Where will the next VEI 8 supereruption (>1000 km3 of erupted volume) of the planet take place? This is the question that these articles are here to answer. To put it another way, this list will evaluate and rank the supereruption potential of several volcanic systems. I didn’t use any objective parameter to calculate which had the greatest probability, the way I ranked them is just my personal opinion regarding how likely or how soon a supereruption could happen in each of them. The order of the volcanoes was in fact changed a few times while making it as I learned more details about them.
All 10 volcanoes featured here show some potential to do a VEI-8 eruption in a GEOLOGIC FUTURE. So first of all and to clear out this important aspect, we are not going to see a supereruption in our lifetimes, thankfully. Perhaps there is a really really really slim chance that one could take place, but due to the very low frequency of these events and because no volcano is showing any signs of being about to immediately throw one of them, I dare say we won’t see it nor will countless future generations to come. Phew… Though I imagine some people being rather disappointed right now.
Also, if you have not read the article Batholiths and Flare-ups, it would be better if you read that first, since it is meant to be an introduction.
The factors used to gauge the supereruption potential should be explained first. One is that the volcano must have dacite or rhyolite (or their subvariants), which are the kind of magmas that make up supereruptions. Someone may come up with an example of a supereruption that had a basaltic or other unusual composition dating back to the Jurassic Period. However these are very rare exceptions under extremely rare situations, like flood basalts.
Another factor is that the amount of eruptible dacite or rhyolite must be very large, ~450 km3 or more. Eruptible means that it is assembled into a single melt-rich body (magma chamber), that will exist within a larger mush system (a batholith) that is not eruptible. Magma chambers usually look like lenses or sills, very spread out, that is why a system that produces a supereruption must be extensive, I considered the ~420 km2 area of Taupo to be the minimum requirement. Ring fissure eruptions can be taken as a factor for the existence of a mature magma body/chamber.
You could be wondering if I am going to take seismic tomography into account here. Problem is that while tomography seems able to very roughly detect the bigger mush bodies it seems to fail or be very bad at locating melt-rich bodies (the magma chambers).
Another way to know roughly how large is amount of melt assembled, is to look at the size of regular eruptions. Although the caldera-forming eruptions are the ones that get most of the attention, the vast majority of eruptions will be much smaller and not involve collapse. Effusive eruptions are very telling since these can only evacuate a very small fraction of a melt body. This is because if magmastatic pressure falls below the point where magma can’t be raised to the surface anymore, then the eruption stops, it lacks the lift from outgassing that explosive eruptions enjoy. At shield volcanoes and stratovolcanoes flank eruptions can release significant pressure since they erupt at low elevations that can reduce much more the magmastatic pressure, but this is not the case for large calderas which are usually at the same level as the surrounding terrain. This is why caldera systems that produce effusive eruptions of more than 2 km3 are extremely rare to find. Lava flows or domes bigger than this indicate extraordinary amounts of assembled melt.
I have also considered how large is the heat flux into the volcano. If new heat no longer enters the system then regardless of how big it is, it should gradually freeze into rock, like your closest granitic mountain landscape. Whether mantle and crustal melting continue below a system is a fundamental question. The heat released by a geothermal field, through geysers and hot springs can also be indicative of a large heat flow.
So taking into account these factors here comes the ranking from least likely to most likely to produce a supereruption. Let’s go!
10. Incapillo (Argentina)
Lonely and barely known Incapillo volcano will at least get a place. With so many calderas in the Central Andes it is quite easy to miss some of them. Like the other big volcanoes of the region, Incapillo was formed due to rollback of the Puna slab, but it lies further south than all the others, far away from the APVC. It’s half standing in the volcanic graveyard of the Pampean flat slab and half in the tumultuous flare-up of the Puna slab. At the very veil I find impossible to guess whether this system will get future supply or not, it is all or nothing.
While it is a small unremarkable 5×6 km caldera, it is surrounded by a much more extensive volcanic field of dacitic and rhyodacitic lava domes large enough to host a VEI-8. A large silicic magma body seems to have attempted to develop but it still needed some assembling to do. However it looks like activity has stopped completely. All the domes seem old and to predate the caldera which is 510,000 years old. Now Incapillo stands in a deep volcanic silence.
At some point in the future, the Pampean Slab is likely to do rollback which will certainly restore a large influx to Incapillo and perhaps lead to a supereruption, but that is in the long-term, very far away.
9. Toba (Indonesia)
A giant among giants, probably the largest caldera in the Planet that can still be considered active. This Indonesian volcano has produced 2 supereruptions so big that make all others in this list look small. The first was 840,000 years ago and ejected 5,300 km3 (bulk), another small collapse took place at 500,000 years. The last collapse was the Younger Toba Tuff, 75,000 years ago, which produced 2,800-5,300 km3 of DRE. The whole area was engulfed by a 100×30 km sized caldera bounded by up to 2 kilometre high cliffs. Some estimates that include distal ash-fall put the eruption as a VEI-9. Could it be true, do VEI-9s really exist!? I don’t know, but whether this is right or not the YTT was undeniably huge!
What is the secret to such a gigantic caldera? What geologic mechanism could be behind it all? There is subduction going on underneath and also extension that is reflected in the formation of NE-SW basins oblique to the Great Sumatran Fault. This is a prominent strike-slip fault system that runs across Sumatra, volcanoes are at or near it. Toba is located 15 km to the northeast of the Great Sumatran Fault in what seems to be one of those NE-SW corridors of extension and above a possible slab tear has been proposed to lie at the melt source. However the combination of extension and subduction, and even slab tears, are quite common in the world, but there is nothing else like Toba out there. The explanation seems incomplete.
