Mount St. Helens erupted on May 18, 1980 after two months of increasing volcanic activity. That event is widely considered the most disastrous volcanic eruption in U.S. history. It killed 57 people, destroyed hundreds of homes, 57 bridges and some 200 miles of roads and highways in addition to leveling tens of thousands of acres of forest land.
The eruption sent an ash cloud more than 12 miles into the atmosphere in just 10 minutes. The ash then spread across the continental U.S. in a matter of days and circled the earth within 15 days, according to the U.S. Geological Survey. The volcano had been dormant for more than 100 years until the seismic activity started to increase in March 1980. READ MORE