The day in May -40 years ago- when Mount St. Helens blew up

By Gordon Williams

On May 18, 1980, Mount St. Helens erupted violently — killing 57 people, producing significant changes in the landscape and providing a vivid reminder that Washington state is home to some of the world’s most dangerous volcanoes. To help mark the 40th anniversary, May has been designated as volcano preparedness month.

This article is the first of two. It tells the Mount St. Helens story, and talks about volcanoes in general.  A companion story, with tips from the American Red Cross on how to stay safe in volcano country, will appear shortly.

The Cascade Range is a 1,300-mile-long string of volcanic mountains stretching from California to British Columbia. It is part of the Ring of Fire, the chain of volcanoes that circles the Pacific Ocean. The fire comes from molten rock seething below the earth’s crust. When volcanoes erupt, millions of tons of molten rock are thrust out — suddenly and often explosively.

The rock may return to earth as volcanic ash, scouring everything it touches, or it may flow out of the volcano as molten lava. The sudden melting of snow and ice on the volcano can produce lahars — massive mudslides that bury everything in their path.

Visit the USGS Volcano Hazards webpage to see the latest activity.

Given its place along the Ring of Fire, Washington is home to five active volcanoes — Mount St. Helens in Skamania County, Mt. Rainier in Pierce County, Mount Adams in Yakima and Skamania counties, Glacier Peak in Snohomish County and Mount Baker in Whatcom County.

That a volcano is listed as active isn’t quite as ominous as it sounds. It simply means the volcano has erupted within the past 10,000 years. But all of the state’s volcanoes are capable of erupting, and all are considered extremely dangerous.

The U.S. Geological Survey (USGS) compiles the National Volcanic Threat Assessment — measuring the danger each U.S. volcano poses. Most dangerous is Kilauea on Hawaii’s Big Island. The second most dangerous is Mount St. Helens, while Mount Rainier is third. Mount Baker is 14th and Glacier Peak is 15th. Mount St. Helens is high on the list because it has remained active, off and on, since the 1980 eruption.

Mount Rainier has erupted at least four times in the past 4,000 years — the last time in 1894-95. While it seems quiet now, Rainier is high on the list because should it erupt, the results could be catastrophic. There is more snow and ice atop Mount Rainier than on all the rest of the Cascades put together. Should it suddenly melt, the resultant lahar could be devastating. More than 150,000 people live in valleys below the peak, carved out by lahars. 

Fortunately, volcanic eruptions — unlike earthquakes — seldom come without warning. The volcano may emit clouds of smoke and gas, or there may be rumbling sounds. You won’t know exactly when the volcano will erupt, but you will be alerted that trouble could come.

Visit RedCross.org for additional volcano safety tips.

The 1980 eruption of Mount St. Helens was shocking because the mountain had not erupted since 1857. Still, Mount St. Helens did send out warnings before it blew. As the USGS explains it, “the picturesque conical volcano had been rumbling for months.”   

But these warning rumbles did not foretell how sudden or how dramatic the eruption would be. Says the USGS, “Fifty-seven people lost their lives as a result of the eruption, and dramatic changes to the landscape occurred and will continue long into the future.”  The headline of the USGS article is “Earth’s Inner Fury Uncorked.”

The eruption began the morning of May 18, when the entire north side of the mountain collapsed in what the USGS calls “one of the largest debris avalanches in history.” The collapse was followed by a blast that leveled trees over 200 square miles and sent an ash plume 16 miles into the sky. The resultant lahar filled the North Fork of the Toutle River valley for 13 miles to a depth of 600 feet. Mount St. Helens was 9,677 feet high before the eruption, and 8,363 feet afterwards.

Nor has Mount St. Helens remained quiet since 1980. The build-up of ash and snow on the crater floor formed Crater Glacier — the newest and only expanding glacier in the Cascade Range. The mountain erupted again in 2004, and remained almost continuously active for the next four years.

Scientists continue to monitor the state’s string of active volcanoes. You can assume you will get advance warning before there is another substantial volcanic eruption. The companion story will offer advice on how to prepare should there be news of another volcanic blast heading your way.