Rome’s world’s weirdest caldera

Italy is a fascinating country, and when it comes to volcanology, Italy has been arguably the most influential location in the planet. The first ever detailed description of a volcanic eruption came from Pliny the Younger writing about the eruption of Vesuvius in 79 AD. Vesuvius was also the first volcano to be watched over by a volcanological observatory, in 1841. Three types of eruptions plinian, strombolian and vulcanian were described in and named after Italian volcanoes. The very name volcano comes from the island of Vulcano. While In Sicily, according to legend, the philosopher Empedocles jumped into Mount Etna believing he was immortal. And was this before or after Zeus threw Mount Etna on top of the monstrous Typhon?

In such an exuberantly volcanic region it is easy to miss some of the other volcanoes that haven’t done so much historically, but are still there, and some of them are genuine wonders. Here I’m going to talk about Colli Albani. A large caldera right next to Rome. The arguably weirdest caldera in the world in terms of chemical composition.


 The Roman Volcanic Province

Colli Albani is part of a remarkable cluster of large caldera volcanoes. The Roman Magmatic Province. The cluster includes four caldera systems generally classified as separate. These are from north to south: Vulsini, Vico, Monti Sabatini, and Colli Albani. The calderas started their major caldera forming eruptions at about the same time 600,000 years ago. They have become inactive in the past 100,000 years, except for Colli Albani which still shows signs of intrusive activity.

The exact number of caldera forming events produced by these volcanoes seems unclear. The Vulsini Complex had at least 5 ignimbrite caldera-forming events. Vico had four caldera-forming ignimbrite eruptions. The largest eruption of the Roman Magmatic Province may have been the 300,000 BP event that formed the Bolsena Caldera of Vulsini, which had a bulk volume of 460 km3, the caldera is now filled with Lake Bolsena.

Vico caldera seen in Google Earth.


The weirdness of Colli Albani

So what makes Colli Albani so special? A unique chemistry. Colli Albani has done foidite ignimbrites, something as far as I know no other calderas in the world have. Of course, throughout the history of the planet there must have been other calderas similar to Colli Albani, but none of them remain active. Remember foidites? My last article was about foiditic magmas, and then Jesper’s Nyiragongo series also touched this magma type. Foidites are some of the most potassic magmas in the world, very rich in certain elements such as potassium, phosphorus, barium, among many others, and depleted in silicon and aluminium. Foidites include magmas such as melilitites, nephelinites, leucitites, and kimberlites, among many other less common designations. Carbonatites are also related to foidites, given that carbonatites come from nephelinites through a partition between silicate and carbonate melts. Colli Albani’s magmas would be classified as leucitites.

Last time, I was talking about Kaiserstuhl, an extinct nephelinite-carbonatite stratovolcano in Germany, and nearby Urach, a field of melilitite maar volcanoes. However, this is not the only province of foiditic magmas in Europe. One of the most important active foidite volcanoes of the world is in Italy, and it is the only one that has made it into a caldera.

We could distinguish four series of magmas given the way that they are classified in the TAS diagram:

-Low-K series (low potassium): Subalkaline/tholeiite basalts, basaltic-andesites, andesites, dacites, and some rhyolites.

-Medium-K series: Alkalic basalts, trachybasalts, basaltic-trachyandesites, trachyandesites, trachytes, and some rhyolites.

-High-K series: Basanite, tephrite, phonotephrite, tephriphonolite, phonolite, and in some highly evolved cases trachyte.

-Extreme-K series: The rocks clasified as foidites in the TAS diagram.

This is called a TAS diagram. I have coloured the classification according to the Google Earth maps that I show later.

Approximate fields spanned in a TAS diagram by several foidite volcanoes that are discussed in this post, or that were discussed in my previous article. Note Colli Albani is not as potassic as Nyiragongo or Ol Doinyo Lengai but is pretty close to it. Oricola corresponds to monogenetic pyroclastic cones close to Colli Albani.

Foidite volcanoes are usually isolated in terms of their chemical composition. The nephelinitic Ol Doinyo Lengai is the black sheep among the trachytic volcanoes of the Ngorongoro complex. Nyiragongo nephelinites contrast with the basanites and phonolites of the other Virunga volcanoes. Colli Albani is a similar case.

Roman Magmatic Province calderas have compositions that are less potassic than Colli Albani. Vico is a medium-K volcano, that has erupted trachytes and rhyolites. Monti Sabatini and Vulsini are more potassic than Vico, and straddle the boundary between the medium-K and high-K series. To the south of Colli Albani lies the Campanian Volcanic Province where volcanoes have mainly medium-K compositions, with the notable exception of Vesuvius which is a high-k phonolitic-phonotephritic volcano.

Map in Google Earth. Each circle is a chemical sample of lava from the extensive EarthChem catalogue. I coloured them according to the series they belong to, in the same way as shown in the TAS above. Red is low-K. Nearly absent. The only active low-K volcanism in Italy is in the Aeolian Islands. Green is medium-K, and blue is high-K which are the dominant series in this area. Purple is extreme-K lavas, the volcanoes that belong mostly to this series are Colli Albani and some of the monogenetic volcanoes like Oricola, or San Venanzo.

Same map as above but showing the Campanian volcanoes.

There are other foiditic volcanoes in Italy appart from Colli Albani, however they are monogenetic. These monogenetic volcanoes make up the so called Umbria-Latium ultra-alkaline district and are located to the east of the Roman Magmatic Province. They are San Venanzo, Acquasparta, Polino, Cupaello, Oricola, and others. Umbria-Latium volcanoes erupted melilitites and carbonatites. Eruptions were mainly explosive forming maars/diatremes and pyroclastic cones. Some lava flows are also present but usually of very small volume. These eruptions have been usually attributed to hydromagmatism. However, I think they were probably driven, at least partly, by the very high gas contents of melilitites, because wherever there is melilitite you find maars and diatremes.

The Umbria-Latium ultra-alkaline district might still be active, however eruptions here are extremely rare and minuscule in volume. Melilitites are some of the most geochemically interesting magmas but also some of the rarest. It is not unusual to find a lonely melilite maar or tuff cone volcano with no other volcano nearby, which probably formed in one day, was a VEI-2, and effused a 200 metre long lava flow. The way of melilitites is modesty.


Caldera-forming Colli Albani.

Colli Albani is 10-km wide caldera that has collapsed repeatedly generating massive pyroclastic flows. The first dated activity of the volcano was at 608 ka (ka means thousands of years before present). This was also at about the same time explosive activity started in nearby Sabatini volcano, which happened at 591 ka. It has been noted that the eruption histories of Colli Albani and Monti Sabatini appear to be connected, and that they have often entered eruption phases at the same time.

Colli Albani. Image from Luca in Wikipedia. It can be found by clicking here, where you can also learn about cloud types.

The first caldera-forming ignimbrites of Colli Albani are less well known. There are 4-5 ignimbrites, depending on the publication, that took place during 2 eruption periods, at 561 ka and 530 ka. The volume is not well constrained, but they seem to have been at least VEI-5 eruptions. One of the 561 ka explosive eruptions was the Tor de Cenci ignimbrite, that is shown in the map below.

A series of larger caldera forming eruptions followed: the >34 km3 bulk Pozzolane Rosse eruption at 456 ka, the 9 km3 DRE Pozzolane Nere at 407 ka, and the >50 km3 bulk Villa de Senni ignimbrite at 365 ka, which ended the caldera-forming period. As such ignimbrite eruptions occurred at intervals of about 50,000 years, although sometimes there may have been two ignimbrites that occurred in more rapid succession. It is not too easy to know how much time elapsed between certain explosive eruptions, and it is difficult to know which ash deposits formed in  separate eruptions or phases of the same event, making things unclear.

