October 3, 2004
By David Ammons, ASSOCIATED PRESS WRITER
Photo: This photo released by the US Geological Survey (USGS) shows smoke and ash rising from the crater of Mount St. Helens October 1. The volcano remains dangerous and could erupt again at any time, scientists warned. (AFP/USGS/John Pallister)
MOUNT ST. HELENS NATIONAL MONUMENT, Wash. -- Scientists kept a watchful eye on Mount St. Helens Sunday after government officials raised the volcano's alert level, cleared hundreds of visitors from the area and warned a major eruption was imminent.
A brief release of steam, followed by two tremors Saturday, signaled more seismic energy since quake activity began Sept. 23 than at any point since its devastating May 18, 1980, eruption. Scientists expect the impending blast to be much smaller than the 1980 explosion, which killed 57 people and coated much of the Northwest with ash.
The volcano alert of Mount St. Helens was raised to Level 3, which "indicates we feel an eruption is imminent, or is in progress," said U.S. Geological Survey geologist Tom Pierson. He said Saturday afternoon that an explosion probably would happen within the next 24 hours.
On Friday, the volcano spewed a plume of steam and ash thousands of feet into the air, but there was a scant release of steam Saturday - a puff of white cloud, followed by a dust-raising landslide in the crater. A volcanic tremor signal that came next was what prompted the heightened alert level.
Later in the day, scientists detected elevated levels of volcanic gases and a weaker, 25-minute tremor indicative of magma movement, USGS officials said Sunday.
USGS ALERT CODE SYSTEMS
Notice of Volcanic Unrest Alert Level ONE
This alert level is declared by USGS-CVO when significant anomalous conditions are recognized that could be indicative of an eventual hazardous volcanic event. The most likely such anomalous condition would be sustained, elevated seismicity. A "notice of volcanic unrest" expresses concern about the potential for hazardous volcanic activity but does not imply imminent hazard. Among the possible outcomes are: (1) anomalous condition is determined not symptomatic of an eventual hazardous volcanic event, leading to cancellation of "notice of volcanic unrest;" (2) symptomatic activity wanes, leading to cancellation of the "notice of volcanic unrest;" (3) conditions evolve so as to indicate progress toward hazardous volcanic activity, leading to issuance of a "volcano advisory" or "volcano alert."
Volcano Advisory Alert Level TWO
This alert level is declared by USGS-CVO when monitoring and evaluation indicate that processes are underway that have significant likelihood of culminating in hazardous volcanic activity but when the evidence does not indicate that a life- or property-threatening event is imminent. This alert level is used to emphasize heightened concern about potential hazard. Among the possible outcomes are: (1) precursory activity wanes, leading either to cancellation of the "volcano advisory" or to a downgrade of alert level to "notice of volcanic unrest;" (2) conditions evolve so as to indicate that a life-threatening volcanic or hydrologic event is imminent or underway, leading to issuance of a "volcano alert." "Volcano advisory" statements, supplemented as appropriate by "updated volcano advisory" statements will clarify as fully as possible USGS-CVO understanding of the hazard implications.
Volcano Alert Alert Level THREE
This alert level is declared by USGS-CVO when monitoring and evaluation indicate that precursory events have escalated to the point where a volcanic event with attendant volcanologic or hydrologic hazards threatening to life and property appears imminent or is underway. Depending upon further developments, a "volcano alert" will be maintained, updated, downgraded to a "volcano advisory," or canceled. A "volcano alert" statement will indicate, in as much detail as possible, the time window, place, and expected impact of an anticipated hazardous event. "Updated volcano alert" statements will amplify hazard information as dictated by evolving conditions.
Hundreds of visitors at the building closest to the volcano - Johnston Ridge Observatory five miles away - were asked to leave Saturday. Some relocated several miles north to Coldwater Ridge Visitors Center, which officials said was safe.
People pitched tents alongside park roads and spent the night waiting to see what the rumbling volcano would do. Saturday was the busiest day ever at visitors' centers on the mountain, with thousands of people packing buildings, crowding parking lots and sitting alongside roads in lawn chairs.
Barbara Jardin, 53, of Camas, said she saw the plume at midday and was afraid she'd miss something if she left the area. "I just stare at it and stare at it. It's too awesome to leave," she said.
Interior Secretary Gale Norton, who flew over the mountain Saturday, said the seismic activity has weakened the 1,000-foot lava dome that began forming in the volcano's crater after the 1980 eruption.
Saturday's tremor lasted about an hour before it was drowned out by a series of earthquakes - one or two a minute, with a maximum magnitude of "well over 2," said Tom Yelin, a USGS seismologist at the University of Washington's seismic laboratory in Seattle.
Norton said the volcano most likely will have moderate ash eruptions.
"The greatest concern at this point is an ash plume and the spread of ash itself that might come from an explosion," Norton said. "This is a concern for aircraft travel."
The growing consensus among scientists is that new magma is probably entering the volcano's upper levels, bringing with it volatile gases that could lead to eruptions, said Bill Steele at the University of Washington lab.
Late Saturday, scientists flew past the volcano to measure its emissions. USGS spokeswoman Stephanie Hanna said for the first time in this Volcano Alert the instruments are detecting elevated levels of carbon dioxide, which escapes as magma rises toward the surface from the Earth's interior.
The increasing rate at which a volcano releases gases like CO2 and sulfur dioxide reflects changes in the volume of magma rising within its reservoir. Scientists at the rim of the volcano smelled hydrogen sulfide, similar to rotten eggs, said Jeff Wynn, chief scientist for volcano hazards at the U.S. Geological Survey's Cascade Volcano Observatory.
In addition, seismic monitors picked up a second tremor last night, but it was not as long as the 50-minute signal they recorded immediately following Saturday's steam emissions.
The USGS said explosions from the crater could occur without warning, possibly throwing rock onto the flanks of the volcano. Still, scientists said the evacuation of the observatory was primarily a precaution in case of heavy ash, which could make it difficult to drive.
"We still feel the risk is confined to this area," Pierson said.
No communities are near Mount St. Helens; the closest, Toutle, is 30 miles west. Few people live near the mountain, the centerpiece of the Mount St. Helens National Volcanic Monument in the Gifford Pinchot National Forest about 100 miles south of Seattle.
The 1980 blast obliterated the top 1,300 feet of the volcano, devastated miles of forest and buried the North Fork of the Toutle River in debris and ash as much as 600 feet deep.
Until late Saturday, air sampling had detected only tiny amounts of the volcanic gases that new magma produces, but scientists said the gases could have been sealed inside the system or have been dissolved by water on the mountain. The volcano holds a 600-foot-deep glacier and has received several inches of rain recently.
Melting of the glacier could trigger debris flows down onto the barren pumice plain at the foot of the mountain, the USGS said, noting a "very low probability" that downstream communities would be affected.
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