In September, 510 earthquakes hit a single region of Yellowstone National Park, located in an area that encompasses the US states of Wyoming, Montana and Idaho - a number that represents almost twice the average.
According to the US Geological Survey (USGS), the tremors occurred near Lake Grizzly, in the northwest region of the park, between the Norris and Mammoth areas, part of a "swarm" of earthquakes that began in July. Since then, there have been around 800 earthquakes in all.
All episodes recorded in September were small. In the entire park, the largest was a magnitude 3.9 earthquake. A shock of this magnitude can be felt, but it rarely causes more than minor damage to structures or objects.
According to the Newsweek website, Yellowstone National Park is one of the most seismically active areas in the US, known not only for the hundreds of small earthquakes that occur there each year, but also for its many geothermal geysers and hot springs. It is also home to the Yellowstone supervolcano.
This is all due to the fact that the park sits atop an extensive network of tectonic faults — fractures between two blocks of rock that allow them to move against each other. This movement can release enormous amounts of energy, which is what causes earthquakes.
Thus, Yellowstone tends to experience sequential earthquakes due to the movement of volcanic fluids along fractures in underground rocks.
Mike Poland, USGS physicist and researcher in charge of the Yellowstone Volcano Observatory, told the publication that while the recent number of earthquakes near Lake Grizzly has been higher than the average — which, he said, ranged between 150 and 200 per month — this is not uncommon.
“There were many months where we saw 800 to 1000 earthquakes,” Poland said. "For example, in July 2021, there was a swarm of over 800 earthquakes under Yellowstone Lake over the course of 10 days."
According to Poland, the largest swarm in recent years occurred between June and September 2017, when more than 2.400 earthquakes took place in the area between Lake Hebgen and the Norris Geyser Basin, which is the most seismically active region of the park.
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"There is no strong seasonality to these swarms as they can occur in winter as well, or in February 2018 when a swarm of over 500 localized earthquakes occurred in the same general range from Lake Hebgen to the Norris Geyser Basin," he said. Poland.
“This area has a lot of pre-existing faults, and when groundwater interacts with them, you get earthquakes,” he explained. "The region was also affected by the 1959 Lake Hebgen earthquake, so it's more prone to small events anyway."
He says this is what makes this area the most seismically active part of Yellowstone.
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