Mount St. Helens Eruptive Activity, 1980-1984
Tephra Emissions
In addition to the dome-building eruptions, vigorous emissions of
gas and tephra have occurred from
fractures and small craters on top of
the dome since late 1980. These periodic outbursts usually last several
minutes, occasionally sending ash plumes as high as 15,000 to 20,000 feet
above the volcano. Most of the tephra consists of fragmented pieces of
dome rock, not new liquid magma, in contrast to the more hazardous
magmatic explosions of 1980. These events are intermittent, sometimes
occurring several times per day, and at other times not occurring at all
for several weeks.
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Mount St. Helens