Duke University Alumni Magazine


Diving party: crewmen from the Atlantis, in background, get the submarine set for submersion
Photo: Monte Basgall

aiting for the foghorn blast that would signal the imminent return of the deep-diving submersible Alvin, geologists scanned the placid Pacific Ocean from an upper deck of the research ship R/V Atlantis and contemplated their surreal circumstance. Instead of plowing through the water like ships normally do, the 274-foot-long Atlantis hovers hour after hour in one spot while the Alvin maneuvers silently and invisibly far below. In the calm waters near the equator known as the doldrums, the ocean seems less like water than a vast expanse of lazily bobbing blue gelatin or rolling glass.

If the waiting scientists let their fancies run wild, they might almost imagine that the ocean has drained away, leaving the motionless vessel suspended in the air like an equipment-laden dirigible. Had the ocean so vanished, they might lean far over the deck railing and peer down to see the upper rim of a chasm a mile below that would rival the Grand Canyon. Down another mile or more on the canyon's rocky north slope is the spot that Alvin left hours earlier to begin its ascent back to the mother ship.

Such reveries are interrupted by a sudden blue flash beneath the water's surface, announcing Alvin's return. The submarine's small orange conning tower soon breaks the surface, raising ripples that shimmer like liquid pearls. Two flipper-clad swimmers then dive from a nearby pontoon-hulled motor launch and paddle swiftly through the shark-haunted waters to board its small deck and plug in a telephone connection. Waiting inside the cramped vessel would be today's dive crew--two scientific investigators and their pilot--who had ventured into the lonely depths where few had gone before. The whole scene resembles the televised water-landings of the Apollo moon flight capsules, which, just like Alvin, returned with collections of rare and precious rocks destined to be studied as specimens for many months at university laboratories.

For three weeks beginning on March 15, an expedition led by Duke geologist Jeffrey Karson worked around the clock to use Alvin and two other sturdy submersible vehicles from the Woods Hole Oceanographic Institution in Massachusetts to explore the black, high-pressure depths west of the Galapagos Islands. Accompanying Karson, a structural geologist who heads the Earth and Ocean Sciences division of Duke's Nicholas School of the Environment, was a scientific brigade intent on learning more about the origins of the Earth's crust. This expedition would prove to be the most fruitful research mission of Karson's career.

The underwater canyon is named Hess Deep, after Harry Hess, father of the theory that new crust is created by erupting magma along the 37,000-mile mid-ocean ridge network encircling the Earth like the seam of a baseball. Plunging a sharp 9,000 feet at its lowest depth, Hess Deep is the tip of a westward moving crack in the ocean floor that points like an arrow toward a mid-ocean ridge called the East Pacific Rise (EPR). Just thirty-six miles east of the EPR, Hess Deep slices through the Earth's crust made "only" in the last million years by volcanoes on the EPR. In keeping with Hess' theory, the ocean floor spreads out from this ridge like a creeping treadmill, carrying within it evidence of ancient EPR eruptions embedded in the rock. Hess Deep offers a rare chance for geologists to examine that evidence in a mile-deep cross-section of the Earth's crust--the equivalent of "taking a knife to a layer cake," says Emily Klein, a Nicholas School associate professor and geochemist who was a co-principal investigator on Karson's recent expedition.

By journeying into Hess Deep, geologists can study the fossilized history of the East Pacific Rise's volcano systems and glean some insight into the very hot and sometimes violent interiors of the mid-ocean ridges themselves. This is the second time Karson has gone to Hess Deep seeking answers to such questions as: How frequently do these crust-forming eruptions occur? Do the inner cores of EPR volcanoes--called "magma chambers" --deflate like spent balloons between eruptions? Karson also wants to know what happens to all the excess lava following the formation of new crust. An especially fast-growing mid-ocean ridge, the EPR rises only about 600 feet above the surrounding ocean floor, so there's not enough room at the top for all the lava to pile up there. "The obvious answer is we have to keep dropping the bottom out underneath, and keep filling it in," Karson says. "But how do you get that material out of the way?"

Karson first rode the Alvin down into Hess Deep in 1990. Two years before that, in 1988, a French geological team visited the same area aboard the Nautile, a similarly equipped research submarine. The two research groups' findings differed dramatically, however. The results of the French expedition offered a neatly ordered textbook example of what fossilized remains of ancient volcanic eruptions should look like after one million years, says Karson. Within the layers of the cross-section, they found regular patterns with a volcanic zone at the top identifiable by the tell-tale pillow-shaped remnants of old lava. Underneath that layer were forests of vertically pointing "dikes." These were stone columns resembling tall stacks of rock pancakes, the remains of channels through which magma once flowed upward.

Two years later, Karson and fellow Duke geologist Stephen Hurst examined a much messier and more interesting scene not far from the Nautile dive site. While the dikes that the French documented were arranged vertically, those that Karson and Hurst discovered tended to be tilted. Contrary to observations made by the French, the Duke-led team found that the thicknesses of the upper volcanic and underlying dike layers also varied markedly from place to place. Moreover, they found younger dikes cross-cutting older ones at different angles.

