C43E-07
Patterns of Rapid Deceleration Observed at Two Tidewater Outlet Glaciers in West Greenland

Thursday, 17 December 2015: 15:10
3002 (Moscone West)
Leigh A Stearns1, Ginny A Catania2, Timothy Bartholomaus3, Dave Sutherland4, Jonathan D Nash5, Emily Shroyer5, Logan C Byers1, Mason Fried3, Denis Felikson2, Ryan T Walker6 and Dustin Carroll4, (1)University of Kansas, Department of Geology, Lawrence, KS, United States, (2)University of Texas at Austin, Austin, TX, United States, (3)University of Texas, Institute for Geophysics, Austin, TX, United States, (4)University of Oregon, Eugene, OR, United States, (5)Oregon State Univ, Corvallis, OR, United States, (6)University of Maryland, Greenbelt, MD, United States
Abstract:
Flow speeds of Greenland outlet glaciers play an important role in modulating ice sheet mass balance. Flow variability is dictated by how outlet glaciers respond to unknown or poorly constrained perturbations in their boundary conditions; identifying the physical processes controlling outlet glacier flow variability is key to improving models of ice sheet evolution. In this study, we use satellite remote sensing data, in situ observations, and numerical models to explore the boundary conditions that control the unique flow behavior of two West Greenland outlet glaciers.

Kangerdlugssup Sermerssua (KS) and Kangilerngata Sermia (KGS), exhibit seasonal flow variability that is anti-correlated with surrounding glaciers. Both glaciers decelerate in the spring when meltwater becomes available. The seasonal deceleration is usually on the order of 10% the annual average speed, and lasts ~2 months. During high melt years, the deceleration is highly exaggerated (~80% of the annual average), causing a near shutdown of glacier flow along the lower 20 km of the trunk. For example, in 2010 KS decelerated from its average speed of ~2000 m/yr to 250 m/yr; the deceleration and the acceleration back to its average speed took roughly 2 months. Force balance analyses show that both glaciers have anomalously low driving stress and basal drag values. We hypothesize that glaciers with low basal drag are particularly sensitive to variations in subglacial water. The discrete decelerations and reactivation of these two unique glacier systems allow us to analyze the complicated evolution of subglacial hydrologic systems and their interaction with ice velocity and force components.

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