We have been warned repeatedly that rising sea levels will wipe small Pacific Island nations from the map of the world thanks to climate change; that they are particularly vulnerable to human-caused emission of carbon dioxide. Not so the island of Hunga Tonga – Hunga Ha’apai. It wasn’t overtaken by rising sea levels. Rather it blasted itself into the sky! Obliterated in an instant. The massive volcanic eruption caused sonic booms, tsunami waves, spectacular lightning bolts, and a giant umbrella cloud that rose to a height of 30 kilometres and reached 500 kilometres in diameter in less than 2 hours.
I was reminded of that exhaustingly long novel ‘Hawaii’ by James Michener – it begins with comment about the relentless surge of the universe, the violence of birth, the cold tearing away of death; and yet how promising was the interplay of forces as an island struggled to be born, vanishing in agony.
This fiction gets closer to the truth than many of the leaders of Pacific Island Nations that lament carbon dioxide emissions from human-sources while apparently blind to the reality that they are standing atop extinct volcanoes that once belched carbon dioxide. And never mind that a recent University of Auckland study found the purportedly ‘at risk’ Marshall Island, Kiribati, as well as the Maldives archipelago in the Indian Ocean, have grown in land area by up to 8 percent over the last six decades, despite rising sea levels – because of the accumulation of coral sediment.
To be clear, most volcanic islands that have persisted, eventually by their very nature gradually sink again because they are effectively floating on top of hot ductile rocks that slowly give way. Observed subsidence of many hundreds of metres in the case of flat-topped wave-eroded seamounts cannot be explained by sea level rise alone. The islands that continue to exist in tropical waters still have corals growing on top of their subsiding summits, with some of the dead coral accumulating as sediment, thrown, or blown above sea level during storms and cyclones. Kiribati, Tuvalu and Marshall Islands in the Pacific, and the Maldives and Seychelles in the Indian Ocean, are all atolls built up from dead corals that grow on-top of long extinct subsiding volcanoes.
The spectacular emergence of Hunga Tonga – Hunga Ha’apai as a small island just a few years ago is evidence that the long-drawn-out geological processes that can create new Pacific islands continue to the present day. The island’s even more spectacular obliteration through an explosion on 15 January, may not be its end. It has erupted on a similar scale at least twice before in the last few thousand years, and this latest eruption is perhaps just a short setback in a million-year long story.
We marvel when a volcano explodes, and mostly ignore them the rest of the time.
Hawaii’s Mauna Loa is the world’s largest active volcano, but it does not erupt explosively.
It emerged above sea level about 400,000 years ago and has been steadily dribbling out low- viscosity basaltic lava, along with lots of steam and some carbon dioxide, for at least 700,000 years. Mauna Loa is the quintessential shield volcano with broad, rounded slopes – growing slowly, and for so long. It is now one of the largest single mountain masses in the world, rising more than 4 kilometres above sea level with a total height of more than 9 kilometres from base to summit. It is an example of ‘hot spot’ ocean island volcanism, characterised by the formation of individual sea mounts. A lot of the world’s coral reefs are hosted by these volcanoes – many of them now extinct and slowly sinking under their own weight into the sea floor.
Most volcanism commences underwater. Much more extensive than ‘hot spots’, the Earth’s mid-ocean ridges are a continuous network of volcanically active undersea ridgelines crisscrossing Earth’s seafloor like stitching on a baseball – the Earth being the baseball. Mid- ocean ridge volcanism is relatively slow and steady, and almost entirely non-explosive. The material that erupts through fissures at what are called ‘spreading centres’ along the ridge lines is primarily basalt, the most common volcanic rock on Earth. This is where the thin and young oceanic crust of the Earth is being created, at what are called constructive divergent plate boundaries.
Volcanologist Arthur Day explained to me that Hunga Tonga – Hunga Ha’apai is not part of the mid-ocean ridge network, nor a ‘hot spot’ volcano like Mauna Loa. The tectonic setting, magma composition, and eruptive style of this volcano is completely different. Hunga Tonga – Hunga Ha’apai sits on the shallow Tonga-Kermadec Ridge and is a volcanic arc volcano. Volcanic arcs occur at convergent zones where the Earth’s crust is being destroyed.
Hunga Tonga – Hunga Ha’apai first appeared above sea level in 2015 as a large crater volcano with a cauldron-like pit in an area of subsidence. Its magma has more silica, making it more viscous and therefore more explosive. In addition, the explosion of Hunga Tonga – Hunga Ha’apai was made all-the-more violent due to two more effects: the sudden depressurisation of dissolved gasses as the magma escaped from its submarine magma chamber, plus the vaporisation of vast amounts of seawater as the then-unsupported chamber collapsed inward. This submarine collapse may have displaced enough seawater to also trigger the associated tsunami.
Those concerned about human-caused climate change have been quick to explain that the amount of carbon dioxide expelled from the depth of the Earth by this Tongan volcano on January 15, was insignificant relative to the relentless activities of humankind. I agree. But the blast did penetrate the stratosphere and could cause global cooling. The eruption of Mount Pinatubo in the Philippines in 1991 caused a drop in global temperatures of 0.6 degrees Celsius for the next 15 months that is visible as a blip in the monthly global satellite temperature record. If Hunga Tonga – Hunga Ha’apai were to trigger catastrophic global cooling, would the rest of the world be entitled to sue the people of Tonga?
