Physical Model of Landslide‐Generated Impulse Waves: Experimental Investigation of the Wave‐Granular Flow Coupling

Large amplitude and unexpected waves are a regular source of natural disasters. Among them, impulse waves generated by landslides can represent a significant threat. Therefore, predicting and measuring the generation of such waves is essential. In this study, the phenomenon is modeled by a 2D‐experimental setup using a steady non‐uniform granular flow along a slope as a forcing wave generator. The present device provides a continuous supply of grains to avoid finite volume effects, as the part of the landslide actually involved in the wave generation strongly depends on the configuration and is not necessarily available in geophysical events. This system consists of an energy transfer between the granular flow and the wave generation which is characterized by a Froude number. It is found that the latter cannot be defined only based on the dry flow properties to characterize the wave. In particular, the dynamics underwater influence wave generation during a finite time. Accordingly, the present study shows that the wave maximum amplitude is governed by a newly defined Froude number, based on both dry and underwater granular flow properties. Moreover, it is shown that the granular deposit, specifically its runout, can be thought as a proxy of the immersed granular dynamics as long as the impact properties are still considered. Plain Language Summary Landslides can cause huge waves if they impact the surface of an ocean, a lake or a sea. The properties of the landslide as well as the wave formation are complex features. In this study, an attempt to model this phenomenon experimentally at the laboratory scale is made, using a controlled granular flow impacting water in a 2D wave channel. The rapid evolution of this system requires a camera in order to extract the dynamics of both the wave and the granular material, simultaneously. From these measurements, it is shown that the wave and the granular flow are strongly linked at early stages. Moreover, after the maximum wave amplitude is reached, the wave propagates freely and may influence the granular deposit. This study proposes to link these processes and the wave characteristics to a single dimensionless parameter, which is a combination of Froude numbers. Key Points A detailed analysis of new impulse wave experiments using a continuous granular supply is presented to highlight the wave‐granular coupling The wave maximum amplitude is shown to evolve non‐monotonically with the deposit runout Considering wave‐g