Short-time-scale variations in flow speed and behavior, Helheim Glacier, East Greenland

We have obtained a suite of detailed geophysical observations, spanning two summer seasons, at Helheim Glacier, East Greenland. This interdisciplinary dataset includes geodetic, seismic, radar, and lidar observations, in addition to tidal, weather, and satellite remote-sensing data. Continuous high-rate GPS observations from a period of 50 days in July--August, 2007, extend a 60-day summer-season time series obtained in 2006. Reoccupation of many glacier sites allows for a direct interannual comparison. Continuous data for periods as long as four weeks were also obtained for the first time on the lowermost part of the glacier, within a few km of the calving front. Analysis of both geodetic and seismic data show significant changes in glacier behavior between 2006 and 2007. The 2006 summer season saw a substantial readvance of the calving front compared with the minimum position recorded in 2005; a retreat of the front was observed in 2007 with respect to 2006. The 2006 summer season was seismically quiescent, with 2007 marking a return to glacial-earthquake activity. While geodetically determined glacier velocities from 2006 can be explained well by simple first- or second-order polynomial models, this is not the case for 2007, where more complex behavior occurring on shorter timescales is observed. We will present a joint analysis of seismic and geodetic data focused on elucidating the nature of short-time-scale variations in glacier flow, including glacial earthquakes.