Global Tonga tsunami explained by a fast-moving atmospheric source

Volcanoes can produce tsunamis by means of earthquakes, caldera and flank collapses, pyroclastic flows or underwater explosions1,2,3,4. These mechanisms rarely displace enough water to trigger transoceanic tsunamis. Violent volcanic explosions, however, can cause global tsunamis1,5 by triggering acoustic-gravity waves6,7,8 that excite the atmosphere–ocean interface. The colossal eruption of the Hunga Tonga–Hunga Ha’apai volcano and ensuing tsunami is the first global volcano-triggered tsunami recorded by modern, worldwide dense instrumentation, thus providing a unique opportunity to investigate the role of air–water-coupling processes in tsunami generation and propagation. Here we use sea-level, atmospheric and satellite data from across the globe, along with numerical and analytical models, to demonstrate that this tsunami was driven by a constantly moving source in which the acoustic-gravity waves radiating from the eruption excite the ocean and transfer energy into it by means of resonance. A direct correlation between the tsunami and the acoustic-gravity waves’ arrival times confirms that these phenomena are closely linked. Our models also show that the unusually fast travel times and long duration of the tsunami, as well as its global reach, are consistent with an air–water-coupled source. This coupling mechanism has clear hazard implications, as it leads to higher waves along land masses that rise abruptly from long stretches of deep ocean waters.
This work was supported by projects: PTDC/CTA-MET/32004/2017 FAST, funded by FCT—Fundação para a Ciência e Tecnologia, I.P.; PTDC/CTA-GEO/28588/2017 - LISBOA-01-0145-FEDER-028588 UNTIeD, co-funded by the European Regional Development Fund (ERDF), through Programa Operacional Regional de Lisboa (POR Lisboa 2020), and by FCT; Spain Ministerio de Ciencia e Innovación proyecto PID2019-104571RA-I00 de investigación financiado por MCIN/AEI/10.13039/501100011033 and a 2020 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation to P.J.G. We would like to acknowledge Instituto Hidrográfico (IH, Portugal) and National Institute of Water and Atmospheric Research (NIWA, New Zealand) for providing sea-level and atmospheric data. We also thank colleagues from IPMA, R. Deus and C. Dutsch (funded by FAST project) for their support in collecting and processing atmospheric and sea-level data, and D. Gamboa for proofreading. Finally, we thank the three reviewers Matthew Alford, Raphaël Paris and Emily Lane for their encouraging comments that helped improve the paper.