Exploring an Underwater Mountain
Nov. 15, 2000 -- The research vessel Atlantis pulled out of the port of St. George in Bermuda recently and headed off to sea in search of a mountain.
Scientists from eight universities will spend a month aboard the ship, based at the Woods Hole Oceanographic Institution, in Woods Hole, Mass., searching for clues to a mystery. Their basic question: Why has a towering mountain risen from the ridges and hills along a fascinating geological structure called the Mid-Atlantic Ridge?
Far beneath the surface of the ocean, 12,000-foot Atlantis Massif is nearly twice as tall as other mountains in the area, and no one is certain why.
During the expedition, scientists will study the mountain with cameras and sonar, and take turns spending two weeks aboard the titanium-hulled submarine Alvin, snapping pictures and collecting rocks for analysis back in their labs. And the rest of us have been invited to go along for the ride.
Reports from the expedition will be published twice a week on the group’s Web site, and questions can be e-mailed to the scientists through their spokesman, Monte Basgall.
“We pulled out Saturday from St. George, Bermuda’s quaint first capitol, which is almost four centuries old,” Basgall tells me by e-mail. The ship set out on a “perfect morning,” he adds, and within moments the scientists had turned to the task at hand.
Young, But High Mountain
The Mid-Atlantic Ridge has long fascinated scientists because it is one of the regions on the Earth — all located under seas — where new crust is being formed. As the tectonic plates pull apart at the ridge, hot rocks from below to rise to the surface and cool into slabs of stone. Many centuries from now, the forces of nature will use some of those rocks to build new mountains along the shorelines, constantly reforming the planet we call home.
The ridge itself is enormous, winding south from Iceland for more than 6,000 miles, and it is one of the largest mountain ranges on Earth. But it is completely under water, usually at least 12,000 feet, except for the few areas where mountains poke through the surface. However, most of the mountains along the twisted, gnarled ridge are relatively modest.
That’s why Donna Blackman of the Scripps Institution of Oceanography in La Jolla, Calif., was so surprised when she and Joe Cann of the University of Leeds in the United Kingdom discovered Atlantis Massif while mapping the ridge a few years ago.
Mountains are common at mid-ocean ridges, but this one is a dandy. It is four to six times wider than other mountains in the area, known as abyssal hills, and it towers over its neighbors like, well, a mountain.
But since it is part of the ridge structure, it must be very young, geologically speaking, because it was formed from new crust welling up through the fissures along the ridge, which is also called a spreading center. Blackman wanted to know how it got there, and why it was so huge. By most reckoning, it should be a lot more puny.
She’s the chief scientist on the expedition. Co-principal investigators are Deborah Kelly of the University of Washington, an expert on the interaction of fluids with oceanic rock, and Jeffrey Karson, a structural geologist at Duke University.
Karson likens the ridge to a “taffy pull.” As the sea floor pulls apart, it becomes thinner, allowing molten rock to push through.
“Happening over and over again, that process produces new oceanic crust, and over geological times it re-paves the ocean basins repeatedly,” he says.
It is a key part of the renewal process that this planet has been going through since shortly after it was formed.
Stretching and Breaking
While no one knows why Atlantis Massif is so big, theories abound.
Some scientists believe the Mid-Atlantic Ridge may be quite similar to the Southwest part of the United States, where new mountains are formed as the ground is slowly stretched apart in response to tectonic forces along the Pacific seaboard. Huge chunks of rock slowly tilt as the crust is thinned, forming the Basin and Range Province and other major mountain ranges.
It is similar to pulling an art gum eraser apart. The eraser gets thinner in the middle and forms deep cracks before it breaks. When that happens in the Earth’s crust, chunks of the “eraser” tilt, lifting one edge up and depressing the opposite side in a classic mountain-building scenario.
Compounding the mystery, however, is the fact that earlier researchers found little evidence of lava, the normal stuff used to build the rocks that form the mountains, so there may be some sort of additional geochemical process going on as well.
Exploring by Sonar, Cameras and Alvin
To try to get the answers, the scientists will drag some sophisticated devices through the water as the ship passes over the mountain. A side-scan sonar that uses sound waves to create images, much the same as a camera uses light waves, will map the entire area. Then they will send a camera down to capture pictures of the mountain.
And finally, they will take turns going down in Alvin, the historic submersible that has probed so many of the world’s oceans. Two scientists and a pilot will be aboard the craft, which can dive down to 14,764 feet and stay there for eight hours.
They will use their eyeballs as research tools, gazing through the 3 1/2-inch thick windows at the steep slopes of Atlantis Massif. Alvin also has two robotic arms that will break off pieces of the mountain and bring them home.
When it’s all over, we should have a better understanding of why Atlantis Massif is so big, and how the forces of nature go about constantly rebuilding our planet.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.