The eruption of Mount St. Helens on May 18, 1980, was the most deadly and destructive volcanic event in U.S. history. The volcano exploded after a massive landslide, blasting ash, gas, and rock across the landscape. The eruption killed 57 people and flattened hundreds of square miles of forest. It also triggered mudflows and ashfall that spread across multiple states. Before the eruption, the north side of the volcano had started to bulge from rising magma. When it finally gave way, the entire s