Mount St. Helens
The eruptive history of Mount St. Helens (Washington) began about 40,000 years ago with dacitic volcanism, which continued intermittently until about 2,500 years ago.
The May 18, 1980 eruptive column at Mount St.
Before May 18, 1980, Mount St. Helens' summit altitude of 9,677 feet made it only the fifth highest peak in Washington State.
During the 9 hours of vigorous eruptive activity, about 540 million tons of ash fell over an area of more than 22,000 square miles.