Since mid-March, there have been a swarm of earthquakes under Mount St. Helens in Washington State, suggesting that the active stratovolcano is now recharging with magma.
According to the U.S. Geological Survey (USGS), over 130 vertical earthquakes ranging from low magnitudes 0.5 to 1.3 have been detected two to seven kilometres beneath the volcano’s crater. There are about 40 earthquakes at the volcano per week, and the occurrences are increasingly becoming more frequent.
“The magma chamber is likely imparting its own stresses on the crust around and above it, as the system slowly recharges,” reads a release by the USGS. “The stress drives fluids through cracks, producing the small quakes.” Source