Explorers Probe Deep-Sea Secrets
Using a small underwater craft, oceanographers witness volcanic activity on the ocean ridge
LA JOLLA, CALIF.
ON this eucalyptus-covered campus sequestered above an azure cove, students listening to a quiet lecture are as excited as if they were hearing about the adventures of Indiana Jones. Armed with pointer, slide-projector, and a professorial air, Rachel Haymon is showing graduate students pictures taken underwater of blizzards, smoke-spitting stalagmites, lava pillars, and the remains of animals scorched by the world's most recent underwater volcano. Suspended in a 7-foot-diameter titanium sphere, 8,200 feet below the ocean surface, Dr. Haymon and crew saw in April what no scientist before them has ever seen: a volcanic eruption from the deep-sea floor.
After 25 days of observing and sampling hydrothermal activity in the eastern equatorial Pacific, the 18-member expedition led by Haymon and co-investigator Dan Fornari concluded that they had come within weeks, days, even hours of the volcano's most explosive episodes.
"When I got out of the Alvin [deep-diving submersible craft], I was babbling," says Haymon, calling the experience her most thrilling in a 15-year study of the sea floor. The sight was a stretch of ocean floor 82 kilometers by 500 meters (51 miles by 1,640 feet) along the crest of East Pacific rise, about 500 miles southwest of Acapulco, Mexico. "I was so viscerally thrilled I dreamed images of the floor for weeks," she says. "I couldn't articulate my amazement."
As if it were not "politically correct," none of this emotion is showing in front of students here at Scripps Oceanographic Institute, where Haymon earned her PhD in oceanography and has returned with her findings.The scientific implications go well beyond the elation of the moment. The 30,000-mile mid-ocean ridge that runs through the world's seas like the seam on a baseball is the biggest geographic feature on earth. It is also where new ocean floor is created.
Magma in the earth's mantle wells up through the cracks created where the earth's tectonic plates diverge, widening the ocean by 11 centimeters a year - a relative sprint by geologic standards. Study of the geophysical and geochemical processes of the mid-ocean ridge is key to understanding earthquakes, volcanoes, raising of mountain ranges, and the chemical makeup of oceans.
"The scientific community is very excited about these discoveries," says Robert Embley, a geophysicist with the National Oceanographic and Atmospheric Administration (NOAA) Vents Program. "We don't have the ability to monitor deep-sea eruptions like we do on land. This is a huge step forward."
"To directly observe a phenomenon that is so remote and so off and on is very rare and exciting," adds Peter Rona, senior research physicist at NOAA.
Hydrothermal vents on the ridge were discovered in 1977. The ridge is known to erupt periodically but with unknown frequency and in unknown locations. Scientists have filmed active lava flows in shallow waters off the large island of Hawaii, but the Hawaiian islands are not connected to the mid-ocean ridge, which is the ocean's greatest source of volcanism.
After discovering so-called "mega-plumes" of hot mineral water 20 kilometers (12.5 miles) across off the state of Oregon, Dr. Embley and others documented a lava flow between 1981 and 1987 using an echo sounder. But the evidence came after the fact.
"[For them to] catch this kind of evidence when it is happening gives the point of reference from which to measure all subsequent phases," Embley says.
Haymon, now assistant research geochemist at the Marine Science Institute of the University of California, Santa Barbara, is one of about 50 United States scientists studying the mid-ocean ridge in field studies. Her chief co-investigator, Dan Fornari, is an associate research scientist at the Lamont-Doherty Geological Observatory in Palisades, N.Y.
As reconnaissance for their April expedition, dubbed the Adventure Program, Haymon and Dr. Fornari spent several weeks in 1989 mapping the ridge for the National Science Foundation (NSF). The foundation's ocean-drilling program needed a site survey to find a proper drilling area for studies into the vertical dimension of the ocean crust.
For three days at a time, the expedition lowered the Argo, an 8-by-4-foot metal-framed cage carrying sonar and video equipment, to just above the ocean floor.
Using information transmitted to the ship by coaxial cable, they made sonar maps of the terrain. They also cataloged and mapped visual observations.
"This had never been done before over such a long stretch of ocean ridge," Haymon says. "For the first time, we could get a more systematic feeling of what the vent distribution was like over space and time, and how it could be related to other geologic features of the ridge."
Returning to the same site in April with more NSF funding to further pinpoint a drilling site, the 18-member Adventure science team took turns riding the submersible Alvin to the ocean floor. The fresh black lava, fried and shredded tube worms, gray ash deposits, fresh chimneys, and water temperature all told them they were visiting a large field of fresh volcanic activity.
"There was water coming out of every nook and cranny," says Haymon. Temperatures measured 386 to 403 degrees C, the highest temperatures yet recorded at ridge hot springs. Lava lakes, bacterial blizzards, venting smoke, and dark, glassy basalt fields completed what she calls a "visceral, aesthetic, and scientific feast."
Carrying three at a time, who sit Indian-style on the small floor, the Alvin takes nearly two hours to make the 8,200-foot drop to ocean floor.
"Your first trip down is both eerie and wonderful," says Dawn Wright, a graduate student and assistant to Haymon who helped catalog findings. Everything lower than 100 meters is pitch black, she says, except for bioluminescent animals shaped like noodles, called siphonophores. After descent, battery-powered strobe lights illumine the sea floor.
"It's literally like being on another planet in broad daylight," she says. "The water is so clear, you seem to be flying in air."
Next comes about seven hours of reconnaissance, using the Alvin's two robotic arms to place water, rock, and animal samples into a mesh basket attached to the submersible hull.
"Nothing replaces the human eye in a submersible," says Haymon, who went on six of 25 dives. Three 7-inch portals are the only view out. Free-swimming under its own thrust, with pinpoint directions from previous Argo reconnaissance, the Alvin could easily locate a one-meter-wide hot spring.
Operated by the Woods Hole Oceanographic Institute in Woods Hole, Mass., the Argo was used in locating both the German battleship Bismarck and the sunken ocean liner Titanic. The Alvin has also helped recover undetonated hydrogen bombs from World War II.
Besides mapping coordinates of such formations as basalt lava pillars, stratas of lava, and hydrothermal mineral deposits, scientists logged observations verbally into a tape recorder. Flowing lava had scorched mussels, clams, and tube worms alike in a so-called "underwater Pompeii."
"There are whole realms of possibility in applying how vent communities derive energy from chemicals of the vent fluids," Haymon says. "A whole ecosystem has developed that is not based on photosynthesis - there are none other on earth that are not sun-based."
Her studies also raise philosophical questions.
"Oceans cover over 70 per cent of the planet, yet we know so little about them, because of the difficulty of studying them," Haymon says. "We need to know more about the earth's large- scale processes - it's the only planet we've got and who knows the extent to which it's influenced by the oceans?"
For Dan Fornari, the success of the expedition was a vindication of the scientific process, one that has been undermined heavily in the past 10 years of federal budget-cutting.
"We put together what are biologically and geologically very important pieces of the puzzle of how the earth works," he says.