Scientists from Instituto Dom Lewis and IPMA reveal the event that triggered the global spread of the Tonga tsunami

A sonic gravity wave from the violent eruption of the Hanga Tonga-Hunga Ha’pai volcano in the South Pacific on January 15 was the origin of the resulting global tsunami. The conclusion of a group of researchers from the Dom Luis Institute, the Faculty of Sciences of the University of Lisbon and the Portuguese Ocean and Atmosphere (IPMA).

Through a combination of sea level, atmospheric and satellite imagery data from different parts of the world, and their use of numerical and analytical models, the scientists demonstrated that “the tsunami was driven by a continuously moving source of acoustic gravity waves.” Volcanic eruptions excite the ocean and transfer energy to it through vibration,” says the study, published in Nature. “Global Tonga Tsunami Explained by Fast-Moving Atmospheric Source”.

The coincidence between the tsunami and the arrival of these acoustic gravity waves, according to the researchers, confirms the existence of a direct link between the two phenomena. “The violent eruption of the volcano generated significant atmospheric waves and generated an exceptionally fast global tsunami,” commented lead author Rachid Omira, a researcher at the Instituto Dom Lewis and IPMA.

The geophysicist gives an example of the fact that the Portuguese coast, on the opposite side of the planet (17 thousand kilometers away) “ten hours earlier than expected”, crossed the seas and caused sea waves of surprising magnitude. , has remote territories.

“This is the first time that a volcano-triggered tsunami has been recorded globally with modern and dense instruments, which provides a unique opportunity to investigate the wind/water coupling processes in its generation and propagation,” says Omira.

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It is common for volcanic eruptions to cause tsunamis, but now trans-oceanic effects are rare. In Portugal, “changes in sea level” were observed in the Azores, Madeira and the mainland, according to IPMA information published at the time. 40 cm in Ponta Delgada, 39 cm in Beniche, 20 cm in Funchal.

“This tsunami spread across different oceans, including the Atlantic, and practically all tide gauge stations operating along the Portuguese coast showed variations in sea level, with amplitudes of less than half a meter,” IPMA was later informed.

The eruption of the submarine volcano, a few kilometers off Tonga, sent a cloud of ash and gases reaching a height of 20 kilometers. Tsunami waves caused damage in New Zealand, Chile, Peru and the United States.

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