Diverse tsunamigenesis triggered by the Hunga Tonga-Hunga Ha'apai eruption

On the evening of 15 January 2022, the Hunga Tonga-Hunga Ha'apai volcano(1) unleashed a violent underwater eruption, blanketing the surrounding land masses in ash and debris(2,3). The eruption generated tsunamis observed around the world. An event of this type last occurred in 1883 during the eruption of Krakatau(4), and thus we have the first observations of a tsunami from a large emergent volcanic eruption captured with modern instrumentation. Here we show that the explosive eruption generated waves through multiple mechanisms, including: (1) air-sea coupling with the initial and powerful shock wave radiating out from the explosion in the immediate vicinity of the eruption; (2) collapse of the water cavity created by the underwater explosion; and (3) air-sea coupling with the air-pressure pulse that circled the Earth several times, leading to a global tsunami. In the near field, tsunami impacts are strongly controlled by the water-cavity source whereas the far-field tsunami, which was unusually persistent, can be largely described by the air-pressure pulse mechanism. Catastrophic damage in some harbours in the far field was averted by just tens of centimetres, implying that a modest sea level rise combined with a future, similar event would lead to a step-function increase in impacts on infrastructure. Piecing together the complexity of this event has broad implications for coastal hazards in similar geophysical settings, suggesting a currently neglected source of global tsunamis.