Unique Elevation Change Pattern Observed Over Shear Zones at Similarly Behaving Outlet Glaciers in SE Greenland

During 2003-2009, ice mass loss in southeast Greenland made up almost half of the total mass loss for the entire Greenland Ice Sheet (GrIS). Helheim Glacier is one of the greatest contributors to this significant regional mass loss. Over the last 35 years, Helheim Glacier together with a few other outlet glaciers in southeast Greenland has exhibited a unique elevation change pattern, consisting of rapid short-term thinning followed by varying amounts of thickening. This behavior was observed along the main trunk region ( 200 km2) of Helheim Glacier from 2000 to present. To study the elevation change pattern, we subtracted a 1981 aerial-photography-derived DEM from a 2007 SPOT DEM for Helheim Glacier and report an elevation change pattern unique to the thinning/thickening/thinning glacier behavior. The largest elevation changes are observed along the centerlines of individual tributaries, rather than the centerline of the entire glacier system. Between converging glacier tributaries in the main trunk region, shear zones observed in visible imagery and velocity fields are expressed as local minima in the elevation change pattern. The elevation change along the length of a shear zone ranges from 0.2 to 0.4 m/yr, however, elevation changes observed at ice outside of shear zones can vary by 0.4 to 0.8 m/yr. To fully assess the evolution of the shear zones through space and time, the elevation and velocity records will be examined at finer spatiotemporal resolutions. Additionally, similar investigations will be conducted at glaciers that exhibit similar thinning/thickening/thinning behavior, such as A.P. Bernstorff and Koge Bugt C glaciers. The shear zones between tributaries may act to control elevation changes at these individual glaciers, perhaps helping to stabilize calving fronts following exceptional retreat events.