Tuesday, January 03, 2006

Mount St.Helen's volcano still showing signs of activity

For more than a year now, Mount St. Helens has been oozing lava into its crater at the rate of roughly a large dump truck load — 10 cubic yards — every three seconds. With the sticky molten rock comes a steady drumfire of small earthquakes.

The movement of lava up through the southwest Washington volcano is "like a sticky piston trying to rise in a rusty cylinder," U.S. Geological Survey U.S. Geological Survey geologist Dave Sherrod said Thursday in a telephone interview from the agency‘s Cascades Volcano Observatory in Vancouver, Wash.

The mountain is about 50 miles north of Vancouver and 100 miles south of Seattle.

St. Helens — now 8,325 feet — rumbled for another six years, extruding 97 million cubic yards of lava onto the crater floor in a series of 22 eruptions that built a 876-foot dome. The volcano fell silent in 1986.

Winter weather has prevented aerial monitoring of the crater since Oct. 24, "but we know what the rate has been. It‘s been relentless," Sherrod said, noting geologists can also rely on a network of remote monitoring equipment to tell them what‘s happening.

All the recent activity has remained within the crater, though scientists — keenly aware of the potential damage that silica-laced ash can pose to jet engines — monitor St. Helens closely for plumes of smoke and ash that can go as high as 30,000 feet.

"This dome collapses and grows and collapses and grows. It changes its location ... it can‘t seem to maintain its height at much more than it is now " — about 1,300 feet. "Then it kind of shoves the sandpile aside and starts over."

At the current rate of extrusion, "three or four months would have been enough time to exhaust what was standing in the conduit. ... The volume is greater than anything that could be standing in a narrow 3-mile pipe," Sherrod said.

"That‘s one of the headscratchers, I guess," Sherrod said.

The mountain is the youngest and most restless of the Cascade volcanos. "Most of what we see today is 4,000 years old," Sherrod said. By comparison, Oregon‘s Mount Hood is 30,000 to 50,000 years old. Parts of Mount Rainier in Washington date back 200,000 years.

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