Columbia Glacier: the retreat is real Essay

A year ago geologists at the U.S. Geological Survey (USGS) announced that the Columbia Glacier in Alaska appeared to be in the initital throes of a dramatic and rapid retreat (SN: 1/21/84, p. 36). In a report released last week, the USGS researchers say they are now absolutely certain that their earlier correct. “Drastic retreat is now evident in all aspects of the glacier flow,” says Mark Meier of USGS in Tacoma, Wash.

During the last year, the glacier shrunk 1,100 meters, almost twice the amount of retreat recorded the previous year. Meier’s group reports that the average rate at which icebergs splintered off from the sea-side end of Columbia increased from 3 cubic kilometers per year (km.sup.3.

/yr) in the second half of 1983 to 4 km.sup.3./yr during the first nine months of 1984. This rate is four times greater than that measured at the end of 1977 and is expected to rise even more in 1985. While the glacier flow — the downslope movement of the ice toward the sea — has also increased, it has not been enough to keep pace with the break-up and expulsion of icebergs.

So the disingegration of Columbia, the last of Alaska’s 52 tidewater glacier, is clearly under way. The glacier retreat is generally following the numerical models developed five years ago. But Meier says that the onset of dissolution is latter than expected and the speed of glacier flow is greater than predicted. Another surprise was that, for several months last winter and spring, a tongue of ice still attached to the glacier at its sea-side end seemed to float. In all previous observations, icebergs separated from Columbia (which is thought to extend all the way down to the bottom of its valley) before sections of the thinning glacier could float. The 1984 measurements bolster USGS’s earlier prediction that the 64-km-long glacier will retreat 32 to 40 km upstream over the next few decades. When this happens, says Meier, the map of Alaska will be very different.

The retreat of Columbia will unveil a fjord longer and deeper than the nearby port of Valdez. Seawater will invade and mix with the freshwater and sediments from the glacier. “As the fjord lengthens, its biota [plant and animal life] will evolve along with the physical structure of the water,” says Meier. “No one’s been able to study this sort of thing before..

.. This grand field experiment has enormous potential in oceanography and ecology in addition to all the glaciological implications.”


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