USGS/Cascades Volcano Observatory, Vancouver, Washington

Geology of Interactions of Volcanoes, Snow, and Water:
Mount St. Helens, Washington

Eruption-triggered floods 1980-1986

An explosive eruption of Mount St. Helens on 19 March 1982 had substantial impact beyond the vent because hot eruption products interacted with a thick winter snowpack. A blast of hot pumice, dome rocks, and gas dislodged crater wall snow, which avalanched through the crater and down the north flank. Snow in the crater swiftly melted and formed a transient pond. The pond deepened swiftly and discharged a destructive flood down the north flank of Mount St. Helens and from there down the North Fork Toutle River valley.

Similar but smaller incidences of rapid snowmelt and consequent avalanche and flood occurred at the beginning of eruptions in April 1982, Ferbuary 1983, May and June 1984, and May 1986.

Waitt, R.B., Kamata, H., and Denlinger, R.P., 1989, Explosions and hot-rock avalanches that rapidly mobilized winter-spring snowpack at Mount St. Helens volcano in 1980-1986 [Abs.], in Continental Magmatism Abstracts: New Mexico Bureau of Mines and Mineral Resources Bulletin 131, p. 285.

Waitt, R.B., and MacLeod, N.S., 1987, Minor explosive eruptions dramatically interacting with winter snowpack at Mount St. Helens in March-April 1982, in Selected papers on the geology of Washington: Washington Division of Geology & Earth Resources Bulletin 77, p. 355-379.

Waitt, R.B., Pierson, T.C., MacLeod, N.S., Janda, R.J., Voight, B., and Holcomb, R.T., 1983, Eruption triggered avalanche, flood, and lahar at Mount St. Helens effects of winter snowpack: Science, v. 221, p. 1394-1397.

URL for CVO HomePage is: <http://vulcan.wr.usgs.gov/home.html>
URL for this page is: <http://vulcan.wr.usgs.gov/Projects/H2O+Volcanoes/Frozen/Geology/MSH/MSH.floods.html>
If you have questions or comments please contact: <GS-CVO-WEB@usgs.gov>
11/03/97, Lyn Topinka

Geology of Interactions of Volcanoes, Snow, and Water: Mount St. Helens, Washington

Eruption-triggered floods 1980-1986

Geology of Interactions of Volcanoes, Snow, and Water:
Mount St. Helens, Washington