| Summary: | 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 a 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 25×106 m3 glacial
thinning-induced rock-ice avalanche 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.
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