Opinion: The huge volcanic eruption in Tonga was an event that once in a millennium

The eruption was remarkable in that it involved the simultaneous formation of a volcanic ash flag, an atmospheric shock wave and a series of tsunami waves.

While details are still popping up and we are still in an outbreak episode that could have several twists and turns, there is several pieces of information that can help us begin to understand this event and why it occurred.

Let’s look at the eruption first. Events of this magnitude occur roughly once a year around the world, but for this volcano, an eruption of this scale is a rarity. Based on my research, using radiocarbon dating to examine the ash and deposits from previous eruptions, it appears that this most recent eruption is a once-in-a-millennium event for Hunga-Tonga-Hunga-Ha’apai the volcano.
It takes about 900-1000 years for the Hunga volcano to fill up magma, which cools and begins to crystallize, producing large amounts of gas pressure inside the magma. As gases begin to build up pressure, the magma becomes unstable. Think of it as putting too many bubbles in a champagne bottle – eventually the bottle will break.
As the magma pressure rises, the cold and wet rock fails over the magma and suddenly releases the trapped pressure. The eruption we saw last Saturday blew up rocks, water and magma 30 km high into the atmosphere and was deep in its energy. Within 30 minutes resulting cloud seen from space was over 350 km (or 218 miles) in diameter, with ash falling on several Tongan islands.
As for tsunami, they are most often caused by earthquakes. When tectonic plates shift under the ocean, it can displace enough water to cause massive waves. So how does a partially submerged volcano in the southwestern Pacific create enough energy to produce tsunami waves that hit The west coast of the United States?
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Although it is still unclear what exactly caused the tsunami, there are at least two different possibilities – and the first has to do with the expansive force of the initial eruption. On Saturday, the eruption of magma from the volcano created a sudden release of pressure, producing supersonic air pressure waves that could be seen from space.
These air pressure waves traveled more than 2,000 km (1,200 miles) New Zealand and was felt as far as to Britain and Finland.
The atmospheric waves and the initial explosion affected the sea surface and caused the giant waves that then hit the Tongan island of Tongatapu and the capital Nuku’alofa. Early videos showed the waves splashing across roads before the ash flag darkened the sky.
Another possible cause of the tsunami waves could have been the remarkable changes in the Hunga volcano. In the wake of the eruption, images from satellite radar images show the central part of the volcano, which previously rose above sea level, has since disappeared below the waves. This indicates when the eruption took place, the sudden loss of magma probably caused the central part of the volcano to collapse, creating a caldera or a hollow depression. This collapse could have displaced the water and generated tsunami waves that radiated across the Pacific Ocean and all the way to California.
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The Hunga outbreak was also astonishing in terms of all the lightning generated. This is caused by the electrostatic interaction of very fine volcanic “ash” particles in the air. Weather satellites and lightning scientists call this one of the most significant events they have ever seen, with lightning peaks at 63,000 events per. 15 minutes.
Previous eruptions from this volcano – such as the eruption in 2014 that created a new island – included many phases of eruptions, and thus we could see more explosions in the coming days and weeks. A moderating factor is that the caldera is now underwater, making it harder for eruptions to break through into the atmosphere.

This could mean a shift to more submarine-like explosive eruptions. Although this would mean a less atmospheric impact, there may still be an increased risk of tsunamis, and people living in coastal areas around the Pacific Ocean should be on high alert in the coming weeks.

Though our previous research has highlighted the importance of the power of eruptions at this volcano, and predicting volcanic eruptions by day and hour is still impossible. This is especially difficult with a volcano so far off the coast, without power and a changing, dynamic environment. The only observations are possible via satellite methods, which at best provide a few minutes warning for the local residents of Tonga.

They say that each major eruption brings with it a new surprise. This event has clearly shown us that volcanoes can be very effective in generating tsunami events, and while Tonga is far away from most other countries, volcanoes can threaten low-lying areas of nations around the globe.

Over the next few days to weeks we will learn more about this fascinating and dangerous volcano and also the dangers of underwater calderas. Early reports suggests that Tonga has experienced significant damage due to the tsunami, where many outlying areas are still out of reach. We can only hope at the moment that everyone in Tonga is doing well.


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