Since 1980, hundreds of small ash-producing eruptions have sent billowing plumes of steam and ash as high as 15,000 feet into the air.
Since 1980, hundreds of small
ash-producing eruptions have sent billowing plumes of steam and ash as
high as 15,000 feet into the air.
Some of these small eruptions
were accompanied by avalanches of hot rocks, snow, and debris.
These eruptions are probably
related to the hot springs and streams fed by heated, mineral-rich water
near the mouth of the crater.
There are also other fluids and
gases that accumulate beneath the dome's surface.
When a new or old fracture, or
crack, in the dome meets a pocket of superheated water or pressurized
gas, the sudden loss of pressure causes an explosive event.
The rapid rise of gas and steam
along rock fractures causes the ejection of rock fragments and ash
skyward.
These small ash eruptions are
very different from the large explosive eruptions of 1980. They are also
different from the 17 dome-building eruptions that occurred between
1980 and 1986.
Those larger eruptions expelled
molten rock in two ways. They violently expelled ash and pumice into the
air...
...or quietly oozed lava onto the
crater floor.
But because there has been no
earthquake activity beneath the volcano, scientists do not consider the
small ash eruptions as the beginning of a stronger, more explosive
eruptive phase.
So far, no new molten rock, or
magma, appears to be moving up into the volcano.
However, the recent activity is a
reminder that Mount St. Helens has not returned to a completely quiet
state.
Return to:
Mount St. Helens & Other
Volcanoes
After the Eruption
Mount St. Helens
VolcanoWorld