What have we learned in the 35 years since Mount St. Helens erupted?

On May 18, 1980 Mount St. Helens erupted, leaving a 229-sq. mile path of destruction in its wake. Fifty-seven people died and the forest that had been built up over hundreds of years was leveled in an instant. This year marks the 35th anniversary of the eruption. Image courtesy of USGS.

On the morning of May 18, 1980, a 5.1 magnitude earthquake shook the ground beneath Mount St. Helens and awakened the volcano located 96 miles south of Seattle, Washington, that had been dormant for more than 140 years.

The earthquake triggered a landslide, uncorked the volcano and allowed a 650-mph explosion of ash, rock and gases to burst forth, blasting rocks northward and releasing a flow of lava.

In a matter of minutes, more than 200 square miles of forest was obliterated. Fifty-seven people died.

“It was a watershed event in volcanology in a lot of ways,” John Pallister, the lead for the U.S. Geological Survey (USGS) Volcano Disaster Assistance Program told PBS NewsHour.

“It was when geologists after the eruption worldwide started recognizing these giant debris avalanches, these giant landslides that are now recognized as a major hazard at volcanoes all around the world, ” Pallister said.

Mount St. Helens is pictured here before (l) and after (r) the devastating 1980 eruption. Images courtesy of USGS.

While the volcano went into repose for 18 years, in September of 2004, a swarm of shallow mini-earthquakes began to shake the ground. Only twice during the volcanic reawakening that lasted until 2008 were there any significant explosions of volcanic ash and gases.

Those eruptions presented an opportunity to test newly developed remote instruments.

Remote monitoring instruments, like the USGS spider, “up close and personally monitor micro-earthquakes that were previously impossible to record from more distant stations,” Pallister said.

Drones can also capture live video and thermal images of active lava flow. These tools minimize the risk to volcanologists working at the sites.

In 1997 snow began to accumulate behind the horseshoe crater left by the 1980 eruption. That ice hardened over the years to form a massive glacier. It is one of the more striking visual changes to the Mount St. Helens landscape. Photo by Dan Dzurisin courtesy of USGS.

Some of the most striking changes following the 1980 eruption were those made to the landscape that more than 300,000 people visit each year.

The volcano’s summit lost several thousand feet in height and a horseshoe-shaped crater was left in its place. In 1997, snow began to accumulate and thicken into a glacier that filled the area.

When asked in a 2010 NOVA special when Mount St. Helens could erupt again, Pallister said it could be two, 20 or 200 years. Today, he says his answer remains the same, but he said researchers now are better equipped to anticipate an eruption, should one occur.

“Now we should have good warning before it happens,” Pallister said. “And once we see the warning signs, we’ll know better when an eruption will occur.”

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