The eruptions, as typical of caldera-forming ignimbrites, were very powerful. A caldera-forming ignimbrite is a particular type of pyroclastic flow of enormous extent which is thought to issue from the ring fault of a caldera through a ring dike. Each Colli Albani ignimbrite started with a plinian/subplianian eruption which rained scoria around the volcano, this phase was relatively small in volume. Each eruption then intensified and a massive pyroclastic flow issued from the caldera, spreading over a radius of 20-30 km all around the volcano, obliterating everything in its way. It would have blown trees to the ground and suffocated animals to death and finally buried them under meters or tens of meters of ash and scoria. Caldera-forming ignimbrites reign supreme among eruptions in terms of intensity. If one of these pyroclastic flows were to occur today, then it would devastate most of Rome. Luckily for Rome, Colli Albani doesn’t seem to be in the caldera business any longer.

The extent of two of the caldera-forming ignimbrites of Colli Albani. The area is as reported in some of the publications cited at the end.

In caldera-forming ignimbrites, the magma type doesn’t seem to matter much. Doesn’t matter if it’s leucitite like Colli Albani, water-rich basalt like Okmok, or rhyolites from the Altiplano-Puna, the eruption intensity is relatively similar. The leucitites of Colli Albani are silica undersaturated. None of the ignimbrites has had more than 50 wt% SiO2. The Pozzolane Rosse eruption, for example, had only 40-44 wt% SiO2. A magma like this is very fluid and gas rich. Normal eruptions will usually be explosive but still have low eruption rates. However, a caldera-collapse is different. Leucitite has enough gas to fragmentate the magma into tephra. The caldera collapse brings in enormous eruption rates that generate the violent pyroclastic flow-style of activity. The only magmas that seem incapable of producing caldera-forming ignimbrites are the gas-poor basalts from intraplate or mid-ocean ridge environments, probably because of the very little volatile content that they carry.

Following the final ignimbrite, the Villa Senni eruption, Colli Albani entered a very active period from ~365 ka to ~350 ka in which many vents erupted from a ring-like area around the caldera, making scoria cones. These eruptions were effusive and explosive. They produced lava flows, but also generated subplinian eruptions that deposited scoria for tens of kilometres to the east of the volcano. Nearby Sabatini volcano also has a similar pattern of concentric fissures which envelop the Lago di Bracciano caldera.

Scoria cones of Colli Albani marked in red circles. The approximate caldera rim is in white.

The three calderas of Monti Sabatini are marked in white. From the left these are Bracciano, Baccano and Sacrofano. Scoria cones are in red, maars are blue. Note the ring-like distribution around Bracciano and Sacrofano calderas.

The distribution of fissures around the caldera suggests to me that they were fed from cone sheet intrusions. Cone sheets are intrusions which face inwards towards the centre of a volcano and, together, multiple cone sheet intrusions make the shape of a cup or an inverted cone, and where they reach the surface, concentric fissures open up that usually run parallel to the rim of the caldera. Such intrusions are typical of caldera systems worldwide. There is a link with caldera resurgence. In order for magma to intrude, it must be able to push away the rock. Cone sheets happen by pushing the rock upwards. Because they face the caldera, they must push the caldera floor up, and if the caldera is already rising up because of an expanding magma chamber below, then the cone sheets will intrude effortlessly towards the surface, taking up the stresses generated by this resurgence.

Drawing of a resurgent caldera which is feeding cone sheet intrusions (red).

Thick successions of scoria fall deposits and lava flows separate the major ignimbrites of Colli Albani. Many scientific publications focus only on the ignimbrites, so that it may seem that the 561-365 ka period of Colli Albani activity simply involved a couple of ignimbrites and there was little intervening activity. In reality, I suspect that very roughly half of the volume erupted from 561 ka to 365 ka, was possibly erupted from circum-caldera fissures fed by cone sheets, similar in style to the activity that followed the Villa Senni eruption. This activity probably would have accompanied caldera resurgence that eventually culminated in the ignimbrite eruptions.

The “reverse” of a cone sheet is a ring dike. While cone sheets thrive in emerging calderas, ring dikes intrude in collapsing calderas. Ring dikes work by pushing the ground downwards. They need a trigger to depressurize the caldera. Most caldera-forming ignimbrite eruptions of Colli Albani started with a scoria fall deposit, which corresponds to a subplinian/plinian eruption. These eruptions would have depressed the floor of the caldera by extracting a large amount of magma from it. The subsidence allows a ring dike to intrude, in turn the dike lubricates the caldera ring fault with magma, and the roof collapses faster, magma shoots out of the ring dike in a caldera-forming ignimbrite eruption, the more the roof collapses the more the dike opens up and the faster it erupts.

Representation of a caldera-forming ignimbrite eruption fed from a ring dike.


Post-caldera Colli Albani

Following the ignimbrite eruptions, Colli Albani became less active, even so it has kept some activity to recent times. After the ignimbrites, activity became centred inside the caldera were it built a small stratocone, the Faete stratovolcano. Faete is known to have been active in 290-260 ka, although may have started earlier. The volcano was mainly constructed from lava flows and subplinian eruptions, but also involved maar style activity that blew away the top of the cone into a 2 kilometre wide crater.

Since 200 ka, Colli Albani has been dominated by maar eruptions. Several maars have been constructed, including three large polygenetic maars southwest of Faete stratovolcano. The largest maar is Albano, which erupted 7 times starting 45 ka. Albano makes up a massive crater of 3 x 4 km, and 200-400 meters deep in relation to the rim of the crater. The explosions of Albano ejected large metre sized blocks of old lava and carbonate rocks and deadly pyroclastic surges swept across the landscape to distances of 15 kilometres to the northwest and southeast of the vent.

The last dated event of Lake Albano in 4.8 ka may have been non-volcanic, and consisting of a lahar. This seemingly repeated in 406 BC, when, as reported by Plutarch, the lake surged over the surrounding hills, unleashing a flood of water that destroyed fields and vineyards, and then poured into the sea. This event may have been related to hydrothermal activity.

The young maar volcanoes of Colli Albani shown in blue. Green corresponds to the ejecta from the maars, mainly pyroclastic surges.

Lake Albano in the Albano maar. The bottom of the lake is 170 meters underwater. Image from Ra Boe is found here.


Will Colli Albani erupt again?

It seems to me that Colli Albani is a waning volcano well past its prime. However, it will probably erupt again.

The Global Volcanism Program reports that Colli Albani experienced inflation between 1993 and 2000, which might still be continuing. The inflation rate in 1993-2000 was about 2-4 mm per year. This is, of course, very little compared to other volcanoes of the world. The inflation is, however, in an ominous location. Inflation is centred in the Albano and Remi maars. Likely there is a magma storage under the large polygenetic maars which is refilling with magma. There is also active seismic activity. 1100 earthquakes took place under the Albano maar in 1989-1990 at depths of 4-5 km.

Should a large maar eruption take place, consequences would be devastating. There are well over 100,000 people living in the area that was affected by earlier pyroclastic surges of the maar eruptions. Two of the larger towns in this area amount to 80,000 people. Many other towns amount together to a probably greater number. So even though an eruption is unlikely to happen anytime soon, Colli Albani should be carefully watched.

One publication has also suggested that Lake Albano could produce a limnic eruption given the CO2 that is being dissolved into the lake. This is, however, considered by them to be an unlikely possibility, given that the concentration of CO2 is presently far from saturation.



Colli Albani has it all. It has bizarre leucitite magmas, the power of a large caldera, and a bit of a mystery regarding Lake Albano, with its earthquakes, inflations, and floods. It is also a volcano that can teach us about calderas.

