Mount Rainier is considered an active volcano and has not had a significant eruption in the past 500 years. However, it is potentially the most dangerous volcano in the Cascade Range due to its height, active hydrothermal system, frequent earthquakes, and heavy glacier cover.

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.