Bering Glacier, the continent's largest, has slid to within 1-1/2 miles of the Gulf of Alaska, raising concerns about ice-covered habitat and icebergs in oil-tanker shipping lanes.
Scientists say galloping glaciers, such as the Bering, are a result of ''bad plumbing,'' when a cushion of water builds beneath the ice and slicks the way for glaciers to flow faster. In glacial terms, that can mean 100 yards a day.
The Bering Glacier, which runs from the Bagley Ice Field in Canada through Wrangell-St. Elias National Park, advanced about six miles last year before stopping. This year, it has moved as much as four miles in some places since early May. The 30-mile-wide, 145-mile-long glacier has nearly reached the point of its farthest advance in history, the Bureau of Land Management says.
Bruce Molnia, who directs a US Geological Survey study of the Bering, says the glacier was moving two feet a day or less before it started surging last year. During its peak, 30 million tons of ice calved from the glacier each day.
Effects of the glacier's surge on wildlife aren't clear. Ice dams could cause flooding that could mar salmon streams. The region's flourishing bird populations may also be affected. About 10 percent of the world's trumpeter swans nest on the margins of the Bering Glacier.