02/28/2003 08:00:00

Antarctic landmarks named afterCaltech experts on glacier ice flow

There aren't too many living individuals who can go to the mall and buy a globe with their name printed on it, but the California Institute of Technology just added two.

Barclay Kamb and Hermann Engelhardt, longtime researchers on the workings of the Antarctic ice streams, have been honored by the American Advisory Committee on Antarctic Names (ACAN) with the renaming of two features near the gigantic Ross Ice Shelf, a Texas-sized mass of floating ice. Hereafter, the feature informally called "ice stream C" will bear the formal name Kamb Ice Stream, and "ice ridge BC" will be formally named the Engelhardt Ice Ridge.

Kamb is the Rawn, Jr., Professor of Geology and Geophysics, Emeritus, at Caltech and is still active in attempting to understand the rapid flow of the Antarctic ice streams and its potential effects on the health of the great ice sheet that covers 98 percent of the Antarctic continent. If the ice sheet were to float rapidly outward into the circum-Antarctic Ocean and melt, the addition of the huge volume of meltwater to the oceans would raise the sea level and have a drastic impact on coastal cities throughout the world.

Engelhardt, a senior research associate in geophysics, emeritus, has collaborated with Kamb for years in the research. They have undertaken a number of expeditions to Antarctica to collect ice-stream data by drilling boreholes down through the ice to the bottom and sending down instruments such as temperature sensors, pressure gauges, ice corers, sediment corers, and borehole video. Previously, they had used these techniques to study surging ("galloping") glaciers in Alaska.

Actually, the news for the Caltech Division of Geological and Planetary Sciences is even better, because two of Kamb's former students were also honored with an Antarctic naming. Ice ridge CD has been formally named the Raymond Ice Ridge after Charlie Raymond, and ice stream F has been named the Echelmeyer Ice Stream after Keith Echelmeyer. Raymond, who earned his doctorate in 1969, is now on the University of Washington faculty; Echelmeyer, who finished his Ph.D. in 1983, is a faculty member at the University of Alaska at Fairbanks.

In announcing the namings on behalf of ACAN, glaciology professor Terry Hughes of the University of Maine said, jokingly, "It looks like Caltech made almost a clean sweep of the ice streams." . The ice streams in Antarctica move through the ice sheet somewhat like an ocean current, such as the Gulf Stream, moves through the ocean. Most of the ice sheet flows a few meters a year, but in those places where ice streams form, the flow of the ice is roughly a hundred times faster, approximately one meter per day. The ice streams are usually about 30 to 50 kilometers wide, 300 to 500 kilometers long, and 1 to 2 kilometers deep.

Why do they move so fast? "That's what we're trying to find out," says Kamb.

After 10 years of study, the researchers have demonstrated that the temperature at the base of the ice streams is at the melting point, whereas it is below freezing at the base of the ice sheet outside the ice streams. The ice streams' basal melting condition allows water pressure to build up under the ice, which tends to lift the ice mass above, and to weaken a layer of glacial sediment (clayey gravel called "till") that underlies the ice streams in a thickness of about one or two meters.

Both of these effects of pressure are capable of increasing flow of the ice streams, which are propelled downslope by gravity, with the soft, weak, till layer acting as a sort of basal "lubricant." The researchers believe that an increase in basal water pressure should result in a marked increase in ice-stream flow, but so far it has not been possible to observe and measure this expected effect in the actual ice streams.

It is believed that friction at the lateral shear margins and at bedrock humps under the ice (also called "sticky spots") prevent the velocity from getting out of control.

"The question is what will happen to the ice streams in the future," says Kamb. "Will they cause a big enough effect on the flow of the ice sheet to contribute appreciably to future sea-level rise? The big issue as to the future behavior of the Antarctic ice sheet is whether it will cause global sea level to rise."

To study the ice streams, Kamb and Engelhardt have made about a dozen National Science Foundation–funded expeditions during the Antarctic summer, in the period from late October to late January. Working in teams of about 13 or 14 people, including Caltech graduate students and support staff from the McMurdo base, the group drills a number of vertical holes, six inches in diameter to the bottom, at a depth of about 1,000 meters. Some of the holes are used to take core samples, while others are used to lower equipment like video cameras to study the character and distribution of till in the basal ice.

The instrumental work has to be completed within about three or four hours after borehole completion, because by that time, the borehole freeze-up process has already progressed to such an extent that the ice "grabs" the equipment still in the hole.

Neither Kamb nor Engelhardt anticipates going again to Antarctica for this particular project, though their studies continue. In fact, some of the equipment purposely left in the bore holes is still sending data.

Contact: Robert Tindol (626) 395-3631