What's Under Antarctica? Quake Waves Give First Look
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Researchers hard at work around a seismograph, an instrument in the orange box buried in a hole in the snow. Solar power runs the seismic station during the summer, and batteries keep it going during the long, dark winter months. CREDIT: Doug Wiens. |
Thanks to a technological explosion in the century since humans first set foot at the South Pole, Antarctic research is thriving.
Yet despite the incredible scientific advances, there are still gaping holes in some very basic knowledge about the frozen continent. Namely, what, exactly, is under all that ice.
It's not simply a question for idle speculation. Figuring out what's going on underneath the colossal Antarctic ice sheets is one important puzzle piece in better forecasting what is happening to the ice itself in a changing climate, some glaciologists say.
Scientists have used radar and other imaging technology to uncover some astounding finds under the East Antarctic Ice Sheet: A vast mountain range that rivals the Alps, and Lake Vostok, one of Earth's largest lakes.
But many scientists are trying to peer deeper still. They want to map the rock that lies many miles beneath the bottom of the ice sheet — in particular, the West Antarctic Ice Sheet. Sensors used to detect earthquakes are helping in that goal.
CREDIT: Mike Roberts.
Westside is the quest side
Researchers have wanted to essentially perform a CAT scan of West Antarctica's geological underpinnings to a depth of about 60 miles (100 kilometers), said seismologist Doug Wiens, a professor of Earth and planetary science at Washington University in St. Louis.
"There are certain qualities about Antarctica that make it particularly interesting," Wiens told OurAmazingPlanet.
By installing a network of seismographs — instruments that record the energy waves from faraway earthquakes — to map out the qualities of the rock deep below the surface, Wiens and a team of researchers hope to figure out "what effect the Earth has on the ice sheet." The project is called Polenet. [See images of the scientists at work in Antarctica.]
Seismograph data can help reveal how mushy the rocks are, and how heat is distributed throughout them — a big deal for understanding the network of mechanisms that govern changes in the ice sheet.
Because Antarctica has been covered with thick ice for many thousands of years, "the whole continent is pushed down," Wiens said. "If you melted all the ice off, it would move back up."
Charting how viscous the underlying mantle — the colossal rocky layer directly below the Earth's crust that, though rigid as steel, still "flows" — will help researchers figure out how fast different parts of the continent would rebound, he said.
"We think hot areas of the mantle will flow easier, so they'll pop up faster," Wiens explained. Cold areas, on the other hand, wouldn't flow so easily. "Sort of like molasses you've put in the freezer," he said. "It doesn't flow, so it won't pop up very fast."
The question of heat distribution and flow from the mantle to the crust is also an important one, he said.
There is compelling evidence that watery-bottomed glaciers flow faster — and scientists have observed a marked speed-up in many Antarctic glaciers in recent years. However, it's not clear what's driving the acceleration. Warming oceans are likely playing a big role. Geology might also be a factor.
"It might have a big effect on the ice sheet and might explain some observations," Wiens said. "If you have a large heat flow from the mantle in a given area, it may form water at the bottom of the ice sheet."
Finally, seismographs can reveal hidden sources of seismic activity — little earthquakes that could be the signatures of active volcanoes hidden under the ice. [Antarctica: Solving Geologic Mysteries]
CREDIT: Doug Wiens.
Success, at last
This year, for the first time ever, Wiens and his colleagues have the data in hand to actually fulfill this geological vision. Until recently, Antarctica's brutal conditions destroyed instruments after only a few months.
But improvements in batteries and data storage have allowed researchers to run a network of about 35 seismographs since 2007, enough time to get a decent picture of what is happening under the West Antarctic Ice Sheet.
This last field season, in late 2011, a team trekked across West Antarctica to retrieve seismographs that have been busily recording years' worth of data. Researchers are now poised to begin the long work of figuring out what it all means. In the end, the work will reveal long-held Antarctic secrets.
"It's really the first time we're able to look at the interior structure of the mantle," said Andrew Lloyd, a WSLU Ph.D. student who traveled hundreds of miles by snowmobile to help retrieve some of the seismographs — and the reams of data they recorded.
"It will enable us to say something really definitive about the tectonics and geology of the region, which is something nobody has been able to do before," Lloyd said.
Wiens said that the data are already revealing a tantalizing picture of what is going on beneath West Antarctica, a place that is, in the words of one scientist, "hemorrhaging ice."
"We do see these big variations in the temperature in the mantle across parts of Antarctica that will have a big effect on the ice sheet," Wiens said.
However, he added, many months of work lie ahead, and it will be some time before scientists are ready to announce to the world what lies beneath the ice.
This story was provided by OurAmazingPlanet, a sister site to LiveScience. Reach Andrea Mustain at amustain@techmedianetwork.com. Follow her on Twitter @AndreaMustain. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.
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