Mount St. Helens Volcano, Washington: Number 2 of America's Ten Most Dangerous Volcanoes

The eruption of Mount St. Helens 30 years ago on May 18, 1980 (pictured), is the most devastating and most studied volcanic explosion in U.S. history. The blast killed 57 people and spewed 520 million tons of volcanic ash, darkening the skies of Spokane, Washington, more than 250 miles (400 kilometers) away.

Over the last 10,000 years, Mount St. Helens has erupted more frequently than any other volcano in the Cascade Range, and has continued erupting, albeit gently, in recent years.

"Certainly it's not possible to replicate the 1980 eruption, because the mountain isn't there anymore—it collapsed," said USGS Volcano Hazards Program coordinator Eichelberger.

"But there's nothing to say that a new, very gas-rich batch of magma couldn't come in under the thing and start a new explosive cycle." Source