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Harding Icefield's Loss is the Ocean's Gain

You know Alaska has a lot of glaciers when Icelanders travel here to study them.

Gudfinna Adalgeirsdottir, who just earned a masters degree from the Geophysical Institute at the University of Alaska Fairbanks, traveled to Alaska from her home in Iceland to research a sample of the 29,000 square miles of glaciers that cover Alaska. Her close look at Harding Icefield showed that it has shrunk perhaps the height of a five-story building during the past 40 years.

Harding Icefield, named for former U.S. President Warren Harding, is an ice cap in the mountains of the Kenai Peninsula. More than 35 glaciers reach out from the frozen mass like tree roots, some touching the ocean, some terminating on land. If you count the glaciers, Harding Icefield covers 1,100 square miles. That's enough ice to blanket Rhode Island. Adalgeirsdottir and her academic advisors Keith Echelmeyer and Will Harrison, both glaciologists at the Geophysical Institute, wanted to see how much of this ice had melted into the Pacific Ocean.

Using USGS maps made in the 1950s, Adalgeirsdottir checked the elevation of the glaciers when the maps were made. While comparing the maps with the 1950s photographs a cartographer used to make the maps, she found some mistakes. The overexposed pictures of the glaciers did not reveal enough detail to pinpoint the elevation of the higher areas. When comparing the actual elevation of rock outcroppings to the elevations listed on the maps, she again found discrepancies, some big and some small.

Though the height of Harding Icefield in the 1950s was in question, the researchers have a unique method for measuring icefields today. Echelmeyer, who is also a pilot, teamed with other institute scientists, electronic technicians and machinists to create a device with which they could measure the elevation of glaciers to within the length of a ruler. The instrument, mounted in the belly of a single-engine Piper, sends a pulse of laser light to the surface of a glacier. A receiver on board catches the bounce of the laser beam, and a computer calculates the distance from aircraft to glacier. The position of the aircraft is confirmed by a global positioning system. By flying over glaciers with the device, Echelmeyer is able to determine glacier elevations along his flight path.

Using the laser-measuring system, Echelmeyer and Adalgeirsdottir flew over the upper regions of Harding Icefield and over 13 of the glaciers that emerge from it. With new elevation data, Adalgeirsdottir compared the findings with the old USGS maps. She found the entire mass had shrunk by perhaps more than 70 feet during the 40-year period. Enough ice melted during this period that it probably raised the planet's sea level by one-tenth of a millimeter over the same period. Another researcher, Mark Meier of the U.S. Geological Survey, found that the melt water of small glaciers may account for one third of the sea level rise during the past century, and more than a third of that probably came from the mountain glaciers bordering the Gulf of Alaska.

Alaska stands to lose a lot of ice if warmer temperatures persist. With the recent study performed by Adalgeirsdottir and the glaciologists at the Geophysical Institute, scientists in the future will be able to accurately tell how much of Harding Icefield is being transformed to Pacific Ocean.