At 8:33 a.m. May 18, 1980, Mount St. Helens was a 9,677-foot-tall volcano with a conical shape that lent it the nickname the Mount Fuji of America. One minute later a 5.1 earthquake one mile under the volcano prompted a massive landslide on the volcano’s north flank. Shortly after, an eruption removed the top 1,300 feet as rock and gases were sent out at speeds ranging from 220 to 670 miles per hour, leaving a more-than-2.5-square-mile crater at the mountain’s top.
Today marks the 35th anniversary of Mount St. Helens’ eruption.
The initial eruption on that Sunday morning destroyed 230 square miles of national, state and private forests and took 57 lives. Some of those who died from shock waves and clouds of hot ash and superheated gases were more than 10 miles away. Others drowned in rivers swollen by mud flows that spilled down local valleys and river beds. Experts say the loss of life would have been much greater had the eruption occurred on a weekday when many more workers would be in the surrounding forests.
The explosive blast blew down some 4 billion board feet of timber, enough to build about 300,000 two-bedroom homes.
A lahar sent mud, snow ice, boulders and sediments racing down the North Fork Toutle River at speeds up to 27 mph, leaving some 45 million cubic yards of sediment in the Columbia River.
The eruption sent ash some 80,000 feet into the sky in less than 15 minutes, and that cloud circled the globe over the next two weeks. The sky as far away as Spokane was darkened and deposits were left across eastern Washington and north Idaho into Montana and Wyoming.
Even today excess sediment is found in river drainages around Mount St. Helens, and communities like Castle Rock, profiled in the Seattle Times, are still managing debris.
A young volcano
Mount St. Helens was formed over the past 275,000 years, as eruptive stages built up the mountain. Most of its modern edifice was formed by eruptions over the past 3,000 years.
The volcano was particularly restless in the mid-19th century, when it was intermittently active for at least a 26-year span from 1831 to 1857. Some scientists suspect that Mount St. Helens also was active sporadically during the three decades before 1831, including a major explosive eruption in 1800. Although minor steam explosions may have occurred in 1898, 1903, and 1921, the mountain gave little or no evidence of being a volcanic hazard for more than a century after 1857.
Today, a 110,000-acre area around the mountain is a National Volcanic Monument. The mountain has been a lot quieter since the events of May 18, 1980; though a smaller series of steam eruptions occurred in 2004, but caused no injuries or deaths.
Prepare for the next eruption
May is Washington’s Volcano Preparedness Month, and you can review the hazards presented by Mount St. Helens on this map developed by our friends at the U.S. Geological Survey’s Cascade Volcano Observatory.
DNR’s Geology and Earth Resources Division works with the U.S. Geological Survey, and other agencies to monitor Mount St. Helens, and the other active volcanoes in Washington State, including Mount Rainier.
See more photos of Mount St. Helens before and after the May 18, 1980, eruption on DNR’s Flickr page.