Yellowstone Region Hit by 1,000 More Earthquakes in 2021 Than in 2020

The Yellowstone region was hit by around 1,000 more earthquakes in 2021 compared to the previous year, according to a new report.

This week, the United States Geological Survey's (USGS) Yellowstone Volcano Observatory (YVO) released its 2021 annual report, which documents volcanic and hydrothermal activity in the region over the past year.

The report identified 2,773 earthquakes in the region in 2021. While this is much higher than than the 1,722 quakes that were recorded in 2020, it is not significantly outside the historical average of about 1,500-2,500 earthquakes per year in and around Yellowstone National Park.

Earthquakes have been monitored in the Yellowstone region since the 1970s, with a network of seismographs in the region—maintained by the University of Utah—monitoring activity.

The Yellowstone region is one of the most seismically active areas in the United States. Since 1973, there have been more than 50,000 earthquakes in the region, although the vast majority are too small to be felt by humans.

Yellowstone National Park
A herd of buffaloes in Yellowstone National Park, Wyoming. The region was hit by around 1,000 more earthquakes in 2021 compared to the previous year.

Yellowstone National Park—located in Wyoming, Montana, and Idaho—sits atop a large, relatively young and active volcanic system that is often referred to as the Yellowstone Supervolcano. This system features magma (subterranean molten rock) boiling and pressurized waters, and a variety of active faults.

While there is a tendency to assume that most earthquakes in the region are related to magma moving beneath the surface, this is not the case, according to Michael Poland, scientist-in-charge of the YVO.

"The vast majority of earthquakes at Yellowstone are due to motion along preexisting faults—it's a very active area in terms of tectonics," Poland told Newsweek. "The fault motion is facilitated by pore pressure from groundwater. So, the combination of lots of subsurface water and lots of faults is sort of a recipe for small earthquakes."

According to Poland, 2021 was the biggest year for earthquakes since 2017 when 3,427 were recorded.

"So really, 2021 was not that unusual. Perhaps on the high side of average, but not by that much," he said.

The vast majority of the earthquakes in 2021 had a magnitude of less than 2, although there were a total of 10 magnitude-3 earthquakes, according to the report. Four of the earthquakes that were reported during the year were felt, meaning people reported shaking.

The largest event of the year was a magnitude-3.6 earthquake that occurred beneath Yellowstone Lake on July 16.

Around 65 percent of the quakes occurred as part of 26 "swarms"—incidents in which many seismic events occur in the same small area over a relatively short period of time without an accompanying main shock.

This type of seismic activity is common in the Yellowstone region and typically accounts for around half of all earthquakes there. The largest swarm of 2021 consisted of 825 events in the period July 15–25 beneath Yellowstone Lake.

While most earthquakes in the region are small, it is important to monitor seismic activity because larger events sometimes do occur, Poland said.

"The big geological threat on human timescales in the Yellowstone area is from strong earthquakes—like the 1959 magnitude-7.3 Hebgen Lake earthquake, which caused massive damage in the region, including a landslide in the Madison Canyon area that killed 28 people and resulted in the formation of a new lake. The Yellowstone region is one of the most seismically active regions in the country, so it is important to track that activity," said Poland.

"The area is also volcanically active, and so of course monitoring seismicity is important for assessing any potential volcanic or hydrothermal (steam-driven) activity," he said. "But the last volcanic eruption was 70,000 years ago. Strong earthquakes, like the magnitude-7.3 in 1959 or the magnitude-6.1 in 1975 within Yellowstone National Park, occur a few times per century on average in the region."

Poland said 2022 has so far been "pretty average" when it comes to seismic activity with more than 550 earthquakes recorded in the Yellowstone area.