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MOUNT SAINT HELENS NATIONAL MONUMENT, WA - OCTOBER 10: Steam erupts from Mount Saint Helens volcano at sunrise breaking an unexpected calm in seismic activity on October 10, 2004 in Mount Saint Helens National Monument, Washington. Seismic activity slowed last week prompting a downgrade from level three, indicating an eruption or imminent danger of one, to level two warning that an eruption is likely though not imminent. In 1980, seismic activity slowed in a similar fashion shortly before the volcano exploded, blowing the top off the mountain with a blast heard 200 miles away and causing the largest landslide ever recorded. The 1980 eruption leveled hundreds of square miles of forest, killed 57 people, and sent volcanic ash around the world. (Photo by David McNew/Getty Images)

MOUNT SAINT HELENS NATIONAL MONUMENT, WA - OCTOBER 10: Steam erupts from Mount Saint Helens volcano at sunrise breaking an unexpected calm in seismic activity on October 10, 2004 in Mount Saint Helens National Monument, Washington. Seismic activity slowed last week prompting a downgrade from level three, indicating an eruption or imminent danger of one, to level two warning that an eruption is likely though not imminent. In 1980, seismic activity slowed in a similar fashion shortly before the volcano exploded, blowing the top off the mountain with a blast heard 200 miles away and causing the largest landslide ever recorded. The 1980 eruption leveled hundreds of square miles of forest, killed 57 people, and sent volcanic ash around the world. (Photo by David McNew/Getty Images)