Mount St. Helens erupted on May 18, 1980. The major explosive eruption took place at 8:32 a.m. PDT after several months of seismic activity and smaller eruptions starting in March of that year. This eruption included a massive landslide, a lateral blast, and a vertical ash column reaching about 80,000 feet (24 km) into the atmosphere. It is considered the most disastrous volcanic eruption in U.S. history.