Velocity and calving response of a major Greenland ice stream to a lake drainage event

Outlet glaciers and ice streams of the ice sheet of Kalaallit Nunaat (Greenland) transport ice from the interior towards the ocean, so understanding their dynamics is crucial in the context of accelerating Arctic warming. Glacier flow dynamics are predominantly monitored by satellites, thus important processes that occur on timescales shorter than the acquisition frequency (typically days) remain undetected. Therefore, the short-term dynamics of fast-flowing glaciers remains poorly understood and insufficiently constrained in numerical models. Here we use high-rate field observations by global navigation satellite system stations and a Terrestrial Radar Interferometer on Greenland’s fastest ice stream, Sermeq Kujalleq in Kangia (Jakobshavn Isbræ), to characterize its response to the drainage of two surface lakes. The ensuing subglacial flood caused a pulse of faster flow that rapidly propagated downstream—over 16 km within 4 hours—towards the terminus, where it triggered a longer than usual calving episode, lasting 2 hours. The undamped and fast propagation of this speed-up pulse, together with the instantaneous response of the surrounding shear margins, indicate strong coupling within the ice-stream system. Our results highlight how inland areas can accommodate large disturbances with minimal long-term impact on ice motion and efficiently propagate them downstream to trigger irreversible changes at glacier termini. Drainage of two surface lakes on Greenland’s fastest ice stream caused a pulse of faster flow to propagate downstream and triggered a long calving episode, suggesting the entire stream is strongly coupled, according to geophysical field observations.