Mount St. Helens is an active volcano located in southern Washington state. Its most famous eruption on May 18, 1980, killed 57 people, destroyed 250 homes, and caused billions of dollars worth of damage. It was the most destructive volcanic event in American history. Fortunately, however, there was a great deal of activity in the months before the eruption. Nearby communities, as well as the rest of the nation, had plenty of warning that a major eruption was coming.