A little more than a year ago, on the night of February 9, the 170-foot research ship Wecoma headed west from the Oregon coast into darkening rough seas. Within hours, the ship was trying to make its way into a gale that drove rain horizontally across the decks. By the next day 45-knot winds were jacking waves up to heights of 30 feet, conditions that could easily have smashed smaller vessels.
The relentless pounding continued for days. Oceanographer Ed Baker remembers February 14 as the worst night of all. Waves crashed and roared over the deck, blurring sky and sea. Then the wind would suddenly change direction without warning, propelling rollers into the ship from an entirely new angle. The Wecoma pitched and bucked violently in unpredictable jerks. "What you can't appreciate until you're out there is the whipping motion," says Baker.
The scientists passed hours trying to drink coffee that
frequently flew out of their cups or trying to rest in tossing
bunks that thrust them to the floor
"If you're not holding on, you can get thrown across the deck." Despite the storm, Baker, a researcher at the Pacific Marine Environmental Laboratory in Seattle, and his colleagues were determined to launch a half-ton deepwater probe into the Pacific from the roller-coaster decks. They knew that a mile below the Wecoma a volcano had blown its top, and only the most unholy of storms would keep them from collecting evidence of a newly discovered side effect of such an eruption: giant underwater twisters of hot water, called megaplumes, loaded with minerals and strange life-forms. As the deck crane cavorted wildly in the wind, the researchers gingerly lowered the probe--a cluster of sampling bottles held by a wire tether--over the side. Once the probe was in the water, they let the tether unspool for 40 minutes until the bottles were a mile underwater. They worried the whole time that the corkscrewing motion of the ship would snap the wire. Then they had to haul the load back aboard. "Swinging is a bad thing," Baker says, remembering the gyrations of the crane. If the bottles slammed against the hull, they would be destroyed. If they slammed against scientists and deckhands, someone would die.
Conditions deteriorated and the captain of the ship banished the scientists inside, where they passed hours trying to drink coffee that frequently flew out of their cups or trying to rest in tossing bunks that thrust them to the floor. Sleeping, Baker says, “was always an adventure.”
The night of the fourteenth was memorable not only because the seas were so rough but also because the researchers had to deploy an acoustic beacon the size of a telephone pole. In the dim glow of deck lights, the crew struggled on the Wecoma’s fantail. The hook of the crane crashed into the device. Although they didn’t know whether the beacon had been damaged, they set out a chain of fragile glass globes that would later bring the device back to the surface. Then they raised the 30-foot-long aluminum shaft. “It’s very heavy, yet very delicate as well,” Baker says. As the ship roared up the face of one wave and then plunged down the other side, the beacon began swinging back and forth. The crew grappled with the heavy lines. One deckhand lost his grip but then grabbed on again before the shaft could crash into anyone. Finally the crane lowered the instrument into the water. Baker remembers, “It went off without a hitch, but that was probably the scariest part of the trip.” Several days later, everyone was relieved when the beacon began broadcasting data.
‘It would have been pretty spectacular if you’d been down
there and seen, really,a boiling cauldron of water popping
up out of the seafloor’
The voyage to the volcano and back took ten days, “probably the worst weather for ten days straight that I’d ever had at sea,” Baker says. But when the Wecoma docked in Oregon, he was a happy man, and not just because he was standing on terra firma. The data he and his colleagues had collected painted a picture of a far more violent spectacle on the seafloor than the scientists had experienced in a storm on the surface.
Researchers lower a probe off the deck of the Wecoma to capture samples of a megaplume.
The first rumblings of that unseen spectacle had begun weeks earlier, on January 25. A network of sensitive hydrophones in the North Pacific, deployed by the U.S. Navy to listen for Soviet submarines, picked up a swarm of earthquakes at the summit of an undersea volcano called Axial. The quakes were a lot less subtle than the quiet hunters of the cold war: they sounded like freight trains rumbling by. Over the course of a day the quakes traveled 30 miles from the volcano, following a scar in the seafloor where two plates of the planet’s crust are pulling apart. The quakes shook loose the rock that had stopped up the volcano’s plumbing. Through the newly cleared rocky pipes came an inferno of molten rock and boiling water driven upward by the intense pressures and temperatures of the inner Earth miles below.
