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.

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.

Mount Rainier on Tuesday experienced its largest seismic activity since 2009, with a swarm of small earthquakes detected. According to the United States Geological Survey, hundreds of earthquakes were recorded.