In harm's way. (consequences of a volcanic eruption at Mount Ranier, Washington)

On a clear day in Seattle, Washington, you can see the snowcapped peak of Mount Rainier 55 miles away. From Tacoma, it's only 40 miles to Rainier, the queen of the Cascades and the Pacific Northwest's postcard emblem. Every year, thousands of people move to the Puget Sound area to be near the high mountains and the region's high-tech industrial base. Few probably realize that they're headed for the most volcanically dangerous terrain in the continental United States.

Mount St. Helens in southern Washington may have public notoriety because of its dramatic 1980 explosion, but scientists are a lot more worried about Rainier, a larger volcano much closer to a populated area. "Mount Rainier is potentially the most dangerous volcano in the Cascade Range," a U.S. Geological Survey report warned last year, "because of its great height, frequent earthquakes, active hydrothermal system and extensive glacier mantle."

Kevin Scott, the lead author of the USGS report, goes further: Rainier poses" probably the greatest volcanic risk in the United States." Scott, who works at the USGS Cascades Volcano Observatory in Vancouver, Washington, says the most immediate …