On May 18, 1980, Mount St. Helens in Washington State erupted in the most explosive volcanic event in United States history. Fifty-seven people and countless animals died, a forest was leveled, and ash blanketed the region as far away as Minnesota.

The volcano remains active today, even as events are being held at the mountain to mark the 36th anniversary of the disaster. Since mid-March, the U.S. Geological Survey has detected a swarm of 130 earthquakes in the surrounding area, suggesting that magma is on the move below the surface. The latest activity is part of a series of changes recorded at the stratovolcano since the dramatic eruption.

That blast ejected 1,300 feet (396 meters) of rock, excavating a