The super shock wave of the Tonga eruption

For the force of the explosion, for the tsunami generated, for the height that the ash reached and last but not least for the roar that provoked the eruption – still under investigation – of the Hunga Tonga-Hunga Haʻapai underwater volcano, which took place on January 15, it never stops being amazed. The latest “record”, if it can be defined as such, concerns the atmospheric wave generated by the eruption that has affected the entire planet several times and has been studied by various researchers around the world, including the Italian des Institute of Geophysics and Volcanology at the Spanish Institute of Advanced Studies in Mallorca, Spain.

The latter, led by Ángel Amores, an oceanographer, analyzed the data collected by various observers and thus confirmed that the atmospheric wave took 36 hours to circumnavigate the globe, spreading out from the volcano in concentric rings and traveling at the speed of sound . Their analysis was published in the journal Geophysical Research Letters.

Simultaneous passage. Similar to the Institute for Advanced Studies on Mallorca, the company Weathernews, which operates a network of thousands of meteorological sensors in Japan, also recorded the atmospheric wave. Many of their sensors picked up air pressure spikes almost simultaneously with the first shock wave on January 15 and also recorded the return wave on January 17 (see video below).

During the voyage, the shock wave caused small changes in atmospheric properties, altered temperature, the presence of water vapor, or created waves that could be seen on some satellite images, see below.

And that happened in the United States, Great Britain, Germany, India, China, Australia and Italy. After about 17 hours in the atmosphere, the sound waves generated by the explosion reached Etna and were recorded by the permanent infrasound network operating on the volcano.

The acoustic waves were not audible because they were below the frequencies (below 20 Hz) that the human ear can perceive; but Etna’s infrasound network was designed precisely to detect the soft “roar” of volcanoes. The second pass of the sound wave was recorded on the 17th at 9:25 am. Assuming a distance of about 40,000 kilometers, the average speed was about 1,111 km/h, close to the speed of sound at sea level, which is 1.35 km/h.

The issue of Focus on newsstands from April 21 to May 20 devotes an article by Liigi Bignami to all the historical eruptions that have had impacts on a planetary scale, altered the climate or made their effects felt even tens of thousands of kilometers away. Check out the preview.

Like the worst atomic ones. Both Amores and other scientists who have been studying similar phenomena for years have defined what caused Tonga as “extraordinary,” because to see anything similar you have to go back to the nuclear explosions in the atmosphere in the 1960s.

According to Brown, the wave produced by the burst was similar in size to that of the largest atmospheric nuclear test ever conducted, that of the Tsar Bomb. It was detonated in the Soviet Arctic in 1961, releasing an energy equivalent to about 50 million tons of TNT. “The explosion in Tonga definitely released more than that amount of energy,” Brown says. The observed changes in atmospheric pressure as the wave traveled around the Earth were relatively small, a deviation of less than 1 percent from the standard pressure. But the changes lasted for tens of minutes and that shows how much energy was at stake.

According to Greg Dusek, a NOAA physicist, this was probably the first time since the massive Krakatoa eruption of 1883 that a volcanic eruption has managed to create a global shock wave, which in turn created sea waves in ports around the world. The Krakatoa shockwave, which damaged sailors’ eardrums on a ship 70 kilometers away, was recorded by barometers around the world and also circled the earth at least three times. “However, this is the first time,” Dusek wrote, “that we have been able to observe such a phenomenon in real time.”

Not just shock waves. In Tonga, the January 15 eruption killed at least three people; Homes, roads, infrastructure and seeding areas have been destroyed or damaged and the coral reef has suffered undefined damage. The main damage – estimated by the World Bank at $90 million – was caused by the volcanic ash and tsunami that followed the eruption. The tsunami spread across the Pacific Ocean, producing waves up to five feet high along the North American coast and the highest in South America. In some locations in the Pacific, the tsunami came at high tide, resulting in the highest water levels since the 1950s.

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