Copyright © 2001 The Seattle Times Company
Local News : Tuesday, May 16, 2000
Mount Rainier: Danger at our door
by Eric Sorensen
Last of a three-part series
Seattle Times science reporter
Mount Rainier was to most minds just another splendid mountain. Big, beautiful, a regional icon. And as volcanoes go, asleep, if not dead.
But on May 18, 1980, when Mount St. Helens brandished the explosive power of 500 Hiroshima bombs, scientists and the public started glancing, uneasily, at the Cascades' largest peak.
The mountain hadn't blown in a big way for 1,000 years, but scientists, who knew it was still active, started reconsidering just how Mount Rainier works. They now recognize it as the most dangerous mountain in the United States.
They believe it has erupted twice as frequently as previously thought. They realize that tumultuous mudflows, created when huge volumes of ice and water slide off the mountain, are most likely to come off the western side, which happens to be the one closest to large and growing populations of people.
And recent research suggests such a big flow could come without the rumblings that warned the world of Mount St. Helens.
Government officials have laid plans to move more than 100,000 people at the mountain's feet from the path of mudflows, called lahars, in as little as 40 minutes. The plans include a one-of-a-kind monitoring system that will automatically detect and send word of a large mudflow soon after it happens, day or night, whether or not it is caused by an eruption.
In towns like Orting and Sumner the plans still have their critics, but long gone is the notion that the looming neighbor is dormant and safe.
"Mount St. Helens having erupted made believers out of everybody," said Willie Scott, scientist in charge at the Cascades Volcano Observatory in Vancouver, Wash. "It was, 'OK, this can happen.' "
Eruptions in 1800s
Northwest Indians called Mount Rainier Tahoma, Tachkoma, T'chakoba and 40-some other variations on the name, with interpretations running from "nourishing breast" to "rumbling noise."
They and newly arrived European settlers reported more than a dozen minor eruptions in the 1800s, including a spurt of dirty steam in 1894. But it wasn't until two years later that U.S. Geological Survey researchers climbed the peak to put together the first theory about the activity.
More recently, researchers have charted its mudflows and traced the ash around it. Mount Rainier's new scientific profile lacks the mysticism of legend, but it retains much of its mystery and power.
Unlike Mount St. Helens, a young spud of the Cascade range at 40,000 years of age, Rainier is a half-million years old.
St. Helens is a tidy mountain, a nearly symmetrical cone until 1980, having been built by alternating layers of lava, ash and volcanic debris. Rainier is a mishmash, a mound of many layers of lava and blast fragments. "Some people say it looks like a couple birthday cakes smashed together," said Carolyn Driedger, a USGS hydrologist.
Mount St. Helens is the Cascade's most seismically active volcano; Rainier is close to being first runner-up, with more than a dozen summit earthquakes a year. But for most people's purposes, the chief difference between the two mountains is how they blow.
Mount St. Helens is the Roman candle of the range, with a more highly explosive eruptive style and greater likelihood of blowing in the coming decades.
And while both can create flows of lava, Rainier's magma - the molten rock that wells up from deep in the earth - has less silica than St. Helens, which makes it less explosive.
But Rainier can get you with fire and ice, as lava and fast-moving pyroclastic flows of rock and gas can turn some of the two dozen glaciers into a powerful surge of ice, mud and water. There is as much water locked up in glaciers and unmelted snow on Rainier as on all other Cascade peaks combined.
Like the other Cascade peaks, Rainier gets its magma from the violent interplay of the Earth's crustal plates. As the Juan de Fuca plate dives from the Pacific Ocean deep beneath the continental crust, it brings with it a muddy mixture of sea water, ocean sediments and calcium-rich rock. Pressure and heat drive the water from the mix. The water in turn lowers the melting point of the rock around it, creating a gaseous rock that starts to work its way to the Earth's surface.
In Rainier's two greatest periods of volcanic activity, which began 500,000 and 280,000 years ago, there was so much magma rising to the surface that it all couldn't escape out the top.
Forced through fracture zones to the east and west sides of the mountain, it brought with it sulfur gases that combined with meltwater inside the mountain to produce a weak sulfuric acid. In a process called "hydrothermal alteration," solid rock became a crumbly orange-yellow clay that is both structurally unstable and, because clay loves to hold water, heavy.
Around 5,600 years ago, a huge mass of this material gave way on the mountain's east side, scalloping off the top 2,000 feet. Nearly a cubic mile of mud and water flowed like liquid concrete and filled the valleys of the White River some 300 feet deep.
The so-called Osceola mudflow, the largest ever on the mountain, moved north and west, covering what is now Sumner, Enumclaw and Auburn. Entire watersheds were shifted, with sediments flowing off for decades afterward to fill what used to be a lobe of Puget Sound, near what is now Federal Way.
Just 600 years ago, a slope on the west side of Rainier gave way and streamed at an average speed of 50 mph down the Puyallup River, snapping six-foot-thick trees. When the mudflow hit the Puget Sound lowland near the town of Electron, it was more than 30 yards thick. The town of Orting is about 20 feet higher because of that flow.
Tom Sisson, a USGS geologist in charge of a seven-year project to figure out Rainier's geologic history, said the Osceola mudflow removed nearly all the unstable, hydrothermally altered rock from the high east side of the mountain. But the west side remains a threat.
Moreover, the Electron flow appears to have begun without any volcanic activity. That means a similar flow could run into populated areas without the days and weeks of seismic activity that precedes an eruption - and tips off geologists and emergency crews.
Chances are that won't be the case, said Sisson.
"It looks like the greatest likelihood of mudflows or lahars would be during periods of volcanic activity," he said. "Which may not sound like good news, but it actually is."