These new findings launched a scientific debate. After both teams published their results in scientific journals, "it was natural that people would say that the French dove in a typical place that conforms to the dogma, and that our 1990 dive program was in a place that was anomalous," Karson says. Even he and Hurst thought that might be the case. "The difference in our findings was one of the big motivations for us to come back."

Karson first proposed a return trip in 1994, but his National Science Foundation funding wasn't approved until 1996. Problems with scheduling a ship pushed the project back another three years. Those delays had a silver lining: "a decade of technical improvement," Karson says. On the second Hess Deep expedition, scientists sailed aboard the R/V Atlantis, a high-tech vessel built for the U.S. Navy in 1997. Operated by Woods Hole, the state-of-the-art research vessel carried thirty scientists and technicians and twenty-three crew members. Klein and graduate student Michael Stewart accompanied Karson to sort and analyze the rock samples wrenched from Hess Deep's sloping walls by Alvin's robotic arms. Stewart will complete a Ph.D. dissertation based on the expedition's findings. Hurst, now at the University of Illinois at Urbana-Champaign, was the expedition's second co-principal investigator. Joined by the remaining scientists and students, the expedition sailed from the port of Manzanillo, Mexico, on the morning of March 12 and spent two days en route to the study site just north of the equator.

On March 16, scientists and crew launched the first probe, DSL 120, which would, over the next two days and nights, sweep the study area with high-pitched sound. The reflections of these sound waves would be electronically processed aboard Atlantis to provide scientists with images of Hess Deep's topography. While Atlantis towed DSL 120 on three passes over the study area, scientists in the dimly lit "control van" aboard Atlantis monitored the probe's readings on color-coded computer screens and examined paper readouts with the aid of flashlights. University scientists and members of the Woods Hole support team staffed the control station day and night in pre-arranged shifts.

Four days later came the launch of the second underwater probe, Argo II, whose floodlights and six on-board cameras promised to provide an avalanche of new information. Inside the reconfigured control van, Argo II's pilots used hand controls to position thrusters and maneuver the probe at the end of a two-mile cable. They also operated a winch that raised and lowered the probe along Hess Deep's wall. This required deft coordination on the part of its navigators, who were assisted by Atlantis' own dynamic positioning system to inch Argo II around looming outcrops. Every three minutes, the probe emitted sharp video images of geological formations that transfixed scientists in the control van. But these images were only tidbits, compared to the feast that would come once the digital images were compiled with the help of computers to yield panoramic "mosaics" of the sprawling underwater formations. This technique, stitching fifty or more images together to form a single superimage, had never been attempted before on an underwater chasm.

After four days of Argo imagery, scientists launched the main thrust of the expedition on March 24 with manned dives into the Hess Deep canyon aboard the submersible Alvin. Funded by the Navy and operated by Woods Hole, the twenty-three-foot-long vessel can carry two scientists to depths of nearly three miles for as long as ten hours. It can travel up to two knots and can maneuver precisely in every direction or hover motionless. Alvin also boasts six exterior cameras and ten lights capable of producing stunning video and still images of oceanic terrain, and insect-like folding mechanical arms that retrieve rocks and stash them in plastic collection baskets. To illustrate the incredible pressures Alvin's hull is able to withstand, scientists attached Styrofoam coffee cups to the outside hull. On Alvin's return, each of the cups had collapsed down to the size of a thimble.

A day confined within Alvin's tiny, cold, damp cockpit can be a demanding endurance test, but the scientists willingly faced that challenge, the only way they could study alien geology in a natural environment. It's like "going to another planet," Karson says over breakfast before the expedition's first dive. "There's no weather, no erosion, no rain, no wind, no sunlight. The rocks are somewhat different from rocks up on the continents. We're constrained by a watery environment that geologists find very frustrating because they can't reach out and grab any rock that they want to look at." A veteran of several dozen previous Alvin trips, Karson still suffers pre-dive jitters, as did Stewart, who made his first Alvin trip on this expedition. Shortly before eight that morning, both Karson and Stewart got the nod to squeeze through the mini-sub's squat conning tower. After they settled in, the hatch was sealed. An A-frame crane with a five-inch-thick braided rope lifted the 38,000-pound craft off its carriage and lowered the vessel over the Atlantis' stern into the water.

Rock crew: undergraduate Aisha Morris, research assistant Michael Stewart, geochemist Emily Klein, and geologist Jeffrey Karson scrutinize samples collected from an Alvin dive
Photo: Monte Basgall

During descent of more than one hour, the vessel is quickly enveloped in utter darkness, but scientists can still peer through the submarine's thirty-two-inch-thick, downward pointing windows to see tiny, glowing sea creatures drift past. The cockpit takes on an otherwordly ambience, replete with beeping noises and flashing lights. Karson typically uses this time to sleep, waking just before the vessel alights on its target area. The windows are suddenly bathed with the reflected glare of the bright floodlamps on the coal-black rocks. After touchdown, every moment is precious; researchers scramble to take photos, scribble notes, and direct the pilot on where to snatch up rock samples with Alvin's robotic arms, all the while dictating their observations into a tape recorder. On this day Karson and Aisha Morris, then a Duke senior, saw and sampled much as Alvin slid past what Karson calls a fantastic dike complex. Easing further up into the volcanic area, they discovered dikes intruding into pillow lavas, with both kinds of structures shattered by mysterious, powerful forces.

