Over 300 minor earthquakes have been detected under the surface of Mount Rainier since the morning of Tuesday, July 8. The swarm is the first of its kind since 2009, and, according to Pacific Northwest Seismic Network Director Harold Tobin,

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.