Hicks, S. ; Svennevig, K. ; Forbriger, T. ; Lecocq, T. ; Widmer-Schnidrig, R. ; Mangeney, A. ; Korsgaard, N. ; Lucas, A. ; Satriano, C. ; Anthony, R. ; Mordret, A. ; Schippkus, S. ; Rysgaard, S. ; Boone, W. ; Gibbons, S. ; Cook, K. ; Glimsdal, S. ; Løvholt, F. ; Van Noten, Koen ; Assink, J. ; Marboeuf, A.

Talk presented at IAGA/IASPEI, Lissabon, Portugal on 2025-09-04

Abstract: 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. Since the original publication of our results, other groups analysed satellite altimetry data captured by NASA's Surface Water and Ocean Topography (SWOT) mission that directly confirms a slowly dissipating, >9-day long, initially 8 m-high seiche. Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere.

Keyword(s): Seiche ; Greenland ; Tsunami