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Taking The Pulse Of Exit Glacier

Kenai Fjords National Park

National Park News

Just what does it mean to move at a glacial pace in Kenai Fjords National Park?  With the help of a radio transmitter and a dozen years of data collection, park staff are now able to better define and quantify the speed of the park’s “Blue Ice.”  

In 1995, park VIP Bob Satin, a retired geologist who later became a seasonal ranger at Kenai Fjords and Hawaii Volcanoes, began the project. Satin got the idea from a newspaper report of a radio-collared black bear whose tracking device revealed that the animal had not moved in several days. This usually meant the collar had come off the animal or that the bear had died with the tracking collar in place. U. S. Fish and Wildlife staff, who collared the bear, tracked the signal to a snow and rock avalanche. The transmitter was still working despite being below the avalanche debris.

According to a newspaper article at the time, Satin “tried this two times before but the bear won’t stay at the bottom of the crevasse.”  After dispensing with such creative approaches, Satin designed a specialized glacier-tracking device. The container for the blue ice transmitter had to be able to withstand crushing glacial pressures and send out regular signals over a period of years. With the help of lithium batteries and a high-pressure polyethylene pipe, Bob’s contrivance excelled in both requirements.  Over the past twelve years, many park rangers have gone in search of the transmitter, and they continue to be amazed at the durability of the design and equipment.

The goal of the project was to obtain internal flow rates of the ice in Exit Glacier. During the early stages of the tube’s movement down the glacier, it was measuring internal flow. After September of 1998, though, it emerged regularly as ablation (surface melting) brought the tube to the surface. Since then, the transmitter has been found on the ice surface each year as the ice overburden continues to melt away. Once discovered, the tube is reinserted in a nearby crevasse to prevent otherwise unwanted movement, such as being washed downhill in a melt water channel. One aspect the experiment has highlighted is the amount of melting taking place on the glacier surface. 

Data from the device shows an average flow rate in the Exit Glacier of approximately 12 inches per day (364 feet/year) from 1995 to 2006.  The “pulse” of the glacier over the twelve-year period varied, with some years showing movement three times as fast as other years. During this same period, the terminus of Exit Glacier retreated approximately 430 feet (39 feet/year). 

These data compare well with past studies of Exit Glacier and other studies in Alaska. In 1985, Bud Rice (currently an environmental protection specialist in Alaska Regional Office) documented summertime Exit Glacier surface ice movement averaging slightly less than two feet per day, or nearly twice as fast as the 1995—2006 average. Yet ice movement is dependent upon location within the glacier and is typically faster in summer than winter.  Similarly, U.S. Geological Survey investigations of Gulkana Glacier near Denali National Park document ice motion of 130 to 165 feet per year in the central reaches of the glacier, and rates closer to half that in the lower ablation zone. While the Gulkana Glacier ice movement rates are slower than Exit Glacier, both glaciers are within typical ranges for ice movement.

Exit Glacier has a pulse, but perhaps not so regular as your cardiologist would like to see.  Whether the lessons learned help to increase our understanding of the impacts of climate change, or clarify the meaning of the term “glacial pace,” this project is an excellent example of how to have a big impact by starting with a simple, well-articulated idea.

Rangers Mike Tetreau, Peter Fitzmaurice and Jeff Troutman initially inserted the tube in late October 1995. Mike Tetreau continued doing periodic location work with the assistance of park volunteers. During the 2007 season, staff members Christina Kriedeman, Heather Wetherbee and Fritz Klasner, together with Roger Robinson from Denali and Chuck Lindsay from the Southwest Alaska Network, provided valuable assistance.


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