The recent loss of Jakobshavn Isbræ’s extensive
floating ice tongue has been accompanied by a change in
near terminus behavior.The recent loss of Jakobshavn Isbræ’s extensive
floating ice tongue has been accompanied by a change in
near terminus behavior. Calving currently occurs primarily
in summer from a grounded terminus, involves the
detachment and overturning of several icebergs within
30 – 60 min, and produces long-lasting and far-reaching
ocean waves and seismic signals, including ‘‘glacial
earthquakes’’. Calving also increases near-terminus glacier
velocities by 3% but does not cause episodic rapid glacier
slip, thereby contradicting the originally proposed glacial
earthquake mechanism. We propose that the earthquakes are
instead caused by icebergs scraping the fjord bottom during
calving.We thank J. Brown and D. Maxwell for field
assistance, and S. Anandakrishnan, A. Behar, and R. Fatland for loaning
GPS receivers. Comments from editor E. Rignot and reviewers S. O’Neel
and T. Pfeffer improved the manuscript. Logistics and instrumental support
were provided by VECO Polar Resources, UNAVCO, and PASSCAL.
Seismic analysis was done with the Matlab waveform object package written
by C. Reyes (http://www.giseis.alaska.edu/Seis/EQ/tools/matlab/). Funding
was provided by NASA’s Cryospheric Sciences Program (NNG06GB49G),
the U.S. National Science Foundation (ARC0531075), the Swiss National
Science Foundation (200021-113503/1), the Comer Science and Education
Foundation, and a CIFAR IPY student fellowship under NOAA cooperative
agreement NA17RJ1224 with the University of Alaska.Ye
