America’s Biggest Volcanic Threat May Come Without an Eruption

After Mount St. Helens erupted in 1980, experts were faced with a precarious question: How can we best prepare for when—not if—the next volcanic eruption in the Cascade Range occurs?

Triggered by a 5.1-magnitude earthquake, the Mount St. Helens volcanic disaster devastated nearby communities in Washington, taking 57 lives and causing $860 million in damage to roads, railways, local infrastructure, and the logging industry—and for researchers, it was a wake-up call for establishing better seismic monitoring and eruption preparedness.

But scientists weren’t necessarily figuring out how to plan for streams of lava or plumes of ash billowing out of a volcano in the Pacific Northwest region of the U.S. Instead, they knew they needed a blueprint for taking on a lesser-known danger, one that could wreak havoc on communities—without a volcano even erupting.

The ruin brought by the Mount St. Helens disaster had less to do with the eruption itself, but rather, the huge lahar the event generated. Experts warn these violent, volcanic mudflows could be the biggest looming threats to people, towns, and the environment in the Pacific Northwest, and the race to analyze lahars—before it’s too late—sits at the center of this gripping Popular Mechanics feature.

What makes a lahar so perilous? Start with its unpredictable behavior, as the slurry of sediment, rocky debris, and water begins at the top of a volcano and travels downslope, moving very quickly and covering large distances. In mere minutes, a lahar can flow down a volcano and level anything in its path. “They are complex phenomena that change a lot during transport,” National Autonomous University of Mexico volcanologist Lizeth Caballero García, told Pop Mech in this feature story. “They can grow, they can dilute.”

And there’s good reason why United States Geological Survey (USGS) researchers have deemed lahars the “most threatening hazard” in the Cascades: They pose a direct danger to surrounding communities. For instance, around 150,000 people live in Washington’s Pierce County—in the middle of the projected lahar path of volcano Mount Rainier, located just around 60 miles from Seattle.

But an eruption or other seismic event doesn’t even have to occur for a lahar to set off, and that’s a crucial reason why scientists have spent decades trying to understand the risks communities near Cascade Range volcanoes face. Everything from dam failures to heavy thunderstorms have spurred fatal lahars around the world, and these no-notice lahars worry researchers, especially those studying Rainier.

A landslide beginning on the western side of Rainier, scientists say, could demolish the towns of Orting, Puyallup, and Sumner in just half an hour, and it would affect over 60,000 residents.

“[No-notice lahars are] the thing that goes bump in the night,” former Cascades Volcano Observatory (CVO) geophysicist Andy Lockhart told Pop Mech. “It creeps me out.”

That’s why it’s vital to keep researching lahars and get better at forecasting their volatile behavior. To improve their analysis of lahar destruction and impact, scientists have developed some key experimental sites, including a custom flume in Oregon’s H.J. Andrews Experimental Forest, funded by the USGS for replicating lahar flows. The CVO has also created an extensive network of monitors throughout the Cascade Range to not only detect lahars and volcanic activity, but also relay signals back to emergency managers in impacted communities so they can take appropriate action.

So when could the next lahar, or another other seismic event, occur? Researchers warn that it could be scarily imminent. And that possibility keeps scientists going, working to evolve lahar research in hopes that with another disaster like Mount St. Helens, we’ll be better prepared to respond and react.

To explore more about seismic monitoring in the Pacific Northwest, and how communities continue to prepare for the threat posed by lahars, read the full feature Pop Mech feature now.