SKAMANIA COUNTY, Wash. — Forty-six years ago today, Mount St. Helens unleashed one of the most devastating volcanic eruptions in United States history, transforming the Pacific Northwest landscape in minutes.
The catastrophic eruption on May 18, 1980, followed two months of intense activity including more than 10,000 earthquakes and hundreds of steam-blast explosions, according to the United States Geological Survey.
A magnitude 5.1 earthquake struck beneath the volcano at 8:32 a.m., setting the devastating eruption in motion, USGS records show. Within seconds, the volcano’s bulging north flank slid away in the largest landslide in recorded history, triggering a lateral blast of hot gas, steam, and rock debris that swept across the landscape at 680 miles per hour.
The USGS reported that blast temperatures reached 570 degrees Fahrenheit. A massive ash plume thrust 15 miles into the sky, where prevailing winds carried approximately 520 million tons of ash across 22,000 square miles of the Western United States.
Unprecedented destruction
The landslide covered 23 square miles and buried 14 miles of the North Fork Toutle River Valley to depths reaching 600 feet, according to USGS data. The lateral blast reached 17 miles northward, covering 230 square miles and destroying over 4 billion board feet of timber — enough to build approximately 300,000 homes.
The ash cloud caused complete darkness in Spokane, Washington, 250 miles away, and circled the earth in 15 days. Swift avalanches of hot ash and gas poured from the crater at speeds up to 80 miles per hour.
Melting snow and ice formed volcanic mudflows that destroyed 27 bridges, more than 200 homes, 185 miles of highways and roads, and 15 miles of railway. The eruption claimed 57 lives.
The Mount St. Helens eruption fundamentally changed scientific understanding of volcanic processes. The USGS continues monitoring the volcano today through the Cascade Volcano Observatory, while Mount St. Helens National Volcanic Monument preserves the area for research and education.
Historical photos of the Mount St. Helens eruption have been recently added to our Digital Archives.
This collection from the Washington State Department of Transportation (WSDOT) features 209 images from May 18-23, 1980, documenting the immediate aftermath of the eruption.
Photographs include aerial views of the volcano and crater, ash plumes and volcanic debris, flooding and mudflows along the Toutle River, damage to bridges and highways, and emergency evacuation and cleanup efforts.
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