ANCHORAGE - Most of Alaska's glaciers have been shrinking in a meltdown that began at least two centuries ago and appears to be accelerating, according to a new comprehensive study that drew on thousands of historical and scientific sources.
After analyzing more than 2,000 glaciers in 11 mountain ranges and three archipelagos - including 780 glaciers that have names - federal glaciologist Bruce Molnia found that only about a dozen of the large, named glaciers have advanced during the past few years.
"We just know that glaciers are continuing to shrink, and they seem to be shrinking at a more rapid rate," Molnia said. "From Anchorage to Valdez, you don't see anything that's showing signs of advance. Retreat is the rule rather than the exception."
One piece of evidence is the receding glacial tongues in the Chugach Mountains near Anchorage.
Eklutna Glacier, in Chugach State Park, has been peeling back for years, creating a steeper and more treacherous face, said mountaineer Mark Miraglia.
"Since 1976, it's retreated at least a half-mile and perhaps more," added park superintendent Al Meiners. "In fact, climbers were having a hard time last year because the face kept changing."
Perhaps the best-known example in Southcentral Alaska can be found across Portage Lake at the head of Turnagain Arm. In 1915, that glacier overran the present location of the popular Begich, Boggs Visitor Center, Molnia said.
"It's been retreating since the beginning of the 20th century," he said. "Only in the last decade did it disappear from view."
Molnia's work - the Alaska portion of an 11-volume report on the status of the world's glaciers - was presented last week at the fall meeting of the American Geophysical Union in San Francisco and will be published next summer by the U.S. Geological Survey.
The author of the Alaska Geographic book, "Glaciers of Alaska," Molnia has been studying the rivers of ice for more than 30 years. He also works with the House of Representatives' oceans caucus and performs high-latitude science for the U.S. Geological Survey.
"Every mountain range and island group investigated is characterized by significant glacier retreat, thinning, and/or stagnation, especially at lower elevations," Molnia wrote. "At some locations, glaciers have completely disappeared during the 20th century."
Another study presented at the same meeting, by glaciologist Keith Echelmeyer of the Geophysical Institute, reported similar findings. Along with five other researchers at the University of Alaska Fairbanks, Echelmeyer developed a laser device mounted to an airplane to measure changes in about 100 mountain glaciers in Alaska and Northwestern Canada.
To document how glaciers had changed since a 600-year cold period called the Little Ice Age, Molnia pored over more than 400 published reports and maps, some made by explorers as early as 1794. Using his own field work and data collected by other prominent glaciologists, Molnia gathered about 10,000 aerial photographs, 500 satellite shots and 100 radar images. The sources of information ranged from spectral images taken from space to rings counted inside ancient trees crushed during glacial advances.
He found almost universal shrinkage among glaciers and ice fields below 5,000 feet in elevation.
Dramatic examples included Glacier Bay, reported in the 1790s as a small "embayment" along the coast that retreated 60 miles inland. The Bering and Malaspina glaciers, the state's largest, have been losing a cubic kilometer of water per year, Molnia said. Research has also shown shrinkage of the glaciers flowing from the Juneau Icefield.
The retreat, however, has increased the number of glaciers in some areas as the rivers of ice pull back and leave remnants.
"The number of glaciers may be increasing, but the total volume of ice is decreasing," he said.
Not all glaciers are dwindling. The Harvard and Meares glaciers in Prince William Sound have been slowly advancing in their fiords, and the Hubbard Glacier is expected to block Russell Fiord north of Yakutat by 2020, according to another USGS paper.