FAST-FLOW ADVANCE AND PARALLEL RAPID RETREAT OF NON-SURGING TIDEWATER GLACIERS IN ICY BAY AND YAKUTAT BAY, ALASKA—1888-2003

For more than a century, tidewater glacier termini in adjacent Icy Bay and Yakutat Bay have behaved differently, experiencing either unusual fast-flow advances or rapid retreats. The non-surging, larger valley glaciers in Icy Bay, such as Guyot, Yahtse, and Tyndall Glaciers, have undergone excessive downwasting and terminus retreat accentuated by calving. Tyndall Glacier became separated from the retreating Guyot Glacier in the 1960s. Since then, it has retreated ~24 km, opening a steep-walled fjord extending to near the base of 5,450-m-high Mt. St. Elias, the summit of which is now ~10 km from the sea. This extreme recession has been accompanied by a general rise in the ELA and associated negative glacier balances over the past 40 years.

In contrast to the region’s dominant negative regime is a continuously strong positive mass balance and advance of the non-surging Hubbard Glacier. In contrast to the glacier's of Icy Bay, Hubbard Glacier’s calving terminus has advanced ~3 km since the 1880s and is currently close to its most advanced recorded position. In 1986 and 2002, Hubbard Glacier temporarily closed the entrance of adjoining Russell Fjord. The Hubbard Glacier’s continued fast-flow advance is the result of increasing positive mass balance on its main névé, at 1,300 to 3,000 m. This is in contrast to significant ice depletion on the main lower elevation névés of the Guyot Glacier, Yahtse Glacier, and Tyndall Glacier systems. These opposing regimes relate to dynamic differences in elevation, geographic position and mean depth of their source firn-packs and hence to their ablation/accumulation ratios (AAR).

The parallel advance and retreat of these major glacier systems provides a unique opportunity for interpreting important changes in global atmospheric circulation. Yakutat Bay has a counterpart in the Alaska Panhandle through the well-documented behavior of the Juneau Icefield’s Taku Glacier, which has rapidly advanced since the 1880’s. In contrast to the Taku Glacier, the adjoining Mendenhall and Herbert Glacier systems, similar to the Guyot and Tyndall Glaciers, have suffered extreme recent terminal retreats.