Yellowstone Volcano Hit by over 1,000 Earthquakes in Ongoing Swarm

More than 1,000 earthquakes have now been recorded as part of an ongoing swarm at Yellowstone volcano since January.

Jamie Farrell, a research assistant professor in the Department of Geology & Geophysics at the University of Utah, told Newsweek the earthquake swarm appears to have periods of heightened activity, before becoming less active.

So far, the swarm was most active between late August and mid-September. In the month of September alone, for example, the swarm, which is located around 12 miles south-south-west of Mammoth Hot Springs near Grizzly Lake, produced more than 500 earthquakes.

In the month of October, the University of Utah recorded 238 earthquakes as part of this swarm, out of a total of 344 in the entire Yellowstone region.

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

Yellowstone National Park—which extends across 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.

The Yellowstone region averages about 1,500-2,500 earthquakes every year, with around half of them occurring as part of swarms.

Earthquake swarms are events in which many seismic incidents occur in a local area over a relatively short period of time without an accompanying main shock.

This year, the ongoing swarm near Grizzly Lake has produced more than 1,000 events and counting, according to Farrell. The swarm began with a small cluster in January but the vast majority of the quakes have occurred in the second half of the year.

The earthquakes in the swarm have not recorded a magnitude greater than 3.9, which is considered minor. An earthquake of this magnitude might be felt and but would very rarely cause damage.

Most of the earthquakes in the swarm are much weaker, with many being imperceptible to humans and only detectable with seismometers.

The phenomenon of earthquake swarms in volcanic regions is not unique to Yellowstone. There are a few theories of why these swarms occur, but in volcanic areas, the most common source is the movement of fluids in the crust, according to Farrell.

"These fluids could be a number of different sources: magma, water, gases, among others," he said. "The most-likely culprit is water moving through the crust but we can't be 100 percent sure about this."

In all of Yellowstone, the University of Utah has recorded more than 2,100 earthquakes since January 1 this year, which falls within the annual average range, with two months left to go in 2022.

In 2021, a total of 2,773 earthquakes were recorded in the region, according to the United States Geological Survey's Yellowstone Volcano Observatory annual report.

While this was higher than the 1,722 quakes recorded in 2020, it is not significantly outside the historical average range. The largest swarm of 2021 consisted of 825 events which occurred in the period July 15–25 beneath Yellowstone Lake.

It is not unusual for earthquake swarms to exhibit large, sudden bursts of activity such as the 10-day event at Yellowstone Lake in 2021.

The largest swarm in recent years occurred between June and September of 2017 when more than 2,400 earthquakes were recorded in the area between Hebgen Lake and Norris Geyser Basin.