Investigating the Cause of the 2012 Acceleration of Jakobshavn Isbræ, Greenland Using High Resolution Observations of the Glacier Terminus

Tuesday, 16 December 2014
Ryan Cassotto, University of New Hampshire, Department of Earth Sciences, Durham, NH, United States; Institute for the Study of Earth, Oceans, and Space, Durham, NH, United States, Mark A Fahnestock, Univ. of Alaska/GI, Fairbanks, AK, United States, Margaret S Boettcher, University of New Hampshire, Durham, NH, United States, Jason M Amundson, University of Alaska Southeast, Juneau, AK, United States and Martin Truffer, University of Alaska Fairbanks, Fairbanks, AK, United States
After decades of relative stability, Jakobshavn Isbræ, a tidewater glacier in West Greenland, started to destabilize at the turn of the century. The glacier thinned, the perennial tongue disintegrated, velocities doubled, and the terminus retreated. The glacier evolved over the next several years as it showed large seasonal variations in speed and a progressive kilometer-scale retreat of its calving front. Then, during the 2012 summer, Jakobshavn set a new record when its speed increased to rates more than four times the 1990s values, and consequently became the fastest glacier recorded by satellite yet. A 2-week field study was conducted along the terminus at that time; ground portable radar interferometers (GPRI), time-lapse cameras, GPS, and a tide gauge were deployed to characterize glacier dynamics along the ice-ocean boundary. We use >10,000 interferograms recorded with the terrestrial interferometers to probe the cause of this acceleration. We observe a 33% increase in glacier speed and a 250% increase in the amplitude of response to tidal forcing during our study period. We explore how the location of the terminus along the reverse bed slope contributed to the observed speedup, and we compare our findings with the long-term record of satellite observations. Our data show that understanding tidewater glacier dynamics requires knowledge of short-term variations along glacier termini that is currently not available from satellites. This study provides insight into such short-term dynamics on spatial scales comparable to satellite InSAR but with temporal resolution similar to GPS.