Earlier this month, Mount Rainier experienced its most powerful seismic swarm ever recorded by the U.S. Geological Survey. More than 1,000 earthquakes have been detected at the mountain since July 8 — far above the volcano’s usual activity level — and the swarm is still continuing. 

However, despite the levels of seismic activity, the USGS’s Cascades Volcano Observatory say there’s no sign of magma movement or volcanic unrest. Instead, they believe the swarm was triggered by underground fluids shifting through cracks deep below the mountain. 

Research geophysicist Alexandra Iezzi joins us to explain what makes Rainier a unique geological phenomenon and what scientists are watching for.