On 18 May 1980, forty years ago today, the Washington-state volcano Mt St Helens exploded, killing dozens of people who had been warned to evacuate days earlier:
I was 150 miles away on May 18, 1980, when Mount St. Helens blew, but my bed shook and the windows on my Oregon A-frame rattled.
I rushed to my radio station and its clacking Associated Press wire machine, and pulled up a pile of wire copy from the floor. The reports coming in from southwest Washington state were hard to believe....
Despite two months of earthquakes, ashfall, and a growing bulge on the north side of the mountain, the night before was quiet. That morning was tranquil. The cone-shaped mountain had a white mantle of snow.
U.S. Geological Survey geologist David Johnston was [10 km from the mountain]. He had a car and camper and was calling in reports to the USGS command post in Vancouver, Wash. The day before, he convinced visitors from the University of Washington to leave. They wanted to camp with him overnight. "It's too dangerous," he told them.
The death toll reached 57 and included ham radio operator Gerry Martin and USGS geologist David Johnston. All but three of those killed were outside the "red zone" established by Washington Gov. Dixy Lee Ray. Geologists had pushed for a larger area with mandatory evacuations. But pressure to shrink the danger zone was intense from cabin owners, campers and hikers, and logging companies, including Weyerhaeuser, the timber giant that owned private forests in the area.
National Geographic explains what we've learned since then:
The volcano’s defiant position out of line perches it atop a zone of rock too cold to produce the magma necessary to feed its furious blasts.
“There shouldn’t be a volcano where Mount St. Helens is,” says Seth Moran, scientist-in-charge at the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver, Washington.
Four decades after Mount St. Helens’ eruption, scientists finally are unearthing some clues to its curious position. In one of the most comprehensive efforts to trace a volcano’s roots, the Imaging Magma Under St. Helens project, or iMUSH for short, used a slew of analyses to bring these subterranean secrets to light. Overall, the volcano doesn’t follow the textbook picture of a peak sitting above a chamber of molten rock. Instead, it seems, a diffuse cloud of partially molten blobs lingers deep below the surface, offset to the east of the edifice, toward the neighboring Mount Adams.
Most of the Cascade volcanoes—and others around the world—take shape above the spots where the plunging slab descends to roughly 62 miles deep, where temperatures get high enough for magma to form. But the situation is different at Mount St. Helens. Standing tens of miles to the west of other volcanoes, the infamous peak perches a mere 42 miles above the subducting plate.
Mt St Helens remains active, having erupted most recently in 2008.