Calderas are calderas, regardless of their magma composition. It is true that rhyolite calderas usually erupt larger volumes. However, leucitite, trachyandesite, or basalt calderas, all of them are frightening systems capable of VEI-6+ eruptions. The ignimbrites of Colli Albani would each have destroyed areas of 1000-2000 km2 within a very short time-span.

In reality, volcanic eruptions are very complex. A lot of factors. There is viscosity, yes, but there is also volatile content, magma chamber size, conduit width, or groundwater interactions. Simple rules like: the more a volcano pressurizes, the worst the eruption will be, or the more viscous the magma, the more explosive, fall short to explain the enormous diversity of volcanic phenomena out there. And in a world full of volcanoes you can still find a volcano that is a one of a kind gem, like Colli Albani.





Late Pleistocene ultra-alkaline magmatic activity in the Umbria-Latium region (Italy): An overview


Integrated approach for the reconstruction of stratigraphy and geology of Quaternary volcanic terrains: An application to the Vulsini Volcanoes (central Italy)


Origins and energetics of maar volcanoes: Examples from the ultrapotassic Sabatini Volcanic District (Roman Province, Central Italy)

Colli Albani:

The Colli Albani mafic caldera (Roma, Italy): Stratigraphy, structure and petrology.

A large K-foiditic hydromagmatic eruption from the early activity of the Alban Hills Volcanic District, Italy

CO2-driven large mafic explosive eruptions: the Pozzolane Rosse case study from the Colli Albani Volcanic District (Italy)

The 1989–1990 seismic swarm in the Alban Hills volcanic area, central Italy

Discussion on ignimbrites:

Classification of ignimbrites and their eruptions

301 thoughts on “Rome’s world’s weirdest caldera

  1. Thank you, Héctor! With the focus on Vesuvius, Etna and Campi Flegrei, it is very easy to forget about Italy’s earlier volcanic history.

  2. The 406 BCE event was likely a limnic eruption of the lake. If so, it may take some time to recover before there is much risk of another one.

    • Interesting. It would make sense if it would have been a limnic eruption.

  3. Love the post! Very interesting to know about this stuff.

  4. Thank you .. What a strange thing with foiditic igmigbrites

    • Thanks Jesper! Colli Albani is really unique no matter how many times I check. It is not as extreme as Nyiragongo or Ol Doinyo Lengai though. And Colli Albani magmas may have evolved from basanites. But yes, world’s only leucitite caldera.

  5. Thank you Hector, for this very interesting post. My knowledge of volcanoes is growing, thanks to people like you.

  6. I am sorry Hector but while the tourist volcano erupts, nothing else will get a lot of attention including this intriguing article about an underrated volcano.

    • That is true. I don’t think I should oppose it though. This is a place for free volcano discussion after all, and it’s better if it keeps that way.

      • True. There are two sides to the VC blog: the articles and the discussion. Often they coincide, often they do not. That doesn’t mean they don’t interact. It is easier to comment on an eruption (‘what is that red glow over there..?’ then a post. The posts do get a lot of attention though, it just doesn’t show as much in the comments. I am happy with this situation: both are very welcome here.

  7. I wonder if Vesuvius is like an early view into the life of Colli Albani. Magma is not the same but both are fluid yet powerfully explosive volcanoes, only one is elderly and the other seems in its teens.

    • That is an interesting question. The chemistry is somewhat similar to Colli Albani being a high-K volcano bordering with extreme-K in its tephriphonolite magmas.

      Unfortunately not much seems to be known about how Colli Albani started, the first well studied eruption is the Tor de Cenci ignimbrite, which was a caldera forming ignimbrite with 42–45 wt.% SiO2. If it had an initial stratovolcano phase like Vesuvius is not known. The stratovolcano would have been engulfed by the later caldera-forming events.

      As for Vulsini I think the historical eruption reports are generally disregarded, unless they were phreatic.

    • These large mafic ignimbrites, I wonder if the same sort of thing happens here as at the large Indonesian stratovolcanoes? As in, rather than evolve their magma to a high degree they seem to mostly go caldera on account of the magma chamber being unable to support their weight. A highly fluid magma presumably would be inclined to erupt out of any available location easily so if such a magma found itself in a collapsing stratovolcano it would self propagate, maybe even much more easily than in a silicic volcano. Being gas rich probably only greatly amplifies this, aking it more likely for a large summit eruption to actually be able to empty the chamber, which probably cabt happen in a tholeiitic volcano like Kilauea. Etna seems to straddle this boundary, its powerful summit paroxysms do relieve pressure, rather than indicate an excess of it, but it also seems to typically do calderas with a large lateral eruption which Vesuvius does not.

  8. Also what of the historical report of an eruption at Vulsini?

  9. There’s a lot of smoke from the top-end of the fissure, now, with the gasses hugging the ground.
    I noticed it a couple of hours ago, and with the dawn it is quite clear something is happening there.

    It could be as simple as the active vents having risen so high that magma is just under the surface all the way to the top of the fissure.

    • I was looking at that, but wonder if it is rain on the hot vents. It looks like it is chucking it down again!

  10. Thanks for a fine exposition Hector! I’ve always been fascinated by the highly alkaline volcanoes like Ol Doinyo Lengai and its eruptions of liquid sodium carbonate. Which I’m sure the flamingos in the soda lakes would welcome if they had the brains to understand.

    • Thanks Bruce. I have an ever-expanding interest in highly alkaline volcanoes.

    • If it aint BoN ! Must be one and the same as the flamingos get a guernsey. Is the forum still operative?

  11. Thanks Hector,

    This article adds interesting backstory to Castel Galdolfo, right there on the edge of Lake Albano, the traditional summer retreat of various Popes.

  12. Been looking at this, fpr a long time now the cross-caldera distance at Kilauea has been climbing rapidly, the caldera is extending. It also looks like the tilt is going up too but not in such an ecponential way. There was a new insar recently that shows no deformation at Kilauea of significant magnitude, and it does show the inflation at Mauna Loa. The degree of movement for the cross-caldera GPS also is much larger than that of the south flank stations, which have typically moved towards the ocean by only a few cm (AHUP is 5 cm south and 7 down, MANE is 3 cm south and no vertical change) compared with about 15 cm of extension across the caldera.

    I dont think this is heralding a change in the eruption, because that appears to be a totally open system now, like it was before 2018, but I cant see such a summit signal as anything other than accelerating magma accumulation. I expected such a signal at some point in the next few years but not now when the lake is not yet 20% full, if it is already looking close to breaking things could get pretty serious, lava lake floods are a completely different sort of eruption to both Pu’u O’o and the rifting fissures like 2018, they are fast and erupt at full force immediately, with rather little warning until it actually happens.

    • The GPS stations BYRL and UWEV have not risen that much though. They are still well below the level when the eruption started. I think some other factors may be contributing to the caldera extension making it seem of a greater magnitude than it really is, probably the southward creeping of the flank, and maybe the deflation of the south caldera sills too.

      • Some of extension of the caldera is probably from inflation, but not all I think. Or maybe it really is from inflation but it appears more than it is. Maybe the early eruption deflation was not very well visible in the cross-caldera distance because of south caldera deflation causing some extension as the same time as the summit deflated.

        • What about the weight of the lava pushing on the sides of the 2018 depression as it fills up? Wouldn’t that have an effect on the cross caldera distance?

