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Under the Volcano

Look out Tacoma and Seattle. Majestic Mount Rainier is overdue for a shattering and deadly eruption

By Jack McClintock
Nov 1, 1999 6:00 AMNov 12, 2019 4:10 AM


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On a sunny Saturday afternoon in June, John Anderson, a 43-year-old sawmill worker, sits in front of his pretty green-trimmed house in a family-friendly subdivision in Orting, Washington, not far from Seattle. He gazes contentedly down the street, scratching his neat goatee and watching the neighborhood kids shoot hoops in a driveway. It's an ordinary day in suburban America, but here in Orting, behind every house, mostly ignored, is 14,410-foot-high, snowcapped Mount Rainier. This is one of the continent's most spectacular sights: a mountain that seems to loom and then recede, sometimes crisply focused and near enough to touch, at other times shifting into the fog, vanishing, then reappearing. "When we get a full moon and it comes up over the mountain, it's really something," says Anderson, leading a visitor into the backyard for a better view.

Anderson takes Rainier for granted. The mountain views came with the house, which cost $120,000 three years ago. In most places, such views would only add to the value of real estate over time, but Anderson's house hasn't appreciated a dime since he bought it. That's because Mount Rainier, the highest point in the Cascades, is not just lovely scenery. It's the most dangerous volcano in the United States. When it erupts— and it will— blistering avalanches of incandescent rock, lava, and ash will sweep down the volcano. Worse, unimaginably large flows of mud hundreds of feet deep, called lahars, filled with melted ice, boulders, and whole forests of uprooted trees, will pour down adjacent river valleys at upward of 25 miles an hour. Like concrete cascading down the chute of a cement truck, the lahars will entomb everything in their path. And that path runs right over Anderson's house.

Rainier is one of a score of volcanoes in the Cascades, from Northern California to British Columbia. Seven Cascades volcanoes have erupted in the past 200 years. All are smoking guns. "They say it's not if, it's when," Anderson says. The only question is how many people will die. As the U.S. population has doubled since 1943, whole towns have been built closer and closer to many of the 68 potentially active volcanoes that bubble away in Western states, Alaska, and Hawaii. Millions of people live in Seattle and Tacoma. Between the two cities and Mount Rainier, at least 100,000 people live on the solidified mudflows of previous eruptions. Orting, population 3,600, is one of the towns built on ground that is itself clear warning of danger. Known for logging and growing hops, Orting has a main street with a Timber Tavern and Frontier Bank on one side, a tree-shaded plaza on the other, and a postcard-perfect view of Mount Rainier at the foot. Inexpensive real estate has encouraged construction of at least three new housing developments like the one Anderson lives in. "And there's a new elementary school going up," he says.

To a layperson's eye, Mount Rainier looks unchanged from the way it appeared two centuries ago when a member of Captain George Vancouver's exploratory crew first sketched it— serene, stately, a symbol of permanence. Here, looks are deceiving. Rainier sits along the boundary of tectonic plates forming Earth's crust. Off the coast of Seattle in the Pacific Northwest, a heavy chunk of seafloor called the Juan de Fuca plate has been ramming itself under the lighter North American plate at the rate of an inch and a half a year, about a third as fast as hair grows. Squeezed and heated, the rock melts into magma, blobs of which rise toward the surface into chambers where it becomes trapped, cooking and rolling like boiling oatmeal. When the pressure becomes too great, it bursts free, throwing out lava, gas, steam, ash, and hot rocks. Rainier is a series of successive lava flows broken up by centuries of ice, water, percolating volcanic gases, and the mountain's own internal heat. When scientists look inside Rainier, they find some of its rock crumbly and weak. The mountain is dangerously unstable, a tall, steep heap of loose rocks held together by the force of gravity and a cubic mile of glacier ice that could be melted or shaken loose.

Of course, volcanoes unpredictably express themselves in several ways: Rainier could blow, or flow, or both. One danger is a ground-hugging avalanche of incandescent rock (as hot as 1,300 degrees Fahrenheit), ash, and gas racing downhill at 80 miles an hour. In 1902, on the Caribbean island of Martinique, Mount Pelée erupted and sent just such a pyroclastic flow sweeping into the town of St. Pierre, killing 29,000 people. Only two residents survived; one of them, Auguste Ciparis, had been serving time in a windowless dungeon. Less frequent is the classic, melodramatic eruption that occurs when pressures that have built up within a chamber of viscous, gassy magma suddenly burst free, throwing out tons of gas, ash, and superheated volcanic rock. Such explosive volcanoes are typically tall and steep and poetically evocative, and often, like Etna, Vesuvius, and Fuji, loom large in history and literature. Mount St. Helens was one, and so was Mount Pinatubo in the Philippines, which in 1991 spewed 15 million tons of ash, rock, and sulfuric acid 22 miles into the stratosphere. Within three weeks, the debris had veiled the globe, reflecting sunlight back into space and chilling that year's winter by at least a full degree. If all the volcanic material had fallen on Manhattan, it would have buried the island 1,000 feet deep, leaving only the tips of a few skyscrapers poking out. Luckily, an efficient warning system saved thousands of lives. Even so, 350 people died.

