Word: silica
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Dates: during 1980-1989
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...activity caught scientists by surprise. Though volcanologists have been able to predict almost to the hour when the volcanoes of the Hawaiian Islands will erupt, Mount St. Helens presents a more difficult problem for would-be prognosticators. The molten rock, or magma, underneath the Washington volcano is a thicker, silica-rich material (unlike the less viscous molten basalt of the Hawaiian chain); more pressure must build up before the hot gases trapped within it are released. Thus the mountain erupts infrequently and violently...
Within four days the worst was over -maybe. The dust had settled in the heavy-fallout area, roughly from the ruptured peak to as far east as Montana. Fine ash particles, mostly glasslike silica, had spread in a gigantic, banana-shaped arc in the stratosphere across the nation and will slowly dissipate into invisible clouds after blowing round the world several times. Outside the Northwestern U.S., people will probably notice nothing more than some spectacularly colorful dawns and sunsets over the next several months...
...mountain, livestock escaped almost unscathed. State officials advised ranchers to put out fresh hay so that cattle would not eat the dusty forage in the fields. Ranchers were also told not to move their herds to avoid increasing the cattle's breathing rate and thus their intake of silica-laden dust. Breeders protected valuable race horses by keeping them inside barns with towels over their noses...