Video above: 1980 Eruption of Mount St. HelensForty years ago, a volcano in the Cascade Mountains in Washington roared, expelling plumes of ash and killing 57 people in the most destructive eruption in modern American history.It was early morning on Mount St. Helens when the volcano shook the Earth. Accompanied by a magnitude 5+ earthquake and a debris avalanche, the eruption changed the future of