What threat does Mount St. Helens pose now?

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by JEFF RENNER / KING 5 News

Bio | Email | Follow: @Jeffrennerwx

KING5.com

Posted on May 18, 2010 at 7:30 PM

Updated Tuesday, May 18 at 4:31 PM

After 30 years, it would seem scientists have learned all there is to learn about Mount St. Helens. But this volcano, like most, gives up its secrets slowly, including what it will do next.

The 1980 lava dome was like a rocky cork popping out of a bottle. Twenty five years later, the new growth shifted south.

It began in mid-November of 2004 with swarms of earthquakes, which brought an end to 18 years of relative quiet. A fresh surge of lava pushed up as much as 1,400 feet -- twice as tall as the Space Needle.

Scientists brought an arsenal of tools to monitor the volcano. An infrared camera could distinguish between hot, young, emerging lava and cooler, older rock.  But the science required the calculated risk of work on the ground.

Geologist John Pallister took samples from the lava dome, seeking to unravel two mysteries. How has the volcano changed and what threat does it pose now?

 "This is a 1980 sample - very light," said Pallister.

Next , the dome sample from 2004.

"You're going to need two hands. That is roughly the same size. That's much heavier," said Pallister.

The story these rocks tell is more than skin deep. It requires precise detective work, a sort of CSI-Volcano. Rock samples no bigger than a postage stamp and as thin as a human hair are scanned under a microscope.

Clue number one: This 1980 sample looks like "Swiss cheese." The blue spaces indicate gas pockets and explosive lava.

Clue number two: This brown mineral called Hornblende, which acts as a sort of lava "speedometer."

"You can see it has a very crisp margin," said Pallister. "That means the magma came up very quickly from depth."

Clue number three: From the 2004 sample, no Swiss cheese appearance, few gas pockets and little explosiveness.

"It did not explode. It came out surprisingly slowly, over a long period of time," said Pallister.

Finally, clue four: A Feldspar mineral shows growth rings like a tree. The center of the crystal may be thousands of years old; the rim perhaps a decade.

"The bottom line: This magma chamber isn't going to go away in the near future. There are going to be new eruptions for Mount St. Helens in the near future. It's a live system," said Pallister.

But could that activity influence our other Northwest volcanoes?

"The plumbing systems of these volcanoes are isolated and relatively small in the Cascades, so we would not expect an eruption at Mount St. Helens to trigger another eruption," said Pallister.

The next eruption could be in a year, a decade or a century. Historians remind us that civilization exists by geological consent. - Mount St. Helens proved that in 1980.  Technology, research and human thought and creativity can be effective tools for understanding and predicting the forces of nature, but not mastering them.

 

 

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