Distribution and thickness (in millimeters) of ashfall in Washington, northern Idaho, and western Montana from the May 18, 1980 eruption of Mount St. Helens. Lines are isopachs which represent locations where the thickness of the ash is equal.
Distribution of ashfall in the United States from the May 18, 1980 eruption of Mount St. Helens. Most areas received only trace amounts of ash.
Foxworthy, B.L., and Hill, M., 1982, Volcanic eruptions of 1980 at Mount St. Helens: The First 100 Days: U.S. Geological Survey Professional Paper 1249, 124 pages.
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