“It would have been pretty spectacular if you’d been down there in the early going and seen, really, a boiling cauldron of water popping up out of the seafloor,” Baker says. A typical volcano on land, such as Mount St. Helens, fills the sky with a plume of ashes when it erupts. But Axial belched forth an equally massive eruption of superhot water. That was followed by streams of lava, some as deep as six feet, flowing down the sides of the volcano. Along Axial’s flanks, fields of geysers suddenly pierced the ocean bottom, shooting up superheated jets of water darkened with heavy concentrations of minerals from Earth’s crust. “We estimated, roughly, that there were ten gigawatts of energy coming out of the volcano’s caldera,” Baker says. “By comparison, Bonneville Dam on the Columbia River puts out about one gigawatt, and that can provide energy for 3 million homes.”
The trip on the Wecoma was launched to find out what happens when all that energy breaks loose. Geophysicists have sketched the broad outlines of plate tectonics—how Earth’s molten mantle of lava rises up to the surface and turns into plates of rigid crust—but many mysteries remain. Answers are not easy to come by because they must be found at places like Axial, obscured by deep ocean. But in recent years researchers have learned how to place sensors on or near volcanoes like Axial. The instruments dropped by Baker and his fellow oceanographers, for example, measured water temperature, current flow, and the chemicals released during the eruption.
Baker was particularly interested in learning more about megaplumes, observed only seven times before. Hot geysers of water, such as those on Axial’s flanks, rise only a few hundred feet above the seafloor, then diffuse like a pall of low-hanging smoke. Megaplumes, however, can soar more than several thousand feet off the ocean floor and spin like slow but gargantuan tornadoes. They can be 12 miles across and travel hundreds of miles. “It’s a bomblike event,” says Baker, who was among a group of oceanographers who discovered the phenomenon in 1986. Shortly thereafter, the researchers dubbed the underwater cyclones megaplumes.
The plumes have attracted interest for three reasons. First, they’re new. “You don’t often get a chance to find something that’s not known to exist,” Baker says. “And this isn’t some tiny feature, like a little rock. This is a whole giant process that no one knew about.”
Second, megaplumes stir up huge amounts of ocean, carrying minerals and gases and heat almost to the sea’s surface. Vertical mixing doesn’t happen easily in the ocean. Cool, dense water tends to stay near the bottom and warmer buoyant water near the top. As they rise from the ocean’s depths, megaplumes may bring energy and food to animals in shallow water. “They could be doing things to the energy of the ocean that we don’t even know about,” says David Butterfield, a chemist at the marine environmental lab.
Third, megaplumes move great distances horizontally too. In their travels, they may have helped some of the oddest and oldest beasts in the world colonize the planet. A hydrothermal hellhole like Axial may seem like a poor choice for a home, but it supports vibrant communities. Bacteria, which feed on methane and other noxious chemicals, provide sustenance for three-foot-long hollow tube worms and tiny clams. These critters can live only in hot spots on the seafloor, yet they have been found all over the world. How do they cross vast nutrient-free expanses of the sea to find new places to live? Megaplumes, which remain intact, spinning and drifting for months and traveling hundreds of miles, could be mobile ecosystems. “Maybe they’re like express buses,” Baker says.
If so, the bus depot is a midocean ridge such as the Juan de Fuca, which runs right below Axial. The ridge’s hot material rises from deep inside Earth, cools at the top, then slides off on both sides to become yet more planetary crust. At various hot spots, the ridge crosses over vertical channels that rise from the mantle. Molten rock rises to within a mile of the surface of the seafloor and forms a magma chamber. There it lies, slowly bubbling away.