Mount Rainier has erupted at least four times in the last 4,000 years and has also triggered numerous devastating mud slides. When it erupts again, high-speed avalanches of hot ash and rock, lava flows, and landslides will decimate areas 10 or more miles away, and lahars— huge mudflows of volcanic ash and debris— will inundate valleys more than 50 miles downstream. Image Courtesy of USGS

When Rainier gets ready to explode, it will announce itself with the same earthquakes, increased gas emissions, and swelling of the mountain that helped scientists warn citizens living near Pinatubo, says Willie Scott, the scientist in charge of the Cascades Volcano Observatory in Vancouver, Washington. Volcanic ash would most likely head east, downwind and away from populous areas. Lava or pyroclastic flow would be unlikely to reach far beyond the boundaries of Mount Rainier National Park.

Less gaudy, far more likely, and far more dangerous to population centers, Scott says, is a lahar— a volcanic mudflow that starts a mud slide. Almost anything could trigger one with little advance warning: an earthquake, a steam explosion, the heat of rising magma, the collapse of a weakened flank of the mountain, or gravity. A small eruption or pyroclastic flow could do it, too, as it did in Armero, Colombia, in 1985. The town had been built, like Orting, on a solidified mudflow from a previous eruption. When snowcapped Nevado del Ruiz emitted a burp of lava and hot rock one day, a river of slurry a fifth the size of the Amazon River roared through town and buried 23,000 people.

Something like that happened about 5,600 years ago near what is now Orting, when a lahar hundreds of feet deep roared off Rainier and spread over 100 square miles, filling the White and Puyallup River valleys with 60 feet of sludge. Giant lahars have reached all the way to the Puget Sound lowlands every 500 years on average. Scientists figure there's one chance in seven of its happening again in the lifetime of anyone who lives in the vicinity. That's why they worry about the Andersons and their 100,000 neighbors in the lowlands around Rainier. The next Rainier lahar could shoot straight through Orting, Sumner, Puyallup, and possibly Tacoma to the sound. The nearest towns will be gone in less than an hour. "You'd only get 10 or 15 minutes' warning," says a Mount Rainier park ranger, "and then it's every man for himself."

A volcanic eruption can't be prevented. But before it erupts, a volcano may rumble for weeks or months as hot magma rises, bulging measurably and producing a symphony of gas seepage, steam blasts, and small events called earthquake swarms. Monitoring such signs saved lives at Pinatubo. Nearly a million people lived nearby, including 20,000 U.S. military personnel. Scientists from the Philippine Institute of Volcanology and Seismicity noticed right away when Pinatubo awoke with steam blasts in early April 1991. A team of specialists from the U.S. Geological Survey worked with the Philippine scientists to set up a network of instruments around the mountain; they studied its eruptive history and concluded that a huge eruption was imminent. They were right. When Pinatubo exploded on June 15, in Earth's largest eruption in 75 years, it filled previously inhabited valleys with 600 feet of ash. Most people had been evacuated, not to mention at least $250 million worth of military equipment. At a cost of $1.5 million, the monitoring seemed quite a bargain.

Still, predicting volcanic eruptions remains an iffy science. The Mount St. Helens disaster in Washington in 1980 taught volcanologists a humbling lesson. They knew it was about to blow. But the timing surprised them, and the blast was three times more powerful than they expected. A wiry 30-year-old geologist named David Johnston was monitoring the mountain from a U.S. Geological Survey instrument truck parked on a ridge that now bears his name. "Vancouver, Vancouver, this is it!" he shouted into his radio seconds before a blast that tore trees into tiny shreds and killed Johnston. His body was never found.

Mount St. Helens killed 56 other people, too, and led to a heightened sense of urgency at Geological Survey monitoring stations in Hawaii, Alaska, and Long Valley, California, as well as the Cascades. Geologists mapped rock deposits from previous eruptions, dated them to determine frequency of deposit, and identified spots likely to be hit again. Scientists analyzed the chemistry and temperature of gas emissions from hot springs and gas vents called fumaroles. As Japanese geochemist Sadao Matsuo once said, "Volcanic gas is a telegram from the Earth's interior." University of Washington volcanologists deployed six seismometers around Rainier to detect the small quakes that often precede an eruption. Others installed tiltmeters, distance-measuring networks, and Global Positioning System satellite receivers to detect subtle ground movements such as bulging, tilting, shifting, and spreading that could herald the next eruption.

