CAN A SMALL EARTHQUAKE TRIGGER A BIG GEYSER ERUPTION?

The mechanisms through which earthquakes alter geyser activity remain unclear. While the surface effects of energetic earthquakes on Yellowstone’s geysers are well documented, less attention is paid to changes following smaller, local earthquakes. On 18 September 2022, Steamboat Geyser in Norris Geyser Basin—currently the tallest geyser in the world with maximum jet heights exceeding 120 m—erupted just 8 hours and 15 minutes after a M3.9 earthquake with an 11 km distant epicenter. The interval between this eruption and the previous was 90 days, a long outlier in the interval distribution for Steamboat’s latest active phase which began in March 2018. A seismometer 340 m from Steamboat recorded a peak ground velocity of 1.2 cm/s during the earthquake, which is the largest ground motion experienced in the area since active phase initiation. Sudden changes in both ambient seismic noise amplitude and relative seismic velocity at narrow frequency bands indicate a subsurface hydrothermal response triggered by the earthquake. If so, the 8.25-hour delay suggests that dynamic strains altered subsurface permeability and flow paths which enabled Steamboat to erupt, but questions remain as to why Steamboat might have reacted to this particular earthquake and not others. More long-term monitoring is required in Yellowstone to identify candidate triggered eruptions and to understand the related processes occurring in the local hydrothermal system.