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The nearly five kilometer retreat of the Portage Glacier terminus during the past century is not simply an effect of glacier melt in a warming climate. A change in climate a century ago triggered subsequent calving processes that dramatically accelerated glacial retreat. The relatively slow flow of ice from the upper reaches of the glacier could not keep pace with the massive loss of ice calving into the lake at the terminus. The rapid retreat of Portage Glacier is not unique. Other glaciers that terminate in water, such as Columbia Glacier near Valdez and Mendenhall Glacier near Juneau, have also experienced accelerated retreats in recent decades that were initially triggered by climate change, then controlled primarily by calving of the glacier terminus. This presentation summarizes the history of the Portage Glacier retreat during the past century and includes photographs of the terminus in 1914, 1939, 1951, 1972, 1984, 1999, and 2006. Future changes of Portage Glacier will depend on a variety of glacier/climate factors. For more information contact: Horacio Toniolo (907) 474 7977 |