3,000 ft (1 km) steam plume on May 19, 1982, two years after the May 18, 1980 eruption
EarthScope GPS stations can record the expansion and contraction of a volcano as magma moves below the surface. EarthScope seismometers can record earthquakes within a volcano. The GPS and seismic data can give us an indication of a volcano's activity level. It may lead to better predictions of future eruptions.
In the overhead view of Mount St. Helens, the colored dots mark recent earthquakes. About 40 earthquakes per month is normal activity for the volcano.