The wave created by the Hunga Tonga eruption was 9 times higher than the Fukushima earthquake

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[EN VIDÉO] Kézako: the secrets behind the creation of tsunamis
Tsunamis are among the most devastating natural disasters. These waves, which can reach thirty meters in height, hit the shores with unstoppable force. Unisciel and the University of Lille 1 reveal to us with the Kézako program the secrets behind the creation of this phenomenon.

Last January, the underwater volcano Hunga Tonga-Hunga Ha’apai exploded violently in the Pacific Ocean and caused a tsunami that spread rapidly through all the world’s oceans. Considered one of the most violent eruptions of the century, this event is notable above all for the amount of scientific information collected. The analysis of the data thus made it possible to study in detail the mechanism behind this powerful tsunami and its characteristics.

It thus appeared that the wave had spread to one velocity record thanks to the acoustic gravity waves generated by the explosion. A phenomenon resonance would have made it possible to amplify the tsunami and cause the destructive wave to travel at a speed far superior to the classical tsunamis produced duringcollapses sides of volcanoes or earthquake.

A wave at the beginning 90 meters high

But the special nature of this tsunami does not stop there. According to a recent study, the wave would have initially reached a height of 90 meters, about nine times the height of the tsunami that hit the coast of Japan in 2011, which produced the nuclear disaster at the Fukushima power plant. This latest tsunami was caused by a very powerful earthquake along the Japanese coast. Remember that this event is one of the largest tsunamis in recent decades, with the one that hit Chile in 1960. However, their initial height was estimated at around ten meters – dwarf waves compared to the one generated during the eruption of Hunga Tonga-Hunga Ha. ‘apai.

However, the tsunamis of 2011 and 1960 were far more destructive and deadly. More than 18,000 died after the 2011 tsunami, while the Hunga Tonga tsunami fortunately caused only a few people to disappear. To explain this difference, it is necessary to take into account several parameters that will influence the height of the wave when it arrives at the shore. There is, of course, the distance between the source of the tsunami and the land, it morphology bottom and coastline, but also other factors, such as fusion several waves (which seems to have been the case in 2011). When approaching the coast, a tsunami wave can thus either be attenuated or amplified.

Fortunately, the Hunga Tonga volcano is located about 70 kilometers from the Tonga Islands. This is certainly what made it possible to avoid a terrible disaster. The maximum height measured at the ribs was just under 1.50 metres. Enough to cause significant damage though.

Tsunami risk: Underwater volcanoes must also be monitored

However, scientists are drawing door bell alarm. Because if the seismic zones that have historically generated tsunamis are now under close surveillance, with especially the development of increasingly early warning systems, the underwater volcanoes are much less monitored. And this latest event reminds us that they pose a threat as serious, if not more so, than larger earthquakes. If Hunga Tonga had been located close to the coast, as is the case with many active submarine volcanoes, the situation could have been extremely dramatic.

The results, published in the journal Ocean Engineering, shows the importance and necessity of developing effective tsunami warning systems that make it possible to evacuate as quickly as possible the inhabitants of the coasts that are likely to be destroyed by several tens of thousands of high waves. At the same time, the monitoring of volcanic activity of underwater volcanoes the most dangerous must be reinforced or even put in place.

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