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The mechanisms of fine particle generation and electrification during Mount St. Helens volcanic eruptionMicroscopical investigation of volcanic ash collected from ground stations during Mount St. Helens eruptions reveal a distinctive bimodel size distribution with high concentrations of particle ranges at (1) 200-100 microns and (2) 20-0.1 microns. Close examination of individual particles shows that most larger ones are solidified magma particles of porous pumice with numerous gas bubbles in the interior and the smaller ones are all glassy fragments without any detectable gas bubbles. Elemental analysis demonstrates that the fine fragments all have a composition similar to that of the larger pumice particles. Laboratory experiments suggest that the formation of the fine fragments is by bursting of glassy bubbles from a partially solidified surface of a crystallizing molten magma particle. The production of gas bubbles is due to the release of absorbed gases in molten magma particles when solubility decreases during phase transition. Diffusion cloud chamber experiments strongly indicate that sub-micron volcanic fragments are highly hygroscopic and extremely active as cloud condensation nuclei. Ice crystals also are evidently formed on those fragments in a supercooled (-20 C) cloud chamber. It has been reported that charge generation from ocean volcanic eruptions is due to contact of molten lava with sea water. This seems to be insufficient to explain the observed rapid and intense lightning activities over Mount St. Helens eruptions. Therefore, a hypothesis is presented here that highly electrically charged fine solid fragments are ejected by bursting of gas bubbles from the surface of a crystallizing molten magma particles.
Document ID
19830003282
Document Type
Conference Paper
Authors
Cheng, R. J. (State Univ. of New York Albany, NY, United States)
Date Acquired
August 11, 2013
Publication Date
October 1, 1982
Publication Information
Publication: NASA. Langley Research Center Atmospheric Effects and Potential Climatic Impact of the 1980 Eruptions of Mt. St. Helens
Subject Category
GEOPHYSICS
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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IDRelationTitle19830003264Analytic PrimaryAtmospheric Effects and Potential Climatic Impact of the 1980 Eruptions of Mount St. Helens
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