Mount Rainier Could Unleash a Mudslide

ByABC News
January 31, 2001, 2:08 PM

Jan. 31 -- An eruption of Mount Rainier in Washington state could release adeadly torrent of mud and rock on populated areas west of thestill-active volcano, government scientists say.

About 30,000 people live in the potential path of the mudflow inthe Puyallup River Valley, though no major cities would be indanger.

The U.S. Geological Survey scientists could not predict when thevolcano might erupt the last time was 150 years ago, and the lastmudflow was about 500 years ago but they employed a new techniqueto identify sections of weakened rock that might give way in aneruption.

The researchers, who reported their findings in Thursday's issueof the journal Nature, took electrical and magnetic measurements byhelicopter of the 14,410-foot mountain and pinpointed 400 milliontons of rock on the western side that have been weakened by heatand steam.

The technique will probably now be used to help identify townsin danger around other active volcanoes.

Deep, Destructive Sludge Rivers

"It sounds like a wonderful technique," said Richard Fiske, aSmithsonian Institution geologist who has studied Rainier. "Anytime you can make measurements without going over those steep, icyslopes, it's an advantage."

Big chunks of a mountain sometimes give way in volcaniceruptions, letting loose enormous mudflows sometimes swelled bylake water or melted snow. Known to geologists as lahars, theselandslides can race downward at 45 mph or more like a 100-foot-deepriver of concrete, plowing away or burying just about anything intheir path.

Lahars killed more than 23,000 people when Colombia's Nevado delRuiz volcano erupted in 1985. About 5,600 years ago, a huge Rainiermudflow drained all the way into Puget Sound, about 50 miles away.

In recent years, instruments have been placed on Rainier tomeasure the shaking of the ground from a large mudflow and give anearly warning for evacuation.

But Steve Bailey, who oversees emergency plans for Pierce Countyto the west of Rainier, said: "I'm not certain I'm comfortable wecan successfully evacuate the entire valley."