Two hundred years of glacial shrinkage in Alaska, and then came the winter and summer of 2007-2008.

Unusually large amounts of winter snow were followed by unusually chill temperatures in June, July and August.

"In mid-June, I was surprised to see snow still at sea level in Prince William Sound," said U.S. Geological Survey glaciologist Bruce Molnia. "On the Juneau Icefield, there was still 20 feet of new snow on the surface of the Taku Glacier in late July. At Bering Glacier, a landslide I am studying, located at about 1,500 feet elevation, did not become snow free until early August.

"In general, the weather this summer was the worst I have seen in at least 20 years."

Never before in the history of a research project dating back to 1946 had the Juneau Icefield witnessed the kind of snow buildup that came this year. It was similar on a lot of other glaciers too.

"It's been a long time on most glaciers where they've actually had positive mass balance," Molnia said.

That's the way a scientist says the glaciers got thicker in the middle.

Mass balance is the difference between how much snow falls every winter and how much snow fades away each summer. For most Alaska glaciers, the summer snow loss has for decades exceeded the winter snowfall.

The result has put the state's glaciers on a long-term diet. Every year they lose the snow of the previous winter plus some of the snow from years before. And so they steadily shrink.

Since Alaska's glacial maximum back in the 1700s, Molnia said, "I figure that we've lost about 15 percent of the total area."

What might be the most notable long-term shrinkage has occurred at Glacier Bay, now the site of a national park in Southeast Alaska. When the first Russian explorers arrived in Alaska in the 1740s, there was no Glacier Bay. There was simply a wall of ice across the north side of Icy Strait.

That ice retreated to form a bay and what is now known as the Muir Glacier. And from the 1800s until now, the Muir Glacier just kept retreating and retreating and retreating. It is now back 57 miles from the entrance to the bay, said Tom Vandenberg, chief interpretative ranger at Glacier Bay.

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