Observers have known for a long time that watching a volcano can be useful. Tremors and uplifting earth were recorded in Pompeii just before Vesuvius erupted on August 24, a.d. 79. In 1993, geologists trekked to the top of the Galeras volcano in Colombia to test monitoring equipment. One of them, Stanley Williams, reported that he noticed an increase in tiny earthquakes and a decrease in sulfur dioxide emissions, suggesting the mountain had bottled up pressures. Williams ran. Incandescent rocks sizzled past his head, fractured his skull, broke his jaw and both legs and tore off his left ear. He was lucky. Six of his colleagues were killed. Even so, Williams has returned to the site many times to take more measurements.

Scott believes data from monitoring is the best hope of predicting when and how Rainier might blow next, but it's by no means a guarantee. "There have been plenty of flows gone down that valley, many of them during times of eruption, so we may have warning, because we'll sense those," he says. But recent studies also show that big mudflows occurred in the past without contemporaneous eruptions. "It's happened before," Scott says.

Of the 13 potentially active volcanoes in the Cascade Range of the Pacific Northwest, 11 have erupted in the past 4,000 years and seven in just the past 200 years.Image Courtesy of USGS

Living in Orting is like staring up both barrels of a shotgun because the town is situated at the joint of a Y, just below the convergence of the Carbon and Puyallup river valleys. "My concern is that a lahar might happen without warning," Scott says. "The rock, altered and weakened by gases and fluids, generates a water-saturated landslide." As he describes the scenario, he sweeps a hand ominously across a tabletop, burying an imaginary hamlet. "The problem in Orting is that by the time a flow starts and is detected, it could be as little as 45 minutes to an hour from town. So warning has to be automatic, and it has to be reliable. The last thing the authorities want is a false alarm."

Scientists and public officials consider this such a likely event that Mount Rainier is the only volcano in the United States other than Mount St. Helens that is permanently monitored for lahars with geophones— microphones placed underground in the river valleys. If the mud slide is coming, they should hear it and be able to trip an alarm system.

Conventional seismographs can't distinguish a debris flow from other loud, persistent sounds such as wind or rainstorms and can't pinpoint its location or progress. "Lahars have higher frequency vibrations than earthquakes, and the geophones detect that," Scott says. The $200,000 network consists of five compact, solar-powered sensors in each valley. They are set at different levels— two high enough to be safe from floods but likely to be hit by a lahar, and three high enough to probably survive a lahar and keep sending. By the time a big lahar hit Orting, it could be 40 or 50 feet deep— a fatal mud wave. Sensors would send radio signals to the Pierce County Department of Emergency Management, which would spread the alarm. In fact, sirens go off in Orting every month as a test of the system. "It's kind of scary even when you know it's a test," says a resident.

With a computerized warning system, an extensive public education program, and yearly volcano drills in which school children are rushed into buses and hauled swiftly out of the valley, Orting is one of the best-prepared towns in the Cascades, says Carolyn Driedger, a U.S. Geological Survey hydrologist who works in public education.

But the sophisticated system covers only a single quadrant of the mountain, the west-facing one, considered most dangerous. And while Washington State's 1992 growth-management law requires considering geological hazards when building, the town still permits high-density real estate development. "The best defense against volcanic hazards is intelligent land use," Scott says.

Some would say it's too late for that. Orting exists, and so do Ashford, Carbonado, Sumner, Puyallup, Greenwater, Tacoma, and other nearby population centers. No one in those towns seems ready to abandon homes in the shadow of this heap of eroded rock permeated with hot water and steam, covered with a cubic mile of ice, and piled atop a superheated lava chamber— a beautiful, potentially unstable mountain that has sired at least 60 gigantic mud slides in the last 10,000 years.

Like John Anderson, most of the people who live here know what the future could hold. And like him, they cling to the hope that it won't happen, or if it does, that they'll be lucky and quick. There's a little decorative wishing well in the Andersons' backyard, and when Anderson stands there gazing up at the mountain, he smiles. "We keep canned goods, water, clothes, and an extra checkbook handy," he says. "Just in case."

The USGS monitors volcanoes all over the world. For reports, fact sheets, and information about current eruptions, see their homepage The Volcano World Web site is a good spot for beginners


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