GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 383-4
Presentation Time: 9:00 AM-6:30 PM


LYLES, Alex S., U.S. Forest Service, Tongass National Forest, Thorne Bay Ranger District, P.O. Box 19147, Thorne Bay, AK 99919, BAICHTAL, James F., U.S. Forest Service, Tongass National Forest, Thorne Bay Ranger District, P.O. Box 19001, Thorne Bay, AK 99919 and KARL, Susan M., U.S. Geological Survey, 4210 University Dr, Anchorage, AK 99508-4626,

The exact extent of the Last Glacial Maximum (LGM) ice sheet and how it progressed across southeast Alaska is relatively unknown. Recent advances in interferometric synthetic aperture radar (IFSAR) and light detection and ranging (LiDAR) mapping give us a preliminary look at how the ice moved across the “bare earth” surface in regions where dense foliage and/or persistent clouds challenge imaging techniques. When combined with NOAA bathymetric data of the shallow waters surrounding the Alexander Archipelago, the land cover data reveal high-resolution surficial landscape imagery of southeast Alaska. This visualization opens up opportunities for interpreting geomorphology of glacial landscapes, including drumlins, crag-and-tails, and terminal and lateral moraines. Integration of these data with field observations enables unprecedented resolution of regional- to local-scale ice flow patterns. Over two hundred and fifty ground-based glacial striation azimuths determined by small-scale indicators such as chatter marks and glacial plucking, combined with the images, revealed that the flow patterns of the Cordilleran ice sheet over southeast Alaska are more complex than previously thought. Additionally, this new mapping provides constraints on the western limit of the ice during the LGM. Our observations indicate that ice flowed north and northwest from a major glacier in Dixon Entrance, including a major lobe that flowed northward up Clarence Strait along the eastern side of southern Prince of Wales Island, and a lobe that flowed northward up Cordova Bay and Tlevak Strait east of Dall Island and coalesced with an ice lobe in the Gulf of Esquibel. These findings, along with others, challenge the general north-to-south movement of ice during the LGM that is commonly accepted and improves our understanding of the impacts of glaciation and deglaciation during the LGM with respect to the complex isostatic crustal adjustments in southeast Alaska.