Impulse wave generated by landslide: investigation of the wave-granular flow coupling

Impulse waves generated by landslide differ from earthquake tsunamis in several aspects, as their generation mechanism as well as their length scale of propagation are not the same. In particular, the wave amplitude can be significant upon generation and may subsequently induce a substantial run-up in a nearby coastal area [1]. In this context, predicting the wave behavior after impact is of crucial interest. To have a better global understanding of this phenomenon, many studies have been devoted to its modelling, with a large variety of approaches, either experimental, numerical or field data investigations (see [2] for a detailed review). Yet, [2] suggest that the physical understanding of the phenomenon remains partial, even though numerous studies have been conducted over the last two decades. It appears then essential to better understand the mechanisms involved during the generation of such a wave in order to quantify the potential hazard it may represent. In our study, the phenomenon is modelled by a 2D-experimental setup using a steady and accelerated granular flow as a forcing wave generator. The study specifically focuses on the coupling between the granular flow and the wave, which is shown to be highly complex. In particular, the granular flow impact and its dynamics underwater can influence both the wave generation and its dynamics toward a propagation phase. The study of the wave-granular coupling during the generation phase leads to an empirical fit of the wave maximum amplitude as a function of a new dimensionless number based on two different Froude numbers, characterising both the impact properties and the granular flow propagation [3]. These new results allow to propose simple models including different finite time generation processes onto linear wave propagations, which are tested and compared to the experimental results.

[1] Fritz, H. M., Mohammed, F., & Yoo, J. Lituya bay landslide impact generated mega-tsunami 50th anniversary., Tsunami Science Four Years after the 2004 Indian Ocean Tsunami: Part II: Observation and Data Analysis, 153-175 (2009).
[2] Heller, V. & Ruffini, G. A critical review about generic subaerial landslide- tsunami experiments and options for a needed step change., Earth-Science Reviews. 242, 104459 (2023).
[3] Darvenne, A., Viroulet, S. & Lacaze, L. Physical model of landslide-generated impulse waves: experimental investigation of the wave-granular flow coupling., Journal of Geophysical Researches: Ocean., Journal of Geophysical Research: Oceans, 129(9) (2024).