Hundreds of small earthquakes are hitting Mount Rainier. Geologists say they're not concerned

A "swarm" of hundreds of small earthquakes are continuing to hit Mount Rainier this week.

The U.S. Geological Survey Cascades Volcano Observatory and the Pacific Northwest Seismic Network said Tuesday that the shaking began around 1:30 a.m. At times, several quakes occurred per minute, ranging from depths of 1.2 to 3.7 miles below the summit.

And Harold Tobin, who heads the Pacific Northwest Seismic Network, said the quakes have persisted Wednesday, though they appear to be tapering off.

Swarms — or clusters of earthquakes that occur in the same area in quick succession — are relatively common on Mount Rainier. About one or two happen every year.

But this week's swarm is the largest Mount Rainier has had in nearly 16 years, Tobin said.

"It's kind of a rare event," he said. "But not unprecedented."

So far, Tobin said, the swarm is "not too different" compared to the one that happened in 2009, which lasted three days. Tobin couldn't say how long this latest swarm will last.

"We will just have to watch and wait," he said.

Tobin stressed there's no indication that this seismic activity is cause for concern.

"What’s happening so far in this swarm is not something that causes us to be concerned that an eruption is building or an eruption is imminent in any sense," he said. "There's no evidence of magma around, under, or inside the volcano, which is what we would see as more of a warning sign."

Plus, none of the latest earthquakes have been felt at the surface — and even the largest quake so far, a 2.2 or 2.3 magnitude, is still well below levels that can typically be felt by people, Tobin said.