Scott R Springer, Earth & Space Research, Seattle, WA, United States, Stefanie L Mack, University of Washington, Applied Physics Laboratory, Seattle, WA, United States, Pierre Dutrieux, Lamont-Doherty Earth Observatory, Palisades, NY, United States, Laurence Padman, Earth & Space Research, Corvallis, OR, United States, Ian R Joughin, Applied Physics Laboratory University of Washington, Seattle, WA, United States and David E Shean, University of Washington, Seattle, WA, United States