Explaining earthquake swarm at Mount Rainier
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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.
Mount Rainier is an active stratovolcano 45 miles southeast of Tacoma and 60 miles south-southeast of Seattle. Its last eruption was "a light dusting of ash" in 1894, the USGS said in a report. Large eruptions haven't occurred for more than 1,000 years.