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.

Hundreds of earthquakes are detected at or near Mount Rainier each year, though typical swarms are smaller than what started last night.