Satellite Observations of Surface Flow Variations at Southeast Alaskan Glaciers

Glaciers in southeast Alaska are undergoing rapid changes that affect global sea level rise, lake formation and water levels, and flood risks. A key to understanding the ice dynamics is knowledge of the surface ice velocities and how they vary through time. Here we present updated maps of surface velocities for several glaciers in southeast Alaska produced through a pixel tracking technique using synthetic aperature radar data (ALOS, TerraSAR-X) and high-resolution optical imagery (WorldView, QuickBird, IKONOS, GeoEye). We focus on several glaciers that have enough data to form multi-year timeseries, including Hubbard, Yakutat, and LeConte. Hubbard Glacier is the largest non-polar tidewater glacier in the world and is currently in the advance phase of the tidewater glacier cycle. The glacier shows strong seasonal variations of more than 5 m/day along the terminal lobe, with the highest speeds occurring between late December and early February and the lowest speeds occurring in late summer/early fall. The region directly above the terminal lobe displays a smaller seasonal variation in speed. Near the terminus of the glacier, an increase in speed from ~8 m/day to more than 11 m/day is observed between Winter 2008 and Winter 2010. The Valerie Glacier, which is separated from the terminal lobe of the Hubbard by a medial moraine, displays a decrease in speed from ~8 m/day to ~4 m/day between March 2009 and March 2011. LeConte Glacier, which is located in the southern Stikine Icefield, appears to have retreated to a stable position. In contrast to Hubbard, the observed speeds along the lower part of LeConte do not vary significantly between years. Peak speeds at the terminus reach ~22 m/day in both 2008 and 2012. The lake-terminating Yakutat Glacier is in a state of collapse, with rapid retreat creating two separate termini in late summer 2011. Our dataset allows us to document the surface velocity variations that occurred during this time and the subsequent years as the retreat has continued.