Mount St. Helens a Volcanic 'Ring of Fire'
WILLIAM McCALL

Posted on Fri, Oct. 01, 2004
Associated Press


PORTLAND, Ore. - Three or four times every minute, Mount St. Helens
shivers. Sometimes the majestic peak even shudders, the trembling
beneath reaching a crescendo, a magnitude of 3.3.

The earthquakes that started a week ago Thursday - almost certainly
precursors to an eruption - are a reminder that the 8,364-foot
sleeping giant is but a part of a volcanic "ring of fire" so vast that
it encircles the Pacific Ocean.

Indeed, the other 12 major volcanoes in the Cascade Range of northern
California, Oregon and Washington state lie within this geological
phenomenon as well.

The entire ring - from the tip of South America up through Alaska,
Japan and the Kamchatka Peninsula of Russia, down through the
Philippines and Indonesia into New Zealand - includes about
three-fourths of the world's active and dormant volcanoes, scientists
say.

Most of the activity is related to shifting in the vast sections of
the Earth's surface known as tectonic plates, continent-size chunks of
crust that float atop the planet's molten core.

Mount St. Helens and the Cascades lie near the edge of the Juan de
Fuca plate, which is diving under the North American plate to create a
700-mile long "subduction zone" along the ocean floor that triggers
earthquakes and pushes molten rock upwards.

Called magma underground and lava when it surfaces, the molten rock is
forced up through fissures and weak spots in the crust.

Mount St. Helens lies along a particularly weak area of the crust,
causing it to be the most active volcano in the Northwest over the
centuries, said Jon Major, a U.S. Geological Survey researcher in
Vancouver, Wash. Its most spectacular showing was in May 1980, with an
eruption that blew the top 1,400 feet off the mountain.

"It sits near the St. Helens seismic zone, an area where the crust is
pulled apart a little bit," Major said. "That lets magma push up and
explains why it's so active and others are not so active."

For example, Mount Adams lies only about 50 miles east of Mount
St. Helens but has not erupted in thousands of years, Major said.

Mount Jefferson, which lies between Mount Hood and the Three Sisters
in the Oregon stretch of the Cascades, appears to have been dormant
since the last Ice Age despite relatively recent eruptions on
neighboring peaks, he said.

In the rest of the Cascade Range, which stretches from Canada to
Northern California, two of the tallest peaks - Mount Rainier in
Washington state and Mount Shasta in California - both have erupted at
least once in the past 200 years and have had several more over the
last 2,000 years. Most were considered minor, according to USGS
figures.

The Northwest, in turn, has been relatively quiet compared to other
areas of the ring, according to Jim Luhr, director of the global
volcanism program at the Smithsonian Institution in Washington, D.C.

The Aleutian Island chain in Alaska, Central America, Japan and
Indonesia have all been more active recently, Luhr said.

"The Aleutians are one of the most vigorous volcanic parts of North
America," he said.

But he noted that other parts of the world have plenty of dormant
volcanoes, including France and Germany.

Luhr recently returned from a trip to Armenia where ancient
petroglyphs show evidence of eruptions.

"There are relatively young volcanoes all over Armenia," he
said. "None have erupted in the last 4,000 years, but clearly ancient
peoples have seen them."

There is a chance that other Northwest volcanoes could erupt. But like
Mount St. Helens, it will probably be mostly rock and ash that spew
forth, not the dramatic, fiery rivers of lava that accompany eruptions
in Hawaii, scientists say.

The Mount St. Helens eruption in 1980 killed 57 people, but other
volcanoes have taken a deadlier toll.

In January 2002, lava rolled down the slopes of the African volcano
Mount Nyiragongo and flooded the streets of Goma, Congo, killing at
least 75 people.