          • I dont think that is a large enough force, its only 0.1 km3 of lava that is sitting at a relatively low elevation compared to the immediate surroundings, and the volume of rock in the south flank of Kilauea is going at many thousands of km3, 5 or even 6 orders of magnitude more than the current lake volume.
            At least as I understand it the cross-caldera typically is controlled by forces acting from below, like two dots on a balloon that is being blown up moving apart. So presumably the actual peak signal is inbetween, somewhere in the caldera, pity that the GPS in that location is not public. There may well be some localised strong inflationor pressurization within the 2018 collapse, that just isnt really showing up too much in the rest of the magma system yet. I guess given the active vent is now basically an open hole in the magma chamber, it would be weighing down a bit, but not yet enough to cause pressure in the rest of the volcano which still is reacting to the first eruption in December 2020 and showing deflation.
            The INSAR was not really localised, it showed the whole island, and mostly to focus on the more obvious deformation at Mauna Loa that is a smaller magnitude and much bigger area, so a change within the 2018 caldera at Kilauea wouldnt resolve or might have oversaturated. It might just not even work at all given the lava lake is a rising dynamic surface that moves up many meters in the relevant timescale.

          • It wouldn’t need to move the entire flank, it would just need to push aside the caldera rim a little, and that could show in cross caldera distance. That could be happening, I think.

      • Then we will get a massive lava shield at Kilaūeas summit perhaps like the 1400 s

        • If the lake overflows and keeps doing that for a long time, then yes, but I am starting to think that is less likely. It might well overflow, and we will know for sure in 2030 or earlier, but I think it is more likely that overflows will not occur or be relatively small in scale, and that further large scale volcanism is more likely at a flank vent. That flank vent could really be anywhere though, it might be at Kilauea Iki or Keanakako’i (although those are probably best considered as summit vents) but it also could be in the same area as Pu’u O’o again, or even further down the rift in areas where it could become hazardous. It is exiting to know that we will actually get to see one of these in the next 10 years though.

          Personally, I think we will see the lava lake rise up and then catastrophically drain, perhaps many times, until either the ERZ or SWRZ becomes a preferred location of eruption, or less likely in the near term is that Mauna Loa acquires a larger share of the magma, like it did in the mid-late 19th century.

  13. This was an amazing read Hector, thank you!

    It’s interesting how volcanism shifts throughout the ages; what made volcanic activity “die” under these calderas (well aside from Colli Albani as you mentioned)? I’m assuming the magma bodies solidified, slowly losing their heat? But what caused that spike in the first place, and what moves it? Has the tectonic environment changed in a few hundred thousand years enough to shift volcanic activity toward Flegrei / Vesuvius?

    • Thanks Ryan.

      Interestingly most volcanoes in Italy seem to be very young. Monte Vulture was active 740-570 ka. Vulsini, Vico, Sabatini and Albani were mainly active from 600 to 100 ka. Roccamonfina caldera was active during a similar timeframe to the Roman Magmatic Province, 650-50 ka. Monte Amiata was briefly active around 300 ka. Weak activity started in the Etna region around 300 ka, but it was not until 130 ka that the main shield volcano started to grow. Pantelleria initiation of volcanic activity might not be well known, but the oldest dated ignimbrite is 190 ka in age. The youngest volcanic province is composed of Ischia, Campi Flegrei and Vesuvius which initiated volcanism at 150-40 ka.

      So most Italian volcanism seems to date to the last 1 million years, and I am not aware of much substantial volcanic activity before that. Only some of the islands in the Thyrrenian Sea are older, like Elba, Capraia or the Pontine Islands. Why did this happen I don’t know and I don’t think anyone really understands. Supposedly the subduction of the Calabrian Arc and the Tyrrhenian Sea back-arc opening started 10 million years ago, and since then tectonics have not changed that much, but there was comparatively little activity until the last 1 million years. And why activity has shifted in the last 100 ka to Campi Flegrei, Ischia and Vesuvius while abandoning the other mainland Italy volcanoes is also much of a mistery.

      • It seems you’re asking the very same question I’m asking myself.

        It’s been bugging me too, what on earth changed relatively geologically recently on the mainland?
        From activity all the way up into Tuscany and now only confined to Capagnia?

      • You’re a treasure trove of insight Hector, appreciate the response as always.

        Some questions about the temporal aspect of volcanic activity in Italy popped into my head while reading this article, trying to logically work out why these large systems seem to flare up, peak, and then decline over (geologically) relatively short periods of time without much change (as you suggested) to the underlying tectonics.

        Barring a more concrete answer, I wonder if it’s just as simple as “globs of heat and magma work their way up from the melted slab slowly over time, accumulate at the surface, but eventually dissipate, while new globs of heat and magma pop up in other areas instead of the same area.”

        Cheers man.

  14. Some crazy people stepped onto the lava field in Iceland and tried to get themselves killed.

    • If the speaker believes what he is seeing is stupid I wonder his thoughts about the fellow last year who raced the lava flow down the cone and the one who climbed to the crater rim and then just disappeared. In the first, if the flow had really been fluid, he’d have bought it!

    • More daylight shows that one of the northmost vents apparently is beginning to release smoke and vapor again. This needs watching.

      • There was an increased development of steam at the end of the gap two days ago. There is also a lot of smoke on the other side of the hill. Could also be an obligatory moss fire.

    • It is about 5 pm local Iceland time, and this vent has stopped emitting any vapors, but left white deposits on the previously emitted lava (at the start of the eruption). The location is very close to the north end of the fissure, on the hill. It definitely was some instability in the fissure which allowed this to take place.

  15. I think we are about to get a lava geyser again, the cone is beginning to enclose the vent and a lava lake is forming within the cone. When that happened last year is when it became episodic. That episodic fountaining also is what made the volcano so big, a proper 100 meters high when most Reykjanes cones are smaller than the current one already is…

    Apparently the effusion rate is less, and about the same as the long term average last year now too, so might remain to be seen if this does become a bigger eruption in the end. When the second fissure last year opened too it was because the first vent was not an adequate pressure release, where now the eruption began stronger than it is at present so I think at least in the immediate future more fissures are unlikely.
    But if this keeps going, it will probably make new vents. And if this eruption stops there will certainly be more, we will end up with a whole line of shields and spatter cones going from Keilir to Natthagi in a decades time, and who knows how long the rift will stay active, Fagradalsfjall has not been active since the deglaciation surge in that area and so could well play by different rules than its neighbors, and throw a slow but ultimately very large eruption. I will still stand by my comparison to Lanzarote, that I made way back last year early in the last eruption, this might be one for the history books.

    • There was a very short lull in the tremor two days ago. It quickly restored, but it was enough to make a clear notch in the tremor graph. It wouldn’t be surprising if the eruption goes into full cone building geyser mode like last time, but I wouldn’t rule out a second fissure opening either. Time will tell.

      By the way, where’s Carl? It’s a bit odd having an icelandic volcano erupt without a single word from him. I hope he’s ok.

    • The FAF highpass 2 hz seismograph trace clearly shows some episodes of geysering ( I believe underground where perhaps the magma is degassing) much similar to last’s years episodes which were clearly visible.


    Nice graphics showing the enormous scale of lava channels on outer planets, preserved flood basalts. I do wonder If Central Atlantic Magmatic Province and Siberian Traps also had lava floods on this scale. Here on Earth flood basalt Provinces are so badely eroded, and thats the problem.

    One of Venus lava channels are 6800 km long, and Mars have gigantic lava channels as well.

    Laki lava flow field is 65 km long for comparsion .. pretty insignificant to these lava flow features. Venus and Mars have thick litospheres.. and that Maybe causes them to boil over at times, While Earth release its heat in constant small eruptions

    • The scale bar to the left, is 100 km for showing How huge these lava flow features are on other planets: Thjorsahraun can almost fit in that scale bar

    • That is a nice page you found. David Leverington has many good articles on those lava channels, although they are a bit lacking in the understanding of magma intrusions.

      Belisama Vallis is to me one of the most fascinating lava channels because it issues from a giant cone sheet intrusion, and also feeds a few giant rootless cone sheets. It is also one of the widest and most complex lava channels of Venus. Like Olympica Fossae, Belisama Vallis disappears twice into a magma intrusion and reappears downslope.

