Laboratory modelling of landslide-generated impulse wave

Impulse waves are waves generated by subaerial landlsides impacting the free surface of a lake or a sea. These waves differs from earthquake tsunami, even if often associated, as the generation mechanism and the scale of influence are not the same. Although they can travel over much shorter distance than other tsunamis, waves generated by landslides can be locally more dangerous [1]. Consequently, predicting the wave amplitude, and particularly its maximum during the generation remain crucial. Even if several studies have been devoted to the prediction of the wave amplitude at the laboratory scale, the mechanisms involved during the generation and particularly the role of the granular material to mimic landslide are still poorly understood [2, 3]. In this context, the presented study aims to better understand the interaction between the landslide and the generated waves, by understanding the physical mechanisms at the origin of the deformation of the free surface and the dry-wet transition of the granular flow. A laboratory model is used consisting of a 2m long chute of varying slope angle ending in a 4m long water tank. More specifically, the landslide is modelled by a monodisperse granular flow of 1mm spherical glass beads.
A picture of the experiment is represented in Figure 1a. The dynamic of the slide when crossing the air/water interface as well as the spatio-temporal structure of the wave are caracterised as a function of the properties of the impacting granular flow. Figure 1b shows the spatial and temporal evolution of the water free surface elevation during the wave generation process. This figure also highlights that the wave crest is stronlgy correlated to the granular front at early stages, while freely propagates in the far field. Based on physical mecanisms during generation, this study allows to discuss existing models relating the maximum wave amplitude to a so-called impulse parameter [4].

  

                                                                                                                                                                                            
Figure 1: (a): Picture of the granular flow penetrating water, (b): Space-time representation of the free surface elevation, compared with granular flow front position.

References:
[1] Fritz H. M., Mohammed F. & Yoo J. Lituya Bay landslide impact generated mega-tsunami 50th anniversary., Pure and Applied Geophysic 166, 153–175 (2009).
[2] Viroulet S., Sauret A. & Kimmoun O. Tsunami generated by granular collapse down a rough inclined plane., Europhysics Letters. 105, 34004 (2014).
[3] Robbe-Saule M., Morize C., Henaff R., Bertho Y., Sauret A. & Gondret P. Experimental investigation of tsunami waves generated by granular collapse into water., J. Fluid Mech. 907, A11 (2021).
[4] Heller V. & Hager W. H. Impulse Product Parameter in Landslide Generated Impulse Waves., Journal of Waterway, Port, Coastal, and Ocean Engineering. 136, 145–155 (2010).