Extraordinary, 9-day long, global seismic oscillations due to a rockslide-generated tsunami in a Greenland fjord

Climate change is increasingly predisposing polar regions to large landslides. Tsunamigenic landslides have occurred recently in Greenland, but none have been reported from the eastern fjords. In September 2023, we detected the start of an unprecedented up to 9-day-long global 10.88 mHz (92 s) monochromatic very long-period (VLP) seismic signal, originating from East Greenland. We demonstrate how this event started with a 25 Mm³ glacial thinning-induced rockslide plunging into Dickson Fjord, triggering a 200 m high tsunami. Simulations show the tsunami stabilized into a 7 m-high long-duration seiche with a near-identical frequency (11.45 mHz) and slow amplitude decay as the seismic signal. An oscillating, fjord-transverse single-force with a maximum amplitude of 5×10¹¹ N reproduces the seismic amplitudes and their radiation pattern relative to the fjord, demonstrating how a seiche directly caused the 9-day long seismic signal. Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere and lithosphere.