phrodeau
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The Mystery of the Disappearing Lakes
The new research proves a theory proposed by Alley and others. Scientists had been puzzled by the fact that the glaciers on Greenland seemed to be moving at an increasing speed (though at less than a tenth of a mile per year, the pace is glacial). The researchers already knew, from observations and calculations, that Greenland's ice is slowly shrinking simply from melting. That process is slow, however. "It would take a lot of centuries to melt the whole thing," says Alley. Yet if the glaciers also started sliding faster to the sea, the loss of ice could be more rapid.
In poring over satellite images, researchers noticed that large lakes form on the surface of the glaciers during the summer. Those lakes then suddenly disappear. "We see these things come and go," says Sarah Das, glaciologist at the Woods Hole Oceanographic Institution in Woods Hole, Mass. One possibility was the lakes simply drain into rivers on the surface. Or, scientists theorized, the water might generate enough pressure to crack the 3,000-foot-thick ice all the way to bedrock, pouring down through the ice.
A team led by Das and Ian Joughin of the University of Washington set out to prove which idea was correct. They flew to an area of glaciers with lakes, and set up camp on the ice. Then they installed an array of instruments. They put sensors in a lake 2½ miles wide to measure the changes in the amount of water it held. They deployed seismometers to detect rumbles in the ice, and put global-positioning units on the ice to chart its movement. They left the instruments in place when they left the study area, and waited.
Ice Disappearing Faster Than We Thought
It wasn't a long wait. "The lake drained about 10 days after we were there," Das says. When they went back, gathered up the instruments, and began to look at the data, it was clear that the crack theory was correct. The water had indeed rushed down to the bedrock. It had spread out under the ice, and raised the huge ice sheet by more than three feet. But there was a also a surprise: It happened in a relative flash. "The entire lake drained in about two hours," says Das. "It was a much more catastrophic drainage than we expected." The volume of water flowing down to bedrock matched the torrent over Niagara Falls. That realization led the team to ditch plans to explore other, still-intact lakes aboard a rubber boat. "We decided we'd leave the boat in its crate," laughs Das.
The data also showed that as the water flowed underneath it, the glacier did indeed speed up, doubling its velocity. That doesn't mean Greenland's ice is about to fall into the sea, since the glaciers move pretty slowly to begin with. But it does mean that the ice will disappear faster than just from melting alone, cutting the time from thousands of years to hundreds.
The Mystery of the Disappearing Lakes
The new research proves a theory proposed by Alley and others. Scientists had been puzzled by the fact that the glaciers on Greenland seemed to be moving at an increasing speed (though at less than a tenth of a mile per year, the pace is glacial). The researchers already knew, from observations and calculations, that Greenland's ice is slowly shrinking simply from melting. That process is slow, however. "It would take a lot of centuries to melt the whole thing," says Alley. Yet if the glaciers also started sliding faster to the sea, the loss of ice could be more rapid.
In poring over satellite images, researchers noticed that large lakes form on the surface of the glaciers during the summer. Those lakes then suddenly disappear. "We see these things come and go," says Sarah Das, glaciologist at the Woods Hole Oceanographic Institution in Woods Hole, Mass. One possibility was the lakes simply drain into rivers on the surface. Or, scientists theorized, the water might generate enough pressure to crack the 3,000-foot-thick ice all the way to bedrock, pouring down through the ice.
A team led by Das and Ian Joughin of the University of Washington set out to prove which idea was correct. They flew to an area of glaciers with lakes, and set up camp on the ice. Then they installed an array of instruments. They put sensors in a lake 2½ miles wide to measure the changes in the amount of water it held. They deployed seismometers to detect rumbles in the ice, and put global-positioning units on the ice to chart its movement. They left the instruments in place when they left the study area, and waited.
Ice Disappearing Faster Than We Thought
It wasn't a long wait. "The lake drained about 10 days after we were there," Das says. When they went back, gathered up the instruments, and began to look at the data, it was clear that the crack theory was correct. The water had indeed rushed down to the bedrock. It had spread out under the ice, and raised the huge ice sheet by more than three feet. But there was a also a surprise: It happened in a relative flash. "The entire lake drained in about two hours," says Das. "It was a much more catastrophic drainage than we expected." The volume of water flowing down to bedrock matched the torrent over Niagara Falls. That realization led the team to ditch plans to explore other, still-intact lakes aboard a rubber boat. "We decided we'd leave the boat in its crate," laughs Das.
The data also showed that as the water flowed underneath it, the glacier did indeed speed up, doubling its velocity. That doesn't mean Greenland's ice is about to fall into the sea, since the glaciers move pretty slowly to begin with. But it does mean that the ice will disappear faster than just from melting alone, cutting the time from thousands of years to hundreds.
