05/18/2026
A day to remember. Where were you when this happened?
On this day in 1980… a 5.1 magnitude earthquake starts a chain of events that will leave Mount St. Helens and its surroundings changed forever. The northern flank of the volcano fails catastrophically, with both the bulge and the summit sliding away in the largest debris avalanche in recorded history.
The debris avalanche sweeps around and up ridges to the north, burying Mount St. Helens Lodge where proprietor Harry Truman has chosen to remain and raising the bed of Spirit Lake by over 200 feet. However, most of the debris is carried westward as far as 14 miles down the valley of the North Fork Toutle River.
Exposure of the cryptodome, a very hot and highly pressurized body of magma that has been growing inside the volcano, triggers a powerful eruption. This lateral blast of hot material overtakes the debris avalanche, spreading northward at speeds of at least 300 mph.
David Johnston, who is among the first to see the avalanche and the beginning of the eruption from the Coldwater II observation post, radios the USGS field office, “Vancouver, Vancouver, this is it”, but they do not receive the message (atmospheric disturbance caused by the eruption probably blocked the signal.) Instead, Johnston's final transmission is picked up and recorded by an amateur radio operator.
A more detailed warning comes from volcano watcher Gerald Martin on the ridgetop north of Coldwater II, who coolly radios a description of the avalanche, the beginning of the eruption, and the progress of the blast cloud. “The camper and the car just over to the south of me [Coldwater II] are covered," he reports. "It [the blast cloud] is going to get me, too." Unfortunately he was right, there was no escape from his position, but Martin’s warning provides precious lead time for the subsequent rescue efforts.
Within 15 minutes the eruption cloud has reached a height of 15 miles (or 80,000 feet). The lateral blast has devastated an area nearly 19 miles from west to east and more than 12 miles northward from the former summit. In an inner zone extending nearly 6 miles from the summit, virtually no trees remain, and just beyond this area, all standing trees have been blown to the ground. The 230 square mile devastated area is now blanketed by a deposit of hot debris carried by the blast.
Stay tuned throughout the day to find out what happens as the eruption progresses...
Sources: Foxworthy, B., and Hill, M., 1982, Volcanic eruptions of 1980 at Mount St. Helens: The first 100 days: U.S. Geological Survey Professional Paper 1249; U.S. Geological Survey, 2023, 1980 Cataclysmic Eruption, https://www.usgs.gov/volcanoes/mount-st.-helens/science/1980-cataclysmic-eruption.
These remarkable photos taken by Gary Rosenquist from Bear Meadows (located about 11 miles northeast of Mount St. Helens), and time sequenced by the USGS, show the first minute of the debris avalanche and ensuing lateral blast.
