Most Alaskan Glaciers Retreating, Thinning, and Stagnating, Says Major USGS Report


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Most Alaskan Glaciers Retreating, Thinning, and Stagnating, Says Major USGS Report

By Catherine Puckett and Bruce Molnia
December 2008

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Scientists estimate that Alaska contains more than 100,000 glaciers—including about 60 active and former tidewater glaciers—which cover approximately 75,000 km², or about 5 percent of the State.

According to a new book published by the U.S. Geological Survey (USGS), most glaciers in every mountain range and island group in Alaska are undergoing significant retreat, thinning, or stagnation, especially glaciers at lower elevations. In places, these changes began as early as the middle of the 18th century.

Although a handful of Alaska's large glaciers are, surprisingly, advancing, more than 99 percent of them are retreating. In the past decade, Alaska's coastal glaciers have added as much (or more) meltwater to the global ocean as the ice sheets of Greenland or Antarctica, making these glaciers a significant factor in global sea-level rise.

Above: August 1941 photograph of Muir Glacier in Glacier Bay National Monument, Alaska, showing the lower reaches of Muir Glacier—then a large, tidewater calving valley glacier—and its tributary, Riggs Glacier (upper right). For nearly 2 centuries before 1941, Muir Glacier had been retreating; in places, a thickness of more than two-thirds of a mile of ice had been lost. Photograph courtesy of the National Snow and Ice Data Center and the Glacier Bay National Park and Preserve Archive. [larger version]

Above: This August 1950 photograph documents the significant changes that occurred during the 9 years between photographs A and B. Muir Glacier has retreated more than 2 mi, exposing Muir Inlet, and thinned 340 ft or more; however, it still is connected with tributary Riggs Glacier. Photograph courtesy of the Glacier Bay National Park and Preserve Archive. [larger version]

Above: This August 2004 photograph further documents the significant changes that occurred during the 63 years between photographs A and C and during the 54 years between photographs B and C. Muir Glacier has retreated out of the field of view and is now nearly 5 mi to the northwest. Riggs Glacier has retreated as much as 2,000 ft and thinned by more than 800 ft. Note that dense vegetation has developed. Also note the correlation between Muir Glacier's 1941 thickness (see photograph A) and the trimline—the nearly horizontal line on the mountainside on the left side of the 2004 photograph, which indicates the past height of the glacier. Photograph by Bruce Molnia. [larger version]

Glaciers of Alaska, authored by USGS research geologist Bruce Molnia, presents a comprehensive overview of the state of Alaskan glaciers at the end of the 20th century and beginning of the 21st century. Richard Williams, Jr., an emeritus senior research glaciologist with the USGS, said the 550-page volume will serve as a major reference work for glaciologists studying glaciers in Alaska for decades to come.

The report uses a combination of satellite images, vertical aerial photographs (black-and-white and color-infrared photos taken from airplanes, looking straight down), oblique aerial photographs (color photos taken from the air at an angle, such as most regular photos), and maps, supported by the scientific literature, to document the distribution and behavior of glaciers throughout Alaska.

The author concludes that, because of the vast areas encompassed by the glaciated regions of Alaska, satellite remote sensing provides the only feasible means of monitoring changes in glacier area and in position of termini—the ends of glaciers—in response to short- and long-term changes in the marine and continental climates of Alaska.

Above left: This August 1980 photograph of Muir Glacier—taken from a ship in Muir Inlet, Glacier Bay National Park and Preserve, St. Elias Mountains, Alaska—shows the nearly 200-ft-high retreating tidewater end of Muir Glacier, with part of its face capped by a few angular pinnacles of ice, called seracs. Note the icebergs in the ship's wake in the lower right side of the photograph. The glacier's terminus is less than a mile from the landward end of Muir Inlet. Photograph by Bruce Molnia. [larger version]

Above right: Photograph taken in September 2003; in the 23 years between photographs, Muir Glacier has retreated more than a mile and ceased to have a tidewater terminus. Since 1980, Muir Glacier has thinned by more than 600 ft, permitting a view of a mountain in the center of the photograph with a summit elevation higher than 4,000 ft. A reexamination of the 1980 photograph shows that the summit of this mountain was visible but blended in with adjacent clouds. Photograph by Bruce Molnia. [larger version]

Alaskan glaciers occur in 11 mountain ranges, one large island, one island chain, and one archipelago. Details about the recent behavior of many of Alaska's glaciers are contained in this richly illustrated book, with multiple photographs and satellite images, as well as hundreds of aerial photographs taken by Molnia during his more than 4 decades of fieldwork in Alaska.

Three other USGS glaciologists authored two sidebar sections of the book: "Columbia and Hubbard Tidewater Glaciers," by Robert M. Krimmel; and "The 1986 and 2002 Temporary Closures of Russell Fiord by the Hubbard Glacier," by Bruce F. Molnia, Dennis C. Trabant, Rod S. March, and Robert M. Krimmel. A third section, "Geospatial Inventory and Analysis of Glaciers: A Case Study for the Eastern Alaska Range," was authored by William F. Manley, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado.

This book (USGS Professional Paper 1386-K), which is available in print and online at URL http://pubs.usgs.gov/pp/p1386k/, is the eighth chapter to be published in the Satellite Image Atlas of Glaciers of the World series. More than 100 glaciologists from the United States and other nations have collaborated with the USGS to produce this series, which will eventually contain 11 chapters. (See USGS Fact Sheet 2005-3056.)

Glaciers of North America—Glaciers of Alaska - USGS Professional Paper 1386-K
USGS

Satellite Image Atlas of Glaciers of the World - USGS Fact Sheet 2005-3056
USGS