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last 15,000 years. But it could send mudflows and floods into some communities east of Portland.
The Growing Threat
Most communities are far enough away from the Cascades that only an unusually large mudflow or flood could reach them. But three towns at the base of California’s Mount Shasta could be demolished by even a small eruption, USGS scientists said. In a chapter of the 1979 book “Volcanic Activity and Human Ecology,” Crandell, Mullineaux and their colleague C. Dan Miller urged people to pay more attention to volcanoes.
Parts of the West, they wrote, “face a progressive increase in the potential impact of future eruptions because of a growing population, increasing recreational use of areas around volcanoes, and accelerating energy needs that may be met in part by new hydroelectric and nuclear power plants downvalley and downwind from volcanoes.”
To reduce the threat, they called for land-use zoning in high risk areas and careful site selection for dams and power plants. The authors conceded, however, that a volcanic eruption in the Cascades remains an unusual happening.
They estimated the chance of a small eruption somewhere in the Cascades at one in 100 for any given year. The probability of a larger blast—on the order of what St. Helens produced May 18—was "perhaps no greater than one in 1,000 in any one year."
94.1%