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Dr Cronin said the Hunga eruption was a one-in-1000-year event.
Radiocarbon dating suggested one major eruption of this scale occurred about AD1100 and another in AD200, he said.
"This, along with other data from the volcanic ash records, suggests a recurrence interval of 900 to 1000 years for very large eruptions at the volcano.
"The current eruption seems to be one of these large events which fits with the timing since the last of these in [circa] AD1100."
All of the larger islands of Haʻapai are in the eastern Lifuka group. The two largest islands are Lifuka and Foa which have 2,205 and 1,392 people respectively as of 2016. The next largest are Nomuka and Haʻano, which have four villages, with a combined population of 910. To the south of these islands is ʻUiha, which has two villages with a combined population of 695. ʻUiha is also the site of ancient burial grounds and an ancient monument.
We’re still in the middle of this major eruptive sequence and many aspects remain unclear, partly because the island is currently obscured by ash clouds.
The two earlier eruptions on December 20, 2021 and January 13, 2022 were of moderate size. They produced clouds of up to 17km elevation and added new land to the 2014/15 combined island.
The latest eruption has stepped up the scale in terms of violence. The ash plume is already about 20km high. Most remarkably, it spread out almost concentrically over a distance of about 130km from the volcano, creating a plume with a 260km diameter, before it was distorted by the wind.
This demonstrates a huge explosive power – one that cannot be explained by magma-water interaction alone. It shows instead that large amounts of fresh, gas-charged magma have erupted from the caldera.
The eruption also produced a tsunami throughout Tonga and neighbouring Fiji and Samoa. Shock waves traversed many thousands of kilometres, were seen from space, and recorded in New Zealand some 2000km away. Soon after the eruption started, the sky was blocked out on Tongatapu, with ash beginning to fall.
All these signs suggest the large Hunga caldera has awoken. Tsunami are generated by coupled atmospheric and ocean shock waves during an explosions, but they are also readily caused by submarine landslides and caldera collapses.
It remains unclear if this is the climax of the eruption. It represents a major magma pressure release, which may settle the system.
A warning, however, lies in geological deposits from the volcano’s previous eruptions. These complex sequences show each of the 1000-year major caldera eruption episodes involved many separate explosion events.
Hence we could be in for several weeks or even years of major volcanic unrest from the Hunga-Tonga-Hunga-Ha’apai volcano. For the sake of the people of Tonga I hope not.
Shane Cronin is the Professor of Earth Sciences at the University of Auckland.
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De mooie zonsopgangen in Australië zijn er al.
“The large and explosive lateral spread of the eruption suggests that it was probably the biggest one since the 1991 eruption of Pinatubo,” added Cronin. This is a contention gathering support in some circles. However, estimations still vary widely, ranging from a mid-VEI 4 to a powerful VEI 6. The full details of the eruption likely won’t be confirmed for weeks.
Cronin and his research team camped on Hunga Tonga-Hunga Ha’apai in 2015 and noticed that the surrounding coral reef was lifting up, suggesting that magma was building underneath the volcano and could cause an eruption in the near future. The team found evidence of two previous mega-eruptions in AD 1100 and AD 200, suggesting they occur roughly once every 1000 years — making us due for a third.
In conclusion, Hunga Tonga’s Jan 15 eruption was not the ‘big one’, it wasn’t that monster VEI 6/7 that cools the planet by 2C and instantly propels us –in combo with an ever-waning sun– into Earth’s next period of global cooling; however…
Chances are, Hunga Tonga-Hunga Ha’apai isn’t quite done yet. The volcano has continued to erupt at a low level since the weekend, and further explosive events are likely over the coming days or weeks. The question is, what does it have left?
“The concern at the moment is how little information we have and that’s scary,” said Janine Krippner, a New Zealand-based volcanologist with the Smithsonian Global Volcanism Program. “When the vent is below water, nothing can tell us what will happen next.”
Superheated magma and a huge volume of volcanic gases rose quickly and met the cool seawater, intensifying the explosion, said Raymond Cas, a professor of volcanology at Australia’s Monash University. The fear is, something similar could be setting up again — further eruptions will be intensified by the vast amount of sea water filling the caldera/chamber, building pressure.
It’s a wait and see, though. “Once the volcano is de-gassed, it will settle down,” said American meteorologist, Chris Vagasky. But we don’t know if we’re there yet. Referring again to evidence of Hunga Tonga’s historical mega-eruptions, which appear to occur once every 1000 years, previously in AD 1100 and AD 200, these ancient sequences have always contained multiple high-level explosions over a closely-spaced period; thus, similarly sized –or even larger– eruptions are expected over the coming days/weeks/months/years — your guess is as good as mine… all eyes on Tonga.
Lane said the only similar volcanic tsunami event was Indonesia’s Krakatau eruption in 1883, which killed tens of thousands of people and obliterated the island.