The eruption of a volcano in Tonga in January 2022 has been confirmed as the biggest explosion ever recorded in the atmosphere by modern equipment.
It was far bigger than any volcanic event of the 20th century, or even any atomic bomb test conducted after World War II.
The assessment was presented in two academic articles, published in the journal Science, which reviewed all the data.
In recent history, it is likely that only the eruption of the Krakatoa volcano in 1883 can rival the atmospheric disturbance produced. This catastrophic event in Indonesia is believed to have killed more than 30,000 people.
Fortunately, the January 15 eruption of this year of the Hunga Tonga-Hunga Ha’apai (HTHH) undersea volcano, located in the South Pacific, resulted in very few deaths, although it also produced large tsunamis.
“Tonga was a truly global event, just like Krakatoa, but now we have all these geophysical observation systems, and they’ve recorded something really unprecedented in modern data.” , in the USA, who is the lead author of one of the articles.
Scientists now have access to an extraordinary array of ground and space instruments, including atmospheric pressure sensors, seismographs, hydrophones and a fleet of satellites that monitor Earth across the entire light spectrum.
The colossal explosion in Tonga, which came after several weeks of seamount activity, produced various types of atmospheric pressure waves that propagated over vast distances.
In the audible frequency range, people 10,000 km away in Alaska have reported hearing repeated bangs.
The global network of detectors created to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty picked up the infrasound signal.
Infrasound has frequencies that are just below what humans are capable of hearing.
Network data indicated that the Tonga volcano explosion produced an atmospheric pressure wave comparable to that of the largest nuclear explosion of all time — the Czar Bomba, detonated by the Soviets in 1961 — but lasted four times longer.
The articles discuss in depth the perturbations caused by so-called Lamb waves, named after the early 20th century mathematician Horace Lamb.
They are energetic waves in the air that propagate at the speed of sound, along a guided path across the surface of the planet. They are also non-dispersive, meaning they maintain their shape as they move and are therefore visible for a long time.
Lamb wave pulses produced by the Tonga eruption have been seen circling the Earth at least four times.
In the UK, which is about 16,500 km from Tonga, these pulses started arriving on the night of the 15th, about 14 hours after the eruption on the other side of the planet.
They lifted the clouds over the UK.
“At the time, we had a laser ceilometer (a device used to determine the height of clouds) looking at the base of the cloud, and as the wave passed through the cloud it was disturbed,” recalls Giles Harrison, an atmospheric physicist at the University of Reading. , in the United Kingdom, and co-author of one of the articles.
“If you ever wanted proof that the atmosphere is remarkably interconnected, it’s here. And what happens on one side of the planet can propagate to the other side at the speed of sound.”
Where Lamb waves joined ocean waves, they were able to generate tsunamis — not just in the Pacific Ocean, but also in the Atlantic Ocean and the Mediterranean Sea.
Scientists are still investigating the generation of nearby tsunamis that hit the coasts of the Tonga archipelago.
Some were undoubtedly created by pressure waves from the volcano pushing the surface of the water, but investigations are ongoing to determine whether the collapse of part of the volcano also contributed significantly.
This will be evident in the seabed mapping projects, the results of which are expected to be released in the coming weeks.
