Ten Ways Mount St. Helens Changed Our World: The Legacy of the 1980 Eruption

Mount St. Helens was once loved for its serene, near-perfect cone, likened to Japan's Mount Fuji, and people nearby assumed it was solid and enduring. That changed in the spring of 1980. On May 18, after two months of earthquakes and small explosions, its over-steepened north flank collapsed in a colossal landslide, triggering a near-horizontal blast and then a powerful vertical eruption.

• The rock-filled, gas-charged blast became a pyroclastic flow that flattened millions of trees, stripped their branches and bark, and scoured soil to bedrock.
• The vertical eruption fed a towering ash plume for more than 9 hours, and winds carried ash hundreds of miles.
• Lahars — volcanic mudflows — buried river valleys.

It was the worst volcanic disaster in the recorded history of the conterminous United States. From 1980 to 1986 the volcano erupted more than 20 more times, building a new lava dome, and from 2004 to 2008 it erupted continuously, oozing near-solid lava into the crater.

The eruption column of May 18, 1980, which reached 15 miles high. USGS photograph by Austin Post.

Mount St. Helens above Spirit Lake in 1979 (top) and 1982 (bottom). Photographs by the U.S. Forest Service and by Lyn Topinka, USGS.

1. The world saw a volcano's destructive power

Small earthquakes shook the mountain from March 16 to 20, 1980; within a week a mile-long crack split the summit and steam explosions opened a small crater — its first activity since 1857. Through April, an excited public followed the news, and residents photographed small bursts of ash and steam from fields and rooftops. It was only the warm-up. At 8:32 a.m. on May 18, three sonic booms and a spreading ash cloud announced the eruption. Hikers 60 miles away at Chinook Pass swept falling ash into lunch bags as souvenirs, then drove home through darkness to Yakima, 85 miles away, where an inch of ash covered everything. West of the volcano, lahars swept logs, boulders, trucks and houses downriver, and officials closed Interstate 5 bridges and the West Coast rail line.

2. Communities invented ways to recover from ashfall

Ash — fine particles of rock and volcanic glass — filled the sky across eastern Washington, Idaho and western Montana. Interstate 90 from Seattle to Spokane closed for a week, and airlines cancelled more than 1,000 flights; truckers later drove slowly side by side to keep ash from stirring. In pre-internet 1980, Yakima's officials found nothing in the library on ash cleanup, so they invented their own: residents swept ash into piles, and more than 120 borrowed trucks, sweepers and graders hauled it to dump sites covered with topsoil — some now public spaces. The eruption also first brought the health effects of volcanic ash to serious scientific attention, and research on its impacts on farming, transport, communications, power and water treatment is now available worldwide.

Ash stopped northbound traffic on Interstate 5; southbound truckers drove side by side to slow traffic and keep ash down. USGS photograph by Carolyn Driedger, May 25, 1980.

3. Rivers are still disturbed decades later

Lahars clogged the Toutle, Cowlitz and, 75 miles downstream, the Columbia, where sediment cut the channel depth from 40 to 14 feet, halting shipping and hurting ports; along the Cowlitz and Toutle, raised riverbeds weakened levee protection. For years afterward, sediment transport was among the highest in the world. The U.S. Army Corps of Engineers dredged the channels and built a structure on the North Fork Toutle to trap sediment while letting water through; it held sediment back for more than a decade, and though now filled to its spillway, still traps some. Rivers still carry sediment at a few tens of times pre-eruption rates, challenging flood protection and fisheries — a lesson that sediment can be an eruption's longest legacy.

Dredging to reopen the Columbia for shipping and the Toutle and Cowlitz for flood control; spoil piles still line Interstate 5. USGS photograph by Lyn Topinka, February 5, 1981.

4. Life came back faster than expected

Many scientists assumed nothing would survive near the volcano and that recovery would take generations. Instead, they found a mosaic of habitats. Snow, ice and animals' habits — nocturnal animals asleep in dens — protected some life; farther out, trees were only singed. Erosion gullies exposed surviving plants and became oases; plants pushed through thin ash; and nitrogen-fixing lupine and alder thrived in thick, nutrient-poor deposits, improving them for others. Though thousands of large mammals and millions of fish, birds and insects died, amphibians and fish emerged from under lake ice within weeks, pocket gophers mixed soil and brought up seeds, and beavers built new ponds. Today the area's diversity of life exceeds that before the eruption, and techniques honed there are used at other disturbed volcanoes.

