[M-IS23] Dynamics of eruption cloud and cumulonimbus; modelling and observation

[MIS23-01] Tsunami caused by the shock wave of the 2022 Tonga volcanic eruption

★Invited Papers

*Masumi Yamada¹, Tung-Cheng Ho¹, James Mori¹, Yasuhiro Nishikawa², Masa-yuki Yamamoto² (1.Disaster Prevention Research Institute, Kyoto University, 2.Kochi University of Technology)

Keywords:tsunami, volcano, Tonga, shock wave, Lamb wave

A tsunami is usually generated by the sudden vertical 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 ocean is 0.2 km/s. The amplitude attenuation is small and the height is about the same at the stations across the Pacific Ocean. These data suggest that the tsunami from the Tonga eruption was excited by a pulse of atmospheric pressure as it traveled from the volcano. We propose that this tsunami shock wave, which was generated by a moving atmospheric source, is the primary cause for the unexpectedly large heights. Due to the continuous generation of the tsunami by the traveling atmospheric source, a tsunami with unexpectedly large amplitudes was observed in distant countries, such as Japan, the United States, and Chile. The new mechanism of tsunami generation suggests even an onshore volcanic eruption can cause a tsunami over 1000 km away. This source of the tsunami in the atmosphere needs to be considered for the tsunami warning system in the future.