Mount St. Helens Releasing Lava At Astonishing Pace
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MOUNT ST. HELENS RELEASING LAVA AT ASTONISHING PACE
Friday, December 30, 2005
SEATTLE, Washington - Roughly every three seconds, the equivalent of a large
dump truck load of lava -- 10 cubic yards -- oozes into the crater of Mount
St. Helens, and with the molten rock comes a steady drumfire of small
The unremitting pace, going on for 15 months now, is uncommon, said U.S.
Geological Survey geologist Dave Sherrod. Experts say it is unclear what the
activity signifies or how much longer it will continue.
"One view of this eruption is that we're at the end of the eruption that
began in 1980," Sherrod said. "If it hadn't been so cataclysmic ... it might
instead have gone through 30 or 40 years of dome building and small
St. Helens' violent May 18, 1980, eruption blasted 3.7 billion cubic yards
of ash and debris off the top of the mountain. Fifty-seven people died in
the blast, which left a gaping crater in place of the perfect, snowclad cone
that had marked the original 9,677-foot peak known as "America's Mount
St. Helens -- now 8,325 feet -- rumbled for another six years, extruding 97
million cubic yards of lava onto the crater floor in a series of 22
eruptions that built a 876-foot dome.
The volcano, about 100 miles south of Seattle, fell silent in 1986.
Then, in September 2004, the low-level quakes began -- occasionally spiking
above magnitude 3. Since then, the mountain has squeezed out about 102
million cubic yards of lava, more in 15 months than in the six years after
Sherrod describes the movement of lava up through the volcano as being "like
a sticky piston trying to rise in a rusty cylinder. These quakes are very
small -- we think they're associated with that sticking and slipping as the
ground is deformed and relaxes."
The dome collapses and grows and collapses and grows, he said. "It changes
its location ... it can't seem to maintain its height at much more than it
is now " -- about 1,300 feet. "Then it kind of shoves the sandpile aside and
It's not entirely clear where the lava is coming from. If it were being
generated by the mountain, scientists would expect to see changes in the
mountain's shape, its sides compressing as lava is spewed out.
At the current rate, "three or four months would have been enough time to
exhaust what was standing in the conduit. ... The volume is greater than
anything that could be standing in a narrow 3-mile pipe," Sherrod said.
That suggests resupply from greater depths, which normally would generate
certain gases and deep earthquakes. Neither is being detected.
"That's one of the headscratchers, I guess," Sherrod said.
All the recent activity has remained within the crater, though scientists --
keenly aware of the potential damage that silica-laced ash can pose to jet
engines -- monitor St. Helens closely for plumes of smoke and ash. Some have
gone as high as 30,000 feet.
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