Volcanoes of the deep

Losing expensive scientific equipment is usually a cause for dismay. But when Maya Tolstoy couldn't retrieve eight seismometers from the bottom of the sea this April, the Columbia University geophysicist was thrilled.

The devices, she suspected, had been buried under a lava flow 1.2 miles below the surface of the Pacific Ocean. When scientists at the Woods Hole Oceanographic Institution confirmed her suspicions a few months later, they also confirmed that her instruments had -- for the first time ever -- captured an undersea volcano while it erupted.

"We've been trying for decades to get instruments on top of a [deep-sea] eruption as it happens," said Tolstoy, who published initial data from two recovered seismometers in the Dec. 22 issue of the journal Science. "We've never recorded this fundamental process on nearby seismic instruments before."

From the new seismic data and a bevy of new scientific efforts launched at the eruption site, researchers expect to get an unprecedented look at the geological, chemical, and biological processes of deep-sea volcanic zones called mid-ocean ridges.

"The largest volcanic chain on this planet is out of sight, out of mind, and yet that's where two-thirds of the earth's crust is formed," Dan Fornari, director of Woods Hole's Deep Ocean Exploration Institute, said from onboard the research vessel Atlantis, which returned Dec. 6 from a two-week trip to the eruption site.

"Each time we have an eruption like this, it gives us an opportunity to better understand the seafloor."

Data from recovered seismometers may help scientists predict future eruptions at the ridges, and patterns of seismic waves may reveal clues about mid-ocean ridge anatomy, showing exactly where and how magma rises to the surface.

Also, the eruption provides scientists with a "Time 0" from which to watch life reemerge and geologic structures form.

The freshness of the lava allows scientists to clearly identify the size, extent, and volume of new flow. Because sediment can quickly cloak new lava, scientists seldom get the chance to make such exact measurements, said volcanologist Adam Soule of Woods Hole.

Soule, who has dived to the seafloor in Woods Hole's Alvin submersible, describes a monochromatic landscape of cooled, glassy black basalt shaped like rivers, jagged slopes, and blobs.

"You start paying attention to textures rather than colors," he said. ". . . Moonscape is a word that comes to mind."

Mid-ocean ridges occur where the earth's vast tectonic plates are spreading apart. Lava periodically pours from the earth's interior to fill the gap, creating new ocean crust and leaving a long, mountainous scar on the seafloor. At the ridge crest, thriving ecosystems of organisms colonize around jets of magma-heated, nutrient-rich hydrothermal fluid gushing from vents called black smokers.

The depth and darkness of mid-ocean volcanism makes the observation of such an event a rare feat. Since April, five research cruises have rushed to further study the site, using rapid-response funds provided by the National Science Foundation -- including a cruise from Woods Hole currently at the site and planning to stay through the new year.

In mid-December, a cadre of researchers presented data, pictures, and videos from the eruption site at the American Geophysical Union meeting in San Francisco.

Located about 400 miles south of Acapulco, Mexico, on a part of the mid-ocean ridge called the East Pacific Rise, the eruption took place in several pulses between November 2005 and late January 2006, scientists estimate.

It paved over about 9 square miles of ocean floor, decimating local ecosystems and leaving a barren plain of basalt.

It's the second volcanic event recorded at the site. In 1991, researchers in the submersible Alvin serendipitously touched down there during the first mid-ocean ridge eruption ever observed.

This year's volcanism confirms prior estimates that eruptions could occur there as frequently as once a decade.

More sophisticated equipment, developed since 1991, including the seismometers, high-resolution cameras, and mapping equipment, has enhanced how much researchers can now learn about undersea eruptions.

For vent organisms, an eruption "is like springtime on the seafloor," providing a pulse of new heat energy and nutrients, said geochemist Rachel Haymon of the University of California, Santa Barbara, who has studied the site since the 1991 eruption. The lava also destroys preexisting communities, leaving space for new organisms to find a foothold.

To understand how ecosystems reestablish themselves after these periodic volcanic poundings, biologists like Stace Beaulieu and her colleagues at Woods Hole have deployed traps in the overlying water column and on the seafloor to capture settling larvae.

Organisms may have washed in from deep-sea vents as far away as 100 miles, said Beaulieu. Scientists want to learn more about biological exchange between the geographically separated vent ecosystems. The vents are "like an island archipelago, where you can have several in a row, but then you have a great distance where there aren't any," she said.

By October, when the research ship Atlantis visited the site, organisms had begun visibly re-colonizing the vents, Beaulieu said.

Giant tubeworms, often considered the poster child of vent biology, hadn't yet returned in large numbers. But a smaller species of tubeworm, Tevnia, had begun growing, possibly encouraged by the lack of the larger worms.

While mapping the extent of the volcanic flow on Dec. 2, Fornari and his colleagues discovered two previously unknown hydrothermal vents 10 miles south of the eruption site.

The chemistry of the vents suggests they, too, were affected by the new volcanism, Fornari said, defining a wider zone of volcanic influence than previously known.

At the frontier of the deep-sea floor, such new discoveries are all part of a day's work, Fornari said.

"It turns out you always see an interesting thing, because you're the first one and possibly the last one to see that part of the ocean floor," he said. "It's very Jules Vernean."