When Mount St. Helens erupted on May 18, 1980, the landscape changed in an instant—the geologic version of an instant, anyway. It was the deadliest eruption the United States had ever seen, leveling everything for miles north of the mountain and blanketing ash as far as Montana. On the 35th anniversary of the event, the scars still shape the Cascade Mountains of Washington state.
That fact that this particular mountain blew its top wasn’t exactly a surprise; before explorer George Vancouver named it after a fellow Brit, the local Cowlitz tribe called it Lawetlat'la, or “The Smoker.” It was known to belch steam and had spewed ash as lately as the 1850s. This volcanic activity is a lot closer to the surface than the magma reservoir recently discovered under Yellowstone; that volcano, if it blew, would dwarf the destruction caused by St. Helens. Fortunately, that three-mile-deep pool of magma is unlikely to surface anytime soon.
The weeks leading up to the May 18 eruption were full of signs. More than 10,000 earthquakes were measured around the 9,677-foot peak and steam escaped through a growing summit crater. “Very clearly it was awake and building toward something,” says USGS volcanologist Seth Moran. “What happened was more extreme than just about everyone was expecting.”
In 1980, USGS scientist David Johnston, just 30 years old, knew an eruption was imminent on the night of May 17. Hydrologist Carolyn Driedger remembers reluctantly packing up her sleeping bag after Johnston told her to go home for the night, though she expected to return the next day for a helicopter study. She was among the last to see Johnston, who died instantly from his post when the lateral blast shot the top 1,000 feet of mountain at him at more than 300 miles per hour.
Today Mount St. Helens is the most-monitored volcano in the Cascades, with weather and seismology stations on every flank. On May 16, 2015, the Johnston Ridge Observatory, a visitor center located near where the scientist died, opens for the season with three days of science education talks, eruption eyewitness stories and a commemoration ceremony. Around the mountain, signs of the massive 1980 eruption are everywhere, telling the story of a cataclysm.
The new top of Mount St. Helens is a crater more than a mile wide, while inside is a new lava dome caused by an eruption—a much less dramatic one—that lasted from 2004 to 2008. “There was lava squeezing out of the ground like toothpaste going out of the tube,” says Driedger. Amazingly, a brand-new glacier formed inside the crater, like part of a donut pierced by the new lava dome. Climbers can reach the volcano rim through routes on the south side of the mountain and peer down at the still-changing interior.