Mount St. Helens evacuated; substantial eruption "imminent"

By Hal Bernton and Christopher Schwarzen
Seattle Times staff reporters

JAMES BRANAMAN / THE SEATTLE TIMES Vehicles snake down a highway near Mount St. Helens after an evacuation was ordered yesterday. Some visitors pulled off at a wayside, but were eventually shooed away by Forest Service officials.

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U.S. Geological Survey (USGS) scientists said this morning they now are beginning to see hot spots and emissions of hydrogen sulfide and carbon dioxide typically associated with a magma move in a volcano.

A harmonic tremor — a sustained, deep movement of the earth within the volcano — was detected about 3 a.m. Scientists said it is further evidence of how active the volcano might be this go-around.

"This is the first time we've detected CO2 well above the crater and dome," said USGS volcano expert Willie Scott. "We've also spotted warm places on the dome from thermal energy."

Yesterday, the USGS increased the danger alert to Level 3, indicating an eruption is imminent with a potential for injury to life and property. Following the alert, the U.S. Forest Service's evacuated the Johnston Ridge Observatory, part of the Mount St. Helens National Volcanic Monument.

The upgraded alert came near 1 p.m. yesterday after a slight steam release was followed by an hour-long harmonic tremor near noon.

Earlier today, the U.S. Forest Service asked the Federal Aviation Administration to close the air space over the volcano, though the closure won't affect any commercial routes, a Forest Service spokeswoman said.

Also, a state Department of Transportation official reminded drivers to stay away from Highway 504, which is closed near mile marker 43. Backups have been as long as a mile as drivers who haven't heeded warnings wait until the last minute to turn around.

Earlier, scientists prepared for an eruption that never came. Instead, shallow earthquakes continued to break up rock beneath the crater, as evidenced by the cracking and deformation of a glacier located there.

The latest harmonic tremor activity only lasted about 20 to 30 minutes with no evidence of a significant change in the mountain's appearance, Scott said. Still, it appears that gases and magma are punching through whatever rock and rubble are blocking their escape.

Officials plan to continue monitoring the volcano's activity while looking for new ways to forecast what might occur.
 
While scientists say an eruption is expected within the next few days to a week, but it would be unlikely to eclipse the catastrophic May 18, 1980, event.

They said the volcano could hurl ash and rocks more than five miles — which would still be in the uninhabited area around the mountain. Last week's seismic activity at the mountain is the most powerful since the 1980 blast that killed 57 people.

Based on the Volcanic Explosivity Index, which measures the power behind an eruption, scientists yesterday predicted a 50 percent chance of a new eruption reaching Level 2 on the scale from 1 to 10, and a 30 percent chance of a Level 3, according to a preliminary estimate from Thomas Pierson, a USGS hydrologist.

By comparison, Friday's combined steam and ash cloud measured less than 1 on the index, while the 1980 eruption measured 5.

Pierson underscored that predicting what will happen with the volcano remains a difficult task and that there remains a substantial "error band" in the new forecast.

"There's a possibility of a new bigger eruption," Pierson said yesterday. "We're not sure how big."

Early last week, scientists were predicting nothing more than a minor eruption based on the belief that magma from a mid-1980s push was moving again. The absence of sulfur fumes and other gases accompanying fresh magma was further evidence, Pierson said.

But yesterday's events led scientists to suspect that magma gases were being absorbed by heavy moisture resulting from area rains.

"Usually with these things, where [the magma and energy] need to go is out," said Steve Malone, a University of Washington seismologist, yesterday. "I can't think of anything but rare cases where you have this type of seismicity and tremors and nothing comes out."

Yet, Mount St. Helens is the exception, Malone pointed out, adding that a deep tremor consistent with yesterday's event occurred more than a month before the 1980 eruption.

"Still, because there's no top this time and it's less stable, it's not going to last that long or be that big," he said, acknowledging that seismic activity in 1980 was registering more than magnitude 5.

The word of yesterday's evacuation spread quickly after 1 p.m.

"They said everyone had to get out of here right now. They were pretty abrupt," said Dan Cherry of Snohomish, who had been at the observatory several hours before the evacuation. "Some of the tourists couldn't get out fast enough, but most wanted to stay as long as they could."

Forest Service officials were in no mood for people to tarry, Cherry said yesterday. "One of them said if I'm not seeing your back, you're headed the wrong way," he said.

The cars, motorcycles and trucks snaked west down Highway 504 for more than an hour after the evacuation order. Some visitors tried to pull off at a wayside near a bridge over Coldwater Creek, but they were eventually shooed away by Forest Service officials trailing the caravan.

"How far do we have to go?" asked one motorist. "As far as we tell you to go," retorted a frustrated Forest Service employee.

The evacuation order also took hikers by surprise, with several emerging from monument trails, only to have to hitchhike to their cars. Most trails around the mountain now have been closed.

By late yesterday afternoon, many found a new viewing spot at the Coldwater Ridge Visitor Center, farther down the mountain. The mountain was quiet except for what appeared to be small plumes of dust kicked up by falling rocks.

"We're staying for as long as we can," said Paul McKerracher, who'd come down from Redmond and was ousted from Johnston Ridge. "If it doesn't happen today, we'll try to come back tomorrow."

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com

Christopher Schwarzen: 425-783-0577 or cschwarzen@seattletimes.com