Grand Pacific Glacier

National Park Service Information

In 2004 Grand Pacific Glacier was about 2 miles wide at the terminus, averaging about 150 feet high at the ice face, up to 60 feet deep at the waterline and over 35 miles long. Much of the ice margin was then grounded at low tide; the calving section probably reached a water depth of only 30 to 60 feet. The ice cliff was estimated to be 60 feet high where it was grounded, but about 150 and up to 180 feet high where it calved into Tarr Inlet. Behind the terminus, the ice may thicken to 900 feet or more. The western two thirds of the ice in the terminus of the Grand Pacific Glacier originate from the tributary Ferris Glacier, and flowed about 1500 feet per year or about 4 feet per day. This latter estimate was based on measurements of aerial photographs taken between 1988 and 1990 and may be higher than 2004 rates based on the fact that the ice had been thinning over the last 7 years or so. The eastern portion of Grand Pacific Glacier moved only about 150 to 180 feet per year based on GPS measurements made by the Cold Regions Research and Engineering Laboratory (CRREL) in 1998-1999. It had advanced at a rate of about 60 feet per year for the last several decades, but it reached a maximum position when it joined Margerie Glacier around 1992. In 2004 those glaciers were no longer together due to recession of the Grand Pacific margin. A small stream flowed between the two termini. The eastern edge was then receding at about 30 to 60 feet per year and showed significant thinning and closure of crevasses. In about 1996, an embayment began to form in the center of Grand Pacific’s terminus. Since then, the center of the ice cliff began to calve more rapidly and was slowly receding at perhaps 30 feet or less per year. In 2004 the CRREL anticipated that retreat would accelerate as the embayment enlarged and the depth at the waterline increased. In such a scenario, retreat was likely to continue until the terminus reaches a position where it will become grounded above mean tide. The grounded western edge of the glacier was also slowing receding (10 to 30 feet per yr) and thinning. Rock debris from landslides and medial moraines cover much of this side of the glacier and extends across almost two-thirds of the ice face. Where this rock debris is more than an inch thick, it insulates the ice, slows melting and results in a thicker ice mass than where the ice is clean. In many areas on the glacier, the debris is more than 3 feet thick.