Comment on nhess-2022-200

Abstract

On 15th January 2022, an exceptional eruption of Hunga Tonga–Hunga Ha’apai volcano generated atmospheric and tsunami waves that were widely observed at oceans globally, gaining a remarkable attention to scientists in related fields. The tsunamigenic mechanism of this rare event remains an enigmatic due to its complexity and lacking of direct underwater observations. Here, to explore the tsunamigenic mechanisms of this volcanic tsunami event and its hydrodynamic processes in the Pacific Ocean, we conduct tsunami waveform and spectral analyses of the waveform recordings at 116 coastal gauges and 38 deep-ocean buoys across the Pacific Ocean. Combined with the constraints of some representative barometers, we obtain the plausible tsunamigenic origins during the volcano activity. We identify four distinct tsunami wave components generated by air-sea coupling and seafloor crustal deformation. Those tsunami components are differentiated by their different propagating speeds or period bands. The first-arriving tsunami component with ~80–100 min period was from shock waves spreading at a velocity of ~1000 m/s in the vicinity of the eruption. The second component with extraordinary tsunami amplitude in deep sea was from Lamb waves. The Lamb wave with ~30–40 min period radically propagated outward from the eruption site with spatially decreasing propagation velocities from ~340 m/s to ~315m/s. The third component with ~10–30 min period was probably from some atmospheric gravity wave modes propagating faster than 200 m/s but slower than Lamb waves. The last component with ~3–5 min period originated from partial caldera collapse with dimension of ~0.8–1.8 km. Surprisingly, the 2022 Tonga volcanic tsunami produced long oscillation in the Pacific Ocean which is comparable with those of the 2011 Tohoku tsunami. We point out that the long oscillation is not only associated with the resonance effect with the atmospheric acoustic-gravity waves, but more importantly the interactions with local bathymetry. This rare event also calls for more attention to the tsunami hazards produced by atypical tsunamigenic source, e.g., volcanic eruption.