Earthquake Swarms Are Shaking Yellowstone’s Supervolcano. Here’s What That Means.

Something is rocking the massive supervolcano beneath Yellowstone National Park.

Thanks to a recent earthquake swarm, the Yellowstone supervolcano has seen upwards of 200 quakes since February 8, 2018 along with countless smaller tremors. The largest earthquake was an unremarkable magnitude 2.9, and all of them have hit about five miles beneath the surface. Larger earthquakes have rocked the region in the past, some as destructive as the Hebgen Lake quake and others causing minimal damage.

With this most recent swarm, scientists say there’s no reason to worry. “Supervolcano” and “earthquake swarm” might seem like daunting terms on the surface, but in Yellowstone National Park, these geologic features are relatively nonthreatening.

Earthquake swarms occur when a single area experiences an increase in quakes over a short period of time without the trigger of a single, larger “mainshock.” Swarms can result from changes in stress along fault lines, which can be caused by either large-scale tectonic forces or pressure buildup due to changes in magma, water, or gas underneath Earth’s surface.

The area where this current swarm is happening—about 8 miles northeast of West Yellowstone, Montana—is under pressure from both these forces, since Yellowstone is a hotbed for seismicity. But earthquake swarms are frequent in the region, accounting for more than half of the parks’ seismic activity. And they haven’t triggered any volcanic eruptions yet.

Last year, a swarm ten times larger than the current one rocked the same region, generating about 2,400 earthquakes between June and September 2017. This year’s swarm could actually be just a continuation of last year’s, since seismic activity in the area can be sporadic but ongoing.

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