Tsunamigenesis on a Buoyant Granular Layer as a Model of Ice Mélange in Ice-choked Fjords

Glacial calving events can often create destructive tsunami waves in ice-choked fjords in the arctic region, posing a threat to local inhabitants and damaging coastlines. Here the sea is covered by a polydisperse granular material called ice mélange, whose properties can affect the wave characteristics. To investigate the role of a buoyant granular layer, as a model of ice mélange, on tsunami generation, or tsunamigenesis, a series of laboratory experiments were conducted by collapsing a column of dense granular material into a body of water with a layer of buoyant particles distributed across the liquid surface. Experiments were performed over a wide range of parameters, including the dense granular column geometry and water depth, allowing for a broad comparison with prior experimental work for systems without buoyant particles. Observed waveforms include solitary waves, bore waves, breaking waves, and non-linear transition waves. The wave morphology is significantly impacted by the buoyant particles, generally leading to higher amplitude, shorter wavelength, and suppression of wave breaking. Notably, as the particle size increases, the breaking action of the waves is further suppressed, indicating a damping mechanism by the buoyant particles. A strong correlation is observed between the maximum amplitude of the waves and the geometry of the collapsed granular material, allowing for the development of a predictive model for tsunami generation in fjords with ice mélange.