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The massive eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano in Tonga on 15 January 2022 at 04:15 UTC had a global impact and triggered an atmospheric wave and a tsunami. We first analyzed observation data from meteorological stations and tide gauges at 12 locations. Low-frequency trends in the observation data were removed by using a high-pass filter. Fourier and wavelet spectral analyses were applied to determine the frequency characteristics of the filtered data. Modal analysis was developed and used to investigate natural oscillation periods based on bathymetry. The results showed that the Lamb wave generated by the atmospheric pressure wave arrived ~ 7 and ~ 44 h after the eruption. The tsunami arrived ~ 11 and ~ 45 h after the eruption, which corresponded to the arrival time of the Lamb wave. The dominant periods of the Lamb waves were ~ 7.7 and ~ 7.5 min, and for the tsunamis they were ~ 9.9 and ~ 28.7 min. The periods derived from the spectral analysis matched the natural oscillation of the eigenperiod derived from the modal analysis, in eight out of the twelve stations. This study provides valuable insight and information regarding the nonseismic and far-field effects of tsunamis generated by volcanic eruptions. [ABSTRACT FROM AUTHOR]

The 2022 Hunga Tonga-Hunga Ha'apai eruption generated tsunamis that propagated across the Pacific Ocean. Along the coast of Japan, nearshore amplification led to amplitudes of nearly 1 m at some locations, with varying peak tsunami occurrence times. The leading tsunami wave can generally be reproduced by Lamb waves, which are a type of air-pressure wave generated by an eruption. However, subsequent tsunamis that occurred several hours after the leading wave tended to be larger for unknown reasons. This study performs multi-scale numerical simulations to investigate subsequent tsunami waves in the vicinity of Japan induced by air pressure waves caused by the eruption. The atmospheric pressure field was created using a dispersion relation of atmospheric gravity wave and tuned by physical parameters based on observational records. The tsunami simulations used the adaptive mesh refinement method, incorporating detailed bathymetry and topography to solve the tsunami at various spatial scales. The simulations effectively reproduced the tsunami waveforms observed at numerous coastal locations, and results indicate that the factors contributing to the maximum tsunami amplitude differ by region. In particular, bay resonance plays a major role in determining the maximum amplitude at many sites along the east coast of Japan. However, large tsunami amplification at some west coast locations was not replicated, probably because it was caused by amplification during oceanic wave propagation rather than meteorological factors. These findings enhance our understanding of meteotsunami complexity and help distinguish tsunami amplification factors. [ABSTRACT FROM AUTHOR]

The 2022 eruption of the Hunga Tonga-Hunga Ha'apai volcano excited an atmospheric Lamb wave, which induced a fast-traveling tsunami. This tsunami was driven by the pressure-forced wave traveling at the speed of the Lamb wave and, thus, was much faster than conventional tsunamis. This was the first case in which ocean bottom monitoring systems widely observed an air pressure-induced tsunami. We found that the pressure-forced waves split and generated ocean gravity waves after passing the Japan Trench based on the S-net data. Our simulations show that changes in water depth can amplify or decrease the pressure-forced wave. Simultaneously, an ocean gravity wave is generated due to the conservation of water volume. Because the ocean gravity wave was slower than the pressure-forced wave near Japan, it was separated from, and traveled behind, the pressure-forced wave. We explained the wave separation phenomenon and reproduced the waveforms of different splitting stages observed by the stations near the Japan Trench. [ABSTRACT FROM AUTHOR]

Meteotsunamis (forced waves) triggered by atmospheric disturbances of Lamb waves due to the 2022 Hunga–Tonga volcanic eruption have been observed in coastal areas surrounding the Pacific Ocean. However, the spatiotemporal evolution of the wavefield of meteotsunamis and meteotsunami-induced free waves remains elusive. Here, we show the detailed spatial distribution of the propagation velocities and directions of these waves in the bathymetric slope area between the Japan Trench and nearshore, using a dense array of 150 absolute pressure gauges deployed at water depths of 100–8000 m. Records show that free wave components (i.e., tsunamis) were generated when the forced wave was propagating over the slope area. Amplitudes of the generated free waves are large in the southern half of the slope area, where the equi-arrival time contour lines are densely paralleled. Such amplifications occur due to the relationship between the incoming direction of Lamb waves and the gradient of the bathymetric slope. This indicates that, if meteotsunamis excited by Lamb waves due to future volcanic eruptions come from different directions to this region, a different spatial pattern of free wave amplification on a regional scale is obtained in the bathymetric slope areas. [ABSTRACT FROM AUTHOR]

The 2022 volcanic eruption in Tonga caused an unusually large tsunami around the Pacific. It travels with a faster apparent velocity and has larger amplitudes at long distances than what would be expected from a conventional tsunami from the volcanic source. This tsunami was generated by the moving atmospheric Lamb wave and traveled at the speed of the Lamb wave (0.31 km/s). Japanese data showed the amplitude of this first tsunami becomes small when approaching the coast, due to the weaker air‐sea coupling at the shallow depth. This wave split when passing the continental slope, and traveled at the speed of the ocean gravity wave. Therefore, the tsunami observed at the coast is delayed by thousands of seconds from the passage of the Lamb wave. Tsunamis generated by this atmospheric mechanism have not been previously observed by modern digital recording systems and should be considered in the tsunami warning systems. Plain Language Summary: A tsunami is usually generated by the sudden changes of the water heights, and caused by offshore earthquakes, coastal landslides, and submarine volcanic eruptions. The generated vertical displacement of the water propagates as a very long wave, and the tsunami waves become compressed with increased heights as they approach the coast. The 2022 volcanic eruption in Tonga caused an unusually large tsunami, which cannot be explained by conventional sources. The speed and amplitude are very different from theoretical values: the speed is about 0.31 km/s, whereas the average tsunami speed in the Pacific is 0.2 km/s. These data suggest that the tsunami from the Tonga eruption was excited by a pulse of atmospheric pressure as it traveled from the volcano. This source of the tsunami in the atmosphere needs to be considered for the tsunami warning system in the future. Key Points: Lamb wave produced by the volcanic eruption excites the sea surface as it travels across the Pacific and generates a tsunami pulseThe effect of the air‐sea coupling becomes weaker as the Lamb wave approaches the coastThe tsunami wave splits when passing the continental slope of Japan causing more complex waves [ABSTRACT FROM AUTHOR]