ONE OF THE 'GREATEST THREATS' TO THE PACIFIC NORTHWEST ISN'T WHAT YOU THINK.

EXPERTS ARE PREPARING THE REGION AGAINST THE THREAT OF DANGEROUS VOLCANIC MUDFLOWS, KNOWN AS LAHARS, WHICH COULD INUNDATE THE COMMUNITIES SURROUNDING MT. RAINIER IN AS LITTLE AS 30 MINUTES.

- WUDAN YAN

ON A SUNNY AFTERNOON IN MAY 1980, CAROLYN DRIEDGER AND MINDY BRUGMAN PULLED UP TO Coldwater II, an outpost for United States Geological Survey researchers on a ridge near Mount St. Helens in Washington.

For the last five weeks or so-after a century-plus of dormancythe volcano seemed to be waking up. Driedger, a glaciologist at the Survey, had joined Brugman, a doctoral student studying glaciers on St. Helens, to collect data on the Shoestring glacier and see how its behavior changed as volcanic activity increased.

The pair had planned to stay the night and catch a helicopter ride out to the glacier first thing in the morning. But David Johnston, a sandy-haired geologist who had been stationed there for weeks, told them to pack up. He believed the recent increase in activity-some small earthquakes and minor eruptionscould be a harbinger of something bigger: that St. Helens could erupt and the entire north side of the volcano would fall away. "We should have as few people here as possible," Johnston said before advising the dejected researchers to stay in Vancouver, Washington-almost a two-hour drive away-for the night and return the next day.

The following morning, Driedger and Brugman once again packed up their car and made the trek toward the volcano. On Interstate 5 between La Center and Ridgefield-a rare stretch of highway where St. Helens is visible on a cloudless day-they noticed a dark plume rising from the volcano's north side.