Movement detected on Mount St. Helens' lava dome

10:22 AM PDT on Wednesday, September 29, 2004

From KGW.com, KING5.com Staff and Wire Reports

KING
Seismologists said the lava dome at Mount St. Helens has moved several centimeters northward and upward.
MOUNT ST. HELENS, Wash. -- The chief scientist studying Mount St. Helens said a “startling” amount of movement on the lava dome was detected early Wednesday morning.

“A rather large mass of rock that is about 300 yards high by 400 or 500 yards across, something is moving it up and northward,” said chief scientist Jeff Wynn, with U.S. Geological Survey.

Tests showed that the dome has moved about four centimeters to the north and about two centimeters upward. Wynn said the movement "sort of suggests that we're getting closer" to an eruption that could hurl rocks and ash a few thousand feet into the air.

“The seismic activity has been accelerating to the highest levels we’ve seen since the swarm began last Thursday, both in frequency and intensity,” added Wynn.

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Swarms of tiny earthquakes — more than 1,000 since the mountain began stirring on Thursday — had increased by Wednesday, occurring at a rate of three a minute around 2.0 magnitude, said seismologist Seth Moran of the U.S. Geological Survey's Cascade Volcano Observatory.

Wynn described the movement as “similar to what scientists saw just before the 1986 eruption.” That's when the mountain had what’s called a dome-building eruption that was preceded by swarms of earthquakes.

Swarms in 1998 and again in 2001 did not result in any surface activity. So, while scientists said something significant could happen within the next couple of days, there's no way to know for sure.

“I would say the next few days are definitely on notice,” Wynn said. “There is a chance we will see a steam and ash explosion.”

Wynn emphasized that the estimates were highly preliminary and inexact because there is only one measuring device on the dome, estimating scientists will need about 48 hours to interpret the data more clearly.

Wynn and his team of scientists planned to board a helicopter sometime Wednesday and go back up on the mountain to test for gas that could verify if there is magma movement. However, Wynn said they would not go into the crater, due to safety concerns.

“There is a threat," said Wynn. "The national monument is staying in very close touch with us. They think it is still safe for visitors at this time.”

Early tests of gas samples collected above the volcano by helicopter Monday did not show unusually high levels of carbon dioxide or sulfur, which would indicate magma. Wynn speculates that a seal on top of the dome may be preventing any gases to be released by magma, escaping detection by scientists.

Scores of scientists continued their close eye on the 925-foot-tall dome of hardened lava that has grown inside the crater since the May 18, 1980, eruption that blew the top off the mountain.

That eruption killed 57 people, leveled hundreds of square miles of forests and dumped volcanic ash across the Northwest.

In October 1980, the lava dome began building in the crater. The last dome-building eruption was in October 1986, but steam explosions have periodically rocked the dome.

Unlike places like Hawaii, were magma is comparatively viscous, or thin, the magma in the Cascades tends to be thick. That can ultimately cause explosions as dissolved gases in the molten rock tries to escape when the magma comes to the surface.

Measurements of ground movement “will tell us whether there’s any new magma coming into the system,” said seismologist Seth Moran, though that data will not be available right away.

“We’re furiously setting up new GPS stations all around the place,” Wynn said, adding about six to the dozen or so already in place. If the units begin spreading apart from each other, “it means something is inflating in between them.”

Geologist Willie Scott said in the event of an explosion, concern would be focused within the crater and on the upper flanks of the volcano. A five-mile area, primarily north of the volcano, could receive flows of mud and rock debris.

Any explosions would not put anyone in danger unless they are inside the cone, researchers say.

U.S. Forest Service officials closed hiking trails above the tree line at 4,800 feet on the 8,364-foot mountain, though the visitor’s center and most other trails at the Mount St. Helens National Monument remained open.

“Standing on the rim, from what geologists tell us, would not be a good idea,” said monument scientist Peter Frenzen.

Hiking about the tree line is by permit only and limited to 100 people a day. This time of year, weekday numbers tend to be low while clear weekends draw near capacity, said Forest Service spokesman Tom Knappenberger. The more accessible visitor center draws as many as 110,000 visitors a month at peak season, tapering down to about 90,000 in September.

The Associated Press contributed to this report.