The BriefMount Rainier is experiencing a swarm of hundreds of small earthquakes, the largest since 2009, prompting close monitoring by seismologists.The swarm, believed to be caused by hot fluids moving through faults, has calmed but could intensify again, with a recent magnitude 2.3 quake recorded.Seismologist Wes Thelen notes that such swarms are not unusual for Mount Rainier, which is not considered particularly active over a long timescale.SEATTLE - Seismologists are closely monitoring Mount Rainier after a swarm of earthquakes struck the Pacific Northwest’s tallest volcano this week. The U.S. Geological Survey (USGS) reports that hundreds of small quakes have occurred since the swarm began, making it the largest such event at the mountain since 2009.AdvertisementAdvertisementAdvertisementAdvertisementWes Thelen, a seismologist with the Cascades Volcano Observatory, told FOX 13 Seattle that the quakes began as a concentrated group of seismic events happening in quick succession.What they're saying"We had an increase in activity in seismic activity up to about 26 events an hour, which is a pretty good event rate for a quiet volcano," explained Thelen. "Since then, it's tailed off."He added that while the swarm has calmed slightly, the activity could intensify again."We don’t necessarily have a crystal ball to understand what is happening under there," he said.By the numbersAs of Wednesday morning, seismic instruments had recorded a magnitude 2.3 earthquake among the latest in the sequence. Thelen said the swarm is believed to be caused by hot fluids moving through pre-existing faults beneath the volcano.AdvertisementAdvertisementAdvertisementAdvertisement"These things at Mount Rainier we have seen before, and we expect to see them again in the future," Thelen explained.Though Rainier last erupted roughly 1,000 years ago, Thelen noted that the volcano is not unusually active when viewed on a longer timescale."Even though it was a thousand years ago, Rainier is not overall in a particularly active state over, let’s say, 10,000 years," he pointed out.News reports from show scientists detected a couple dozen earthquakes at Mount Rainier back in 2017. These too were classified by USGS as "swarms."Texas flooding: More than 80 people dead, 10 girls still missingAdvertisementAdvertisementAdvertisementAdvertisementReward to find Jonathan Hoang now at $100kTeen's birthday party ends with 1 person dead in Sedro-WoolleySeattle hospital treats dozens of fireworks-related injuriesWoo, Muñoz, Rodríguez named to AL All-Star roster for Seattle MarinersTo get the best local news, weather and sports in Seattle for free, sign up for the daily FOX Seattle Newsletter.Download the free FOX LOCAL app for mobile in the Apple App Store or Google Play Store for live Seattle news, top stories, weather updates and more local and national news.The SourceInformation in this story comes from original reporting by FOX 13 Seattle reporter Lauren Donovan.