Mount St. Helens, United States, 1980
The May 18, 1980, explosion of Mount St. Helens was the United States' deadliest and most destructive volcanic event, with 57 lives lost. The massive eruption, complete with a 15-mile-high ash plume, was preceded by a 5.1 magnitude earthquake, which caused a large chunk of the mountain to slide away. The volcano erupted violently for nine hours, taking Mount St. Helens from a symmetrical, dome-shaped, snow-capped peak to a topless mountain sporting a massive crater. Quite the makeover. The volcano has continued to belch steam and even magma since the eruption as it slowly rebuilds its dome. As for another big eruption in the future? We've got our eye on it.