Orting tied to Rainier
Looking due east at more than 14,000 feet of glacier and rock, the town of Orting has long had an intimate relationship with Mount Rainier.
The glacier-capped peak graces the top of the carved "Welcome to Orting" sign. A new elementary school slated to open this fall is called Ptarmigan Ridge, for the prominent ridge on the mountain's northwest side. The school's team name: the Mountaineers.
Three years ago, middle-school teacher Dawn Wood and students in her eighth-grade arts class took a picture of the mountain every day.
"We celebrate the mountain," said Rex Kerbs, the elementary school's principal, whose office features a painting of the mountain with an intact Mount St. Helens in the distance. His mother-in-law made it in 1979.
In the wake of St. Helens' 1980 eruption, Orting's relationship to Rainier has become like a marriage tinged with distrust.
Schoolchildren are regularly put through evacuation plans. Old Fire Department and air-raid sirens have been posted around town. City leaders have grown weary of media types looking for a story about life in the shadow of a volcano.
"Any day now - at least according to government geologists - the little town of Orting, Washington, will cease to exist," according to a 1997 Time magazine article.
"They're a little hesitant to be identified as the poster child of Mount Rainier," said Steven Bailey, director of Pierce County's Department of Emergency Management. Of course, he added, "They are the poster child."
USGS scientists figure most lava or pyroclastic flows from the volcano would be contained roughly within the boundaries of Mount Rainier National Park, never getting at least as far as Orting. Mudflows are a different matter.
A moderate lahar, which they estimate could occur every 100 to 500 years, could bring flooding all the way to the Tacoma lowlands. It probably would come from a pyroclastic flow, so it would likely be detected in advance by sensors monitored at a University of Washington seismology lab in Seattle.
A large lahar can be expected every 500 to 1,000 years with an unexpected flank collapse, reaching Tacoma as well but cutting a faster, wider swath on the way.
Of the five river drainages a lahar might follow off the mountain, three are on the more vulnerable west side. Two of those - the Carbon and Puyallup rivers - wrap around Orting. Each of the two roads out of town must cross one of those rivers.
Chances are one in seven - worse than the odds of having a house fire - that a moderate lahar will happen in a person's lifetime. It would take only 40 minutes for the mudflow to make it from the mountain to Orting.
It would hit hard. Old-growth forests slowed past mudflows, but the trees that would protect the town went through the town on rail cars decades ago.
Pierce County has forbidden the construction of essential structures such as schools and hospitals inside volcano zones, but the law applies only to unincorporated county lands. When the county told Orting officials they could not build an elementary school just outside town, they moved the building site within city limits. The change met the letter of the law, but the school ended up farther from a safe escape route.
The town has taken protective steps along with other Puyallup Valley towns, the Puyallup tribe, USGS and the Pierce County Department of Emergency Management. The most sophisticated measure is a system of special microphones attuned to the difference between the ground vibration of a mudflow and, say, an earthquake or volcano.
Installed in 1998 some 15 miles from town on the Carbon and Puyallup rivers, the sensors will transmit a warning to the state Law Enforcement Support Agency in Tacoma and the Washington State Emergency Operations Center at Camp Murray. The warning is a key step, said Bailey.
"In the village of Armero in Columbia in 1985, 20,000 people were killed by a lahar because they got no warning and they could not scramble 40 feet up the valley," he said.
But in Orting, at the head of the broad Puyallup Valley, getting just 40 feet uphill can be a formidable task.
The 183-bed Washington Soldiers Home and Colony has plans to move its elderly residents about one-quarter mile up a county road, where a shipping container full of supplies would double as a shelter.
But about 90 of the residents would need assistance. If a mudflow were to come in the middle of the night, only seven staffers would be on hand to help, said Gary Condra, assistant superintendent of the home.
The town's 1,700 students have been put through drills in which they can be on buses and in cars within 10 minutes. But the drills start with buses idling in the parking lot; a real emergency could come in the middle of the day, when bus drivers are off duty.
When Ptarmigan Ridge Elementary opens this fall, Kerbs, the principal, is considering having students walk along a dike and across a bridge to safety. The two miles could be covered in 20 minutes, Kerbs said. In the heat of the moment, some students might cut that to 13 minutes.
"You want to think it'd be an orderly evacuation, but I don't think we'd all be walking," he said.
Emergency officials are in the midst of a public education effort so all 100,000 mostly Pierce County residents at the base of the mountain are aware of the right evacuation procedures. But the going has been tough.
"When you have an event that has something of a low probability in their lifetime, getting people's attention is very difficult," Bailey said.
"It could be 600 years, 1,000 years," said Matt Nunnally, a real-estate salesman worried more about the impact volcano movies and stories can have on the local housing market. "And the way you guys report it, it's going to come to Orting and stop, and that's not the case."
So far, the town's housing market has grown unfettered in the years since Mount St. Helens. Several new housing developments are sprouting across the valley. The town's population, at 3,825, has nearly doubled in 10 years, making Orting one of the fastest-growing communities in the state.
In general, residents don't seem particularly concerned about the volcano risk.
"I guess I just feel I'm going to take the chance it's not going to happen in my lifetime," said Dave Lillie, 45, who bought a new three-bedroom house and moved to Orting from Kent three years ago.
"I've lived here for 30 years, and I just choose to not worry about the `what-ifs,' " said Sandy Shirley, a school secretary, while leafletting for a school levy with Dawn Wood, the middle-school teacher.
"It's the same reason people live in the Midwest and know about the tornadoes," she said. "You just take the good with the bad. You got to go somehow."
"So why not under six feet of mud?"
Eric Sorensen's phone message number is 206-464-8253.