Finally, after dropping weights to increase buoyancy, the mini-sub rose slowly toward home with a precious load of two hundred pounds of rocks, breaking at last into the welcome sunlight and bobbing gently on the ocean's surface. Once back on Atlantis' deck, the elated first-timer Stewart was doused with buckets of ice and sea water--a rite of passage for Alvin dive rookies that was repeated during the next fourteen days as every member of the scientific team participated in at least one trip to the ocean floor.

Meanwhile, Argo II's continuing photographic forays provided more digital images, which in turn yielded new mosaics, the best of which the scientists pinned to shipboard laboratory walls. Others served as guides for the next day's dive. After each Alvin trip, researchers immediately began the arduous work of transcribing every dive audio tape, mapping the path of their dive, and reviewing video tapes. Morris was given the title "dive czarina" and charged with ensuring that all the divers completed detailed records of their observations as an absolute prerequisite for diving again. In addition to assisting the team, Morris was completing an independent-study thesis on Hess Deep dikes.

Each evening, scientists huddled around Alvin's rock-collection baskets and meticulously catalogued newly arrived samples before stowing them away in large white buckets. While each submarine dive costs around $16,000, the value of some of these hard-won samples is priceless. Klein and Stewart joined other "rock hounds" in sawing up the black-coated basaltic stones and examining their crystalline features with small magnifying hand lenses. Larger slabs were divided into smaller ones to be shared by other members of the Hess Deep crew.

The expedition ended in a flurry of last-minute transcribing, image analysis, logging of data, and cataloguing of samples. As their final duty, Klein assigned each member of Duke's entourage a white bucket full of the precious rocks to hand-carry with them when they checked their luggage on return flights from Manzanillo.

Once back at Duke, the scientists began what promises to be years of excruciatingly careful research on the rocks now stored in the Old Chemistry Building. Stewart sliced some of the samples thin enough to be examined using a microscope and ground others into powder for chemical analysis. Stewart and Klein will study the crystalline and atomic makeup of Hess Deep's rocks for clues on how new crust is forged and then altered by heat and ocean currents. Their analyses will also help structural geologists like Karson solve the mystery of dikes and lava channels of the East Pacific Rise.

Looking back on this most recent adventure, Karson pronounces it "far and away the most scientifically gratifying cruise I have ever been on, as well as the most harmonious, and, on a personal level, enjoyable. I've been waiting twenty years to do this project, for the technology to catch up to my vision of how to do geology on the sea floor."

The Hess Deep expedition was so successful in part because of perfect weather, an exceptional array of utterly reliable equipment, and the compatibility of the researchers, scientists and students alike, says Karson. But most importantly, the expedition yielded scientific findings that will do much to overturn prevailing scientific dogma, fueling dozens of scientific papers, graduate-student theses, and doctoral dissertations.

The massive array of images and data also confirmed that Karson and Hurst's observations on their 1990 dive of the "messy" geology of Hess Deep was the norm rather than the exception. "Our previous notion of what is typical and what is anomalous has been turned on its head," says Karson. Collectively, the Hess Deep observations suggest that crust made along the East Pacific Rise is violently rearranged as it rolls off the assembly line, he says.

Observations along the twenty-one-mile study area suggest that forces yet unknown regularly tilt the blocks of crust made on the Rise, producing fractures between them that make them slip like leaning books on a bookshelf. That movement could have caused the volcanic lava layer above the dikes to slip in the opposite direction, a tendency "we've seen beautifully displayed in the Argo images," he says. Because hot magma tends to rise vertically, the tilt of the dikes also suggests that whole blocks of crust rotated after dike formation, a hypothesis reinforced by the observed fracturing. The intersecting dikes hint that there may have been multiple eruptions between multiple rotations, all occurring before the crust ever left the mid-ocean ridge on the treadmill.

Morris: zeroing in on her thesis subject
Photo: Monte Basgall

"Everybody seemed to be the most excited about the mosaics we made using Argo," Emily Klein says. "This is a scale of observation that has never existed before on the ocean floor." For the first time, these photomontages allow scientists to see ocean bottom features at something approaching "the scale that geologists are used to working at," she says. "That's the scale of looking from a perspective as high as that of a several-story building."

As geochemists, both Klein and Stewart were also excited by the unprecedented opportunity to gather samples of rock created at different times in the last million years, which will allow them to compare the chemistry of one era with that of another. "Nobody in the world has samples like this from crust created in the East Pacific Rise," says Stewart. "Whatever we learn from this is going to be significant."

Basgall is senior science writer for Duke's Office of Research Communications. For more information, including dispatches written while the Hess Deep expedition was under way, see www.env.duke. edu/hessslide.html.

Share your comments

Have an account?

Sign in to comment

No Account?

Email the editor