Iceberg Menace in Alaska

"Growlers"and "bergy bits"threaten oil traffic

Now that the trouble-plagued trans-Alaska pipeline is in full operation, Alaskan oil is flowing in great volume overland. But its journey to U.S. West Coast ports may soon be interrupted at sea --by icebergs in the tanker shipping lanes. The source of these floating hazards is the Columbia Glacier, a 425-sq.-mi. mass of ice that ends less than seven miles from the tanker lanes for Port Valdez.

The 40-mile-long glacier originates high in a watershed east of Valdez, where it is fed by massive snowfalls. From there, it flows inexorably down toward Columbia Bay, where it terminates on a shoal across the fjord in shallow water. Like all glaciers that end at the sea, Columbia continually "calves" or drops chunks of ice off its face as it moves forward. This process can speed up dramatically when changing climatic conditions cause a glacier to begin thinning out. This decrease in thickness can destroy a glacier's delicate equilibrium and radically increase calving in a process called "drastic retreat" that may last for decades.

Columbia is the only calving glacier in western North America not to have experienced a drastic retreat in several thousand years. But ominous signs of instability have been reported by a U.S. Geological Survey team. Upstream from its face, the glacier has thinned by more than 30 ft. in one year, and since 1974, there have been periods of accelerated calving every summer. Says U.S.G.S. Glaciology Project Chief Mark Meier: "This suggests that there is not enough ice coming forward to keep up with the iceberg calving."

As a result, the glacier's front end could shrink back off the shoal into the deeper water upstream. Its new face, extending to the bottom of the fjord, would then be three or more times the height of the old, and quite unstable. Calving could accelerate five to 50 times its current rate. As much as a cubic mile of ice might be dumped into the bay each year for the next 30 to 50 years, until the glacier retreats to a new and stable foothold.

Driven by winds and currents, enough of these icebergs could drift southeastward into Prince William Sound and the waterways now used by supertankers ferrying oil south to virtually halt traffic. Explains Coast Guard Captain Ronald Kollmeyer: "When you have literally thousands of icebergs in the shipping lanes, you can't drive an 800-to 900-ft. tanker through that sort of gauntlet." Last August, the glacier's calving increased enough to force closing of the Valdez lanes to night traffic for nearly a week.

To avoid more serious shutdowns if the glacier retreats, the Coast Guard has been considering a number of alternatives. One proposal, to build a powerful radar station near Valdez to monitor icebergs, would require large amounts of money before geologists can confirm that the glacier is indeed retreating. Also, most icebergs calved by Columbia Glacier are "growlers" (20-ft.-wide slabs of ice that rise less than four feet above the water line) and somewhat larger "bergy bits" that are not easily picked up by radar. Another idea is to tow bergs out of the shipping lanes. But both solutions would be impractical if thousands of icebergs moved into the lanes.

What appears to be the most promising solution may also be the simplest: a cable of thick nylon strands would be strung across a 3.1-mile-wide passage near the glacier to block outbound icebergs. Similar barriers already help keep Greenland harbors free of drifting bergs. A feasibility study directed by Kollmeyer concluded that 20 men could put the cable in place within 40 days after the glacier's retreat is confirmed. Estimated cost: $31.1 million. Declares Don Ryan, a marine safety specialist for the Coast Guard: "So far, no one has suggested that our study is wrong or that the barrier approach won't hold water." Or ice.

While the Coast Guard watches Alaska's "growlers," British scientists are tracking something bigger: a 768-sq.-mi. Antarctic iceberg adrift in the South Atlantic and heading slowly for Africa. But the penguin-inhabited berg, 36 times the size of Bermuda, poses no threat to shipping; it should break up and melt as it hits warmer waters.

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