      Of course Martian lava channels are by far the biggest and most spectacular of them all, particularly the lava channels issuing from the Valllis Marineris dike swarm which channelized millions, if not tens of millions, of cubic kilometres of lava in what probably was a very short timespam, like Kasei Valles, Ares Vallis or Maja Valles.

    • It might be telling that the three main CAMP flows have distinct but matching chemical signatures up and down the US Atlantic seaboard, and also that the feeder dikes extend far beyond the remnant rift valleys into the surrounding crystaline highlands, suggesting that all the current remnants were in fact part of singular flows in the past.

  17. First of all, I am not a geology or volcano expert. But my homeland (Italy) is littered (really !) with any volcano and related structures: active volcanoes (Etna, Stromboli, Vesuvio etc), volcano remnants that are mostly but not only in the western side of the Peninsula (e.g, Mount Vulture in Basilicata), starting from south of Naples to Mount Amiata in Tuscany passing from Lazio ex-volcanoes, but many and many other remnants of volcanism can be tracked looking at thermal springs that can be found everywhere in the Apennines, and not only. Think that every city in Italy which has “terme” or “bagno” in its name is a place where hydrothermal activity is in some way connected to volcanism.

  18. Watch 1:26 – 2:22 very nice video showing How very fluid the basalt lava was last year at Fagradals close to the vent. Possible one of the most fluid normal sillicate lavas ever caught on camera: If the lava is very hot then the SiO2 content becomes less important, as the polymerisation is broken down. Thats why thoelitic basalts with 50% Sio2 can display remakabely low viscosity despite its quite sillica saturated compared to truely ultrabasic magmas like Basanites and Nephelinites. Their high temperatures breaks down the Sio2 polymerisation. The viscosity At Fagradalshraun last year close to the vent, was very low perhaps in range of Nyiragongo, because of the high temperatures of Geldingadalir that was over 1200 C for 2021 eruption. Kilaueas summit also display these very low viscosities with similar composition to 2021 fagradals.

    The 2021 – 2022 eruptions at Reykjanes and the Holuhraun 2014 are the first time since 1980 s Krafla eruptions that Iceland produced really really low viscosity basalt. Because these eruptions are not sourced from shallow magma chambers like the shallow ones of under the central volcanoes in Iceland like Grimsvötn, Hekla, Katla that acually erupt colder shallow magmas even If they are closer to the Icelandic Hotspot because they have shallow chambers many of the central volcanoes in Iceland can have supprisingly cool viscous lavas.

    Its very difficult to know What is the most fluid frequently erupting sillicate lava today, because magmatic viscosity depends on a combination of sillica content and temperatures as well. My own bet is on Kilaūea, Nyiragongo and deep eruptions in Iceland. Another likley candidate for the most fluid frequently erupting sillicate lava, coud be the Thoelitic Basalts that emerge from Superfast spreading Ridges like EPR in pacific, because there very hot mantle is very close to Earths surface, just a kilometer or two for the very fastest ridges, basicaly fresh mantle melt directly out in the seafloor Without evolution in the crust.

    But the most fluid possible silicate based lavas today are probaly ultra-rare ultra alkaline sillicate lavas, like Nephelinite and Melilitites some direct mantle examples of these like the old Miocene german Urach and Vogelsberg magmas that push down to 20% Sio2, Souch lavas will have much lower viscosity than basalt If they are erupted at same temperatures. Souch lavas are never produced in Iceland because partial melting is too large in Iceland.
    Hawaiis deep lavas as well at 1650 C will be as liquid as steel If it erupted

    But Fagradals 2021 is defentivly one of the most fluid ”normal sillicate” lavas ever seen by cameras so far

    • 20 % SiO2 is the Igwisi Hills for example. Urach doesn’t reach that low, it was about 35 % SiO2 if I recall correctly. Urach has some of the most silica undersaturated lavas on the planet, to the point that many of its samples fall outside the TAS diagram. Igwisi Hills is an even stranger volcano, kimberlites usually have compositions more similar to Urach, the extreme-silica undersaturation of Igwisi Hills is pretty rare. Vogelsberg is basanites and basalts so relatively normal.

      • It is, it does fit the criteria. However it also has some distinguishing peculiarities, like having no potassium and sodium, or having very little silica.

        • Would it not be incorrect to call the Igwisi Hills magma an ultramafic magma? As I understand it such magmas are characterised by very high Mg/Fe to Si (all oxides obviously) ratios. Komatiite has lower SiO2 than a typical basalt but it overlaps, it is the very high Mg content that gives it the name ultramafic, by definition over 16% in the melt. Some picrite basalts are ultramafic overall too, but are basalts which have picked up a lot of olivine so sort of cheated. I think the highest Mg basalts from Kilauea and Mauna Loa are actually very close to that 16%, so Hawaii is probably the most mafic volcanism today, but not quite ultramafic.

          Kimberlite I recall you said has a very high Mg content too and also a way lower silica content than a komatiite as the level of melting is much lower. It also usually has a lot of alkali metals too though which will take it in another classification. But if Igwisi Hills has actually got very low Na+K I dont know what else it could be other than true ultramafic magma. It might be a very evolved magma that went in a weird direction backwards on the chart somehow.

          • Hawaii may have some very high Mg lavas, but those are probably picritic, lavas that have built up excess olivine crystals rising the Mg contents. Often Hawaiian lavas are picritic, like those erupted in 1840 from Kilauea. Kilauea summit lavas and south caldera lavas have usually ranged historically in 7-11 wt% MgO which better represents the original composition.

            Igwisi Hills is much more magnesium rich, it has 21 wt% MgO on average. I just checked it up on an excel I have with samples from Urach, Vogelsberg, Lac de Gras, and Igwisi Hills, with data from GEOROC. In the Alex Strekeisen website kimberlites are described as rocks with more than 25 wt% MgO. Lac de Gras kimberlites do average 29 wt% MgO

            Urach has 18 wt% MgO on average. Vogelseberg basanites average 12 wt% MgO, while Vogelsberg tholeiites/basaltic andesites have 7 wt% MgO.

            More potassic magmas are more magnesium rich, they are also enriched in chromium and nickel two elements that behave similar to magnesium, being among the first to crystallize away from the magma.

          • ~10% MgO is still rather high for a primitive basalt. Numbers for Holuhraun,which was also close to primitive composition, are around the low end of Kilauea, even though it was hotter and came up quickly from depth. Grimsvotn is at about 5-6% for the Laki lava.

            Also you may be interested:
            Does make you wonder about the Pauahi and Pu’ulena craters south of Leilabi Estates. Officially they are hydrovolcanic but I have never seen anything in detail about them, and they could be entirely magmatic.

    • Hekla doesnt have a shallow system yet, it is not old enough, otherwise it would probably be a caldera already. It seems that it is evolving its magma deeper down and maybe also has significant crustal contamination. Hekla is known for the fluorine poisoning of livestock that occures after it erupts, but tholeiite series volcanoes like those in Hawaii or Iceland have typically low F and very high levels of sulfur relative to overall volatile content. Hekla erupts crystal poor andesite and basaltic andesite mostly.

      Magma temperature for Grimsvotn eruptions since 1996 has been somewhere generally around 1100 C, so not fresh hot but the lava would not be viscous still, Grimsvotn is not crystal rich. Katla I dont know, but the Eldgja vents look to have erupted a very low viscosity magma, just one that is probably much more volatile rich than typical tholeiite given that Katla is more alkaline.

