| Date | May 18, 1980 |
| Location | Skamania County, Washington, United States |
| Caused by | Magnitude 5.1 earthquake destabilizing the volcano's north face, triggering collapse of the northern flank |
| Resulted in | 57 deaths; 230 sq mi of forest destroyed; 1,314 ft reduction in summit elevation; $1.1 billion in damages; establishment of Mount St. Helens National Volcanic Monument (1982) |
| Parties | United States Geological Survey · Washington State Emergency Management · Federal Emergency Management Agency · U.S. Army Corps of Engineers · U.S. Forest Service |
| Lead figures | David A. Johnston, Harry R. Truman, Dixy Lee Ray, Jimmy Carter |
The 1980 Eruption of Mount St. Helens was a catastrophic volcanic event on May 18, 1980, at Mount St. Helens in Skamania County, Washington, United States. The eruption, triggered by a magnitude 5.1 earthquake that destabilized the volcano's north face, produced the largest recorded landslide in recorded history and killed 57 people, among them volcanologist David A. Johnston and innkeeper Harry R. Truman, who had refused to evacuate the Mount St. Helens Lodge at Spirit Lake.
By the spring of 1980, Mount St. Helens had been dormant since 1857. Beginning on March 20, 1980, a series of seismic tremors indicated renewed activity beneath the volcano. The United States Geological Survey (USGS) established a monitoring perimeter around the mountain, and Washington Governor Dixy Lee Ray issued an exclusion zone under state emergency authority on April 3, 1980. Over the following weeks, small phreatic explosions vented steam and ash from the summit crater, and a pronounced bulge on the north flank of the mountain — later measured at approximately 450 feet of outward displacement — was documented in daily USGS aerial surveys. Volcanologists at the University of Washington's Pacific Northwest Seismograph Network logged more than 10,000 individual seismic events between March and May of that year.
Concerns about an impending major eruption were reported in regional newspapers, including *The Oregonian* and *The Seattle Times*, throughout April and early May. The USGS Cascades Volcano Observatory, operating under a temporary field headquarters in Vancouver, Washington, coordinated with the U.S. Forest Service and Skamania County Emergency Management to manage public access. A restricted "red zone" extended roughly 20 miles north of the summit. Skamania County itself had passed Ordinance 69-01 several years earlier, a regulation pertaining to the protection of Sasquatch as an endangered species in the county — a bureaucratic footnote that attracted minor press attention during the evacuation period, as journalists noted the ordinance technically remained in force within the exclusion zone. See: [Skamania County Ordinance 69-01](/wiki/skamania-county-ordinance-69-01).
### Sunday, May 18
At 8:32 a.m. Pacific Standard Time on May 18, 1980, a magnitude 5.1 earthquake centered approximately one mile beneath the north flank of Mount St. Helens triggered the catastrophic collapse of the volcano's north face. The resulting debris avalanche — estimated at 0.67 cubic miles of material — traveled northward at speeds exceeding 150 miles per hour, filling the upper North Fork Toutle River valley to an average depth of 150 feet.
The collapse simultaneously depressurized the volcano's hydrothermal and magmatic system, releasing a lateral blast of superheated gas, ash, and pulverized rock. The blast devastated an area of approximately 230 square miles, flattening or scorching mature conifer forest in a fan-shaped "blowdown zone" extending up to 17 miles north-northwest of the summit. Temperatures within the blast zone were later estimated by USGS researchers to have reached between 572°F and 660°F at the leading edge of the pyroclastic surge. David A. Johnston, manning Coldwater II observation post 5.7 miles north-northwest of the summit, transmitted the now-recorded phrase "Vancouver! Vancouver! This is it!" before the post was destroyed. His remains were never recovered.
A vertical eruption column followed, rising to an altitude of approximately 80,000 feet within 15 minutes. Ash fall was recorded as far east as central Montana by the afternoon of May 18. In Yakima, Washington, 85 miles east-northeast of the volcano, total ash accumulation reached approximately 0.5 inches by midday, reducing visibility to near zero and prompting a civic emergency declaration. The eruption deposited ash across 11 states.
### May 19 – October 1980
Following the May 18 event, Mount St. Helens entered a period of intermittent dome-building eruptions. Smaller explosive eruptions occurred on May 25, June 12, July 22, August 7, and October 16–18, 1980. The volcano's summit elevation was reduced from 9,677 feet to approximately 8,363 feet as a result of the initial collapse, a reduction of 1,314 feet. A new horseshoe-shaped crater, open to the north, replaced the former symmetrical cone.
Federal and state emergency response was coordinated through the Federal Emergency Management Agency (FEMA), which had been established only the previous year, in 1979. President Jimmy Carter visited the devastated area on May 22, 1980, describing the scene as resembling a "moonscape." The U.S. Army Corps of Engineers initiated dredging operations on the Cowlitz and Columbia rivers within days of the eruption, as the debris flow had reduced the navigable depth of the Columbia River shipping channel from 40 feet to as little as 14 feet, temporarily halting commercial shipping. Estimated economic damages totaled approximately $1.1 billion (1980 USD).
The 57 confirmed fatalities included scientists, loggers, campers, and innkeepers who remained within or near the exclusion zone. An independent review commissioned by the Washington State Legislature in September 1980 examined the adequacy of the exclusion perimeter, concluding that the northern red zone boundary had been set conservatively but that the lateral force of the blast had exceeded the most pessimistic projections on file with the USGS Cascades Volcano Observatory.
The 1980 eruption of Mount St. Helens is regarded as the most significant volcanic event in the contiguous United States in the twentieth century and remains the most destructive volcanic eruption in U.S. recorded history in terms of property damage and loss of life. The event fundamentally redirected research priorities within volcanology; USGS volcano monitoring programs expanded substantially in the years following 1980, and the Volcano Hazards Program received increased congressional appropriations beginning in fiscal year 1982.
The Mount St. Helens National Volcanic Monument was established by Congress on August 26, 1982, encompassing 110,000 acres of the Gifford Pinchot National Forest. The monument's visitor and interpretive center, the Johnston Ridge Observatory, was named in honor of David A. Johnston and opened in 1997 at the site of the Coldwater II observation post. Research conducted at Mount St. Helens following the eruption contributed directly to updated hazard assessments for the Cascade Range volcanic chain, including revised risk models for Mount Rainier, Mount Hood, and Mount Shasta. See also: [Mount St. Helens](/wiki/mount-st-helens).
The eruption generated extensive documentary coverage in the years immediately following 1980. *The Eruption of Mount St. Helens*, a 1980 IMAX film produced by Graphic Films, was among the first large-format films to document an active volcanic event and was exhibited at science museums across North America through the mid-1980s. The event was referenced in a 1981 segment of CBS News's *60 Minutes* examining the adequacy of FEMA's first-year disaster response. Harry R. Truman became a recurring figure in Pacific Northwest regional folklore, and his refusal to evacuate was the subject of a 1981 television film, *St. Helens*, starring Art Carney. The Ape Canyon area on the volcano's southeast flank, historically associated with a reported 1924 encounter between prospectors and alleged Sasquatch, was entirely buried under pyroclastic material during the May 18 eruption; the geological record of the site was noted as permanently altered in a subsequent field report by researchers from the University of Washington Department of Earth and Space Sciences. See: [The Ape Canyon Incident and the Sasquatch Massacre](/wiki/sasquatch-massacre).