  Ice flow velocities close to the terminus of major outlet glaciers of the
Greenland Ice Sheet can vary on the time scale of years to hours. Such flow
speed variations can be explained as the reaction to changes in terminus
geometry with help of a 3D full-Stokes ice flow model. Starting from an initial
steady state geometry, parts of an initially 7 km long floating terminus are
removed. Flow velocity increases everywhere up to 4 km upstream of the
grounding line, and complete removal of the floating terminus leads to a
doubling of flow speed. The model results conclusively show that the observed
velocity variations of outlet glaciers is dominated by the terminus geometry.
Since terminus geometry is mainly controlled by calving processes and melting
under the floating portion, changing ocean conditions most probably have
triggered the recent geometry and velocity variations of Greenland outlet
glaciers.
