Animated graphic: How volcanoes work

Glacier Peak in Snohomish County is one of 18 volcanoes in the U.S. listed as a “very high threat.”

While Glacier Peak, at 10,541 feet, has relatively few seismic monitoring stations, volcanic experts believe they have enough seismometers that watch for clusters of earthquake activity to know when an eruption could be imminent.

Glacier Peak, along with the other volcanoes in Washington, is a composite type volcano. To see how volcanoes work, click on the graphic above.