Thursday, May 19, 2005
Is Mount Rainier the next one on the list of possible volcano eruptions?
One day, the peaceful hush of this small town will be broken by a rumble that sounds like a thousand freight trains. If everything works right, sirens will wail and the town's 4,400 residents will have less than 45 minutes to evacuate — or be buried by an avalanche of mud and debris tumbling off the flank of Mount Rainier.Scientists know that Mount Rainier, an active volcano, will one day awaken as Mount St. Helens did in 1980.
It could gradually build up and explode, or part of it could simply collapse, perhaps with very little warning. It could happen in 200 years, or it could happen tonight."People get burned by these kind of events because they think it can't happen in their lifetime," said U.S. Geological Survey vulcanologist Willie Scott. "We can't rule out a flow of troublesome size being generated almost at any time."A mudflow would likely be troublesome indeed for Orting.
Two rivers, the Carbon and the Puyallup, drain off the mountain, hug the town and converge just beyond it, putting Orting squarely in the mountain's strike zone. The town was built atop a 500-year-old mudflow that buried the valley 30 feet deep.Construction crews working on new housing developments for Orting's growing population have dug up massive tree stumps — the remnants of a forest buried there the last time Mount Rainier hiccuped.
The USGS ranks Mount Rainier as the third most dangerous volcano in the nation, after Kilauea on Hawaii's Big Island and St. Helens, both of which are currently active. Other studies call Rainier the most dangerous volcano in the world — not just for its explosive potential, but because of the 3 million people who live in the Seattle-Tacoma-Bellevue metropolitan area. At least 100,000 people live on top of old Rainier mudflows that have solidified.Dawn So is one of them.
When she moved to Orting from SeaTac two years ago, she didn't worry about volcanos or mudflows. She was just looking for a good place to raise her children and open a quilting store."I wanted to have my kids in a better school district, a smaller town," she said. "I like to let them play in the front yard without having to worry about them."She and her children have planned their escape routes, and she's confident they could get to high ground in time.
But she doesn't spend much time thinking about Rainier's threat."It's such a highly improbable situation," she said. "Disasters can happen wherever you're at."Disaster could strike in at least three different ways. The mountain could go through a Mount St. Helens-type buildup, with magma rising in the mountain's core and then exploding, literally blowing Rainier's top and sending mudflows crashing down on the valleys below.Or, the magma could build up inside the mountain, never explode, but still trigger mudflows by weakening the rock and melting glaciers.
Or, part of the mountain could simply collapse without any magma buildup, weakened by centuries of hot, acidic liquid coursing through the rock. Scott said the west flank of Rainier, overlooking the Puyallup River valley, is the oldest part of Mount Rainier and thus the most likely to collapse.In any case, rock and mud would mix with melted glaciers to create a flow with the consistency of concrete, moving as fast as 50 miles per hour. The mudflow would sweep down the valleys, picking up trees, bridges, and whatever else got in its way.Most of the mudflows — also called lahars — from Mount Rainier were triggered by an eruption, Scott said.
But the most recent, the Electron mudflow that buried Orting 500 years ago, didn't seem to follow that pattern."Maybe it was just a gradual weakening," Scott said. "That one sort of keeps us honest."About 5,600 years ago the Osceola mudflow blanketed about 200 square miles northwest of the mountain. The flows reached as far north as Kent, a Seattle suburb, and drained west into Commencement Bay, now the site of the Port of Tacoma.
The risk of catastrophe every couple thousand years hasn't stopped brisk development on ancient mudflows. But as scientists identified Rainier as a threat in the decades after Mount St. Helens' eruption, government officials and citizens have begun preparing.Last week, federal, state and local officials gathered at Fort Lewis for an exercise called "Cascade Fury III" — simulating the emergency response to an earthquake, eruption and massive mudflow from Mount Rainier.