Story Photos
 Photo by Roger Werth Wednesday's sunrise bathes Mount St. Helens in a pink glow at 5:30 a.m. |
A 26-year question
Wednesday, May 17, 2006 9:46 PM PDT
By Barbara LaBoe
Printable version
E-mail this articleTwenty-six years after Mount St. Helens' massive eruption, and 20 months after a smaller eruption began, the volcano remains an enigma in many ways.
Researchers have relentlessly studied and charted the mountain since even before its May 18, 1980 eruption. They've learned much about active volcanoes in the process, but they still have questions.
They do know that the volcano has pumped out enough lava in the last 20 months to fill the Trojan cooling tower at least 60 times over.
But they don't know why the volcano suddenly rumbled back to life in 2004. They don't know the eruption will continue, slow down or accelerate. And researchers won't even hazard a guess as to when this eruption will stop.
"Certainly there's still lots of questions we don't have answers for," said Tom Pierson, a USGS research geologist/hydrologist with the U. S. Geological Survey in Vancouver.
Scientists believe the magma in today's ongoing eruption is from the same batch that trigged the catastrophic eruption 26 years ago today. The eruption killed 57 people and obliterated 230 square miles of forest. It's ensuing mudflows destroyed 200 homes and a dozen bridges, and its ash cloud circled the earth.
Researchers believe the magma sat relatively close to the earth's crust for more than 20 years, slowing venting the high levels of gas present in 1980s magma. The gas in magma is what triggers explosive eruptions, and scientists believe this eruption is consistent and nonexplosive because so much gas has been vented off, Pierson said.
The magma that built a lava dome from 1980 to 1986 was more fluid and appeared in several dozen small eruptions that lasted days or weeks, Pierson said. The current eruption is producing solid, rock-like lava and hasn't stopped since October of 2004.
Scientists use words like slow and steady for this eruption, but it's also a workhorse.
The mountain has thrust more than 100 million cubic yards of volcanic rock into the crater since the fall of 2004. It took six years in the 1980s to squeeze out 97 million cubic yards.
The current production is so large that if you evenly spread it out on a football field it would rise 10 and a half miles into the sky, Pierson said.
If the mountain continues erupting at this rate -- and that's a big if -- scientists estimate the crater would be filled and the old summit replaced in 100 years. A new mountain peak would be visible before then, but Pierson said there are too many variables to estimate when that would be.
"Every time it tries to poke up a little higher it falls apart and drops," he said of the new growth. "This past year it's been see-sawing back and forth around a height of 7,700 feet at the top of the new dome."
The eruption and connected small earthquakes have slowed in recent months, but officials don't know if that means the eruption is winding down or just settling in to a slower activity level. There's also no guarantee it couldn't suddenly pick up its pace.
"Future eruptions all depend on what's coming behind the magma that's there now," Pierson said. "We know that there's a conduit full of this fairly cool, fairly crystal-rich material that is solid when it comes out. But what is pushing this stuff up? We really don't understand that."
"Basically, we're just doing everything we can think of to get as good a handle as we can on what's happening," he said.
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