Clouds lifted Wednesday above Mount St. Helens to reveal much of the volcano’s new lava dome has crumbled since the last time scientists got a clear view three weeks ago.
“The dome’s changed quite a bit,” said Willie Scott, a geologist for the U.S. Geological Survey in Vancouver. “It’s really broken up.”
For almost two weeks, the mountain has been rocked by the strongest earthquakes since lava first emerged on the crater floor in early October. Scientists weren’t sure whether the intensified quaking meant the lava dome was breaking apart or whether underlying magma had begun to strain against the growing mass of the new dome.
For all of the high-tech gadgetry employed by the USGS at Mount St. Helens, scientists needed an assist from Mother Nature to solve the mystery.
An unexpected break in the weather permitted scientists to fly across the volcano and sling new instruments inside the crater. The aerial views revealed the back end of the dome, nestled against the inner south wall of the crater, had largely broken apart.
Scott described a large gash on the dome’s northeast side, where the youngest rocks tumble down into fresh snow. The front end of the new dome is streaked by striations indicating that magma continues to pulse onto the crater floor.
Nonstop seismic activity suggests the volcano continues to extrude lava, as it has since reawakening with a flurry of earthquakes Sept. 23. The recent quakes remain relatively shallow, within a mile of the surface.
“We don’t think the big earthquakes mean there’s a higher or lower chance of an explosion,” said Steve Malone, professor of earth and space sciences at the University of Washington.
The bigger quakes, which began March 25 and continue at a rate of three or four a day, have been measured as large as magnitude 3.4. Although the quakes are barely large enough to be felt by someone standing in the crater, scientists said they represent a substantial release of seismic energy.
“It seems a little large if it is rock cracking in the new dome,” said Bill Steele, seismology lab coordinator for the UW.
The last major explosion at Mount St. Helens was March 8, when a billowing cloud of steam and ash unfurled to a height of 36,000 feet within a few minutes. The cloud dropped ash as far away as western Montana.
Scientists don’t see any evidence to indicate the mountain is building toward a 1980-style eruption that obliterated 230 square miles of forest, turned day into night across Eastern Washington and killed 57 people around the mountain.
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