The Antarctic ice sheet is buttressed by floating ice shelves that calve icebergs along large fractures called rifts. We report the first-ever seismic recording of a multiple-kilometer rift propagation event located in Pine Island Glacier Ice Shelf. The rift grew 10.5 km at a speed of 34.8 m/s, the fastest known ice fracture at this scale. We simulate ocean-coupled rift propagation and find that hydrodynamics control rupture velocities. During rift propagation, ocean water flows into the rift at a rate of at least 2300 m3/s and causes mixing in the subshelf cavity. Our observations support the hypotheses that large ice shelf rift propagation events are brittle, hydrodynamically limited, and exhibit sensitive coupling with the surrounding ocean.

Ice shelves regulate the stability of marine ice sheets. We track fractures on Pine Island Glacier , a quickly-accelerating glacier in West Antarctica that contributes more to sea level rise than any other glacier. Using an on-ice seismic network deployed from 2012 to 2014, we catalog icequakes that dominantly consist of flexural gravity waves. Icequakes occur near the rift tip and in two distinct areas of the shear margin, and TerraSAR-X imagery shows significant fracture in each source region. Rift-tip icequakes increase with ice speed, linking rift fracture to glaciological stresses and/or localized thinning. Using a simple flexural gravity wave model, we deconvolve wave propagation effects to estimate icequake source durations of 19.5 to 50.0 s, and transient loads of 3.8 to 14.0 kPa corresponding to 4.3 to 15.9 m of crevasse growth per icequake. These long source durations suggest that water flow may limit the rate of crevasse opening.