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

Seismologists are closely monitoring Mount Rainier after a swarm of earthquakes struck the Pacific Northwest’s tallest volcano this week.