Neal Iverson, associate professor of geology and atmospheric sciences
at Iowa State University, is leading a team of seven researchers to a
spot 700 feet under ice to get a first-hand look at how glaciers move
across rock and sediment and how they shape the landscape. They are the
only team that lives and works beneath a thick glacier to do their research.
The team that will be heading to Norway's Svartisen Subglacial Laboratory
includes Iverson; Denis Cohen, a research associate in geophysics at Yale
University; Tom Hooyer, an assistant professor at the Wisconsin Geological
Survey; Urs Fischer, a research professor at the Swiss Federal Institute
of Technology (ETH); Miriam Jackson, a research scientist at the Norwegian
Water Resources and Energy Administration; and graduate students Peter
Moore (Iowa State) and Marie Rousselot (ETH).
For three weeks (April 3-24), Iverson and his colleagues will live and
work beneath a 700-foot-thick river of ice. The laboratory is located
in a tunnel excavated in rock beneath the Svartisen Ice Cap. It contains
living quarters and equipment that allow sustained, direct study of glaciers
as they slip over substrates.
The tunnel was constructed in 1993 by the Norwegian state power company,
which collects the water from the glacier for hydropower. Inside the tunnel,
the temperature will be a constant 35 F, and humidity will be near 100
percent. The only opportunity to see the Sun will be a 30-minute walk
down the tunnel, once every couple of days.
"It's not a pleasant place to work," Iverson says. "But
it's a great natural lab to study glaciers and glacier motion in large-scale
experiments."
"We want to learn about the mechanics of what is going on at the
bottom of the glacier, where ice meets rock or sediment," Iverson
said.
Specifically, they want to find out what controls the glacier's speed,
how certain physical conditions at the ice/rock interface influence the
glacier's speed and how sediment is moved via glaciation. Previous studies
have shown that ice at the bottom of a glacier is softer and flows easier
than ice higher in the glacier, and that sediment beneath the ice may
shear and help glaciers move over their beds.
"Glaciers can move very rapidly," Iverson said. "Surging
glaciers can slip over their beds as fast as 50 meters per day, more than
half the length of a football field. We want to learn exactly how glaciers
slip over rock and sediment.
"Understanding how glaciers move, and what causes them sometimes
to greatly increase their speed, will ultimately lead to a better understanding
of how they impact Earth's climate. Glaciers not only respond to climate
change but also sometimes trigger it," he said.
Once at Svartisen, the researchers (working from the tunnel in rock under
the glacier) will melt a 10-foot-by-10-foot tunnel through the ice for
about 100 feet to a spot on the glacier bed where they worked last year.
At that spot is a bed-sized trough. They will fill the trough with sediment
and instruments for measuring stresses on the sediment and its deformation
beneath the ice.
They also will place instruments flush with the rock surface to measure
the friction between the ice and rock. The instruments (load cells, extensometers
and thermistors) will record the stresses on the rock, and the speed and
temperature of the ice as it slips across the glacier's bed.
While doing this they will need to continually "blast" away
at the ice, using hot water to cut and re-cut tunnels into the glacier.
Iverson said because of the extreme forces put on ice at these depths,
it acts like toothpaste and flows into any cavity it can find. As a result,
the tunnels melted at the bottom of the glacier disappear in as few as
two days.
With their instruments in place, the researchers will let the tunnels
fill back up with ice and then measure the stresses on the bed and rates
of glacier movement. Iverson said the research team will repeat the experiments
they did last year in an effort to reproduce the results.
To vary the range of physical conditions at the ice/rock interface, the
team will pump water into their heavily instrumented, sediment-filled
trough. This simulates the full range of water pressure expected to occur
in the pores of sediment beneath glaciers.
"We found that when water pressure is low, there is no shear deformation
of sediment and the ice moves slowly," Iverson said. "When water
pressure is medium high -- about 50 to 70 percent of the downward ice
pressure - sediment shears beneath the ice, which allows the ice to increase
its speed. When water pressure is really high, when it's more than about
70 percent of the downward ice pressure, the ice decouples from the sediment.
The ice floats on top, which can cause rapid movement of glaciers."
Iverson would like to see the results of the research applied to larger
ice masses, which feed water to the oceans and affect global climate.
He added that the team also would like their data to lead to better mathematical
models of glacier movement.
"During the ice ages, glaciers profoundly affected much of Earth's
climate and landscape," Iverson said. "A full understanding
of how modern glaciers move is required to determine how they've triggered
climate change and shaped landscapes. This includes the landscape of central
and northern Iowa, which was shaped by a glacier 14,000 years ago."
Iverson's research is funded by the National Science Foundation.
--Skip Derra
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