Recap of Yellowstone's 2021 activity and December's monthly update
Before we get into what happened during the month of December 2021, let’s review what happened at Yellowstone over the past year.
Typically, there are 1,500 to 2,500 earthquakes located every year in the Yellowstone region. In 2021, there were 2,773 located earthquakes scattered throughout the Park. Consistent with previous years, most earthquakes were caused by water circulating and interacting with existing faults, which are found throughout the region.
There were 27 earthquake swarms in 2021 (earthquakes located in tight clusters during short periods of time). The most noteworthy swarm occurred in mid-July beneath Yellowstone Lake, which included over 800 earthquakes. In 2021, about 65% of the earthquakes were part of swarms.
The radar interferogram (composed of radar images acquired from satellites) shows us how the ground surface is changing. The colored fringes show changes in the elevation of the ground measured on a fine scale (mm to cm). The interferogram shows subsistence of the Yellowstone caldera by a few cm or about an inch or two over the course of this past year (from September 2020 to September of 2021).
On the north side of the caldera, not too far from Norris Geyser Basin, the interferogram shows an area of uplift, of about 1-2 cm (less than an inch). Uplift in this area was observed in the late 1990s and early 2000s, so we will keep an eye on it to see if this behavior continues.
2021 Geyser activity
Geyser activity was not particularly abnormal during 2021. There were 20 major water eruptions of Steamboat Geyser during the past year. This is less than half of the eruptions that occurred in 2020 and 2019 (48 water eruptions in each year).
December 2021 activity
The University of Utah Seismograph Stations, which is responsible for the operation and analysis of the Yellowstone seismic network located just 43 earthquakes during the month of December. There was no swarm activity.
Subsidence trends observed since 2015 continue in the caldera. There are brief pauses in the summer when snow melts into the subsurface and the ground soaks it up like a sponge. The most recent series of large storms in mid-December produced a signal that looks like sudden, rapid subsidence. The signal will return to previous levels once the storms abate.
Steamboat Geyser had one water eruption on December 16. The temperature profile in the outflow channel for Steamboat indicate that the geyser is likely headed toward another eruption in January.