A Season in Antarctica

Most people think of Antarctica as an endless frozen waste, windblown and flat as a tabletop. Vast it is, and 98 percent ice, but the near-mythic "southern land," with an area larger than Australia, isn't exactly featureless. Mountain ranges, including a few active volcanoes, dot its topography. One of these ranges, the Transantarctic, splits the continent into east and west, its rugged peaks in places topping 14,000 feet. It's an upwelling on the order of the Rockies.

Barne glacier, Ross Island. The dark shapes in mid-frame are seals.
Don Voigt

Barne glacier, Ross Island. The dark shapes in mid-frame are seals.

Therein lies what Penn State geophysicist Andy Nyblade calls "a geologic puzzle." The Transantarctic, Nyblade explains, is "the only major mountain range we know of that was not formed by a collision of tectonic plates."

What, then, caused it? That's one of the questions behind the Transantarctic Mountains Seismic Experiment, or TAMSEIS, a study being led by Nyblade and colleagues Sridhar Anandakrishnan of Penn State and Doug Wiens of Washington University in St. Louis. Here's another: Why does the east Antarctic plateau, a land mass larger than the continental U.S., sit so high above sea level?

"Actually, the rock is just about at sea level," says Anandakrishnan. "But if you removed all the ice, it would bob up to about a kilometer, compared to about 300 meters for most of North America. It isn't clear why Antarctica should be so high."

To answer these questions, researchers need to know what's going on under the surface, in the crust and upper mantle. And the best way to do that—the only way, in a place where the surface lies under hundreds, sometimes thousands, of meters of ice—is to measure the waves from earthquakes. Seismic waves spread like pond ripples from the point of an earthquake's origin. They race or tarry according to the density of what they pass through: Cold, dense rock makes a fast course, while warmer, less-dense stuff slows them down. So, by staking out seismometers—sensitive recorders of the slightest surface vibration—and accurately measuring the time it takes waves to travel between them, Nyblade says, "we can construct an image of what's under the surface. The mathematics is similar to what's used to make a CAT scan."

A reliable image requires a lot of measurements and a good-sized network of seismometers. Setting up such a network was the first phase of the TAMSEIS experiment. Over eight weeks at the end of last year, Nyblade, Anandakrishnan, Wiens and their team installed 42 seismometers, each equipped with a small computer and hard drive for recording data, and a rig of solar panels for power. Starting with a dense array in the vicinity of McMurdo Station (hub of the U.S. Antarctic program), they went on to establish a 1,400 kilometer chain of instruments across the vast east Antarctic plateau.

With these arrays, they hope to record data from 200 to 300 earthquakes, which should be enough, once the numbers are crunched, to construct an accurate picture of the geology under the Transantarctic range. Then they'll compare that picture against current hypotheses about Antarctica's interior. One leading idea, Nyblade says, posits that the mantle beneath this area is "warmer than normal, and this heat helped the mountains to rise by making the rocks less dense, and more buoyant." Excess heat could also account for the eastern plateau's elevation, Anandakrishnan says. "Warm air rises—and so does warm rock." If this hypothesis is accurate, Nyblade says, "seismic waves should travel through these rocks relatively slowly."

Barne glacier, Ross Island. The dark shapes in mid-frame are seals.
Don Voigt

Looking south from Diamond Hill, along the shore of the Ross Ice Shelf.

He and his colleagues won't begin to know if that's the case until November, when they go back to Antarctica to retrieve the hard drives with their first year's data. They can only hope that collecting goes as smoothly as deployment did. "We were very lucky with the weather," Nyblade says. "There were only two days when we couldn't fly."

The weather was fine, but even so. . . . For the toughest part of the trip, team members spent two weeks at a remote camp on the plateau, where 12,000 feet of altitude and 20-knot winds combined with daytime highs of minus 25 degrees Celsius. To give a feel for what it's like to work under such conditions, team member John Pollack, a freelance journalist, filed the following series of reports from the ice.

Last Updated September 09, 2013