How and Why Etna is Unusual

A correspondent sent me THIS LINK. It is based on THIS ACADEMIC PAPER. Both links are quite complex and the best summary of them can be provided by Chat GPT.

The GA will visit Etna this June and I will be there! I look forward to hearing what degree of complexity we hear when we are on the slopes!

Here is ChatGPT's summary.

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The article explains how scientists may finally understand the unusual behaviour of Mount Etna, one of the world’s most active and puzzling volcanoes. Although Etna is over 500,000 years old and sits above a subduction zone where tectonic plates collide, its eruptions don’t match typical volcanic models. Instead of producing the kinds of magma expected in such settings, Etna frequently emits alkaline lava more typical of hotspot volcanoes like those in Hawaii—despite no hotspot being present nearby.

To solve this mystery, researchers analysed the chemistry of Etna’s lava over hundreds of thousands of years. They found that its composition has remained remarkably consistent, even as surrounding tectonic conditions changed. This suggests the magma feeding Etna is not newly formed each time, as in most volcanoes, but instead comes from a long-lasting, stable source deep underground.

The study proposes that Etna is fed by pockets of magma trapped about 80 kilometres beneath the Earth’s surface, in a region between the upper mantle and tectonic plates. As the African Plate moves beneath the Eurasian Plate, pressure squeezes this stored magma upward through cracks in the crust, much like water from a sponge.

This mechanism resembles that of so-called “petit-spot” volcanoes—small volcanic features usually found on the ocean floor. However, Etna is vastly larger, making it an unusual and possibly unique example of this process operating on a massive scale.

These findings reshape scientists’ understanding of how volcanoes can form and function, suggesting Etna may not fit into standard categories. The research also has practical importance, helping improve assessments of volcanic hazards in nearby populated areas such as Catania and Messina.

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 The Hunga-Tonga Eruption Hid its Effect

A correspondent sent me THIS LINK. It concerns the 1922 eruption of Hunga-Tonga. This occurred under water and this had the effect of disguising its impact. 

The release of sulphur dioxide (SO₂) is often used to measure the cooling affect of eruptions, but Hunga-Tonga released little SO₂ to the atmosphere. And therefore it was assumed that it had little affect on the climate. The SO₂ released reacted with sea water - I assume sulphuric acid will be somewhere in the reactants.

But the lack of SO₂ in the atmosphere does not mean that the eruption had little climactic affect. 3 billion tons of water vapour went into the atmosphere in 1 hour! And it went very high - into the stratosphere and mesosphere. And there it had complex climatic results.

Read the article to understand some of the complexities!

 Another Huge Eruption Sometime (Geologically) Soon

A correspondent has sent me THIS LINK concerning a volcano which produced the largest eruption of the Holocene. Recent research indicates that the magma chamber is slowly refilling.

When one considers the damage the Holocene eruption did to what was then a sparsely populated area - just south of Japan's southernmost large island, Kyushu - another similarly sized eruption today would be catastrophic. Population densities are rather higher nowadays!

The researchers have found that the magma refilling the magma chamber is new stuff - not the leftovers of the last eruption.

You can get a better idea of the article by reading a summary provided by ChatGPT.

The article describes new research into the Kikai Caldera, a largely submerged volcano Japan responsible for one of the most powerful eruptions in Earth’s recent geological history. Around 7,300 years ago, the volcano produced the Akahoya eruption—the largest known eruption of the Holocene—ejecting vast quantities of material, spreading ash across Japan and beyond, and likely devastating the ancient Jōmon population.

Although the volcano has remained relatively quiet since then, scientists have now discovered that its  magma chamber is slowly refilling. Using advanced seismic techniques, including air-gun pulses and ocean-bottom seismometers, researchers mapped the subsurface structure beneath the caldera. Their results reveal a large magma reservoir that appears to be the same system responsible for the ancient eruption. 

Importantly, the magma currently accumulating is not simply leftover material from the previous eruption. Chemical analysis shows it is newly injected magma, indicating an active replenishment process. This is supported by evidence of a lava dome forming within the caldera over the past several thousand years, suggesting continuous magmatic activity.

The findings provide insight into how giant caldera systems “recharge” over long timescales. Researchers propose a model in which fresh magma is gradually injected into shallow reservoirs, eventually rebuilding the conditions necessary for another large eruption. This mechanism may apply not only to Kikai but also to other major volcanic systems such as Yellowstone and Toba.