5. Congress preserved the landscape

To balance public demand for access with protection and study, Congress in 1982 set aside 110,000 acres as Mount St. Helens National Volcanic Monument, managed by the U.S. Forest Service. Visitors can hike and climb the volcano while research continues with little human interference; Washington State Parks' visitor centre and Weyerhaeuser's Forest Learning Center also tell the story.

Visitors at Johnston Ridge Observatory. USGS photograph by Carolyn Driedger, June 2016.

6. Scientists and officials learned to work as teams

A 1975 USGS report had identified Mount St. Helens as young and explosive and likely to erupt again, possibly before the end of the 20th century — but officials hardly knew it, and the awakening took the public by surprise. Scientists, land managers and public-safety officials quickly learned to coordinate: scientists supplied the best data, officials the structure to manage hazardous areas and inform the media and public. That team approach continues across the Cascades — which run from British Columbia to northern California — where officials and scientists meet regularly to plan and practise for the next crisis.

Officials from Puyallup, Washington, more than 40 miles downstream of Mount Rainier, practise evacuating their school district from a lahar. USGS photograph by Carolyn Driedger, May 8, 2019.

7. A new generation of volcanologists

Before 1980 USGS volcano monitoring centred on Hawaii's non-explosive eruptions at the Hawaiian Volcano Observatory. The eruption drew worldwide interest, and in 1982 the USGS opened the David A. Johnston Cascades Volcano Observatory; the University of Washington's Pacific Northwest Seismic Network also expanded. Hundreds of foreign volcanologists have studied the mountain, and in 1986, after the devastating eruption of Nevado del Ruiz in Colombia, that experience helped create the Volcano Disaster Assistance Program — funded by USAID and the USGS — which has responded to more than 70 crises and strengthened response capacity in 12 nations.

8. New insight into the volcano's history

On May 18 people saw — some photographed — a debris avalanche, one of nature's most destructive processes, letting scientists link such events to their deposits. They found two smaller ones from 2,500–3,000 years ago and one about as large from about 20,000 years ago, and have since recognised the pattern at more than 200 volcanoes. The volcano proved older than thought — with eruptions as long as 270,000 years ago — though most of today's mountain grew in just 4,000 years, in styles from violent explosions to runny Hawaiian-style lava.

Layers of ash from high-powered eruptions about 3,500 years ago. USGS photograph by Larry Mastin, August 2019.

9. Better knowledge of Cascades hazards

New studies found some Cascades volcanoes erupt more often than thought. The yearly chance of an eruption ranges from about 1 in 100 at Mount St. Helens to far less at Mount Jefferson, Oregon; overall there is a 1–2 percent chance each year that at least one Cascades volcano erupts, and many eruptions go on intermittently for years.

10. A revolution in monitoring

In 1980 only one seismometer stood within 30 miles of the mountain. Today networks run by the USGS, the Pacific Northwest Seismic Network, UNAVCO and others track earthquakes, ground deformation, temperature and volcanic gases, following magma in real time, while studies of erupted rock reveal what drives eruptions. When the volcano reawakened in 2004, scientists had the data and the communication channels in place — proof of the value of long-term monitoring.

Laser-scanning the upper North Fork Toutle River to measure how the valley changes. USGS photograph by Jon J. Major, 2010.

Sources

• Driedger, C.L., Major, J.J., Pallister, J.S., Clynne, M.A., Moran, S.C., Westby, E.G., and Ewert, J.W., 2020, Ten ways Mount St. Helens changed our world — The enduring legacy of the 1980 eruption: U.S. Geological Survey Fact Sheet 2020–3031. https://pubs.usgs.gov/publication/fs20203031
• The photographs and captions come from the fact sheet's PDF. Two photographs credited as used with permission are not reproduced.
• Rewritten in hubnx's own words.