Mount Rainier on Tuesday experienced its largest seismic activity since 2009, with a swarm of small earthquakes detected. According to the United States Geological Survey, hundreds of earthquakes were recorded.

Mount Rainier experienced a significant earthquake swarm, the largest since 2009, with hundreds of small quakes detected near the summit. Experts attribute the tremors to hydrothermal fluids interacting with pre-existing faults beneath the volcano.

Mount Rainier, the active volcano towering above southwestern Washington state, started rumbling — very lightly — on Tuesday. A swarm of small earthquakes was detected under the mountain triggering focused monitoring from officials. But researchers have determined there is no current threat of an eruption.