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Originally published Saturday, March 5, 2005 at 12:00 AM

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Seafloor earthquakes signal eruption off Vancouver Island

Mount St. Helens may not be the only Northwest volcano spitting out lava these days. A scientific SWAT team from Seattle is sailing this...

Seattle Times staff reporter

Mount St. Helens may not be the only Northwest volcano spitting out lava these days.

A scientific SWAT team from Seattle is sailing this afternoon for a spot off the coast of Vancouver Island, where they suspect an underwater eruption is under way.

"We really don't know what to expect," said Edward Baker, an oceanographer at the Pacific Marine Environmental Laboratory, which is part of the National Oceanic and Atmospheric Administration (NOAA). "If we're very lucky, we may get pictures of brand-new lava on the seafloor."

Their observations will help improve understanding of the Juan de Fuca plate, a tectonic time bomb capable of producing earthquakes and tsunamis on par with the disaster that struck the Indian Ocean in December.

Baker is co-leader of the 20-person team, which has been scrambling since Sunday, when swarms of earthquakes started rattling the ocean bottom 200 miles offshore. In the past six days, the area has been rocked by nearly 4,000 temblors, most tiny, but some exceeding magnitude 4.

"It has been going on long enough that we're pretty sure lava is moving," Baker said.

The researchers keep scientific instruments packed and ready to go so they can act quickly when an underwater eruption starts. This time, they were especially lucky because the University of Washington had a research vessel docked at Portage Bay, between assignments.

Team members from Hawaii, Oregon, Canada and Massachusetts canceled lectures and family gatherings to make the weeklong cruise, funded by the National Science Foundation and NOAA.

"We know so little about what goes on when these volcanoes erupt," said Joe Resing, an ocean chemist at the marine laboratory. "Opportunities like this are very rare."

The rapid-response team, which has raced to seven underwater eruptions over the past 10 years, is the only one of its kind.

Among their main tools is a network of Navy hydrophones originally used to monitor enemy submarines. The sensitive instruments can detect underwater earthquakes that are too faint and far away to be picked up by land-based seismographs.

"It's left over from the Cold War, and it's become very useful," Baker said. "But even I'm not allowed to know where the microphones are," he added with a laugh.

The sensors located the shaking on the Juan de Fuca Ridge, where fresh oceanic crust forms as tectonic plates pull apart and magma wells up from deep within the earth. This seafloor spreading is slowly forcing the Juan de Fuca plate under the North American plate, creating a subduction zone that has unleashed massive earthquakes in the past.

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An eruption along the ridge doesn't directly raise the risk of an earthquake on the subduction zone, Baker said. But the regions are closely linked, like pieces in a puzzle.

"It's the same plate movements which cause the earthquakes on the spreading ridge and allow new magma to come up that also cause the subduction earthquakes on the other side of the Juan de Fuca plate," he said. "They're both expressions of the Juan de Fuca plate movement, and everything we can learn about how that movement is expressed will give us a better insight into the whole package."

To try to figure out what's going on nearly two miles below the sea surface, the scientists will lower instruments into the water to collect samples and measure temperature, salinity and the chemicals and particles given off by underwater eruptions.

"It's sort of like drilling holes all over the Earth's crust to look for oil," Baker said. "We're going to be drilling holes in the water to look for evidence of hot fluids."

Though underwater volcanoes are little more than cracks in the crust, they produce the same plumes of gas as land-based volcanoes like Mount St. Helen's, Baker said.

"If there's a big eruption, it's very obvious in the water."

The team will also lower a camera-equipped sled to the ocean floor, hoping for a glimpse of lava.

If they see it, it may still be warm — but it won't be molten, said Resing, who as a graduate student used to scuba dive during Hawaiian eruptions, to study what happened to lava when it hit the water. "It just cools instantaneously," he said.

It's also possible that magma is moving underground, but hasn't breached the surface yet, Baker said.

In that case, the pictures will at least reveal how much the volcanic unrest has rearranged the seafloor and affected marine life in the area, which researchers have mapped in the past.

The shaking is near the well-studied Endeavour hydrothermal vent field, populated by giant tube worms, clams and other creatures that live in scalding hot, acidic water — and it's possible the effects might have been felt there.

"Some of the greatest, most rapid changes that occur in these ecosystems are during eruptions," Baker said. "These are catastrophic events on the seafloor."

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com

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