St. Helens stirs

Monday, September 27, 2004
By ERIK ROBINSON, Columbian staff writer

Magma may be moving within Mount St. Helens for the first time since October 1986, a potential precursor to a new round of dome-building or even another eruption.

    Or it could signal the notorious volcano is still simply letting off steam.

    A flurry of earthquakes that began last Wednesday increased in magnitude over the weekend. By Sunday evening, scientists at the David A. Johnston Cascades Volcano Observatory in Vancouver named for the U.S. Geological Survey scientist who died in the catastrophic eruption of May 18, 1980 said they couldn't rule out another eruption.

    "We're seeing a pattern of earthquake activity that we really haven't seen in the recent past," said Willie Scott, a geologist with the USGS.

    Most of the earthquakes are less than magnitude 1 on the Richter scale, too small to be felt even by someone standing in the mountain's crater. But they are coming as frequently as one a minute, and between 10 and 15 registered above magnitude 2 starting Saturday morning and continuing through Sunday afternoon. The largest quake registered 2.8 on the Richter scale.

    It's the largest number of significant earthquakes within a day's time since the last dome-building event on Oct. 21, 1986.

    Between 1980 and October 1986, magma, which is liquid or molten rock, pushing up through the geologic piping system created a lava dome that now rises 876 feet above the crater floor. The dome, measuring 3,500 feet in diameter, rumbled to life again from late 1987 through 1992. A series of earthquakes indicated magma was burbling within the conduit linking the dome to magma four or five miles below the Earth's surface.

    Today, scientists will fly over the volcano with instruments capable of measuring carbon dioxide and hydrogen sulfide telltale signs of magma rising toward the surface. Scientists speculate that deep and significant earthquakes probably would have signaled any large amount of magma spurting upward.

    "There hasn't been any indication that we need to do any evacuations," said Dave Cox, undersheriff of the Skamania County Sheriff's Office. The volcano is in Skamania County.

    U.S. Forest Service officials closed hiking trails above 4,800 feet on the mountain because of the danger of sudden steam explosions blasting rock out of the crater. Although visitor centers and most trails will remain open, Forest Service officials don't want climbers exposed to a sudden gas or steam explosion while peering over the crater rim.

    "Standing on the rim, from what geologists tell us, would not be a good idea," said Peter Frenzen, scientist for the Mount St. Helens National Volcanic Monument.

    Although scientists say the earthquakes remain relatively shallow, about a half-mile below the surface, the persistence and increasing magnitude prompted officials to issue a volcano alert Sunday afternoon. The Federal Aviation Administration also has been notified, so that pilots can be forewarned in case ash spews high enough to choke the engines of jetliners approaching Portland.

    Despite the warnings, scientists said the mountain is more likely to simply quiet down than it is to continue rumbling. It's far too early to reasonably forecast an eruption, geologists said.

    "It's like saying the kid might become a dancer when he's 18 and he's 6 months old now," said Cynthia Gardner, a geologist for the USGS.

    Geologists late last week suspected the swarm of earthquakes to be the result of autumn rainfall and water from the newly formed glacier seeping into the mountain's still-toasty interior lava dome, then flashing to steam capable of cracking rock.

    Now, they aren't so sure.

    Scientists said the flurry of seismic activity could signal that gases and steam are interacting with hot rocks inside the lava dome. Scott said a progression of volcanic activity could result in steam and gas eruptions spewing pumice and ash, or possibly melt a newly formed glacier on the mountain "before it even has an official name."

    Forest Service officials expect any activity to be limited to the crater itself, but scientists are keeping a close eye on the mountain.

    "Collectively, there's a lot of energy being released," Frenzen said. "So there's a potential for a steam burst of some power there. Equally of concern is if an explosion caused land-sliding on the crater floor or the melting of a mass of ice. You could have a slurry of melt-water, rock and ash, and a debris flow that would come down and impact that area north of the crater."

    News of the volcano acting up brought reaction around the area.

    At Jack's Grill in the community of Yale, owner Alyson Harbick said: "They closed the mountain down and we were one of the first to know because we sell the climbing permits to go up the mountain."

    Was she concerned?

    "I'm not concerned. ... I'm not worried about having to evacuate."

    And her customers?

    "There were some climbers who were let down because they couldn't go up."

    Most of the access to the volcano is through Cowlitz County.

    "We're certainly going to keep our eyes on it," Cowlitz County Sheriff's Sgt. Brad Thurman said Sunday night. "We haven't taken any official action yet."

    Although the volcano is inside Skamania County, Cowlitz deputies patrol to within five miles of Mount St. Helens. Thurman has been with the sheriff's office for 17 years. But he remembers 1980.

    "I was living up in Longview, so I definitely remember it well."

    Columbian staff writers Margaret Ellis and Dave Kern contributed to this report.

    Did you know?

    Important dates in Mount St. Helens' modern history:

    * May 18, 1980: After making a series of steam eruptions beginning almost two months before, the volcano erupted at 8:32 a.m. on a Sunday. The largest landslide in recorded history uncorked a blast that blew away the north face of the once-symmetrical peak, and obliterated 150 square miles of alpine forests, meadows and lakes. Fifty-seven people died.

    * May 25, 1980: Activity continued with a plume said to be nine miles high.

    * July 22, 1980: Three explosions; June dome destroyed.

    * Oct. 16, 1980: Explosion destroyed dome built in August.

    * Sept. 6, 1981: Gas and ash emissions; start of extrusion.

    * March 19, 1982: Most explosion activity since October 1980.

    * Feb. 7, 1983: Eruptive activity and dome growth.

    * May 24, 1985: Minor mudflows in crater; activity for 17 days.

    * Oct. 21, 1986: Activity for four days, the last known dome-building event possibly until this week.

    Source: Web site of the David A. Johnston Cascades Volcano Observatory in Vancouver

    Trails closed

    The U.S. Forest Service closed the following trails until further notice due to volcanic activity at Mount St. Helens:

    * Loowit Trail 216 between the junction with Windy Trail 216E and Studebaker Ridge.

    * Truman Trail 207A between the junction with Boundary Trail No. 1 and Windy Trail 216E.

    * The entire Willow Trail 207A between the Truman and Loowit trails.

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