Mount Rainier was experiencing "the most significant seismic activity" at the volcano in more than 15 years as an "earthquake swarm" hit the site starting on Tuesday.

On Tuesday, hundreds of earthquakes were detected, with depths ranging from 1.2 to 3.7 miles below the summit.

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.