Explosive Eruption Forecast for Mount St. Helens

SEATTLE, Washington, October 4, 2004 (ENS) - Earthquake activity under Mount St. Helens is elevated at this hour as it has been since Friday, although no explosive eruption or ash is currently occurring at the volcanic mountain in southern Washington. The Cascades Volcano Observatory suggests that "an explosive eruption with little or no warning is possible."

A small explosive eruption of Mount St. Helens on Friday - the first in more than a decade - followed a week of increasing earthquake activity beneath the volcano and some deformation of the lava dome.

The eruption sent a steam and a plume of ash high above the mountain. Pilot reports from the area indicated the plume extended to an altitude of 16,000 feet above sea level.

Mount St. Helens sends up a plume of ash and steam to about 16,000 feet above sea level. (Photo courtesy USGS )

The U.S. Geological Survey (USGS) issued a Level III Volcano Alert on Saturday, which included the evacuation of the Johnston Ridge Observatory.

USGS scientists said they issued the elevated alert due to a change in the character of seismic signals. A 50 minute long tremor occurred immediately after a steam emission at 12:16 pm, recognition of ongoing uplift of the crater floor, and reports of sulfur gas odor. "We believe," the USGS said, "that there is a significantly increased probability that gas-rich magma is moving toward the surface."

When Mount St. Helens last erupted in 1980, the event claimed the lives of 57 people and left a thick coating of ash hundreds of miles away from the explosion.

"Volcanic ash plumes pose a costly and potentially deadly risk to planes and their passengers, should they fly through them," said Greg Withee, assistant administer for the Satellites and Information Service of the National Atmospheric and Oceanic Administration (NOAA).

David Johnson, director of the NOAA National Weather Service, said, "It's critical that pilots know in advance where the ash clouds are headed to avoid these risks, and keep passengers safe."

The NOAA Aviation Weather Center in Kansas City, Missouri, part of the NOAA Weather Service, relays Volcanic Ash Advisory Center statements to pilots, he explained.

Snow still covered the peaks of the Cascade Ranges in mid-June 2002 when the crew photographed Mount St. Helens from the Space Shuttle Endeavor. The crew observed blast zone from the 1980 eruption of the volcano, the mud-choked North Fork of the Toutle River, and fallen timber that still floats in rafts of logs on Spirit Lake. (Photo courtesy NASA)

Results from GPS measurements show no change in the shape of the volcano's outer flanks, but visual observations and photographic analysis show uplift of part of the glacier and a nearby segment of the south flank of the lava dome. "This suggests rise of magma to shallow levels," the USGS scientists said. "Additional steam and ash eruptions could occur at any time. There is also an increased probability of larger magnitude and more ash-rich eruptions," they predict.

Sunday field crews took additional thermal images of the dome and crater and conducted gas sensing, infrared and geologic observation flights. Deformation crews retrieved data from GPS instruments and lowered a new GPS station from a helicopter onto the dome.

In addition, two telemetered microphones are now operating to detect explosions.

U.S. Forest Service officials have closed roads in the vicinity of the volcano including State Route 504 starting at milepost 43, the Coldwater Lake-Hummocks Trail.

Forest Road 81 north of Kalama Horse Camp is closed to its junction on the east with Cougar Mountain Snow Park. Also closed are the Climbers Bivouac, June Lake, Lava Canyon, Ape Canyon, Smith Creek Redcross Pass and Blue Lake trailheads, and the Marble Mountain Snow Park.

Shown by the largest blue box on this map, Mount St. Helens is located in south-central Washington state. All the other boxes are earthquakes too - blue within the past two days, yellow within the past two weeks. (Map courtesy The Pacific Northwest Seismograph Network)

The Windy Ridge viewpoint has been closed since Friday on the east side of Mount St. Helens, four miles from the volcano’s crater. Three hiking trails on the north side of the crater were closed Sunday, and no climbing above the 4,800 foot level on the volcano is permitted due to an increased potential for steam explosions from the lava dome that could propel rocks and ash above the crater rim.

The Coldwater Ridge Visitor Center remains open as usual. The road remains open to Cascade Peaks viewpoint, and Cascade Peaks Restaurant and & Gift Shop remains open.

From space, NOAA scientists and researchers use geostationary and polar-orbiting satellite imagery to track volcanic ash eruptions and ash clouds.

"NOAA researchers keep a constant check on the pulse of the Earth," said NOAA Administrator Conrad Lautenbacher, "so we can protect our citizens from dangerous natural occurrences like volcanic eruptions or hurricanes or tsunamis and to improve the scientific information needed for sound policy decisions in the future."