Mount St. Helens Historic Site

• DATE: About forty thousand years old; erupted on May 18, 1980
• LOCALE: About fifty miles northeast of Portland, Oregon, and about sixty-one miles southeast of Olympia, Washington

SIGNIFICANCE: Mount St. Helens exploded violently in May 1980, causing the worst volcanic disaster in the recorded history of the United States. The cataclysmic eruption and related events rank among the most significant geologic events in the United States during the twentieth century.

The 1980 eruption of Mount St. Helens ensures its place in American history. It was the first volcanic eruption in the continental United States outside Alaska since 1921, when Lassen Peak in northern California erupted. The processes, effects, and products of the chain of events in 1980 were the most intensively studied and photographed of any explosive volcanic eruption in the history of the world. Mount St. Helens has provided an unprecedented opportunity for scientific research on the dynamics and potential hazards associated with an active composite volcano.

Historical Background

Based upon the age of windblown deposits associated with Mount St. Helens, it is estimated that volcanic eruptions from the mountain may have occurred as long as eighty thousand years ago. The oldest rocks found at Mount St. Helens are between forty thousand and fifty thousand years old. The mountain was probably first discovered by Native Americans who crossed the Bering Strait land bridge and colonized part of the North American continent. Northwest Indians referred to the mountain as La-wa-la-clough, meaning “smoking mountain,” or Tah-one-lay-clak, which means “fire mountain.”

According to Native American legend, the mountain was once a beautiful maiden known as Loo-wit. When Wy’east and Klickitat, two brave sons of the Great Spirit Sahale, fell in love with Loo-wit, she had difficulty choosing between them. The two braves fought over her, burying villages and forests as they threw fiery rocks at each other, causing many earthquakes. Sahale became furious, smote the three lovers, and erected a mighty mountain from which all three fell. Because Loo-wit was so beautiful, the mountain (Mount St. Helens) dedicated to her was a symmetrical cone of dazzling white. Wy’east (Mount Hood) lifts his head in pride, but Klickitat (Mount Adams) weeps to see the beautiful maiden wrapped in snow, so he bends his head as he gazes on Mount St. Helens.

The name “Mount St. Helens” was given to the mountain by George Vancouver while he supervised the surveying of the northern Pacific coast between 1792 and 1794. He named it on October 20, 1792, in honor of British diplomat Alleyne Fitzherbert (1753-1839), whose title was Baron St. Helens. Meriwether Lewis and William Clark sighted the mountain from the Columbia River between 1805 and 1806. Although they reported no evidence of eruptive volcanism, reports from the Sanpoil Indians of eastern Washington indicated that a major eruption had occurred around 1800.

Meredith Gairdner, a physician at Fort Vancouver, wrote about darkness and haze during possible eruptive activity at Mount St. Helens in 1831 and 1835. On November 22, 1842, the Reverend Josiah Parrish reported an eruption of Mount St. Helens, which was corroborated by missionaries who reported ash fallout at The Dalles, Oregon, forty-five miles southeast of the volcano. Based on contemporary sketches and paintings by Paul Kane, as well as a number of other reported observations, scientists think that eruptive activity at Mount St. Helens occurred intermittently between 1847 and 1857. Although minor steam explosions and large rock falls were reported in 1898, 1903, and 1921, Mount St. Helens gave little or no evidence of being a volcanic hazard for over a century after 1857.

Geographic and Geologic Setting

Surrounded by the Gifford Pinchot National Forest, Mount St. Helens is part of the Cascade Range, which extends from British Columbia, Canada, to Lassen Peak in northern California, a distance of about 930 miles. Being the youngest of the fifteen major volcanoes in the Cascade Range, it consists of several coalesced dacite domes, lava, and interlayered ash deposits. Volcanic cones with this internal structure are known as composite cones or stratovolcanoes. Mount St. Helens is located about thirty-five miles almost due west of Mount Adams, which is in the eastern part of the Cascade Range, about fifty miles from Mount Rainier, the giant of Cascade volcanoes, and about sixty miles southeast of Mount Hood.

