How far did the ash spread on the day Mt. St. Helen's erupted?

rocky Katherine Feuer

Dear Katherine,

The eruption began at 8:45 a.m. At noon, the ash plume (in the upper troposphere and lower stratosphere) had reached Moscow, Idaho. By about 3 p.m. it was near Missoula, Montana and starting to spread south. By 6 pm it was east of Pocatello, Idaho. At the end of the day, about 16 hours after the eruption started, the ash plume was near central Colorado.

Steve Mattox, University of North Dakota

Sources of Information:
Danielsen, E.F., 1981, Trajectories of the Mount St. Helens eruption plume: Science, v. 211, p. 819-821.

Sarna-Wojcicki, A.M., Shipley, S., Waitt, Jr., R.B., Dzurisin, D., and Wood, S.H., 1981, Areal distribution, thickness, mass, volume, and grain size of air-fall from the six major eruptions of 1980, in Lipman, P.W. and Mullineaux, D.R., (eds.),The 1980 eruptions of Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1250, p. 577-600. 

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