Glaciers and Perennial Snowfields of the U.S. Cordillera

Of more than 8,000 glaciers and perennial snow-fields on 21 mountain ranges in the western U.S. (excluding Alaska), only 120 are larger than 1 km2, and just one exceeds 10 km2. Where changes in size are known, the overwhelming majority of glaciers are shrinking. There are a few that are growing. These changes, with a few exceptions that relate mainly to rock debris abundances on the glaciers, are due overwhelmingly to climate change, though it is a complex relationship. Analysis of ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) imagery has been used in special case studies, along with published field data, to track changes in debris loads of glaciers on Mt. Rainier, show the effects of a lahar from Mt. Rainier, and track the continued shrinkage of Grinnell Glacier in Glacier National Park. The response time of glaciers in the region varies from under a decade to over a century. Blue Glacier (Olympic Mountains) is a fast responder; its length, area, and volume fluctuation history indicates that it is responding to decadal climate fluctuations as well as local long-term warming in the 20th and 21st centuries, which is probably related to greenhouse gas-driven global warming.