USGS/Cascades Volcano Observatory, Vancouver, Washington
REPORT:
Effects of Volcanism on the Glaciers of Mount St. Helens
--
Brugman, M.M., and Post, A., 1981,
Effects of Volcanism on the Glaciers of Mount St. Helens:
U.S. Geological Survey Circular 850-D, 11p.
Abstract
The cataclysmic eruption of Mount St. Helens May 18, 1980,
removed 2.9 km2 (about 0.13 km2) of glacier snow and ice including a large part of Shoestring, Forsyth, Wishbone, Ape, Nelson,
and all of Loowit and Leschi Glaciers. Minor eruptions and
bulging of the volcano from March 27 to May 17 shattered
glaciers which were on the deforming rock and deposited ash on
other glaciers. Thick ash layers persisted after the May 18
eruption through the summer on most of the remaining snow
and ice, and protected winter snow from melting on Swift and
Dryer Glaciers. Melting and recrystalization of snow and ice
surviving on Mount St. Helens could cause and lubricate mudflows and generate outburst floods. Study of glaciers that remain on this active volcano may assist in recognizing potential
hazards on other volcanoes and lead to new contributions to
knowledge of the transient response of glaciers to changes in
mass balance or geometry.
Introduction
This article briefly summarizes the effects which the 1980 eruptive activity of Mount St. Helens had on the snow and ice masses on the volcano. The volcanic activity from March 20 through October 6, 1980, is divided into three periods, and topics such as glacial outburst floods, mudflows, and ash blanket effects are discussed. Areas, depths, and volumes of ice before and after May 18, 1980, are displayed in two tables, indicating the magnitude of the explosion which removed 2.6 km3 (99 billion ft3) of the volcanic cone and about 0.1 km3 (3.5 billion ft3) of glacier snow and ice within minutes. Studies of the role of snow and ice in the damaging effects of the 1980 eruptions is essential for three major reasons: scientific understanding, predictions of the effects of future eruptions of Mount St. Helens, and evaluating potential hazards presented by glaciers on other volcanoes.
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03/07/07, Lyn Topinka