Professor And Student To Study Structure Of Ocean Crust -- From Way Under The Sea

March 04, 1999

CHAMPAIGN, Ill. -- On March 9, University of Illinois structural geologist Stephen Hurst will leave the land-locked plains of Central Illinois for a monthlong research cruise in the South Pacific. The trip will include numerous dives in Alvin, a submersible deep-sea vessel.

Funded by the National Science Foundation, the cruise is focused on investigating the structure and formation of the upper oceanic crust. The work will be done at depths of 2,300 to 3,800 meters below sea level at the Hess Deep Rift, which is about 500 miles west of the Galapagos Islands.

Hess Deep is a large crack in Earth's crust caused by sea-floor spreading, Hurst said. "What's happening is the relatively new crust being created at the East Pacific Rise spreading center is being cut into and rifted apart by the Galapagos spreading center. The result is a huge chasm nearly 4,500 meters deep."

Hess Deep is one of the few places on Earth where the oceanic crust is exposed this way -- cracked open like a split watermelon. This naturally occurring cross-section offers researchers an opportunity to examine how the crust is formed, and how it is deformed as it is pushed away from the spreading center.

"Diving at Hess Deep in Alvin is like spending a night in a blimp off the side of a cliff in a heavy thunderstorm," said Hurst, a veteran of eight Alvin dives, including one to Hess Deep in 1991. "It's truly an unforgettable experience."

Descending to the floor of Hess Deep takes nearly two hours. The researchers typically spend the time rechecking their equipment and reviewing procedures.

"You can't sit back and enjoy the view," Hurst said, "because there is no view. Sunlight doesn't penetrate the ocean much past the first 100 meters, so for nearly the entire ride down it's dark as night outside."

Although Alvin is equipped with powerful floodlights, they are rarely used during the descent in order to conserve battery power. The need to save power also makes it pretty dark inside the sub.

"There's a faint glow given off by various indicator lights, but that's about it," Hurst said. "So it's dark, it's quiet, and it's cold. At a depth of 4,000 meters, the water temperature is close to freezing, and the cold travels easily through the sub's metal hull."

At the bottom of their dive, the researchers will have about five hours to maneuver the sub, examine their surroundings, and pluck rock samples from the cliff face before the batteries run out, forcing a return to the surface.

"We anticipate completing 15 dives," Hurst said, "during which we will examine the structure of this piece of ocean crust in an attempt to better understand the processes of sea-floor spreading and rift formation."

Hurst is one of three principal investigators for the cruise; the other two researchers -- Jeff Karson and Emily Klein -- are from Duke University. Also aboard the surface-support vessel will be a scientific team of 13 specialists, technicians and students, including U. of I. undergraduate Anna Sutton of Oswego.

A sophomore geology major, Sutton will base her senior thesis -- for which she is currently enrolled -- on work she is to perform both during and after the cruise.

"On the cruise, I will work on processing images obtained with the side-scan sonar," Sutton said. "This sonar will be towed along the cliff face to identify interesting features for Alvin to investigate."

Sutton also will help prepare the rock samples for future petrological and geochemical analyses to determine their composition. After the trip, she will work on making mosaics of electronic images from both Alvin and Argo (a remotely operated camera sled) and prepare geologic maps of the site.

"I'm very excited about participating in the cruise, and about the possibility of diving in Alvin," Sutton said. "I know space is very limited -- the submersible only holds three people, one of which is the pilot -- but I hope I can go on at least one dive."

A certified scuba diver, Sutton is quite comfortable in the water. To test her stamina at being confined in a small space surrounded by inky blackness for several hours, however, she recently spent six hours exploring a cave.

"It didn't bother me at all," she said. "I'm not in the least bit claustrophobic."

Nevertheless, she admits to feeling a little nervous about having a mere 2 inches of titanium hull separating her from the crushing pressures found in the ocean depths. Hurst, however, has absolute confidence in the submersible and its experienced pilots.

"Because of the enormous pressures we will encounter, it's not uncommon to see Alvin's hull festooned with net bags full of Styrofoam cups and mannequin heads," he said. "The water pressure squeezes them down to a tiny fraction of their original size, making neat souvenirs of the dive."

University of Illinois at Urbana-Champaign

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