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The schematic representation of the birth of a volcanic island is from Shutterstock.com
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Is all CO2 reef bleaching science now proven to be wrong?
https://www.bbc.co.uk/news/science-environment-60047368
What does Peter Ridd have to say?
Met him in London in 2019 and he said it was all questionable, is this the proof reef studies are corrupt that we’ve been looking for?
A good summary of the geology, Jennifer.
We noted the quick emergence of AGW activists to downgrade the impact of this explosion on AGW – and it was of moderate CO2 concentration.
Yet we’ve also seen the quick emergence of activists implying that AGW caused the explosion. Your high quality summary here is a useful rebuttal to that utter nonsense. Ian Plimer has written a similar article for this week’s Spectator edition – and for much the same reason.
It is the overall increase in volcanism that is the ‘elephant in the room’. The static nature of temperature and precipitation produced by repeating Solar-induced Orbital Dry Cycle Hierarchy influences, is overlaid by the planetary overall cooling induced by increased volcanism, wind-blown dust and ice – and subsequent self-perpetuating increase in albedo and ice-cover.
The sequence of 81 years between repeat Orbital Dry Cycle ‘chains’ – combined with the over-riding influence of increased volcanism, means there are NO valid temperature or precipitation ‘averages’.
BoMs and so-called Climate Institutes around the world are peddling fraudulent data – and using it to advance their baseless, funding-driven mantras, supporting the fantasy of ‘Exponential Anthropogenic Global Warming’.
Thanks for another great article, you are a gem. Not too long now and all this Climate Nonsense will disappear into the history books. Cheers
All is NOT sweetness and light with “Gaia”, nor is the planet set in aspic.
Silica content is important, as is WATER content.
In oceanic subduction zones, the seabed “diving” under the adjacent plate, carries with it prodigious quantities of water. If this soggy substrate goes deep enough and gets hot enough, the water will like wise heat; a LOT. Being held down by billions of tonnes of overlying rock is OK, until deep subterranean movement encounters a plate “spreading zone. Then it can get exciting.The water, essentially dissolved in the hot rock and the gases, CO2 for starters, dissolved in the water, can start to expand.If all of this activity happens at shallow depths, and slowly, the leakage will be barely noticeable. But if the overlying material is “weak”, things may happen a a lot faster.
Krakatau is a classic example of what can happen when there is a sudden injection of water deep into an active volcano.
Lateral faults, like the San Andreas produce some specific activities. “Uplift” folds and faults like the Cascades in North-West USA, have generated some impressive volcanic activity.
Italy has some ripper sites. Most people will say “Pompeii / Vesuvius”. The burial of Pompeii and its “port” of Herculaneum was not a singular event. Vesuvius was known to “cough” from time to time. The “big one” involved not just the obliteration of a couple of major towns, but the burial of thousands of hectares of agricultural land and associated villages under the ash and pyroclastic flow. and a significant land uplift that left Herculaneum a greater distance from the sea. If you ever get there, take note of the depth of the compressed / welded ash overlay on top of Herculaneum; VERY impressive.
Literally, just down the road is the modern city of Naples. It is built on top of a huge volcanic ash field. Since at least Roman times, the locals have been tunneling into this stuff for shelter, excavating giant water cisterns etc, accessible by a myriad staircases, these caverns also served as air-raid shelters in WW2.
But, the best part is seen on maps and aerial photos. The Bay of Naples is almost perfectly round.
Any guesses why?
Closer to home, Brisbane is built on a huge bed of “Welded Tuff”. This was a popular construction stone in Colonial times and there are huge exposures of the stuff all over South East Queensland, and in colours ranging from brown to almost white. VERY visible in the little state park near Spring Mountain / White Rock, not far from Ipswich.
This stuff appears to have come as ash-fall / pyroclastic flow from the Mega-Volcano that is currently the site of the Northern Rivers District in NSW. The past really was a blast. For some additional perspective, check out the height and construction of the “Border Escarpment” that forms a “northern wall” to the old caldera and also aligns with the Qld / NSW border in places like the southern boundary of Lamington National Park. The contour lines on the map are many and VERY close to each other.
The University of Auckland study showed the Tuvalu group of islands had grown in area by 73 hectares over the last 40 years or so and was almost universally ignored by the MSM and “climate scientists”.
Although it is well known that coral atolls are formed by storm action and/or rising sea levels over many years.
Sometimes small atolls disappear and reappear some years later.
I have seen this personally on the GBR.
But one of the great rising sea level furphys that recently sent the media chooks into a cacophony of clucking was about the Torres Strait Islanders who reportedly are going to sue the Australian Government for not doing enough to stop climate change.
This alleged inaction was responsible for their islands being drowned by rising sea levels – this article is typical of the ill-informed climate propaganda peddled almost daily by global media.
https://www.abc.net.au/news/2021-10-27/australian-government-sued-for-failing-to-take-climate-action/100569558
It would only take the research talents of my ten years old grand daughter to delve further into the matter and find this study ;
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3156165/
As the authors point out “vertical ground motion” must be included in any discussion about apparent rising sea levels anywhere coastal.
“We show that the Torres Islands are subject to strong vertical motions during and in between earthquakes and that the observed sea-level rise on the Torres Islands is, in fact, dominated by these motions.”
Not allowed to post as termed abusive content from this site according to others ….
Hilarious in a way?