Toba has the typical internal plumbing of large caldera systems. It crowns an uplifted area of Sumatra that is 220 × 100 km across, linked to intrusions and crustal thickening. A deeper reservoir of basalt mush is located at 30-50 km depth and contains 50,000 km3. While shallower reservoirs contain intermediate and silicic magmas. The earliest volcanism was a 500 meter thick succession of andesites and basaltic-andesites around 1.3 Ma, suggesting that the formation of a layer of andesitic melts preceded the silicic volcanism and caldera activity.
What about the future of Toba? A few small post-collapse domes have erupted along margins of the caldera while Samosir Island is being uplifted by a resurgent dome. However this doesn’t really mean much, some calderas undergo resurgence only to later become extinct. Caldera cycles of Toba have lasted ~400,000 years, so it is unlikely that enough time has passed since the YTT eruption for Toba to be anywhere near recovering. Toba could do more caldera collapses in the future, but not yet, this giant is going to need a long time to build up melt.
8. Nevados Ojos del Salado and neighbours (Argentina-Chile)
Another familiar name? We are back to the Central Andes and the Puna Slab. The last 10 million years of flare-up in the region is a tale of 4 giant andesitic MASHs/mush bodies. The more famous and bigger Altiplano-Puna is well known but it has coexisted with Lazufre, Cerro Galan and Incahuasi, each has brought forth a couple of calderas.
From a mush-wide perspective Incahuasi remains the most active of the 4, it has the youngest ignimbrites among them. This was the Cerro Blanco eruption around 4,200 years ago which produced more than 170 km3. There are also extensive basaltic volcanic fields which show that melting of the mantle over a wide area is still going down below, something that seems largely over in the 3 other complexes.
Nevados Ojos del Salado is part of the Incahuasi Complex and is also the highest volcano in the world at 6879 m. It is not much of a sight though, instead of an elegant conical stratovolcano what we find is a bunch of irregular domes and cones. Broad doming above the Incahuasi batholith helps this volcano grow so high even though the prominence above the surrounding ground is small (only 2 km higher).
The main reason it makes it into the ranking is a lava dome located on its west flank. It is called El Solo. It doesn’t have any volumes estimates that I could find so I made my own, the dome and pyroclastic flows from dome collapse together seem to be at least 15 km3 (bulk). According to GVP the eruption took place 1000-1500 years ago, although I couldn’t locate the original source.
There is a large body of molten rhyodacite that fed the El Solo eruption and there are also some sizable domes to the east. The region however shows mixed volcanism with andesite and basalt flows together with the more evolved domes. There is no sign that gives away the existence of a single broad melt film: was it just a transient chamber that fed El Solo and will now disappear? or is it the start of a new long-lived large caldera system? The Nevados Ojos del Salado group is 70×30 km which could host a VEI-8 caldera, but the system could fall short with a VEI-7 or not even collapse at all. It will take a long time but the supply is strong and secure so it provides a promising means to eventually achieve something interesting.
7. Tatio (Bolivia-Chile)
At first it might seem like a group of volcanoes unrelated to each other but there a signs of a large magma chamber hiding here. Its location is the Altiplano-Puna, a giant batholith that was properly presented in the introduction article and mentioned over and over again. When you have used the word giant in front of the word batholith it is because this no ordinary system. But despite its tremendous size the complex is well into decline.
The Altiplano-Puna is a result of the Puna slab steepening, starting around 12 Ma. Short pulses of ignimbrite activity took place at 8.4, 5.5, and 4.0 Ma that produced the largest eruptions of the complex. Volcanic activity has died off in most of the flare-up area and remains only in the active arc above the subducting plate, consisting of generic stratovolcanoes (a typical arc activity). Has the Altiplano-Puna burnt off all of the extra melting from the slab steepening? It does seem possible.
Then why am I putting an APVC volcano in this ranking? This is because Tatio might be the last remnant of major silicic activity in the region as well as maybe the last shot it will get at doing a supereruption.
The 40 km3 DRE Tatio Ignimbrite is the youngest major explosive event of the APVC. It happened 750,000 years ago. Its exact source is unclear, but it is located next to a hyperactive geyser field and 3 voluminous lava domes. The geyser field, known as El Tatio, is the 3rd largest in the Planet: it has been active for 27,000 years.
Geysers require several conditions to be met. First is the abundance of water circulating through fractures. Second is silica rich rocks which provide the material (dissolved silica) that through its dissolution and precipitation create geyser conduits. And last, a strong source of heat to boil the water. This shows there is a large and active source of heat below, molten dacite in all likelihood.
Of the 3 massive domes the most remarkable is the dacitic Cerro Chao <100,000 years old and with an impressive volume of 26 km3, this is the size expected if it was fed from a supereruption-sized melt rich body. All the above-mentioned features coexist within an area of 50×20 km, which is the speculative Tatio Magma Body.
However these are the last steps of the great APVC: with the dwindling melt influx nothing guarantees this volcano won’t freeze to death without accomplishing anything truly remarkable. While the slowing supply is its weakness, its strength is that it is already very advanced in the melt assembly process, shown by Cerro Chao. Vast amounts of dacite have built up underneath these remote and barren landscapes much like it happened back when the flare-up was at its peak, will it be a failed attempt? or the successful rebirth of a former glory?
To be continued…
History of the Altiplano-Puna Volcanic Complex: