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This satellite image, provided by the Cooperative Institute for Research in the Atmosphere (CIRA) and the National Oceanic and Atmospheric Administration (NOAA), shows the Hunga Tonga-Hunga Ha'apai eruption on January 15, 2022.
Photo: CIRA/NOAA HANDOUT/EPA
About 30 kilometers southeast of the island of Fonuafo'ou, also known as Falcon Island, in the Kingdom of Tonga, an undersea volcano erupted on Saturday: the Hunga-Tonga-Hunga-Ha'apai.
The volcano spewed ash, steam, and gas for miles.
The water around the volcano piled up.
The shock waves from the eruption could be measured almost anywhere on the globe.
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Residents of the surrounding islands and archipelagos of Tongatapu, Ha'apai and Vava'u have been advised to remain indoors as much as possible, wear masks outdoors and cover rainwater reservoirs.
After all, volcanic ash can be toxic.
And if volcanic ash particles settle in the lungs and airways, it can be a health hazard.
Also, they should stay away from the coast.
A total of around 105,000 people live in the Pacific state.
The island nation's king, Tupou VI, was reportedly transferred from his palace in Nuku'alofa to a villa far from the coast.
Internet and mobile phone connections collapsed, air traffic was massively restricted.
New Zealand's Prime Minister Jacinda Ardern said Sunday that a tidal wave had caused "significant" damage to parts of Tonga's capital, Nuku'alofa.
The city is covered with a "thick layer of volcanic ash, but otherwise the situation is calm and stable".
As soon as the situation permits, the New Zealand Air Force will launch a reconnaissance flight to Tonga's more remote islands.
The volcano has been active again since 2009
This eruption was not the first of the Hunga-Tonga-Hunga-Ha'apai, but it was an eruption of unusual proportions.
An eruption in 1912 is documented, and the volcano also spewed ash in 1937.
From 2009 it erupted several times and has been active again since December 2021.
And only on Friday had experts observed a smaller eruption of the volcano.
Tonga Geological Survey chief Taaniela Kula said this eruption is at least seven times larger than the last on December 20.
The radius of the eruption can be estimated at around 260 kilometers.
On Saturday, the outbreak followed again – with even greater force.
Comparable to a magnitude 5.8 earthquake
The tremors were equivalent to a magnitude 5.8 earthquake right on the surface, according to the US Geological Observatory.
The effects of such an earthquake are generally rated as medium on the Richter scale, which classifies and describes the strength of earthquakes: Less robust buildings can suffer major damage, stable buildings tend to suffer little damage, and the extent of the destruction is usually spatially limited .
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But when a volcano erupts in the sea, the destruction can be more widespread: tsunami warnings have not only been issued for Tonga, but for eight other countries - the USA, which has the American Samoa territory, Fiji, Vanuatu, New Zealand, Australia, Ecuador, Chile and Japan. Tsunami waves - albeit smaller ones - spread across the Pacific, causing flooding in Alaska, Oregon, Washington State and British Columbia. Measuring stations in California, Mexico and parts of South America also registered smaller tsunami waves. What exactly triggered the tsunamis is not yet clear.
In Japan, hundreds of thousands have been affected by the effects of the outbreak.
The Japanese meteorological authority had warned of waves up to three meters high, on Sunday more than 200,000 people in eight prefectures in Japan were called to evacuate, they should go to higher areas to safety.
In some regions, high waves hit the land, after local time in the early afternoon, the precautionary measures were lifted again.
So far there have been no reports of deaths or injuries.
Steam can also explode
Still, the volcano's power and global impact may come as a surprise.
Finally, the tip of Hunga-Tonga-Hunga-Ha'apai - which is made up of the two small uninhabited islands of Hunga-Ha'apai and Hunga-Tonga - rises a little more than 100 meters out of the water.
And you might think that the cool ocean is slowing down volcanic activity.
But: Under water, the volcano reaches a height of around 1800 meters - and a width of 20 kilometers.
A volcano can also develop explosive power under the sea.
How, explained for example the volcanologist Shane Cronin, who works at the University of Auckland in New Zealand, in a contribution for the news network »The Conversation«.
He describes the phenomenon as follows: seawater normally cools magma down.
Even at temperatures of around 1200 degrees Celsius, a thin vapor film forms between magma and water.
This film acts as an insulating layer, cooling the outer surface of the lava flow.
But this only works if the magma flows slowly into the sea water and turns into lava.
When magma full of volcanic gases is ejected from the ground, the insulating vapor layers are breached.
The hot rock liquid thus comes into direct contact with the comparatively cold water.
A violent explosion occurs, tearing the magma apart.
The also red-hot magma fragments come into contact with the water, which causes further explosions.
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The eruption observed now may have been so strong, the scientist writes, because the last major eruption occurred around the year 1100.
This was shown by geological data.
Since then, molten rock has been able to collect at depth and form a magma reservoir.
If the huge reservoir of magma finds an opening, there will be a violent depressurization, emptying much of the molten reservoir in a violent explosion -- an explosion like the one that happened Saturday.
There is an eruption like this about every 1000 years.
The timing is therefore not surprising.
Has the danger passed?
If an eruption of this magnitude occurs only once in a millennium, will the danger have been averted for the time being? That cannot be said with certainty at this point in time. It's possible that Saturday's eruption ejected most of the magma from the volcano's interior. However, it is also conceivable that residues will remain that can lead to new outbreaks. Volcanic activity is monitored by various authorities around the world. However, this is made more difficult by the remote location of the volcano.
In addition, the Hunga-Tonga-Hunga-Ha'apai is far from the only active volcano in the region.
It has to do with plate tectonics.
Simply put, because the Pacific Plate is continuously pushing under the Australian tectonic plate, water seeps into the rocks of the Earth's crust, which lowers the melting point and contributes to the formation of magma.
So the danger of a volcanic eruption in the Pacific region is never completely averted.
With material from dpa, AFP and Reuters