“We are under-prepared for volcanic tsunamis,” says Research author after finding the wave created by Tonga volcanic eruption was among very few tsunamis powerful enough to travel around the globe

The initial tsunami wave created by the eruption of the underwater Hunga Tonga Ha’apai volcano in Tonga in January 2022 reached 90 metres in height, new research has found.

By comparison, the largest tsunami waves due to earthquakes before the Tonga event were recorded following the Tōhoku earthquake near Japan in 2011 and the 1960 Chilean earthquake, reached 10 meters in initial height. Those were more destructive as they happened closer to land, with waves that were wider.

The research was carried out by analysing ocean observation data recordings of atmospheric pressure changes and sea level oscillations, in combination with computer simulations validated with real-world data.

The research team found that the tsunami was unique as the waves were created not only by the water displaced by the volcano’s eruption, but also by huge atmospheric pressure waves, which circled around the globe multiple times. This ‘dual mechanism’ created a two-part tsunami—where initial ocean waves created by the atmospheric pressure waves were followed more than one hour later by a second surge created by the eruption’s water displacement.

This combination meant tsunami warning centres did not detect the initial wave as they are programmed to detect tsunamis based on water displacements rather than atmospheric pressure waves.

The January event was among very few tsunamis powerful enough to travel around the globe—it was recorded in all world’s oceans and large seas from Japan and the United States’ western seaboard in the North Pacific Ocean to the coasts within the Mediterranean Sea.

Dr Mohammad Heidarzadeh, Secretary-General of the International Tsunami Commission and a senior lecturer in the University of Bath’s Department of Architecture & Civil Engineering, authored the research alongside colleagues based in Japan, New Zealand, the UK and Croatia. He notes that the Tonga tsunami should serve as a wake-up call for more preparedness and understanding of the causes and signs of tsunamis cause by volcanic eruptions. 

“The Tongan tsunami tragically killed five people and caused large scale destruction, but its effects could have been even greater had the volcano been located closer to human communities. The volcano is located approximately 70 kilometres from the Tongan capital Nuku’alofa—this distance significantly minimised its destructive power.”

“This was a gigantic, unique event and one that highlights that internationally we must invest in improving systems to detect volcanic tsunamis as these are currently around 30 years behind the systems we used to monitor for earthquakes. We are under-prepared for volcanic tsunamis.”

The paper “Estimating the eruption-induced water displacement source of the 15 January 2022 Tonga volcanic tsunami from tsunami spectra and numerical modelling” is published in Ocean Engineering (2022). Materials provided by Daniel Stolte, University of Bath.

This story was written by David Bressan, originally published at Forbes on 21 August 2022, reposted via PACNEWS.

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