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.

Hundreds of small earthquakes have rattled Mount Rainier this week in the largest swarm of tremors in more than a decade.

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