Temporal evolution and kinematics of a mega-crevasse at Jakobshavn Isbræ revealed by dense GNSS observations

We analyze the temporal evolution and kinematics of a large mega-crevasse situated in the northern sector of Jakobshavn Isbræ, West Greenland, roughly 50 km north of the glacier’s main flowline. Our study relies on continuous surface-displacement measurements collected by a dense array of 18 permanently operating GNSS stations deployed across and around the crevasse system. These stations recorded ice-surface motion at high temporal resolution over nearly two years, enabling us to capture both seasonal trends and short-term dynamical fluctuations. The resulting displacement time series reveal how strain, opening rates, and relative motion across the crevasse evolved through time, providing new insight into the mechanisms controlling crevasse initiation and growth in this highly dynamic sector of the ice sheet. Fourteen of the GNSS stations are arranged along a profile oriented perpendicular to multiple crevasses, allowing us to quantify both rapid deformation associated with episodic crevasse-opening events and longer-term, seasonally driven variations in crevasse activity linked to meltwater input.Spatial patterns of GNSS-derived velocities show strong tensile strain concentration at crevasse locations, which coincides with the spatial distribution of icequake activities recorded by a colocated array of 18 seismic geophones. We show not only hydrofracture-driven crevasse activities during melt seasons, but also that the presence of mega-crevasses modulates basal sliding velocity by promoting the transfer of surface meltwater to the glacier bed. Our results of field observations provide a foundation for future modeling of crevasse mechanics.