Mount St. Helens was generated along an ocean-continent subduction boundary, where the Juan de Fuca Plate is subducting under the North American Plate. The subduction zone has existed for approximately 20 million years. In the 2020s, the Juan de Fuca Plate was moving east-northeast at about 1.6 inches per year, while the North American Plate was moving west-southwest at about one inch per year. The pre-1980 landscape of Mount St. Helens was dominated by dense coniferous forests, clear streams, and lakes. The elevation at the summit was 9,677 feet. Following the 1980 eruption, the elevation at the summit was reduced to 8,363 feet. During the 1980s and 1990s, more than a dozen thick, pasty lava extrusions built a mound-shaped lava dome in the mountain’s crater. This dome grew to be 3,609 feet in diameter and 886 feet tall. Since the 1980s, several lava domes have formed inside the crater, but each has been destroyed during subsequent volcanic activity. In 2023, geologists recorded hundreds of earthquakes below Mount St Helens, a sign the mountain is still very seismically active.

The 1980 Eruption

Including the 1980 eruption, Mount St. Helens has erupted at least forty-five times. Four major eruptions, each with at least 0.27 cubic miles of resulting deposits, are known to have occurred. The largest was probably the one in 1480, which was about five times larger than the 1980 eruption. After lying dormant for about 123 years, Mount St. Helens began to stir with a series of small earthquakes initiated on March 20, 1980. After a week of increasing local seismic activity, the mountain began to eject steam and ash. In April, the U.S. Forest Service and Washington state officials closed all areas near the mountain, which ultimately saved thousands of lives.

During April and May, numerous geologists gathered at Mount St. Helens to conduct a wide variety of studies. By the end of April, a large bulge on the northern flank of the mountain had developed, 1.24 miles long and 0.62 miles wide, expanding horizontally at a steady rate of 4.9 feet per day. Geologists carefully monitored the bulge, seismic activity, and gas emissions, hoping to detect any significant change that would indicate an imminent large eruption. However, no anomalous activity occurred, and seismic activity actually decreased. On May 15, thirty-nine earthquakes were reported, but only eighteen on May 17.

On Sunday morning, May 18, the mountain was silent. Only minor plumes of steam rose from two vents. At 8:32 a.m., a complex earthquake of 5.1 on the Richter scale shook the volcano, removing the confining pressure and causing a huge, 0.64-cubic-mile landslide that removed the bulge and the upper 1,312 feet of the volcano, leaving a 1,969-foot-deep crater with a width of 1.25 miles. The landslide quickly developed into a debris avalanche that sped at 68 to 87 miles per hour down the North Fork Toutle River. In addition, melting snow and ice from the mountain produced flooding and aided the movement of debris.

Parts of the avalanche entered Spirit Lake, eight miles from the summit, blocking the lake’s outlet and causing the water level to rise 197 feet. The debris buried Toutle Valley to a depth of nearly 165 feet. It swallowed up 200 homes, cabins, cars, logging trucks, and timber, carrying them downstream and destroying bridges, highways, and other construction. Over 186 miles of highways and roads and 15 miles of railways were destroyed or extensively damaged. Trees amounting to more than 4 billion board feet of salable timber were damaged or destroyed. A thick layer of volcanic ash deposited over a wide area destroyed many crops, including wheat, apples, potatoes, and alfalfa. All birds, most small mammals, many big game animals, and millions of salmon and other fish in the area perished.

When the top of the mountain was blown away at about 8:45 a.m., some observers described the noise and shaking as similar to being next to ground zero in an atomic bomb blast. Visibility dropped to zero as the thick volcanic dust hid the sun, and day became night as far away as 500 miles. Over 250 miles away, Spokane, Washington, was in complete darkness at 3:00 p.m. Bolts of lightning flashed from Mount St. Helens, sparking numerous forest fires. The air was so full of smoke and pumice that people could not survive outside. The volcanic ash and gases irritated skin, eyes, and lungs, making breathing extremely difficult. As the eruption spread horizontally outward across the collapsing slope, rock, ash, and suffocating gases caused numerous injuries and the deaths of fifty-seven people. Lighting fires was impossible in the thick ash fall and volcanic gases. The ash cloud rose to an altitude of eleven miles, fanned out eastward, then moved in a broad arc across the United States, completely circling the earth by June 5. Many earthquakes and aftershocks accompanied the eruption, and the volcanic activity completely changed the surrounding landscape for miles. The total damage from the eruption rose to over $1.1 billion. The closing of the eruption episode was marked by the slow rise of magma through the central chamber to form a new lava dome in the summit crater.