      • The shallow summit magmas at Grimsvötn are probaly Looking like fimmvörðuháls and Etna If they where visible, its a cooler Thoelitic Basalt and 2011 was 1110 C

  19. Galapagos caldera also must have cone sheets
    For their ring – fault eruptions

    • Yes, is the most common location for cone sheet intrusions, many have been observed with InSAR. Alhtough most publications use the term circumferential dikes, or ring dikes for Galapagos intrusions, but I prefer the term that was originally applied to these intrusions in the ancient volcanoes of Scotland like Ardnamurchan or Mull. Cone sheets. In Galapagos cone sheets often grade into radial dikes or rotate from sills. And most importantly they do NOT follow ring faults, if you observe closely the concentric fissures are well outside the ring fault, best seen in Sierra Negra. They follow the stress field.

  20. Well, the new effusion rate average came out at 10.4 cubic m/s for the August 4-August 14 period. I’ll give credit to Reykvolc, who proved to be correct with their estimates of 10 cubic Meters per second. I was sure wrong, saying it must’ve been higher like 15-25 cubicm/s in response to their estimates

  21. I must add this too, in addition to the average lava effusion rates update. Lava thickness map

    • It looks at least to me like the lava flow initially went over the top of last years lava but later on broke through into the liquid interior and is lifting it up. The lava that is moving at the end of Meradalir near its exit is solid pahoehoe that is being pushed. I would guess that is the only reason it hasnt overflowed yet.

      • Yeah but surely it’ll break out of meradalur soon though. Maybe give a week or month depending on when more lava builds there.

          • No it is Meradalur, because it is only one valley out of what used to be several that were joined and had names. I think though it might be questionable if the southern half of the valley still exists today though.

            Icelandic is challenging and very hard to learn properly yet also feels strangely familiar, there are probably alot of common words with English just that they have evolved away from an obvious connection in the latter over time as English became a hybrid language. Dalir/Dalur (Dal?) is the same as Dale, which has evolved into Vale and then that has become Valley in modern English. Still lots of places are still called somethingvale today 🙂

  22. I suppose there is an upside to a slow effusing eruption from the mantle like this. Now the lava effusion must be even lower because from August 5 to August 14 I calculated an effusion rate of 9.64 Cubic meters per second and the blue FaF tremor plot kept decreasing until August 12 when it finally stabled somewhat (except for the sudden drop in the morning of August 13 Icelandic time) which may mean the Effusion rate kept decreasing until the 12th if there wasn’t any other reason for the decrease in noise. I would guess the more short term effusion rate is now between 5-8 cubic m per second. If it stabilizes and doesn’t increase like the last eruption after a few months, then I think we can be in for a much longer eruption.

  23. Could someone here please post the current URLs for:

    a) FAF drumplot
    b) FAF tremor highpass
    c) The map page(s) that link(s) to the above?

    The URLs from last year have apparently changed ( and etc.) and I can’t for the life of me find the current ones by browsing the site.

    • They are the same as last year. Check that you’re requesting http and not https. I had problems viewing them before, but it turned out that my browser was really keen on using https, so unless I typed the full link, starting with http:// it wouldn’t work.

      • That’s broken on their part. Either https should return the same results as http, or the https port (443) should be closed, leaving only the http port (80) open.

        Having both port 80 and port 443 open, and an http server responding on each, but serving different results for the same URLs, is a flagrant violation of web standards! Especially when everyone is moving to https-always-when-port-443-is-open now.

      • Please can a admin or moderator delete this since I found the direct links to the highpass and faf gif, thanks.

    • I found the link to the faf highpass

      (http:) //

      Now onto the search for the other

    • Here is the other 👍

      (http:) //

  24. Some impressive fountaining happening right now in Meradalir, activity seems to be picking up again. Saw some appear to reach at least twice as high as the cone itself.

    • Height can be estimated as 5t^2, where t is the time in seconds it takes for a blob at the peak of its trajectory to fall all the way back down to the lava. (4.9t^2 is more accurate, but much harder to ballpark in your head; 5t^2 is only 2% too big and a good enough approximation for this purpose).

      So, if it takes (just over) 4 seconds for a blob thrown up by the fountaining to land in the lava pond or splatter onto the cone, it went 80 meters high.

      This also lets us gauge the height of the cone. A 4-second-to-fall outburst goes to about 3x the height of the front wall of the cone (front as seen from the RUV camera with its nice new close-up zoom setting, that is). So the cone is well over 20 meters high. 3 meters is about one storey, so the cone is taller than a mid-rise Manhattan apartment brownstone. Put another way, the booby-trapped building from Home Alone 2: Lost in New York is knee-high to this thing … and it is still dwarfed by the “Nar” cone from 2021 in turn. The width of the cone is roughly a city block. That river of lava coming out of the southwest quadrant of it is as wide as a four-lane highway or thereabouts.

      For another movie comparison, it’s already about the size of “Mt. Wilshire” as seen at the end of the movie Volcano … and still growing. The “Nar” cone, a good indication of how large it could become, if plopped into the middle of LA would bury an entire neighborhood and tower over everything nearby aside from LA’s downtown skyscraper district.

      • It is probably going to get a lot bigger, I expext. Probably at least as big as the Nar cone. When all is said and done the drive from Keflavik to Reykjavik will ger a new skyline 🙂

        • I guess I haves to name this cone too after some Tolkien landscape features

  25. There’s a new lava breakout on the southwest side of the spatter cone at Geldingadalir. It start at around 2:20 UTC on Aug 16. It will be interesting to see if this is temporary or eventually takes over from the main flow.

    • shows the steaming on a vent next to the hillside, but the dual cone lava release is stalled out and nothing is leaving on the west side now. I think the leak is because of this and the venting also, both due to magmatic pressure from the dual cone. Timestampe about 5:52 am Iceland time Tuesday August 16, 2022.

  26. The cone now is completely enclosed and has a raised lake in it. The fountain is still going but I think might be close to going into geyser mode, all of this has really only happened in the past couple hours.

    • Hmmm lets name the lava field Gorgoroth ..named after the volcanic plateau of darkness around Orodruin.
      Infact Iceland thats pretty much High Fantasy in itself should have only Tolkien names in its landscapes 😉 Icelands Highlands coud perhaps be Mordor. The old 2021 s cone left of Rag – nar I named Morgoth

      This photo of Pakgil in Iceland says pretty much everything about Icelands landscapes 🙂 Icelands landscapes formed by volcanism interacting with past glaciers and with a cold temperate oceanic climate gives the show. I really really like Icelands High Fantasy feel .. so I wants to move there. Iceland also kind of like have that dark medevial feel, or end of the world feel

      Iceland is the only place so far that I knows that haves these moody, dramatic landscapes in large ammounts, the green moss and black lava cliffs, and dark heavy clouds is insane really ..

      In the Middle Age Europe Iceland was seen as a dark and mysterious land, where gigantic dangerous forces where at work and full of annomalies
      And it was Icelandic Sagas and its landscapes that was one source of Tolkiens inspirations togther with germanic European mytology.

      Well Faroe Islands have similar landscapes as well .. as its lava flows too

    • It’s changed a lot. I wonder how this one will develop over time?

  27. Thanks Hector for a really interesting article. Been fielding a two year old for the last few days while his mum was in hospital having a second child. Not an easy task for an elderly lady over 70! Finally they are all back home and I can get back here to find a post about one of Italy’s many interesting volcanoes. A fascinating country and an article about a volcano I have very little knowledge of. Thanks for making an article that even an old lady can understand and enjoy.

    • And thanksJesper for the YouTube link. That baby has grown into a teenager already! Fascinating to see the growth after just a few days away.

  28. I hope the IGEPN knows what they’re doing, I can see the tremor on the seismographs and while it’s weak, it’s constant and other earthquakes are on the rise once again. I am seeing a lot of tornillos which could indicate that hydro-thermal system is pressurizing and if that’s the cause that means that either a significant amount of volcanic gas or magma is only a couple of steps from reaching the surface. Once again there hasn’t been a complete report on the deformation and LP earthquakes in months and I am starting to get a bit conspiratorial.

