Mt St Helens is quite active, and has been for quite some time. In
recent history... It had just erupted when Lewis and Clark came through,
and not long after settlers came to Oregon Territory, it spouted again,
and continued off and on until 1857. Then, in 1980, it woke up in a
famously big way. Dome
building stopped completely in 1992. Thousands of earthquakes in
1998 seems to have been movement of magma, but the 'plug' held, and no
material was released. Another eruption occurred in 2004, and
after that the Dome Building has resumed... at the
incredible early rate of 7 cubic yards per second - a dump
truck every 3 seconds! It slowed to an average of .14 cubic
yards a second, which ended up being about 4 Olympic-Sized
swimming pools a day. The new lava dome grew to be
more than 130 million cubic yards (which would fill more
than 200 large sports stadiums) The growth continued through
2007, and stopped in February 2008.The differences during
the latest dome building eruption are quite visible... one
effect being the glacier that was in the crater was squeezed
out, and was turned into the fastest advancing glacier in
the US
Here's the time and depth location chart for
Mt St Helens... I've pasted several together, to get a
longer chain of events... its pretty impressive to see how
active its been over the years!
 Mount St. Helens
(2,549 meters - 8,364 feet ((9,677 feet before May 18, 1980)), located
in southwestern Washington about 50 miles northeast of Portland, Oregon,
is one of several lofty volcanic peaks that dominate the Cascade Range
of the Pacific Northwest. Geologists call Mount St. Helens a composite
volcano (or stratovolcano), a term for steep-sided, often symmetrical
cones constructed of alternating layers of lava flows, ash, and other
volcanic debris. Composite volcanoes tend to erupt explosively and pose
considerable danger to nearby life and property. In contrast, the gently
sloping shield volcanoes, such as those in Hawaii, typically erupt
nonexplosively, producing fluid lavas that can flow great distances from
the active vents. Although Hawaiian-type eruptions may destroy property,
they rarely cause death or injury. Before 1980, snow-capped, gracefully
symmetrical Mount St. Helens was known as the "Fujiyama of America."
Mount St. Helens, other active Cascade volcanoes, and those of Alaska
comprise the North American segment of the circum-Pacific "Ring of
Fire," a notorious zone that produces frequent, often destructive,
earthquake and volcanic activity
Some Indians of the Pacific Northwest variously called Mount St.
Helens "Louwala-Clough," or "smoking mountain." The modern name, Mount
St. Helens, was given to the volcanic peak in 1792 by Captain George
Vancouver of the British Royal Navy, a seafarer and explorer. He named
it in honor of a fellow countryman, Alleyne Fitzherbert, who held the
title Baron St. Helens and who was at the time the British Ambassador to
Spain. Vancouver also named three other volcanoes in the Cascades-
Mounts Baker, Hood, and Rainier-for British naval officers.
Frequent dacitic eruptions during the previous 2,500 years had produced
pyroclstic flows, ash falls, debris flows, lava domes, and lava flows of
andesite and basalt. Pyroclastic flows and lahars accompanied most
eruptive periods and were largely responsible for forming fans around the
base of the volcano, some of which dammed the North Fork Toutle River to
form Spirit Lake between 3,300 and 4,000 years ago. The magnitudes of the
1980 eruptions were not exceptional by worldwide historical standards;
however, they were the first volcanic eruptions in the conterminous United
States since 1914 (Lassen Peak) and focused national attention on events
leading up to the climactic eruption of May 18, 1980. That eruption led to
exceptional opportunities for scientific observations, data collection,
and the study of infrequent and often inaccessible geologic events and
processes.
Mount St. Helens
Location: Washington
Latitude: 46.20 N
Longitude: 122.18 W
Height: 2,549 Meters (8,364 feet (9,677 feet before May 18,
1980))
Type: Stratovolcano
Number of eruptions in past 200 years: 2-3
Latest Eruptions: Between 1600 and 1700; about 1800-1802; 1831;
1835; 1842-44(?); about 1847-1854; 1857; 1980-?
Present thermal activity: Extrusion of Volcanic Rock - Primarily
Dacite
Remarks: Continuous volcanic activity since October 2004...
Occasional eruptions of steam and ash; steady extrusion of dome-forming
lava.
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