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Map shows earthquake swarms in Yellowstone National Park

This map shows the recent swarm of earthquakes -- indicated by yellow circles -- in and near the northwestern corner of Yellowstone National Park. The area is south of Bozeman, and northeast of the small town of West Yellowstone, which is shown on this map.

BUTTE — A recent swarm of more than 400 earthquakes in and near Yellowstone National Park has caused some people to worry that Yellowstone could soon be lost to a blaze of molten rock and ash from a super volcano.

In the past seven days seismologists have recorded 477 seismic events in an area east of Hebgen Lake. Several of the events were earthquakes that measured over a magnitude of 2, the strongest occurring around 7 p.m. June 15 with a magnitude of 4.4.

Mike Stickney

Mike Stickney, seismologist for the Montana Bureau of Mines and Geology, displays a seismograph Wednesday afternoon at the Natural Resources Research Center at Montana Tech in Butte. The large marking in the upper left corner represents a 4.4 magnitude earthquake that was recorded June 15 in the northwest corner of Yellowstone National Park. The earthquake was one among 477 recent seismic events that occurred in an area east of Hebgen Lake.

Mike Stickney, seismologist for the Earthquake Studies Office, Montana Bureau of Mines and Geology on the Montana Tech campus in Butte, said Wednesday earthquake swarms in Yellowstone are nothing new.

The last significant swarm was in 2010, Stickney said, and the largest he’s observed in his career occurred in 1987. In addition, Montana was host to several earthquakes in the 20th century measuring over magnitude 6.0, including in 1959, when a 7.3 earthquake struck the Hebgen Lake area, killing 29 people.

But what’s also not new, Stickney said, is the response from media outlets, which he said can sometimes sensationalize earthquake swarms with depictions of doom and gloom.

The sensational headlines are a result of the fact that Yellowstone sits atop a caldera, or what some people refer to as a “super volcano.”

What makes a caldera different from your run-of-the-mill volcano is its explosive power, Stickney said.

“They’re so violent they don’t even form a typical volcano-shaped mountain on top,” he said.

Part of the power of the Yellowstone caldera can be attributed to its magma, which sits in a chamber below the earth’s surface, Stickney said. This magma has a higher viscosity than what one would find in Hawaiian volcanoes, which Stickney said tend to be more like liquid.

Yellowstone National Park Caldera graphic

Because of the more viscous magma at Yellowstone, moisture and gas can get trapped below the earth’s surface, which can build up pressure over time, he said.

“If you release the pressure, the gases expand and form a froth that breaks up into volcanic ash,” said Stickney. “It’s an absolutely huge eruption.”

Stickney said the last major eruption from the Yellowstone caldera occurred 640,000 years ago. The explosion produced 1,000 cubic kilometers of ash, which rose into the atmosphere and was carried by winds into the central United States and Gulf of Mexico. By comparison, Stickney said, the eruption at Mount St. Helens in 1980 produced only 1 cubic kilometer of ash, 1,000 times less than the Yellowstone eruption.

Despite the apparent danger, Stickney said the caldera isn’t likely to erupt anytime soon.

“Yes, Yellowstone is a super volcano,” said Stickney. “But the chances of it exploding are extremely remote. It’s an extremely rare occurrence. There’s a lot of activity that happens at Yellowstone that does not portend to a big eruption.”

Stickney said it’s possible for seismic activity to precede an eruption, but other signs include changes in the gases that come to the park’s surface, ground tilting and harmonic tremors, none of which have occurred. In addition, Stickney said, the quakes haven’t occurred on top of the caldera but rather about 12 miles away.

But if the earthquakes at Yellowstone aren’t a sign of the end of the world as we know it, then what are they a sign of?

Stickney said earthquake swarms are not well understood but that the prevailing theory is that Yellowstone’s faults are being lubricated by gas and water seeping up from the molten rock, leading to slippage between faults.

Although the last major eruption at Yellowstone occurred a long time ago, heat and molten rock still reside below the park’s surface. Since that last eruption, 75 minor eruptions have been recorded, signifying that Yellowstone remains a dynamic place. It’s what makes Yellowstone the park with iconic geysers and hot springs that draw hordes of tourists to Wyoming each year, Stickney said.

But these facts haven’t stopped people from imagining the worst, the seismologist said.

“I guess because of Hollywood everybody thinks that the only thing that can happen at Yellowstone is the big one,” said Stickney, adding that the apocalypse “would be a big news story.”

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