The Principal Investigators request support for an interdisciplinary, high-resolution study involving remote sensing and field investigations at two of Greenland's largest outlet glaciers. The study of the Helheim and Kangerdlugssuaq Glaciers will integrate seismological, glaciological, and geodetic observations to build an understanding of flow dynamics at major outlet glaciers, which represent a critical junction between the atmosphere, cryosphere, and hydrosphere. The project would be the first long-term occupation of an outlet glacier by a GPS receiver network, and would address questions of flow variation on earthquake to interannual time scales. Recent discoveries have made it clear that our understanding of the dynamics of flow at large outlet glaciers is limited and inadequate for understanding the ways in which the outlet glaciers, and the ice sheets they drain, respond to external forcings. The spectrum of timescales over which significant velocity variations in outlet glacier flow can occur appears to be much broader than previously believed, with significant variations occurring on timescales of 10s of seconds to several years. Analysis of glacial earthquakes suggests that significant volumes of ice may move at speeds 1000 times faster than their average annual velocities for periods of a minute or two and a doubling of average annual flow speeds over only a few years has been observed at some glaciers. Multiple observations now indicate that glacier flow behavior can respond quickly to environmental changes, including rapid climate change. It is not currently clear, however, what mechanisms or combination of mechanisms allow for, or drive, the temporal variations, nor is it clear how variations in flow behavior at different timescales are related to one another. Understanding the changes in force balance that control variations across the range of timescales from minutes to years requires observations at higher resolution in both space and time than are currently available, and achieving a comprehensive picture of the interactions between short- and long-timescale processes, and between external forcings and glacier flow behavior, requires the integration of data and expertise from several traditionally separate disciplines..
Intellectual Merit. The research will lead to a greatly improved understanding of the dynamics of flow at the large, fast-moving outlet glaciers that drain the Greenland ice sheet and of the temporal variability in their rates and modes of flow. It will provide insight into the processes controlling glacial earthquakes and possible connections between glacial-earthquake activity and global climate change.
Broader Impacts. Understanding the controls on flow configuration at major outlet glaciers, and the timescales over which they may respond to climatic forcing, is of great importance for proper modeling of systems affected by the transfer of fresh polar meltwater to the world's oceans. A better understanding of glacier and ice-sheet response to climate change will allow for improvements in modeling of the coupled ice ocean atmosphere system, and of its interactions with the solid Earth. The geodetic instrumentation and processing techniques developed under this proposal will benefit researchers in a variety of environments such as glacier and volcano monitoring involving rapid, large-scale motions and the risk of instrument loss.