An Undersea Yellowstone?

A group of scientists trolling the depths of the North Atlantic to study an undersea mountain range has unexpectedly discovered the largest hydrothermal vent system ever seen, with structures so tall and dramatic, they have been dubbed “The Lost City.”

“If this vent field was on land, it would be a national park,” said Jeff Karson, a Duke University geologist who got the first close-up view of the towers last week while diving in the submersible Alvin.

Hydrothermal vents are ocean floor fissures that spew superheated, acidic water and support luxuriant colonies of undersea life at great depths. Most such structures are less than 80 feet tall and many appear to be mounds. The tallest vent previously found was a 135-foot monster vent dubbed “Godzilla,” 200 miles off the western coast of Canada, that was discovered in 1991.

“We thought the altimeter was broken. We could not believe something was that tall,” said Veronique Robigou, co-discoverer of that vent and a marine geologist at the University of Washington. Godzilla has since toppled to half its original height, and Robigou, happy to see the height record broken, said of the new finding: “Every time we think we understand the system, something else comes up and forces us to rethink everything we know.”

The new vents tower more than 180 feet above the sea floor, making typical vents “look like a dollhouse in comparison,” the scientists said Tuesday, when they announced their findings. Some of the cones in the structure were clearly active, they said, spewing hot water that appeared to shimmer.

The dramatic field of hot springs is composed of numerous towering vents with multiple spires, some wide-mouthed, others needle thin. Many are capped with feathery deposits of minerals that precipitated from fluids flowing through the vents. The sides of the vents are covered with delicate white mineral ledges intertwined with stalagmites. The site, researchers said, was awesome.

“The best way I can describe my feelings are how I felt the first time I walked into a redwood grove with a group of friends or visited the Grand Canyon at sunrise,” said Debbie Kelley, a University of Washington expert on hydrothermal vents who was the only other person to dive to the structures. “There is something that happens in places like this--quiet, odd feelings mixed with awe and excitement that stay with you for a long time.”

The scientific team first spied the vents Dec. 4, using Argo II, a vehicle with cameras to explore the ocean bottom. They then scrambled to reorganize so they could study the vents.

“It was immediately obvious to me that this was a major discovery and that my plans of just minutes prior had to be scrapped,” said Donna Blackman, a geophysicist at the Scripps Institution of Oceanography, who is the expedition’s chief scientist.

The next day, two members of the team dove directly to the vent aboard the deep sea submersible Alvin. All the vehicles were aboard the research vessel Atlantis, a 274-foot craft run by the Woods Hole Oceanographic Institution.

Long Filaments of Microbes Wave in the Water Like Kelp

The new vents are unique because--unlike others--they are not formed from iron, zinc and copper-rich sulfides spewed from undersea hot springs in young volcanic rock. Instead, they are made of carbonate and silica--which may have come originally from the Earth’s mantle--and may be the kind of vents that grew during the planet’s formation.

One hundred and sixty-degree water trapped within the complex architecture supports long filaments of microbes that wave in the water like kelp. Mysteriously, the vents are devoid of the large communities of animals--shrimp, mussels and spectacular feet-long tube worms--that crowd other hydrothermal vent environments. The structures contain some still-unidentified worm and anemone-like creatures, which will be studied later.

The team is studying an area on the mid-Atlantic ridge at about the same latitude as Houston--30 degrees North. They are looking at a wrinkled, hilly underwater landscape where the sea floor is spreading apart and forming new crust.

The unusual vents rest, not in a newly formed area, but on million-year-old ocean crust, and not near obvious heat sources like volcanoes. They may be an oceanic analogy to Yellowstone’s hot springs, caused by a volcanic “hot spot.”

The team was in the area to explore a 12,000-foot undersea peak called the Atlantis Massif, which Blackman helped discover in 1996. She returned to determine how the mountain is being formed from the Earth’s crust and whether or not the process is similar to mountain building in California and Nevada’s Basin and Range region, which also lies over an area of tectonic plate-spreading. The expedition is especially challenging because the mountain’s summit lies 3,000 feet below the ocean’s surface.

Blackman is specifically interested in the bottom of the young mountain, where landslides and faults have exposed crystallized rocks normally buried far beneath the sea floor. The vents, she now suspects, may play a role in the evolution of the mountain.

The team obtained samples of the rocks that make up the ledges for further study. Aboard the ship, the team could only conduct “primitive tests”--dipping chips of rock into acid to see if they fizzed, as carbonate rocks do, or sniffing rocks for unusual odors, said Gretchen Frueh-Green, a Swiss expedition member and expert on rock chemistry.

The unexpected finding of the vents-- like that of the undersea mountain and the shorter Godzilla vent--were completely unexpected, showing “how little we know about the ocean,” said team member Joe Cann. Now that the discovery has been made, the team vows to go back for more.

“There is much left to explore in this field and much more to learn,” Kelley said. “One Alvin dive is only a tease for us.”

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The expedition’s Web site is at: https://earthguide.ucsd.edu/mar/index.html.

Usha McFarling can be reached at usha.mcfarling@latimes.com.