Comprehensive Mapping of Ice Flow From Landsat 8: Two Years of Surging and Seasonal Change for Alaska's Glaciers, and Counting…

While it has been known for years that rapid changes in ice flow occur on many Alaskan glaciers due to phenomena that span a gamut from tidewater glacier retreat to surging, it has not previously been possible to capture the spatial and temporal extent of this variability. We report on a comprehensive mapping effort, utilizing feature tracking in Landsat 8 imagery, that is producing a spatial and temporal picture of ice flow variations across southern and southeastern Alaska for glaciers half a kilometer in width and larger. We show that coverage and image characteristics for Landsat 8 enable sampling that is sufficient to track seasonal variations in flow speed for tidewater outlets; surge termination, initiation, and surge front propagation; and summer/winter flow variations for other land-terminating systems. Using the example of the 2014-15 surge of Walsh Glacier, seasonal changes on Columbia glacier, and comprehensive mosaics of ice flow across southern Alaska on a quarterly basis, we will demonstrate that we have entered an era when flow variations can be tracked in near real time, over large areas, with coverage suitable to follow evolving seasonal patterns even in frequently cloudy areas. As the Landsat 8 record continues to grow, it becomes possible to delimit surging and non-surging systems based on their flow speed history, rather than incomplete records of past flow and appearance.