The blast killed 57 people.
In an instant - the eruption destroyed the top 1,300 feet of the mountain.
On Friday, climbers reflected on Mount St. Helens' transformation.
"When the weather turns bad and the conditions get ugly, we have a saying, well it'll be there next week," climber Joe Whittington said. "We know that's not always the case."
The mountain in southwest Washington may be the best known volcano in the state, but it's not the only one or the most dangerous.
The U. S. Geological Survey says Mount Rainier could be one of the deadliest volcanoes in the world because of its location near Tacoma and Seattle. Volcanic gases could rapidly melt snow and ice and generate a huge mudslide called a lahar that could flow through some populated areas.
Other volcanoes in Washington are Mount Baker in Whatcom County, Glacier Peak in Snohomish County and Mount Adams in Yakima County.
Meanwhile, the U.S. Forest Service and Mount Saint Helens Institute just unveiled a new Web site.
It includes a collection of information about the mountain - its eruption - and recovery.