While there is no indication of an imminent eruption, the study highlights the importance of monitoring such systems. Given today’s dense populations, even a moderate eruption could have severe consequences. Ultimately, the research aims to improve understanding of volcanic cycles and enhance the ability to detect warning signs well before future catastrophic eruptions occur.

Can Volcanoes be Connected?

 Can Volcanos be Connected?

A correspondent has sent me THIS ARTICLE. For ever geologists have thought that volcanoes could be studied in isolation but, more recently it has been discovered that magma does not just travel towards the surface but can also go sideways - it can move from one volcano to another, sometimes many kilometres apart. And, sometimes the type of rock erupted can change - which seems very odd.

Iceland’s Fagradalsfjall fissure system erupted multiple times between 2021 and 2023, after which the Svartsengi fissure system seemed to take its place.

The article in Quanta Magazine (which has some wonderful photos) describes, at length, coupled volcanos. I recommend reading it. I attach a summary produced by ChatGPT.

The Quanta Magazine article “When Coupled Volcanoes Talk, These Researchers Listen” explores a growing realization in volcanology: volcanoes are not always isolated systems, but can be physically connected and interact through shared underground magma pathways. By tracking how magma moves between volcanoes, scientists are uncovering “conversations” between volcanic systems that could improve eruption forecasting and deepen understanding of Earth’s interior dynamics.

The article begins with the famous 1912 eruption in Alaska involving Mount Katmai and the Novarupta vent. For decades, scientists assumed Katmai itself erupted and collapsed after expelling its magma. However, later geological mapping revealed that the eruption actually occurred about 10 kilometres away at Novarupta, which had effectively drained magma from Katmai. This discovery provided early evidence that magma can move laterally across significant distances, linking separate volcanic structures.

Modern research has expanded on this idea, showing that such connections are not rare. Advances in monitoring technologies—such as seismometers that detect magma movement and satellite-based measurements of ground deformation—allow scientists to track magma migration in near real time. These tools reveal that magma does not always rise vertically, as once assumed, but can flow sideways through complex subterranean networks.

A key focus of current research is Iceland’s Reykjanes Peninsula, where volcanic systems appear to operate in sequence. After eruptions at one fissure system, activity can shift to another nearby system, suggesting that magma is redistributed underground. This behaviour gives the impression that volcanoes are “talking” to each other—when one system quiets down, another becomes active. Such patterns indicate that volcanic regions may function as interconnected networks rather than independent vents.

Scientists are now attempting to map these hidden magma pathways and understand the physical mechanisms behind them. Magma behaves like a complex fluid mixture, with its viscosity depending on composition—silica-rich magma is thicker, while low-silica magma flows more easily. These properties influence how magma travels through the crust and how it links different volcanic systems.

Understanding these connections has practical importance. If magma can shift from one volcano to another, monitoring a single volcano in isolation may be insufficient for predicting eruptions. Instead, researchers must consider entire volcanic regions as integrated systems. By identifying patterns of magma transfer, scientists hope to anticipate where eruptions might occur next, even if the triggering signals originate elsewhere.

Ultimately, the research highlights a shift in how volcanologists conceptualize volcanic behaviour—from isolated eruptions to dynamic, networked systems. By “listening” to how volcanoes interact through shared magma, scientists are developing a more nuanced and predictive understanding of volcanic activity. This approach could lead to better hazard assessments and earlier warnings for communities living near active volcanic regions.

 

 What Caused the Younger Dryas

The Younger Dryas was a cold period which started 12,870 years ago. The last glacial maximum had finished about 20,000 years ago, so there had been about 7,000 years when things had been getting warmer. At 12,870 years ago thing got cooler quickly - in Europe the average temperature dropped 6⁰C in just 3 years! I suspect this would make life difficult for the people in the area. This cooling lasted for 1,170 years.

The causes of this are discussed in THIS ARTICLE, partially based on this JOURNAL ARTICLE, and this MAGAZINE ARTICLE. Possible culprits include:

1. A meteor strike
   
   
2. Drainage from a large glacial lake, disrupting the North Atlantic Drift.
   
   
3. An unknown volcanic eruption. (But not the Laacher See eruption - wrong trace elements and a bit later than the start of the Younger Dryas.)