Since the 1980 eruption, there have been smaller explosive eruptions. They have been smaller in terms of lesser amounts of magma involved, as well as less mountain in which to allow the pressure to accumulate. Consequently, eruptions can occur after smaller amounts of gas have exsolved.

Places to Visit

Despite the troubled economy due to unemployment and reduced tourism caused by the 1980 eruption, thousands of visitors began flocking back to the area to marvel at the effects of the eruption. On August 27, 1982, President Ronald Reagan signed a law that set aside 110,000 acres around the volcano as the Mount St. Helens National Volcanic Monument, the nation’s first such monument, managed by the United States Forest Service. Many trails, viewpoints, information stations, campgrounds, and picnic areas have been established to accommodate the increasing number of visitors each year. Since the summer of 1983, visitors have been able to drive to Windy Ridge, only four miles northeast of the crater. This spectacular vantage point, which overlooks Spirit Lake, offers a firsthand view of the awesome evidence of the volcano’s destruction, as well as a picture of the remarkable, gradual recovery of the land as revegetation proceeds and wildlife returns.

Since 1986, mountain climbing to the volcano's summit has been allowed. Hikers most commonly take the Monitor Ridge Climbing Route—a five-mile route with over 4,500 feet of elevation gain. Winter exploration of the crater is a challenging but rewarding adventure. The majestic Mount St. Helens Visitors’ Center was completed in December 1986 at Silver Lake, about thirty miles west of Mount St. Helens and a few miles east of Highway 5. During the mid-1990s, an interpretation complex about five miles northwest of Mount St. Helens was opened in Coldwater Lake, Washington, from which visitors can see inside the crater and its dome. The visitor’s center underwent extensive renovations in the early and mid-2020s.

Although Mount St. Helens has not erupted for many years, volcanologists believe it will likely erupt again within a few decades or a century at most. The volcanic activity is carefully monitored to provide ample warning and mitigate the effects of any future eruption.

Bibliography

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Decker, R. W., and Barbara Decker. Volcanoes. W. H. Freeman, 1989.

Ellenbecker, Lauren. "400 Earthquakes Recorded under Mount St. Helens since Mid-July." The Columbian, 7 Nov. 2023, www.columbian.com/news/2023/nov/07/400-earthquakes-recorded-under-mount-st-helens-since-mid-july. Accessed 5 June 2024.

Goldner, Kathryn A., and Carole G. Vogel. Why Mount St. Helens Blew Its Top. Dillion Press, 1981.

Hamblin, W. Kenneth, and Eric H. Christiansen. Earth’s Dynamic Systems. 8th ed., Prentice Hall, 1998.

Harris, S. L. Fire Mountains of the West. Mountain Press, 1988.

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"Mount St. Helens National Volcanic Monument." US Department of Agriculture, www.fs.usda.gov/visit/national-monuments/mount-st-helens. Accessed 10 Oct. 2024.

"Mount St. Helens National Volcanic Monument." U.S. Geological Survey, 2 Nov. 2023, www.usgs.gov/volcanoes/mount-st.-helens/science/mount-st-helens-national-volcanic-monument. Accessed 10 Oct. 2024.

Perry, Ronald W., and Michael K. Lindell. Living with Mt. St. Helens. Washington State UP, 1990.

"Plate Tectonics." Pacific Northwest Seismic Network, 2024, www.pnsn.org/outreach/about-earthquakes/plate-tectonics. Accessed 4 June 2024.