Mount Saint Helens

Mount Saint Helens, active volcano in the Cascade Range of the southwest region of Washington. Long considered dormant, the volcano became seismically active in Mar. 1980 and erupted for the first time in 120 years on May 18, 1980. Preceded by two magnitude-5 earthquakes, the eruption was the first in the 48 coterminous states since Mt. Lassen erupted in 1915. More than 60 people were killed; there were widespread floods and mudslides. Surrounding forests were scorched or devastated, and much of Washington, Oregon, Idaho, and Montana was blanketed with volcanic ash.