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Abstract:
The 2022 Tonga volcanic eruption generated a surprisingly large air-pressure wave (lamb wave) and a locally damaging tsunami. The tsunami generation is still puzzling because both the air wave and submarine explosion drove changes in sea level. Here we have derived observational evidence from satellite altimetry (a rarity for a volcanic tsunami), assisted by a combined atmospheric and oceanic tsunami model, to shed light on its genesis. We found that three satellites had captured the sea level signal of the tsunami: the AltiKa satellite observed the near-field tsunami, 29 minutes after the eruption, while the Sentinel-6 Michael Freilich and Jason-3 satellites in tandem 30 seconds apart captured the tsunami through the volcano center and encountered the tsunami wave at about 54oS about 5 hours after the eruption. We proposed a mass-conserving tsunamigenic mechanism, which couples the volcanic ejecta to ocean waters filling in the erupted crater, to reconcile the satellite observations with other in-situ measurements. We concluded that the erupted air-waves had increased the tsunami’s destructive power through the inverted barometer effect during their overlapping period in the near field, and orchestrated the far-field disturbance in the Pacific Ocean and beyond. Our study also demonstrated an altimetry procedure to isolate tsunamis from ocean dynamic features and a data-based approach to quantify volcanic tsunami source for early warnings.
