A rockslide-generated tsunami in a Greenland fjord rang Earth for 9 days

Climate change is increasingly predisposing polar regions to large landslides. Tsunamigenic landslides have occurred recently in Greenland (Kalaallit Nunaat), but none have been reported from the eastern fjords. In September 2023, we detected the start of a 9-day-long, global 10.88-millihertz (92-second) monochromatic very-long-period (VLP) seismic signal, originating from East Greenland. In this study, we demonstrate how this event started with a glacial thinning–induced rock-ice avalanche of 25 × 106 cubic meters plunging into Dickson Fjord, triggering a 200-meter-high tsunami. Simulations show that the tsunami stabilized into a 7-meter-high long-duration seiche with a frequency (11.45 millihertz) and slow amplitude decay that were nearly identical to the seismic signal. An oscillating, fjord-transverse single force with a maximum amplitude of 5 × 1011 newtons reproduced 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. A large rockslide occurred in Greenland on 16 September 2023 that generated a local tsunami. The event was energetic enough to generate a global signal that resonated for 9 days. Svennevig et al. used a range of geophysical tools to detail the sequence of events that occurred and then determined the origin of the global signal. The authors found that the signal was generated by standing waves in the Dickson fjord due to the rockslide. Climate change drives feedback among the cryosphere, hydrosphere, and mass wasting events, and signals such as the one the authors observed may provide a different way of understanding these interactions. —Brent Grocholski