Tsunami generated by subaerial gravity flows – Slide2Wave

The Slide2Wave project aims to understand the physical mechanisms that control the entrance of gravity flows into water and the generation of tsunami, and to propose strategies for hazard assessment.
Although most of the tsunamis are generated by earthquakes (and warning systems being suited only for earthquake sources), other potential sources such as volcanic eruptions with landslides or pyroclastic flows or eruptive column collapses can generate tsunamis, as demonstrated by the Anak Krakatau flank collapse in 2018 and the Tonga eruption of 2022, but are less known and underestimated. The physics behind these gravity flows might be very different from one case to another and thus requires different experimental and modelling strategies for hazard assessment.
Slide2Wave will combine the use of new laboratory experiments and advanced numerical models to understand the physical mechanisms of gravity flow tsunamis and move the frontiers of our knowledge towards the complexity of natural cases, apply these models to well-documented case studies, and propose reliable strategies for hazard evaluation. This will give the fundamental basis on which better risk assessment could be proposed in a near future.
The Slide2Wave project is structured in three tasks each mixing experiments and simulations conducted by physicists and geophysicists from three laboratories of fluid mechanics (FAST Lab in Orsay, IMFT in Toulouse and ?’Alembert in Paris) and the Laboratory of Magmas and Volcanoes in Clermont-Ferrand. In a first task devoted to the entry of dense flows into water, experiments of gravity collapse of cylindrical granular columns in a tank are proposed coupled with VOF-type simulations. In this three-dimensional configuration modelling of the collapse of volcanic islands, it is the influence of radial dispersion that is particularly sought. The second task concerns the impact in water of a densely stratified granular layer flowing along an inclined plane in a channel, with a dense basal layer topped by a turbulent dilute layer. In this configuration, the gaseous fluidization of the granular flow is important and the emphasis will be on the influence of grain polydispersity and of high grain temperature. The simulations will be of two complementary types, with an Euler/Euler type approach and a thin multi-layer approach to address the largest scales. In a third task, the vertical impact of a column of gravity-falling polydisperse grains in water will be studied. The laboratory experiments will be coupled here with Euler/Euler simulations, which are well adapted to rather dilute grain flow in air and water. In each task, it is the generation of waves at the water surface by the entry of the grains in water that is at the center of the project for its tsunamigenic character.
These different experimental configurations coupled with the different types of numerical simulations will make it possible to better understand the mechanisms of tsunami-type wave generation by gravity flows of dense or diluted or mixed grains, and also of the shape of final deposits.
Beyond the promotion of results in international journals and conferences, outreach actions will be carried out among the general public and actions will also be carried out to help in defining risk prevention strategies.