The fact of being away from inhabited cities avoided a great tragedy, affirms an investigation
The initial wave of the tsunami created by the eruption of the submarine volcano Hunga Tonga Ha’apai in Tonga in January 2022 reached 90 meters in height, about nine times higher than that of the 2011 Japanese tsunami, which was highly destructive, new research has found. This size was reached at the very moment of the eruption and progressively decreased.
An international research team has warned that the eruption should serve as a wake-up call to protect people from similar events in the future. They also warn that detection and monitoring systems for tsunamis caused by volcanoes are 30 years behind the tools used to detect earthquakes.
Mohammad Heidarzadeh, secretary general of the International Tsunami Commission and a professor at the University of Bath, authored the research along with colleagues based in Japan, New Zealand, the UK and Croatia.
By comparison, the largest tsunami waves due to earthquakes before the Tonga event were recorded after the Tonga earthquake. Tōhoku near Japan in 2011 and the 1960 Chile earthquake, which reached 10 meters in height initial. Those were more destructive as they passed closer to land, with waves that were wider.
could be a great tragedy
Heidarzadeh says that the Tonga tsunami should serve as a wake-up call for greater preparedness and understanding of the causes and signals of tsunamis caused by volcanic eruptions. He says that “the Tonga tsunami killed five people and caused large-scale destruction, but its effects could have been even greater if the volcano had been located closer to human communities. The volcano is located approximately 70 km from the Tongan capital Nuku’alofa; this distance significantly minimized its destructive power.”
“This was a gigantic and unique event that highlights that internationally we must invest in improving systems to detect volcanic tsunamis, as they are currently around 30 years behind the systems we use to monitor earthquakes. We are not prepared for volcanic tsunamis.”
The research was carried out by analyzing ocean observation data records of atmospheric pressure changes and sea level oscillations, in combination with computer simulations validated with real-world data.
atmospheric pressure waves
The research team found that the tsunami was unique in that it the waves were created not only by the water displaced by the eruption of the volcano, but also by huge waves of atmospheric pressure, which went around the world several times. This ‘dual mechanism’ created a two-part tsunami, where the initial ocean waves created by atmospheric pressure waves were followed more than an hour later by a second wave created by the displacement of water from the eruption.
This combination meant that tsunami warning centers did not detect the initial waveas they are programmed to detect tsunamis based on water displacements rather than atmospheric pressure waves.
The research team also found that the January event was one of the few tsunamis powerful enough to travel around the world: was recorded in all the oceans and large seas of the world from Japan and the western coast of the United States in the North Pacific Ocean to the coasts within the Mediterranean Sea.
Aditya Gusman, a tsunami modeler at the New Zealand-based geoscience service, says “The 2018 Anak Krakatau volcano and 2022 Hunga Tonga-Hunga Ha’apai volcano eruptions clearly showed us that coastal areas surrounding volcanic islands are at risk of being hit by destructive tsunamis. Although it may be preferable to have low-lying coastal areas completely cleared of residential buildings, such a policy may not be practical for some locations, as volcanic tsunamis may be considered infrequent events.”
Co-author Jadranka Šepić, from the University of Split, Croatia, adds that “the important thing is to have efficient warning systems, which include both real-time warnings and education on what to do in the event of a tsunami or warning, because such systems save lives. Also, in volcanic areas, monitoring of volcanic activity should be organized, and it is always a good idea to conduct more high-quality research on volcanic eruptions and endangered areas.”
Separate research led by University of Bath atmospheric physicist Corwin Wright, published in June, found that the Tonga eruption triggered atmospheric gravity waves that reached the edge of space.
Reference study: https://www.sciencedirect.com/science/article/pii/S0029801822014810?via%3Dihub
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