Phreatic Increased steaming from crater area noted by pilot but not reported until after eruption began. Fumarolic activity in crater had not been visible for previous 3 years. Seismic activity at background. Steam plume rising from north side of crater visible from Anchorage.
Seismic activity shows dramatic increase and warning of potential eruptive activity issued.
National Park Service over-flight observes vigorous steam plume in north crater area about 30 minutes prior to eruption. 10 Km, NE First major explosive event from vent in summit crater. 12 Km, NE Explosive events interspersed with seismic tremors. Major explosive event generates pyroclastic flows and debris avalanches down Drift glacier. Major debris flow and flooding in Drift River Valley.