Landslide‐generated tsunamis at Réunion Island

Abstract

Landslides that occur on oceanic volcanoes can reach the sea and trigger catastrophic tsunamis. Réunion Island has been the location of numerous huge landslides involving tens to hundreds of cubic kilometers of material. We use a new two‐fluid (seawater and landslide) numerical model to estimate the wave amplitudes and the propagation of tsunamis associated with landslide events on Réunion Island. A 10 km3 landslide from the eastern flank of Piton de la Fournaise volcano would lift the water surface by about 150 m where it entered the sea. The wave thus generated would reach Saint‐Denis, the capital of Réunion Island (population of about 150,000 people), in only 12 min, with an amplitude of more than 10 m, and would reach Mauritius Island in 18 min. Although Mauritius is located about 175 km from the impact, waves reaching its coast would be greater than those for Réunion Island. This is due to the initial shape of the wave, and its propagation normal to the coast at Mauritius but generally coast‐parallel at Réunion Island. A submarine landslide of the coastal shelf of 2 km3, would trigger a ∼40 m high wave that would severely affect the proximal coast in the western part of Réunion Island. For a landslide of the shelf of only 0.5 km3, waves of about 2 m in amplitude would affect the proximal coast.