There is evidence of volcanism at the start of the Younger Dryas. Where it was is still unknown. But the meteor strike is now discounted. We are left with culprits 2 and 3. And they do not rule each other out.

Below I attach a summary of the article which started this post, produced by ChatGPT.

The Earth-logs article argues that the long-debated cause of the Younger Dryas cold interval—an abrupt return to near-glacial conditions about 12,870 years ago—is now effectively resolved. The Younger Dryas interrupted the gradual warming that followed the last Ice Age, with temperatures in parts of the Northern Hemisphere dropping dramatically within just a few years and remaining cold for over a millennium.

Historically, several explanations have competed. One popular idea was that a massive influx of freshwater into the North Atlantic disrupted ocean circulation, particularly the Gulf Stream, reducing heat transport to higher latitudes. Another controversial hypothesis proposed that a comet or asteroid impact triggered the cooling, but this has largely been rejected due to lack of reproducible evidence.

The Earth-logs post highlights newer geochemical and ice-core evidence that points instead to a major volcanic trigger. Ice cores from Greenland show a pronounced sulphate spike at the onset of the Younger Dryas, indicating a very large volcanic eruption. While the well-known Laacher See eruption in Germany occurred around the same time, its scale and chemical signature do not match the observed sulphate anomaly. This implies that a much larger, as yet unidentified eruption injected vast quantities of aerosols into the atmosphere.

Such an eruption would have rapidly reduced incoming solar radiation, causing sharp cooling. Crucially, this initial volcanic cooling could have pushed the climate system past a tipping point, weakening ocean circulation and locking the Northern Hemisphere into a prolonged cold state. In this view, volcanism acted as the trigger, while feedbacks within the ocean–atmosphere system sustained the millennium-long chill.

The article concludes that this combined explanation—a large volcanic event initiating a cascade of climatic feedbacks—best fits the available evidence. It reconciles the abrupt onset seen in ice cores with the extended duration of the Younger Dryas, offering a coherent solution to a long-standing geological puzzle.

 Down to Earth Extra April 2026

The April 2026 edition of Down to Earth Extra has been published. you can download it HERE or you can read it below.

Subducted Slabs - Where and How

Earth-Logs, one of this blogs favourite sources has come up with an interesting article which you can find HERE. It is based on THIS ARTICLE which will appear in a Nature Journal soon.

It concerns subducting plates and what happens to them. It is thought that mineral density changes are the main control, but the authors of the paper suggest that another control is viscosity changes caused by cooler slabs entering the mantle. Their paper is summarised below (by ChatGPT) and further summarised in the diagram at the bottom of this page.

This is fascinating stuff but all the evidence is gained at a distance and we will never get there. So we have to be content with speculating about phase changes and viscosity. But these are the best explanations we have for the observations we make.

Seismic tomography does not support the idea that oceanic slabs sink intact all the way to the core–mantle boundary. Instead, many slabs stall and accumulate at depths around 660 km and 1000 km. The 660 km boundary is reasonably explained by pressure-driven mineral changes (especially in olivine) that increase density and resist further sinking. However, no equivalent mineral transition explains stagnation at ~1000 km depth.

Recent research by Jing Li and colleagues proposes that variations in mantle viscosity, rather than just mineral density changes, control slab behaviour. Their combined experimental and modelling work suggests that as slabs descend, they trigger recrystallization in the surrounding mantle, reducing grain size and creating localized low-viscosity zones. These zones can either facilitate or hinder slab movement, leading to complex, uneven descent.

They identify four subduction modes depending on trench retreat speed and mantle properties:

• Slow retreat + low-viscosity patches → slabs penetrate past 660 km but stagnate at ~1000 km
• Slow retreat + uniform mantle → slabs buckle between 660–1000 km
• Fast retreat (with or without low-viscosity zones) → slabs stagnate at ~660 km

The study also suggests that older, “fossil” slabs may weaken the mantle and create low-viscosity regions that influence later subduction. These processes help explain seismic observations and imply that the mantle is highly heterogeneous.

Overall, the findings highlight that mantle dynamics are complex, with past tectonic activity influencing present-day plate motion, deep mantle convection, plume formation, and the chemical diversity of mantle-derived magmas.