Geoscientists have for the first time revealed the magma plumbing beneath Mount St. Helens, the most active volcano in the Pacific Northwest. The emerging picture includes a giant magma chamber, between 5 and 12 kilometers below the surface, and a second, even larger one, between 12 and 40 kilometers below the surface. The two chambers appear to be connected in a way that could help explain the sequence of events in the 1980 eruption that blew the lid off Mount St. Helens.