Seconds from Disaster: Mount St. Helens Eruption Mt. Saint Helens slept for 123 years. And then, despite the constant watch of U.S. geologists, the giant awoke, flattened everything across 220 square miles, launched millions of tons of ash 12 miles into the air, and turned day to night for 250 miles around. The most destructive volcanic eruption in U.S. history killed 57 people, caused over a billion dollars in damage and caught geologists by surprise. Why did Mt. St. Helens erupt so explosively? Could it happen again? Videos 46:08Mount St. Helens Eruption2:47St. Helen's EruptionNo Video Photos Episode "Mount St. Helens Eruption"