The November 2021 YVO Yellowstone Volcano update comes to you from a very snowy Norris Geyser Basin with a story about Porkchop Geyser’s 1989 explosion.

Porkchop Geyser was named in the 1960s because it had a shape that looked a lot like a pork chop. In the 1970s to 1980s, it started having intermittent geyser eruptions, becoming more and more active. On September 5, 1989, Porkchop Geyser exploded. The vent for the geyser became so constricted that its pressure increased and it blew up. Rocks were thrown 200 feet from geyser and are visible around the geyser today. A lot of people witnessed the hydrothermal explosion, and the potential hazard is one of the reasons thermal basins are carefully monitored. But since 1989, Porkchop's been a relatively calm pool.

During the month of October, seismicity in Yellowstone was at background levels. The University of Utah Seismograph Stations, which is responsible for the operation and maintenance of the Yellowstone seismic network, located 267 earthquakes in the region. The largest was a magnitude 2.6, located just to the east of the Norris Geyser Basin. There were three swarms in the region, one north of the Old Faithful area, one east of Norris, and one northeast of West Yellowstone, Montana.

For deformation, there is a downward trend (subsidence) of several centimeters or about an inch per year that has been recorded at the White Lake GPS station over the past two years; there are pauses in subsidence during the summer caused by seasonal groundwater recharge. The same is true at the Old Faithful continuous GPS site. In the Norris Geyser Basin, it appears that the area may be returning to a period of uplift, after a few years of no deformation.

At Steamboat Geyser, there were two water eruptions, on October 13 and 25, for a total of 17 eruptions this year.