Some of these tunnels provide access to the base of the glacier, offering scientists the unique opportunity to observe a glacier from below. Elsewhere scientists drill out ice cores thousands of feet deep—but can't see what's happening below the glacier.
Rivers of Ice
One area of the team's research has focused on glacier movement, studies of which were first conducted in the Alps during the 1800s. Fast-moving glaciers, like some in Alaska, can slide 150 feet (about 50 meters) a day, threatening villages or oil pipelines in their path—and marching rapidly toward the sea.
The team blasted ten-by-ten-foot (three-by-three-meter) temporary tunnels into the brilliant blue ice with a warm-water "drill." Then they placed various instruments underneath 700 feet (200 meters) of glacial ice: a friction-measuring device, a thermometer to gauge heat coming from bedrock, an instrument to measure glacier speed, and gauges to measure the weight of the overlying ice and the water pressure where rock and ice meet.
The scientists had to work quickly. Glacial ice behaves like a viscous fluid, so the walls quickly closed in. "The ice acts like toothpaste," Iverson said. "If you quit melting back these tunnels, it would take only a few days to be swallowed up."
Putting the Brakes on Glaciers
Iverson wants to know what puts the brakes on glaciers. "Why don't they catastrophically slide down a mountain, like an ice cube on a inclined sheet of glass?" he asked.
The idea has been that bumps in the bedrock hold glaciers back, explained Thomas Hooyer, a glacial geologist at the Wisconsin Geological and Natural History Survey and part of Iverson's team.
But from their unique worm's-eye view, the scientists discovered another force at work: friction.
What they discovered was that the debris in the "dirty" ice at the glacier's base acts much like sandpaper to slow the huge masses of ice—and the amount of friction is up to 20 times greater than was previously thought.
"What we learned was that friction between the debris in the ice and underlying bedrock was the dominant factor holding ice back—which will have to be factored into efforts to predict glacier movements," Iverson said.
Some glaciers sit on bedrock, like Svartisen, but others—including the faster-moving Antarctic glaciers—rest atop gritty sediment called till that is usually saturated with water that is under high pressure. One idea is that these "soft bedded" glaciers move by shearing the sediment away.
To test this idea, the team also blasted a hole in the rock bed and filled it with sediment. Various instruments were placed in the sediment to measure movement, water pressure, and the weight of the overlying ice and sediment.
Warming
Since the industrial revolution, concentrations of greenhouse gases in Earth's atmosphere have skyrocketed. Carbon dioxide has increased by 30 percent, methane has doubled, and nitrous oxide has risen by 15 percent. The United States, with 5 percent of the world's population, emits about a quarter of the world's greenhouse gases.
When ancient polar ice samples were compared with newly frozen ice, researchers discovered that carbon dioxide concentrations in the atmosphere are now higher than any time in the last 400,000 years, according to Theodore Scambos, a glaciologist at the National Snow and Ice Data Center at the University of Colorado.
These atmospheric changes will continue to affect glaciers. "We know that with a warming climate, glaciers are ultimately going to recede on a longer time scale—like a century—but we also need to know how they'll behave on a yearly or decadal scale," Hooyer said. "Glaciers are pretty sensitive to climate change."
That's because each summer, meltwater on the surface flows thousands of feet down through cracks and holes. Pressure builds and the water lubricates the ice, so it slides more quickly over the bedrock underneath.
Iverson says that, in principle, more summer melt could also make glaciers more unstable.
Predicting the Future
"We're getting nervous about the long-term health of the ice sheets, Alley said. "There's worries about both poles. We're not yet hitting the panic button, but we want to allow people to make wise decisions."
Those decisions could include the construction of seawalls or adaptive coastal zoning to protect from flooding.
But scientists don't yet know enough about ice sheets to make accurate predictions. "We are reasonably confident that we can do a better job than we are now of predicting the future," Alley said.
Iverson sees glaciers as one of the forces changing world weather. He mentioned the fast-moving Laurentide Ice Sheet as an example.
About 14,000 years ago, it ripped through the U.S. Midwest before retreating northward. It changed the amount of fresh water in the ocean and disrupted the flow of rivers: Many drained into the Gulf of Mexico instead of the North Atlantic.
"I'm sure that had a huge affect on global heat in the atmosphere," he said. "Glaciers don't just respond to changes in climate. They also cause it."
For more global warming news, scroll down.
|
SOURCES AND RELATED WEB SITES
|
