survey, Montana Bureau of Mines and Geology, and Idaho Geological Survey (see sidebar on YVO on p. 3). The USGS arm of YVO also has the operational responsibility for monitoring volcanic activity in the Intermountain West of the United States, including Arizona, New Mexico, Utah, and Colorado. Despite the decrease in activity compared to the previous 3 years, Steamboat Geyser continued to impress visitors with 20 major water eruptions in 2021. This episodic activity is typical of many geysers in Yellowstone National Park, as demonstrated once again in 2021, when Sawmill Geyser returned to its usual pattern of multiple eruptions per day after about 4.5 years of quiescence. Monitoring measurements indicate background levels of seismicity, deformation, and thermal emissions. The number of located earthquakes (2,773) was the most since 2017, when 3,427 earthquakes were located, but the 2021 value was still not significantly different from the average number of annual located events. GPS measurements indicated no significant deformation at Norris Geyser Basin throughout the year, and Yellowstone Caldera continued to subside at rates of a few centimeters (about 1 inch) per year, as it has since 2015. One noteworthy change in deformation style was detected by satellite radar, which documented about 1 centimeter (0.4 inch) of uplift centered on the north side of the caldera, south of Norris Geyser Basin, between late 2020 and late 2021. The deformation strongly resembles that which occurred during 1996-2004 but is yet too small to be strongly apparent in nearby continuous GPS stations. Heat flux estimates from both satellite imagery and river chemistry indicate no major changes with respect to previous years. The COVID-19 pandemic limited field work in 2021, although critical equipment maintenance and deployments and several scientific studies were still carried out. Temporary deployments of seismometers in Norris and Upper Geyser Basins collected information that will be used to better understand geyser plumbing systems, and a new continuous gas-monitoring station-the first of its kind in Yellowstone National Park-was deployed near Mud Volcano in July. Geologic investigations focused on better understanding the age and history of hydrothermal explosion craters in the Lower Geyser Basin, revising geologic maps in the areas around Mount Everts and the Sour Creek resurgent dome, improving age constraints on post-caldera rhyolite lava flows, and investigating the sources of hydrothermal travertine within Yellowstone Caldera. Additional sedimentary cores were collected from Yellowstone Lake to better constrain the characteristics and extent of lake-bottom hydrothermal activity and triggers for hydrothermal explosions. New research results will be highlighted in future editions of YVO's weekly series of online articles, Yellowstone Caldera Chronicles, which can be accessed at https://www.usgs.gov/volcanoes/yellowstone/caldera-chronicles, as well as in annual reports, monthly updates and videos, and public presentations.