On This Day

Mount St. Helens, Mount St. Helens eruption, Mount St. Helens plume, Mount St. Helens explosion
Joseph Rosenbaum/USGS

On This Day: Mount St. Helens Erupts

May 18, 2011 06:00 AM
by findingDulcinea Staff
On May 18, 1980, a massive volcanic eruption of Mount St. Helens in Washington state killed 57 people and devastated a 230-square mile area.

Earthquake Triggered Largest Landslide in Recorded History

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Mount St. Helens had a history of more than 4,000 years of sporadic eruptions. The year leading up to the eruption was marked by signs of growing volcanic activity, including a bulge growing on the mountain’s northern slope.

On March 16, 1980, a series of small earthquakes suggested that Mount St. Helens was stirring. More earthquakes and steam explosions opened a crater in the ice cap at the volcano’s summit on March 27. The crater grew to approximately 1,300 feet in diameter within a week, and giant cracks appeared at the summit.

“By May 17, more than 10,000 earthquakes had shaken the volcano and the north flank had grown outward at least 450 feet to form a noticeable bulge,” according to the  U.S. Geological Survey. “Such dramatic deformation of the volcano was strong evidence that molten rock (magma) had risen high into the volcano.”

At 8:32 a.m. on May 18, the mountain erupted. It began when an earthquake measuring 5.1 on the Richter scale triggered a massive landslide, shearing away the mountain’s north side. The landslide caused the volcano to depressurize and explode with a force “equal in power to 500 atom bombs,” the Mount St. Helens Institute explains. Ash shot into the sky and pieces of the mountain blasted sideways, destroying everything in its path.

The ash and rock reached more than 600 degrees Fahrenheit and traveled at 300 mph, devastating 230 square miles and permanently transforming the area’s landscape, according to the USGS.

The Mount St. Helens Institute reports that the ash blew more than 12 miles into the air and circled the globe within 17 days. The eruption killed 57 people and caused more than $3 billion in damage.

Harry Truman, “Icon of the Eruption”

The mountain had been a popular tourist destination, but the area was evacuated in the weeks prior to the eruption. All but a few residents heeded public warnings and left the immediate area.

Harry Truman, an 83-year-old man who owned Mount St. Helens Lodge on Spirit Lake, became a local celebrity after refusing to leave his home. He died during the catastrophic blast and remains buried near the shores of Spirit Lake with his pink Cadillac, sixteen cats and all of his earthly belongings, under approximately 150 feet of ash and soot.

Mount St. Helens Recovers

The Mount St. Helens Institute explains that despite the fact that a majority of wildlife in the area was destroyed by the volcano, “plant and animal life has reestablished itself far faster than expected.” Millions of deer, cougars, birds, fish and trees have returned to the area.

The Institute also reports that Mount St. Helens “entered a state of continuous eruption” in the fall of 2004. However, in July 2008, scientists reported that Mount St. Helens is officially asleep. Scientists aren’t sure how long the volcano will remain at rest, but they are sure it will resume activity.

Images of Mount St. Helens

The U.S Forest Service Volcano Cams allows you to catch a real-time glimpse of Mt. Saint Helens. No serious activity has been reported since an eruption in 2004.

National Geographic provides images, videos and information about Mt. Saint Helens, as well as other volcanoes, for students to compare and contrast the eruptions.

Related: Larger Volcanoes

Although Mount St. Helens is one of the most famous volcanoes in the U.S., it pales in comparison to the Yellowstone  “supervolcano” and Tambora, history’s largest recorded eruption.

Yellowstone’s last giant eruption happened 642,000 years ago, creating a caldera (sink) measuring 40 by 25 miles. This eruption was 1,000 times bigger than the eruption of Mount St. Helens, ScienceDaily reports, and the eruption “covered as much as half the continental United States with inches to feet of volcanic ash.”

Tambora, located on the Indonesian island of Sumbawa, erupted and killed an estimated 100,000 people in 1815. The volcano shot 400 million tons of gas about 30 miles into the sky, NPR states.

Reacting with water vapor in the atmosphere, the gas formed sulfuric acid droplets that became trapped in the stratosphere, creating a shield from the sun that covered much of the earth. As a result, the year that followed the eruption, 1816, became known as “the year without summer.”
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