RETRACING THE FOOTSTEPS OF THE EARLY GIANTS - DOCUMENTING ALASKAN LANDSCAPE CHANGE AND EVOLUTION THROUGH GROUND-BASED AND AERIAL REPEAT PHOTOGRAPHY

If a picture is worth a thousand words, then imagine the information that can be derived from a comparison of pairs of photographs with the same field of view that span many decades or even a century. This is the rationale behind a USGS investigation that is revisiting the 'locations' of many historic ground-based and oblique aerial photographs to gain insights into how rapidly the glacierized Alaskan landscape has changed in response to post-Little Ice Age climate. Alaskan ground-based photographs date from the 1880s, while Alaskan aerial photographs date from 1926. Many of these photographs were made by giants in the history of Alaskan geology and exploration, including: G. F. Wright, Harry F. Reid, Israel C. Russell, Frank LeRoche, Edward S. Curtis, W. C. Mendenhall, Grove Karl Gilbert, Alfred H. Brooks, Stephen Capps, Ernest Leffingwell, Alfred G. Maddren, Walter C. Mendenhall, C.W. Wright, U. S. Grant III, D. F. Higgins, John B. Mertie, William Cooper, and William O. Field Jr. Among the first of the aerial photographers was Bradford Washburn. His 1934 survey was partially funded by GSA's Penrose Research Fund.

The USGS effort has revisited more than 150 locations in Glacier Bay and Kenai Fjords National Parks, and Chugach National Forest. More than 20 of Washburn's 1930s aerial photographs in Glacier Bay National Park have also been rephotographed. Results document: glacier length, area, and thickness change; rapid landscape evolution; vegetative succession; sedimentation filling deep fiords; vegetative succession transforming bare bedrock into dense forest; and new habitats being developed that support complex ecosystems. For Glacier Bay, results document: that following initial rapid post-Little Ice Age retreat, large areas of the Bay and individual glaciers demonstrated unique behaviors with some continuing to retreat, some advancing, and some fluctuating; complex patterns of temporal variation in individual glaciers and simultaneous variation between different Bay regions; that differences in patterns of individual glacier behavior appear to be in response to complex regional variations in climate; that vegetation becomes established rapidly following ice retreat, generally within a decade, and quickly transforms the landscape; and that at some locations, glaciers have completely disappeared.