Ready to RUMBLE!

More than 100,000 people live within range of the deadliest volcano in the United States.

Early last July, on a ridge halfway up Washington’s Mount Rainier, I carried my skis to some patches of snow left over from the winter. A chilly mist swirled as I paused to look around me. Every now and then, the mist parted like a curtain to reveal the huge white mountain above.

I’ve seen the volcano a thousand times. Mount Rainier (elevation 4,392 meters or 14,410 feet) is so tall that it looms over Seattle, where I live, 112 kilometers (70 miles) to the northwest. Each time I see it, Rainier amazes me once again with its awesome beauty and enormous size.

Now, it scares me, too. Mount Rainier, say geologists, is the most dangerous volcano in the United States.


For a long time, nobody thought Mount Rainier was a big threat. Most people thought it was dormant, or in a quiet period geologically. They were wrong.

Recently, geologists have learned a lot more about Mount Rainier. And the news is not good. Careful study of ash layers on Rainier has revealed that the volcano has erupted far more frequently and recently than previously thought. And geologists have found the remnants of ancient lahars that once buried valleys where people now live. Lahars are speeding floods of volcanic ash, mud, and water from landslides and melted snow and ice. Lahars are most often triggered by volcanic eruptions.

Mount Rainier is relatively young as mountains go–only about half a million years old. It formed as an eastward-moving piece of Earth’s crust, called the Juan de Fuca plate, began to descend slowly under the Pacific Northwest landmass. As the plate descended, it heated up, and some of it melted into magma, or molten rock. That magma worked its way to the surface, where it burst out as Mount Rainier and the dozens of other volcanoes in Washington, Oregon, and California. The Juan de Fuca plate is still moving under those states, and as long as it keeps doing that, there’s the threat of volcanic eruptions.


So what will happen next? Will Rainier someday spew a glowing cloud of poisonous ash and fumes? Will sizzling avalanches of lava roll across forests, homes, and towns? Will lahars race down, sweeping away everything in their path? All those things have happened at other volcanic sites in the world.

In 1980, Mount St. Helens, a volcano about 80 kilometers (50 miles) south of Mount Rainier, exploded. The eruption was much bigger than geologists had expected. And lahars caused some of the worst damage.

Mount St. Helens was a real wake-up call. Afterward, everyone living near Mount Rainier, including me, started looking at the mountain differently.


Because of what scientists now know about Mount Rainier and what happened at Mount St. Helens, the lahars worry us most. “You aren’t going to get charred bodies from Mount Rainier,” explained geologist Tom Sisson. “But you’ll get houses crushed by lahars.”

Lahars worry us for several reasons. Mount Rainier has 25 glaciers–more than any other mountain in the United States outside of Alaska–that could melt into lahars. And unlike lava flows, lahars can travel fast and far. More than 100,000 people live directly in the way of potential Rainier lahars.

To make matters worse, lahars don’t need an eruption to happen. Lahars can be–and geologists say have been–triggered by earthquakes or landslides on Mount Rainier.

The past activity of the volcano, the number of glaciers on it, the large human population living in its shadow–all those factors make Mount Rainier the most dangerous volcano in the United States. “No doubt about it,” Bill Lokey, an emergency planner, told me. “Mount Rainier could produce the largest, most deadly disaster in the history of the United States.”

Now everybody wonders: How soon? A massive eruption and lahar on Mount Rainier–far bigger than the recent ones on Mount St. Helens–occurred about 5,600 years ago. Only 1,100 years ago, another lahar buried a whole forest not far from where Seattle now stands. And just 600 years ago, a third Rainier lahar mowed down 1.8-meter-(6-foot-) thick trees and filled valleys two stories deep with debris. Geologically speaking, that’s practically yesterday. Geologists say the next lahar could happen at any time–with or without an eruption.


One sunny day a few weeks after my July ski trip, I returned to Mount Rainier to hike. I trekked past a glacier and then up through a beautiful old-growth forest. Finally, I came to a high mountain meadow, where a rainbow of wildflowers bloomed. The mountain towered above me, as incredible as ever. Among all the wonderful scenery, I thought about something Bill Lokey had said to me: “We live here by geological consent.”

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