Alaska Glacier ‘Gallops’ Toward Sea : Geology: Cushion of water beneath the ice slicks the way for the mass to flow faster.

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.

“We don’t know what’s going to happen,” said Edward Bovy with the Bureau of Land Management in Anchorage. Meanwhile, the Coast Guard is keeping the glacier under surveillance; recently, the glacier generated one iceberg that measured up to a half-mile wide.

Scientists say galloping glaciers, like the Bering one, 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, about 75 miles southeast of Cordova, 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 145-mile-long glacier has nearly reached the point of its farthest advance in historical times, the BLM said. That last big move came in 1902; other advances were recorded at intervals of 20 or 25 years.

The Bering is roughly 30 miles wide; its largest lobe is 126 miles long. The flow extends from the Bagley Ice Field in Canada and runs through Wrangell-St. Elias National Park.

An underwater trough shows that in earlier geologic eras, the Bering was a tidewater glacier. Now it could reach the ocean again.

Glaciers move faster over water than over land. The Bering is now advancing on Vitus Lake, which used to be a body of water 15 miles wide and about 7 miles long.

The lake, once a popular recreation destination, is nearly covered by glacier. “When it hits land, it will ride up on those forelands, and it may pause,” Bovy said. Or maybe not.

The forelands are composed of the earth and rock churned by the glacier which separate it from the Gulf of Alaska.

Last summer, the Bering made a major advance but paused in September. A major blowout released tons of muddy water from beneath the glacier, allowing it to settle on solid ground.

“The mechanism is fairly well known--it’s bad plumbing,” said University of Alaska Fairbanks physics professor Will Harrison.

“Lots of water goes into the glacier, especially at this time of year,” said Harrison, who studies glaciers at the university’s Geophysical Institute. If the water is trapped under the glacier, ice will float and move downhill much more freely.

“This ice is squeezable stuff, like honey,” Harrison said. As it advances, the glacier also may pick up speed.

Harrison is among scientists studying surges at Variegated Glacier, a small but active river of ice near the coastal town of Yakutat. The Variegated recently advanced more than one-half mile--a major move for a glacier only about 10 miles long, Harrison said.

Surges in glaciers cause tremendous stress far from the face. Last year, scientists found evidence that the Bering Glacier had pulled away from its headwalls 100 miles “upstream.”

In some areas, the glacier dropped four to six feet against the headwall. Fractures and crevasses in the glacier have made it impossible to land on the Bering, scientists say.

Bruce Molnia, who directs a U.S. Geological Survey study of the Bering, said the glacier was moving at the rate of two feet a day or less before it started surging last year.

It accelerated to an average of 100 feet a day, with occasional bursts of 300 feet a day. During its peak, an estimated 30 million tons of ice calved from the glacier each day.

Molnia set up a USGS camp near the glacier last year and planned to be there again this summer. The Bering also is monitored by satellite.

Effects of the glacier’s surge on wildlife aren’t clear. Ice dams could back up water and cause flooding that could mar salmon streams in the Yakataga State Game Refuge, just east of the glacier’s face.

Similar flooding occurred last year when nearby Berg Lake broke through an ice dam formed by the Bering and water roared down to the ocean, leaving house-size icebergs where a 270-foot-deep lake had been.

Experts are concerned for the region’s flourishing bird populations.

About 10% of the world’s trumpeter swans nest on the margins of the Bering Glacier. Areas now covered by ice once attracted roughly 8% of the world’s population of dusky Canada geese, which number about 7,000 birds.

The geese have moved to forelands, but scientists say the area could be overrun by moving ice.