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News / Clark County News

Volcano seemed safe – until it suddenly wasn’t

In wake of the eruption, the state of science also exploded dramatically

The Columbian
Published: May 17, 2010, 12:00am

Three decades ago, area residents viewed Mount St. Helens as just that — a mountain.

When a pair of U.S. Geological Survey researchers published a 25-page booklet in 1978 characterizing Mount St. Helens as a volcano — an active one at that, probably due to erupt before the turn of the century — many Northwest residents scoffed.

A volcano seemed an absurd way to describe the white-capped conical peak that had glimmered above the emerald-green waters of Spirit Lake for generations.

“People thought of a lot of the mountains as prehistorically active, but not active now,” said Larry Mastin, a volcanologist with the U.S. Geological Survey in Vancouver.

That perception changed radically approximately two months after the mountain had reawakened with the first of hundreds of small to moderate earthquakes that reshaped the terrain.

A magnitude 5.1 earthquake at 8:32 a.m. on May 18, 1980, caused the bulging north flank of the mountain to slip in the biggest landslide witnessed in modern history. The collapse of the mountain’s north face uncorked a gas-charged jet of magma that leveled 230 square miles of forest, killed 57 people and jetted a 15-mile-high ash plume that turned day into night as it drifted east.

The fledgling scientific field of volcanology has matured in the 30 years since.

Today, the combination of satellite technology with improved networks of conventional seismometers enables scientists to discern the tiniest activity. In 2001, using comparative satellite images, scientists detected an uplift of 10 inches across an area measuring 9 to 12 square miles near the South Sister mountain outside Bend, Ore.

Every week, the Vancouver-based Cascades Volcano Observatory updates the public about earthquakes that routinely rattle Cascade mountains.

Research has shifted from documenting ancient eruptions to real-time monitoring of active hazards.

Geologists have long understood that stratovolcanoes such as Mount St. Helens built up over millennia with magma pulsing out from a single conduit. They didn’t fully grasp that volcanoes can suddenly fall down — until they saw it on the bright blue morning of May 18, 1980.

USGS geologist David A. Johnston died in the lateral blast.

At the time, Mastin said, the USGS had been planning to dispatch an armored personnel carrier to Johnston’s post 5½ miles northwest of the volcano. Officials believed the carrier could have shielded Johnston from debris falling out of a vertical plume — not a lateral explosion.

“They were trying imagine the worst thing that could happen to Dave,” Mastin said.

In the aftermath, scientists began to recognize patterns in landscapes elsewhere around the globe. In one example, the tall hummocks that formed out of landslide debris along the Toutle River valley appeared eerily similar to unexplained landforms around Mount Shasta in Northern California.

“Almost as soon as that landslide had settled down, people said, ‘Whoa, this looks exactly like the corridor by Mount Shasta,’” said John Wolff, a volcanologist and geochemist at Washington State University.

More than anything, Mastin said, the 1980 eruption emphatically demonstrated that Cascade mountains can be as dangerous as they are beautiful.

“It opened up everybody’s eyes to the fact that this is a very active place,” he said.