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Generation of pyroclastic flows and surges by hot-rock avalanches from the dome of Mount St. Helens volcano, USA

R.A. Mellors·R. B. Waitt·D. A. Swanson
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Abstract

Several hot-rock avalanches have occurred during the growth of the composite dome of Mount St. Helens, Washington between 1980 and 1987. One of these occurred on 9 May 1986 and produced a fan-shaped avalanche deposit of juvenile dacite debris together with a more extensive pyroclastic-flow deposit. Laterally thinning deposits and abrasion and baking of wooden and plastic objects show that a hot ash-cloud surge swept beyond the limits of the pyroclastic flow. Plumes that rose 2-3 km above the dome and vitric ash that fell downwind of the volcano were also effects of this event, but no explosion occurred. All the facies observed originated from a single avalanche. Erosion and melting of craterfloor snow by the hot debris caused debris flows in the crater, and a small flood that carried juvenile and other clasts north of the crater. A second, broadly similar event occurred in October 1986. Larger events of this nature could present a significant volcanic hazard. ?? 1988 Springer-Verlag.

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R.A. Mellors, R. B. Waitt, D. A. Swanson. 1988. Generation of pyroclastic flows and surges by hot-rock avalanches from the dome of Mount St. Helens volcano, USA. https://doi.org/10.1007/bf01047505

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