    • I would lean more to hydrothermal at present. If magma was actually that shallow only in the last km, with how viscous it seems to be I think there would be some sort of obvious St Helens type cryptodome forming that would be so obvious we would know by now. Not to say magma isnt rising but maybe not that fast. If it was rising fast it is probably already degassing and in this context probably would have already resulted in an eruption.

      It does seem very likely now though that the system will erupt, eventually. And a more active hydrothermal system could still explode and very suddenly too so…

      • If the volcano has a strong enough plug, it would stand to reason that there could be a decent amount of volcanic gas or magma just below the surface, Magma rose from 30 km to 1 below the surface in just a few months and just I can’t imagine that it hasn’t rose anymore. The low level tremor is indicative of constant motion and the recent VT quakes could be s sign of plug straining

    • The surrounding populations are holding bi-national “eruption drills” this week, and I’ve been keeping close tabs on the press coming out of the area relating to the unrest. While some things could be translation inaccuracy, I definitely get the sense there’s a growing unease down there and an awakening to the possibility of near term eruption.

      Still far from certain; it may do nothing and just continue to shake and grumble for a while. But, at the very least, it seems concern has been growing throughout the summer. I keep seeing reference to the 5.2 quake from a few weeks ago and how that sort of exemplifies the strong, sustained unrest at the system.

      • The IGEPN has begun a new campaign to study the magma bodies at Chiles-Cerro negro using gravimetric analysis. Assuming everything moves at good pace, and all of the good data is released we should see how big this volcano really is soon. I am glad to see some action but I want to view more data.

  29. Thank you Hector, Top class article, plenty of well researched details, facts, theories, mysteries and new things to learn. *****

    • I think too much lava effused initially and the flow from the mantle couldn’t keep up. Perhaps after a few days or even weeks we may see new fissures if it struggles to pick up the effusion rates and the dyke fills up with a over-abundance of magma. Another scenario is that the current fissure has a increased effusion rate and in that case new fissures are less likely. Ultimately the eruption could end altogether though, due to many reasons that I’m unable to go over due to a lack of knowledge. One way I think this could end though is that new fissures fail to open up and the lava effusion rate remains below 5 cubic meters per second for a prolonged amount of time.

      • 🙄 I keep making typos. I wish I could delete things I says that isn’t right. I meant effused obviously. Sorry for the long string of foolish text, Admin(s).

    • It is clearly different from the 2021 eruption, when eruption rates increased as the eruption went on. Perhaps the eruption is really soon to end. That would open an interesting debate on why the 2021 eruption and this one are so different. Let us see what happens.

      • That sure would be interesting Hector, but actually the effusion rate did go down in the week and a half of the 2021 eruption, as low as 2.6 cubic meters/s on day 11. The preceding event of this minimum early on, was the opening of new fissures about a week later after that measurement. The effusion rate rose back up to 10 cubic m per second. Perhaps this eruption is following those footsteps, or perhaps not. Like you said, let us see what happens 🙂

      • Perhaps the numbers reflect a couple of things?

        Since the current eruption is ‘drowning itself’ being on a plain, it is fighting itself. That could be a cause. Secondly, there have been periods of little to no lava being sent out of the cone due to collapses and thus blocking egress. This may well add to the smaller numbers as well.

        If the higher elevation vent had continued (the one to the northwest on the slope), the rate could well be different, since there would be a constant escape route for the lava to do it’s thing.

        But as you stated, let’s see what happens over the next few days/weeks/months…..

      • Is it really ending though? Or is it just not flowing out through the cone anymore and is instead going through tubes, with the cone being a gas vent and lava lake. If SO2 isnt lower then that would support the above case.

        Also that even though the cone last year was 100 m high the actual vent opened above the old deep part of Geldingadalir, this time the vent basically flooded itself immediately. Last year actually, in the last stage, it looks like the vent did manage to open into what was before the rootless lake in the valley, hence why it formed many satellite vents and then flooded out to the south, but maybe this was ultimately too much pressure.

        Maybe another factor, Fagradalsfjall is basically a gravel mountain, the last 200 meters of the magma ascent might have seen it go all over the place at very shallow depth, maybe why it started so silently and slow, and formed a sort of small magma chamber to act as a buffer. This time it started at the bottom of the mountain where presumably this couldnt happen at least not quickly.

        • I have a feeling the eruption isn’t ending. The current fissure actually might though in my opinion. Also the lava tubes never had an impact on the aerial photogrammetry measurements. Even if the lava is flowing through lava tubes, that’d still be accounted for. My guess is that two factors are for this drastic decrease in effusion rate:

          1. The eruption started off too strong, and there was less magma available to begin with than the 2021 eruption. The mantle supply rate was likely a 3rd or half of the effusion rate average in the first few days of the eruption therefore it now has to be made up for.

          2. Not only was the effusion rate higher but the lava thickness built up quicker and while not initially the cone built up quicker once it started to for. Now coupled in with the lack of magma in the upper dyke, it is taking more pressure and gases to push it out.

          If this is a mantle supplied eruption as indicated by the magma composition, then in the next few days to weeks, either new fissures pop up or the current fissure start effusing more. This early on, I don’t find it likely that the eruption ending if there is still supply flowing from the mantle.

  30. A note for the planetary lava channel discussions…

    The US Pacific Northwest has a lot of old lava channels, going to far as even cutting through the Cascade Mountain Range. Mind you, for the most part they are old. But, they are still hanging around!

  31. If not mistaken it appears their been a breach of the cone, allowing for the lava to freely flow out.If so, no surprise as newly form cones always undergo changes to its structure on the whole.

    • Yes and perhaps lava effusion rates picked up a few cubic meters per second unless it was flowing into lava tubes before the breach.

  32. I get the feeling the Blair Witch Volcano’s effusion level is up again, based on the sea of lava developing to the southeast of it and the rapid movement of the lava in that sea …

  33. Have Holuhraun solidifyed yet?
    Cooling rates depends more on the thickness of a lava flow than its extent. .. If fagradalshraun is deeper and thicker since its a lava filled valley, it will take longer to solidify

    • Most of the lava field at Holuhraun is under 20 meters, the lava field seems to be very extensive for its volume. So it probably is solid but still very hot. Parts near the vent are much thicker though going close to 100 meters so that might still be incandescent. Fagradalshraun is almost the opposite, it is very small for its volume, so very thick in many areas.

  34. I looked in on Iceland’s new volcano, only to see it is so windy today the camera is shaking! The other views are half lost in rain and fog. Summer in Iceland!

  35. Taal looks like it’s about to erupt, pulses of volcanic tremor are on the rise with elevated gas emissions and huge amount of steaming. Phivolcs are making fools out of themselves by not raising the alert; while it’s likely that this volcano will produce more small Phreatomagmatic bursts, a larger VEI 4+ explosive eruption could be on the cards and it’s better to be cautious then to be sorry. They don’t need to start a huge evacuation but raising the alert from the 1 to a 2 or 3 would be nice

    • I don’t know Taal very well. Is there evidence of magma intrusion and, if yes, at what depth?

      • There might be a continued collapse, with a ring dike growing that may eventually result in a VEI 5 eruption. Taal erupts through pressure, like the Galapagos volcanoes, and it lost 0.5 km3 of magma in 2020 during that years intrusion, it would take decades to recover from that. So actually the fact it is erupting and still active is a scary sign. As Hector has said in a previous comment, the eruption in 1749 was similar to what happened in 2020, amassive rifting event, with a somewhat bigger eruption in that year vs 2020 but not too different. Taal was active and steaming for 7 years before undergoing a caldera collapse and VEI 5 eruption, a 6 month long event that saw many repeating phases of plinian eruptions, violent fountaining and maybe ignimbrite. The products of that eruption, and all recent lavas from Taal, are all high Al calc-alkaline basalts of about 48% SiO2. Taal has erupted silicic magmas, probably related to the wider caldera, but all Holocene products are mafic, including the most recent ignimbrite 7000 years ago.

