From space, the moment before the Tonga disaster 0:42
Editor's note:
Shane Cronin is a professor of volcanology at the University of Auckland, New Zealand.
He has published more than 200 scientific articles on the chemistry and physics of active volcanoes and strives to understand the dangers they pose, especially in the Asia-Pacific region.
The opinions expressed here belong solely to the author.
(CNN) --
The eruption of the Hunga-Tonga-Hunga-Ha'apai volcano on Saturday was so big it was a sight best seen from space.
The eruption was notable in that it involved the simultaneous formation of a volcanic ash plume, an atmospheric shock wave, and a series of tsunami waves.
Although details continue to emerge and we are still in the midst of an eruption episode that could have more twists and turns, there are several pieces of information that can help us begin to understand this event and why it occurred.
How is and where is Tonga, the country affected by the eruption of an underwater volcano?
First of all, let's look at the eruption.
Events of this magnitude occur about once a decade around the world, but for this volcano an eruption of this scale is a rarity.
Based on my research, using radiocarbon dating to examine ash and deposits from previous eruptions, it appears that this latest eruption is a once-in-a-millennium event for the Hunga-Tonga-Hunga-Ha'apai volcano.
The Hunga volcano takes approximately 900 to 1,000 years to fill with magma, which cools and begins to crystallize, producing large amounts of gas pressure within the magma.
When the gases begin to build up pressure, the magma becomes unstable.
Think of it like putting too many bubbles in a bottle of champagne: eventually the bottle will break.
As the pressure of the magma increases, the cold, wet rock above the magma fails, suddenly releasing the pent-up pressure.
The eruption we saw on Saturday launched rock, water and magma 30 km high into the atmosphere, and it was deep in its energy.
Within 30 minutes, the resulting cloud, seen from space, was more than 350 km in diameter, and ash fell on several Tongan islands.
From space, the moment before the Tonga disaster 0:42
As for tsunamis, the most common is that they are caused by earthquakes.
When tectonic plates move under the ocean, they can displace enough water to cause massive waves.
So how can a partially submerged volcano in the Southwest Pacific create enough energy to produce tsunami waves that hit the West Coast of the United States?
Although it is still not clear 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 volcano's magma eruption created a sudden release of pressure, producing supersonic waves of air pressure that could be seen from space.
These atmospheric pressure waves traveled over 2,000 km to New Zealand and were felt as far as the UK and Finland.
Atmospheric waves and the initial explosion affected the ocean surface, causing the tidal waves that later hit the Tongan island of Tongatapu and the capital of Nuku'alofa. Early videos showed waves splashing onto roads before the ash plume darkened the sky.
Another possible cause of the tsunami waves could have been the remarkable changes inside the Hunga volcano. After the eruption, satellite radar images show that the central part of the volcano, which previously rose above sea level, has disappeared under the waves. This indicates that when the eruption occurred, the sudden loss of magma likely caused the central part of the volcano to collapse, creating a caldera, or hollow depression. This collapse could have displaced the water, generating tsunami waves that radiated out into the Pacific and as far as California.
Hunga's eruption was also amazing because of all the lightning generated.
This is due to the electrostatic interaction of very fine particles of volcanic "ash" in the air.
Weather satellites and lightning researchers consider this to be one of the most significant events they have ever seen, with as many as 63,000 lightning strikes every 15 minutes.
Another sign things are getting weird: Arctic lightning increased dramatically in 2021
Previous eruptions of this volcano, such as the one in 2014 that created a new island, included many eruption phases, so we could see more explosions in the coming days and weeks.
One moderating factor is that the caldera is now underwater, making it more difficult for eruptions to reach the atmosphere.
This could mean a shift towards more explosive submarine-type eruptions.
Although this means less atmospheric impact, there could still be an elevated risk of tsunamis, and people living in coastal areas of the Pacific should be on high alert in the coming weeks.
Although our previous research has underlined the importance of the power of eruptions at this volcano, it remains impossible to predict volcanic eruptions with precise day and time.
This is especially difficult in a volcano so far from the coast, without energy and with a changing and dynamic environment.
The only observations are possible through satellite methods, which at best give local Tongan residents a few minutes' notice.
They say that every big eruption brings with it a new surprise.
This event has clearly shown us that volcanoes can be very effective in generating tsunamis, and although Tonga is a long way from most countries, its volcanoes can threaten low-lying areas in nations around the world.
In the coming days or weeks, we will learn more about this fascinating and dangerous volcano and also about the dangers of submarine calderas.
Early reports suggest that Tonga has suffered significant damage from the tsunami, with many outlying areas still out of reach.
We can only hope that, for the time being, all Tongans are safe and sound.
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