The Hunga Tonga-Hunga Ha'apai eruption on January 15 in the Kingdom of Tonga was an incredibly powerful explosion. It produced the loudest sound in over a century, sent a plume of material into the stratosphere, and generated a tsunami that spread across the Pacific. The height of the initial wave has now been estimated to have been 90 meters (295 feet), which is significantly higher than the deck of the Golden Gate Bridge, at is 75 meters (245 feet) above water.
The research is published in the journal Ocean Engineering and focused on atmospheric pressure waves and ocean oscillation. The Tonga tsunami was a volcanic tsunami and it had two components. The first waves were created by atmospheric pressure waves that circled the globe a few times. And the second surge was created by the water displacement about an hour later, with the initial wave reaching that incredible height and a length of 12 kilometers (7.5 miles).
“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,” lead author Dr Mohammad Heidarzadeh, Secretary-General of the International Tsunami Commission from the University of Bath, said in a statement.
The initial wave was nine times taller than the Tōhoku earthquake that hit Japan in 2011. The smaller casualty list is only thanks to how remote this event was.
“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 kilometers [43 miles] from the Tongan capital Nuku'alofa – this distance significantly minimized its destructive power,” Dr Heidarzadeh explained.
The research shows that the tsunami waves traveled not just through the Pacific, but across the world. The tsunami is one of the few recorded that are capable of doing this, with waves even reaching the coast of the Mediterranean Sea.
“The 2018 Anak Krakatau volcano and 2022 Hunga Tonga-Hunga Ha'apai volcano eruptions clearly showed us that coastal areas surrounding volcano islands are at risk of being hit by destructive tsunamis," Dr Aditya Gusman, Tsunami Modeller at GNS Science, explained.
"Although it may be preferable to have low-lying coastal areas completely clear from residential buildings, such a policy may not be practical for some places as volcanic tsunamis can be considered infrequent events.”
Co-author Dr Jadranka Šepić, from the University of Split, Croatia, added: “What is important is to have efficient warning systems, which include both real-time warnings and education on what to do in a case of a tsunami or warning – such systems save lives. In addition, at volcanic areas, monitoring of volcanic activity should be organized, and more high-quality research into volcanic eruptions and areas at hazard is always a good idea.”