Insights into the generation, propagation, and impacts of volcanogenic tsunamis: from Fogo to Tonga

Séminaire de Ricardo Ramalho (Lecturer in GeoEnvironmental Hazards, Cardiff Univ.)

Abstract: Volcanoes can be the source of devastating tsunamis, through different generational mechanisms including earthquakes, caldera and flank collapses, pyroclastic flows, and explosions. In this talk I will review two of these mechanisms – mass wasting and submarine/subaerial explosions – and discuss how field and instrumental evidence may be used to calibrate and improve numerical models for the generation, propagation, and impact of these tsunamis, and ultimately to better constrain the hazard potential of such events. I will start by exploring in detail how field evidence (supported by isotopic geochronology) from the Cape Verde Archipelago confirms that indeed large scale flank collapses of oceanic islands are capable of triggering megatsunamis with devastating consequences, especially in the near field. I will also explore how, by using an integrated onshore/offshore approach coupled with numerical modelling, we can gain insights on the processes of generation, propagation and inundation of collapse-triggered tsunamis, to ultimately address the controversial question of the far-field impacts of these waves. Insights into possible return periods for these events will also be offered. Finally, I will also explore how a wealth of sea-level, atmospheric and satellite data from across the globe, along with numerical modelling, shows that the tsunami generated by the recent colossal eruption of the Hunga Tonga-Hunga Ha’apai volcano had a global reach and was driven by a constantly moving source in which the acoustic-gravity wave fronts radiating from the eruption transfer energy into the ocean via a resonance mechanism.