Steam still spews from the mountain, much like it does from the geysers at Yellowstone National Park.
Rock slides occur every few minutes, and earthquakes show up daily on the experts' instruments.
The volcano erupted May 18, 1980. Only about 100 people enter it every year, and they have to be there for an academic or professional reason, Feeley said. MSU was only the second group allowed in this summer, and even that trip was almost cancelled when seismic activity started picking up dramatically in July. As it ended up, the MSU group was in the crater when two small earthquakes occurred on Aug. 25. Feeley, who has colleagues at the Cascade Volcano Observatory in Vancouver, Wash., studies volcanoes in the high Andes of Chile and Boliva.