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Emergency assessment of Mount St. Helens post-eruption flood hazards, Toutle and Cowlitz rivers, Washington

Circular 850-I
By: , , and 
https://doi.org/10.3133/cir850I

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Abstract

During several periods of volcanic-ash eruption at Mount St. Helens, Wash., (March 30, May 25-26, May 30-June 2, and June 12-13, 1980) strong winds from the north occurred at high altitudes. As a result, the volcanic ash fell some 50 miles to the south in the Bull Run watershed, the principal water-supply source for the metropolitan area of Portland, Oreg. Water samples collected from three stream sites within the watershed were compared with samples collected during the same season in previous years. No detectable changes were noted in chemical characteristics. Precipitation samples collected immediately after the June 12-13 ash fall ranged in specific conductance from 20 to 41 micromhos per centimeter at 25C and in pH from 4.0 to 4.3 pH units. Stream samples collected during the May-June period ranged in specific conductance from 18 to 28 micromhos per centimeter at 25C and in pH from 6.7 to 7.5 pH units. Volcanic-ash samples were collected and analyzed for particle size, chemical composition, and weight. Significant differences in particle size of ash were found in samples from two separate eruptions. (USGS)

Suggested Citation

Jennings, M.E., Schneider, V., and Smith, P.E., 1981, Emergency assessment of Mount St. Helens post-eruption flood hazards, Toutle and Cowlitz rivers, Washington: U.S. Geological Survey Circular 850, v, I1-I7 p. :ill., map ;26 cm., https://doi.org/10.3133/cir850I.

ISSN: 2330-5703 (online)

Publication type Report
Publication Subtype USGS Numbered Series
Title Emergency assessment of Mount St. Helens post-eruption flood hazards, Toutle and Cowlitz rivers, Washington
Series title Circular
Series number 850
Chapter I
DOI 10.3133/cir850I
Year Published 1981
Language ENGLISH
Publisher U.S. Geological Survey, 1981
Description v, I1-I7 p. :ill., map ;26 cm.
Additional publication details