Yellowstone Volcano Hit by Over 500 Earthquakes in Grizzly Lake Swarm

A total of 510 earthquakes occurred in a single region of Yellowstone National Park in September—a number that is around double the average.

The quakes took place near Grizzly Lake in the northwest region of the park, between the areas of Norris and Mammoth, as part of an earthquake "swarm" there that started in July, according to the United States Geological Survey (USGS).

Since then, there have been roughly 800 earthquakes altogether.

All of the earthquakes in September were small. Across the whole park, the largest was a magnitude 3.9 quake. An earthquake of this magnitude might be felt by a person but would rarely cause anything more than minor damage to structures or objects.

Yellowstone National Park is one of the most seismically active areas in the country, known not only for the hundreds of small earthquakes that occur there every year but also for its many geothermal geysers and hot springs.

It is also home to the Yellowstone supervolcano.

This activity is due to the fact that the park sits atop an extensive network of fault lines—fractures between two blocks of rock that allow them to move relative to one another. This movement can release huge amounts of energy which is what causes earthquakes.

Yellowstone tends to experience earthquakes in swarms due to the movement of volcanic fluids along fractures in underground rock.

Mike Poland, a research physicist at the USGS and Scientist-in-Charge of the Yellowstone Volcano Observatory, told Newsweek that although the recent number of earthquakes near Grizzly Lake was higher than average—which he said was roughly between 150 and 200 per month—it is not unusual for swarms to exhibit such sudden activity.

"There have been plenty of months where we've seen 800-1000 quakes," Poland said. "For example, in July 2021, there was a swarm of over 800 quakes beneath Yellowstone Lake over the course of 10 days.

"The largest/longest swarm of the past few years happened in 2017, when over 2400 earthquakes (max M4.4) were located in the area between Hebgen Lake and Norris Geyser Basin, which is the most seismically active area of the park, during June to September of that year.

"There isn't a strong seasonality to these swarms, as they can occur in winter as well, like February 2018 when a swarm of over 500 located earthquakes occurred in the same general band of Hebgen Lake to Norris Geyser Basin.

"This area has lots of preexisting faults, and when groundwater interacts with them, you get earthquakes. The region was also stressed by the 1959 M7.3 Hebgen Lake earthquake, so it is more prone to small events anyway. That's what makes it the most seismically active part of Yellowstone."