Monday, May 30, 2005

Newly discovered underwater volcano home to eels and other life forms

Craig Young has seen a lot of strange things living around the volcanic fountains of hot water that jet up from cracks in the sea floor.

But what he found last month on an expedition to a newly discovered underwater volcano was the oddest thing yet. Instead of the more usual clusters of undulating tubeworms or a few ghostly, eyeless fish, Young and his fellow researchers found, for the first time ever, schools of wriggling, foot-long eels.

"I was astounded, because it was the last thing in the world we would have expected," said Young, a professor and director of the University of Oregon's Institute of Marine Biology. "Nothing like this has been seen at all."

Young was the co-chief scientist on the April expedition to the Vailulu'u volcano, a 14,000-foot-tall seamount in the South Pacific near American Samoa. He took part in one of three dives by the deep-sea submersible Pisces V that explored the Vailulu'u caldera, where eels weren't the only discovery.

The research team, co-led by Hubert Staudigel of the Scripps Institution of Oceanography, also found a new, 1,000-foot volcano growing in the Vailulu'u caldera. Scientists first learned about it the night before their first dive, when sonar tracks found something big on what earlier soundings found to be a flat caldera floor.

Eels, not the more typical tubeworms or clams, dominate the biological picture near Vailulu'u.

"We were surprised that there was this new structure in the middle of the caldera," Young said. "Two years before, it had been a 1-kilometer deep, flat-bottomed caldera, and suddenly there's a mountain in the middle of it."

The new volcano was named Nafanua after the Samoan goddess of war. Its discovery kept the geologists and geophysicists busy, but what interested Young were the eels.

While it's not unusual to find a few small eels in colder water deep beneath the surface, it is unprecedented to find hundreds or perhaps thousands of eels dominating the biological community around a hydrothermal vent. Compounding the mystery is the near-total lack of any of the more typical organisms that populate such places, things such as tubeworms, mussels and clams.

So, Young wonders, what do the eels eat? About the only organic material other than the eels were thick, yellow mats formed by microbes that feed off the chemical-rich water gushing from the vents, and he said it's anyone's guess whether that makes a meal for an eel.

"So the puzzle to me is what are these guys doing for food," Young said. "To have (a vent) that just has microbial mats and fish seems very odd to me."

The eels were found around vents near the top of the Nafanua cone - a site dubbed "Eel City" - where the 48-degree water is only about 10 degrees warmer than the surrounding ocean. So it could be that the eels are able to swim someplace else for food, Young said.

Although the water from the top of the cone is relatively cool, the volcano probably is releasing much hotter water elsewhere. Hydrothermal vents can form chimneylike structures known as "black smokers," where the water temperature can top 700 degrees.

Scientists learned Vailulu'u was active only recently, when they took water samples that showed large amounts of a kind of particulate matter produced by black smokers. Staudigel said the amount of particulate indicated perhaps as many as 50 black smokers, which Young said would make it "one of the hottest, most active hydrothermal systems in the ocean."

But the team didn't find any high-temperature vents, probably because turbidity from the particulate formed a kind of volcanic fog around the base of Nafanua that reduced visibility to less than 10 feet. They hope to learn more when Young, Staudigel and other team members return for eight more dives in July, when they also will try to catch some eels to determine whether they are a new species.

In the meantime, the volcano continues to grow at the rate of about 8 inches a day. The top of the caldera is 2,000 feet below the surface, and scientists say that in as little as a few decades, it could be close enough to the surface to become a hazard to ocean navigation.

Staudigel said that's because as the volcano rises, the water pressure that acts like a cork to keep explosive eruptions in check decreases. That allows two things to happen: Gas comes out of the magma much faster and the heat from lava starts converting water to steam instantaneously, both of which add up to big explosions.

Given the current slope of the volcano's flanks, it would take a tremendous amount of magma to build the volcano high enough to break the surface, Staudigel said. But it could easily top out at just 300 feet below the surface, right in the prime zone for explosive eruptions that could disrupt navigation or, should the volcano collapse like Mount St. Helens did, trigger a tsunami.

"The chances are quite good that at some point it becomes explosive, but the chances of it actually forming new land is much less," Staudigel said.

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