The Initial Giant Umbrella Cloud of the May 18, 1980 Explosive Eruption of Mount St. Helens.
AEROSPACE CORP EL SEGUNDO CA SPACE SCIENCES LAB
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The initial paroxysmal explosive eruption of Mount St. Helens on May 18, 1980 involved a complicated sequency of landslides, vertical explosions and a devastating horizontal blast, or pyroclastic flow. All these events took place within a few minutes and were immediately followed by the rapid ascent of an enormous eruption cloud that reached a height of nearly 30 km within 20 min. Data from military satellites allow the detailed behavior of this eruption column to be studied. This report presents these data, considers how the giant cloud relates to the initial events of the eruption, and interprets the data in terms of theoretical models of atmospheric convection. The most significant new observation is that the plume spread laterally at spectacular rates, forming a giant umbrella cloud. The umbrella cloud spread 15 km upwind. The implications of this behavior for understanding large-magnitude explosive eruptions are discussed.
- Geology, Geochemistry and Mineralogy