Which volcano in Washington State erupted catastrophically in 1980?

The Washington volcano that erupted catastrophically in 1980 was Mount St. Helens. Its climactic eruption began on May 18, 1980, after months of earthquakes, steam explosions, and a growing bulge on the mountain's north flank.

At 8:32 a.m., a magnitude 5.1 earthquake triggered the collapse of the entire northern side of the volcano. The collapse rapidly exposed gas-rich magma, producing a devastating lateral blast of hot rock, ash, and volcanic gases. The eruption column rose roughly 80,000 feet, while lahars—volcanic mudflows formed from melted snow and ice—raced down surrounding valleys.

The disaster killed about 57 people and caused roughly $1.1 billion in property damage. It also reduced the mountain's summit elevation by about 1,300 feet and left a large, horseshoe-shaped crater. Mount Rainier, Mount Hood, and Mount Shasta are also Cascade volcanoes, but none was responsible for Washington's famous 1980 catastrophe.