        It does seem concerning, maybe the authorities are comparing it to Pinatubo and their decisions made accordingly. Realistically the two almost couldnt be more different, and Taal is a much more violent volcano despite the lower VEI numbers. There might not really be any good comparison, but in terms of behavior Grimsvotn might be the best fit.

        • When you talk of caldera formation, are you talking about Talisay volcano or Volcano Island?

          • Volcano Island, the wider caldera seems to be older and might actually be very old, it is possibly an extinct structure, but that is maybe a too big assumption. There are two dacitic ignimbrites that have no definitive age but date from the Pleistocene, those probably created or were at least erupted when the wider caldera formed. But in the Holocene all eruptiosn have been from probably where Volcano Island is now, and mafic in composition, so there is probably no active evolved magma at taal today and might take a long time to return (or might never return). The last ignimbrite was about 7400 years ago, and was basaltic andesite, it was a VEI 6 so definitely not responsible for the formation of the wider caldera, which would have required a VEI 7. There is not too much data on how extensive this was though, it might have been a really explosive eruption that had the intensity of a much higher VEI than the volume would suggest. Taal is known for its very explosive eruptions, even if its magma is not viscous, so even a VEI 5 might be a bigger blast radius than Pinatubo. That is maybe what we get at worst case today.

            I dont think Volcano Island is big enough today to do an eruption that would escape the outer caldera, probably the island as we see it now is entirely younger than the last ignimbrite, it might even only be 1000-2000 years old or so, a very young volcano.

    • Yeah, this seems rather odd:

      Read the beginning and then the part where PHIVOLCS maintain alert level 1; it seems somewhat contradictory as clearly this shows an elevation in the level of unrest.

      Things can happen quickly, though. I’m sure if periods of tremor continue coupled with high gas emissions and steaming, they’ll have to raise the alert.

      Any word on deformation lately?

      • Well, they are not allowing people onto Taal Lake or Volcano Island, that is enough to avoid casualties in most eruption scenarios, even some of the worst ones. Only a very powerful pyroclastic surge would be able to cause casualties beyond Taal Lake. Even most episodes of the 1754 eruption were relatively harmless to people along the shoreline, if the few historical records are to be trusted. Of course, in case of an intense eruption happening, PHIVOLCS should certainly evacuate additional areas.

  36. Apparently, the lava flows that went all the way to the far end of Meradalir were heavy enough that the lava from last year was pushed out at the margin.

    • And the squeezed out lava was still hot enough to form a nice pahoehoe flow.

      • It is maybe something that gets missed, that the extreme insulation of lava will mean it takes a very long time for a deep flow to even begin to cool in its interior, even if the outside is cold. I would expect some of the 2018 lava down in Puna is still as hot as it was when it erupted, deep in the lava delta, it will be that way possibly for decades. Not to mention the bigging of Kilaueas current eruption, that began with re-eruption of the lava from earlier in 2021 too (and a 200+ meter fountain at that)

  37. Looking at this view of the Icelandic eruption
    it appears that the lava is once again flowing through tubes. I make this assumption in view of the very clearly being lave starting to flow well away from the eruption site. Lower middle right on the screen. Would this sort of activity affect the perceived lava flow rates?

    • That sure does mean lava is flowing through lava tubes. To us it would indeed impact our perception of the Effusion/flow rates, but luckily the aerial photogrammetry aircraft can account that within the volume numbers. I remember during the 2021 eruption there was a period of several days or weeks if I remember correctly, that all the lava output was flowing into lava tubes and than back up to the lava surface over a kilometre away. The measurements still accounted that within the lava field volume numbers. Over the past day the weather has been bad, too bad because I think the lava output is up slightly because of the partial wall collapse of the crater. Maybe a day or two we’ll have updated numbers. I expect the output to be similar for several days unless new fissures open up.

      • Thanks so much for the reply volcano fan, It helps me learn so much. Which is why I visit this site as much as possible. I have learned so much here and although a high percentage slips from my memory at my age, overall I am learing more than I am losing. 🙂

        • That is great to hear. I get most of my knowledge from here too. There are so many knowledgeable individuals that comment and post in this forum.

          Over the past two years I have been lurking due to the eruption in march 2021. I didn’t know much about volcanology then, except for some very basic stuff on why volcanoes erupt and how they form. I have learned that there is an astonishing amount more to volcanology than what ordinary people who learned it from a classroom says to you.

          • 🙂 🙂 🙂
            I first became interested in Volcanoes after watching Surtsey erupting. Since then I have learned so much from Volcano blogs but when Vocano Cafe first started, (and don’t ask how long ago that was) I have been an avid fan and follower. I know some people appear to dislike any focus on Icelandic eruptions but just those eruptions were the start of Volc ano Cafe and I am proud to say that despite have limited geologic or volcanologic education this site has provided me through the years with so much knowledge since the very birth of Volcano Cafe. sSo very many thanks to Carl Rhenberg (hope the spelling is correct) and to all the many others who put so much into starting this fascinating forum and so many thanks to the various contibuters of articles through the years. In the words of Star Trek fans, may they live long and prosper!

          • Alice
            Look at the header on the main page of the website.

            “10 years of EWESOME”

            The Ewe is a reference to something that happened a long time ago.

          • Me?
            Do I have a last name?
            Very Swedish concerns, we are incredibly informal and go by our first names only.
            (Thank you!)

          • Carl Ewe, is it? 😄
            Glad you made it to the holy grounds again !

  38. Wow it seems like the eruption in Meradalur has entered some sort of explosive phase. Nothing of any proportion to La Palma but something of it’s own

  39. Looking at the persistently steaming spot at the top northwest end of the fissure, I’m thinking more and more that this would be due to rainwater/groundwater coming down the hill from Meradalahjnukur and meeting the hotter ground in this area, rather than magma being just under the surface.

    Magma is indeed close, as is evidenced by the vent erupting nearby, but I don’t think it is close enough to break through at the moment.

  40. Morning everyone!
    Albert is on vacation, and I am right back from vacation.
    So, fair warning… Grumpmaster B in da House 🙂

    It seems most likely according to the GPS stations that this fissure will close and a new one open, quite like during the 2021 eruption.
    The pressure is still increasing, but the outflow is decreasing.

    • I think I might be giving you a run for your money on the grumpy front this morning, especially after reading some of the comments this morning…

    • Where is the data for pressure increasing?
      I hope they fix the Langholl webcam, if a new fissure opens it will very likely be further northwards than the existing one and that cam is perfect to see it open.

    • Welcome back Carl! It’s been very odd having an icelandic volcano erupt without a single word from you. I think the volcano felt the same and slowed down a bit, awaiting your return. Now that you’re back it will soon resume with full force through a new fissure. Let’s just wait for it and enjoy the show when it happens. 😉

    • Welcome back!

      Looking forward to your next article Carl.

      Been lots of good discussion on Nyiragongo (thanks Jesper) and alkaline magma chemistry, then a good bit on Chiles Cerro Negro lately and more explosive concerns as well.

      Good to have you back.

  41. Speaking of “Carl’s Fissure” (sounds painful), on looking at the repaired Langholl camera I see there is some considerable smoking from top of the original fissure. It might be just veg smoking. But I’m going to watch that space until the camera falls over again. It might be the beginning of an extension.
    Hope you had a good holiday, Carl!

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