Ibu, an overlooked caldera

Indonesia is a country of volcanoes. An impressive amount of subduction-related volcanoes. The country features four different volcanic arcs, chains of volcanoes above subducting oceanic plates. The most important one is the Sunda Arc, home to way too many famous volcanoes like Toba, Krakatau, Galunggung, Merapi, Semeru, Bromo, Kawah Ijen, Batur, Agung, Rinjani, or Tambora. Marapi and Lewotobi made the news more recently. The Sunda arc is nearly 4000 kilometers long, arguably the longest volcanic arc on the planet. It includes many unusually large and productive volcanic complexes, particularly the stretch that goes from Sumbing to Tambora is a continuous row of giants. Tambora itself has a volume of over 1000 km3, erupted probably within the last 1 million years, and there are some additional 10 complexes of similar or superior size and very young age to the west.

Apart from Sunda, Indonesia hosts three additional volcanic arcs in the east of the country, in a very complicated geologic setting of colliding micro-continents. There’s the small and uneventful Banda Arc where the volcanoes barely emerge from the sea as tiny islands. There’s also the Sangihe Arc between Sulawesi and the Philippines, home to some fairly active volcanoes, including the Ruang volcano, which has produced two plinian eruptions in recent weeks. And lastly, we find the Halmahera Arc, a 300 km long arc with volcanoes that are not very exceptional in terms of productivity. But two volcanoes in Halmahera have always interested me which lie next to each other at its northern end. Ibu and Dukono volcanoes.

Dukono has been in continuous eruption since 1933. It’s a volcano with little topographic prominence but with an unusually complex and vast structure in terms of vent distribution, with two lines of volcanic activity that intersect perpendicularly over the summit. First, a SW-NE area of low volcanic cones, some of them polygenetic, that occur irregularly over the landscape and extend over a length of 30 kilometers and a width of 10 kilometers, I suspect an area above a vast sill or similar. Second, there is a NW-SE line of fissure vents 35 km long that cuts the summit of Dukono near its middle and includes a series of scoria cones and maars erupted along fissures and sometimes inside broad grabens, probably lateral dike intrusions originating from the summit of Dukono and extending along a rift. The last lateral dike intrusion may have been in 1550 when lava flows erupted from the northern rift zone of Dukono. This eruption, according to GVP, also included earthquakes, property damage, and fatalities. The southeast rift has a young-looking maar, which erupted along a fissure and is filled with a 4 km-long lake. Since 1933 the volcano has been continuously erupting, usually low-level ash emissions from a small tuff cone on the broad summit of the volcano, and sometimes lava flows that cover the area around the cone for short distances.

Topographic map of Dukono, generated in opentopography.org.


But Mount Ibu is the protagonist today. On May 16, the volcano monitoring agency of Indonesia upgraded Mount Ibu to alert level 4 based on explosions more powerful than usual and escalating seismic unrest. This volcano seems to have a caldera about 13 km long and 9 km wide. I have not seen any mention of this caldera in the few scientific literature that showed up in Google Scholar, but it’s very clear in topography and it seems extremely unlikely it could be anything other than a caldera. Because this volcano seems to have an earlier caldera and a vent arrangement that could loosely suggest caldera-style activity, when I saw the news I decided to look more into it. I was surprised to find it does have a magma composition that is caldera-like, so I thought this to be something important to talk about.

Topographic map of Mount Ibu generated at opentopography.org.

Structurally the volcano comprises a 13 km long caldera, it’s very shallow, largely filled up by inflation or eruptions. A 1 km tall stratovolcano rises from the east side of the caldera, Mount Ibu, with very steep upper slopes and a large central crater that is 1.5 km wide, with a smaller nested crater inside that is 700 hundred meters across that was formerly a deep cylindrical pit but is now filled with lava. Cones and craters are found over the caldera floor. On the west side of the caldera three craters up to 1 km wide, probably formed in energetic explosive eruptions, lie immediately next to multiple villages. Just to the north of the caldera another cluster of three craters up to 1.5 km wide are found, two of them filled with water lakes, so may be called maars. There are also some hills that from their shape may have originally been fissure-fed silicic lava flows, but through the thick vegetation, it’s hard to say. Some fault scarps are found around Ibu which suggests some weak extension. There’s not much scientific literature about Ibu so its history or anything about it seems little known.

The interesting data about its magma chemistry comes from a 2014 article by Ugan Boyson Saing, Philipson Bani, and Kristianto. This bit of information is very important to understand the present state of activity of the volcano and is a description of the recent lavas erupted from Mount Ibu. After 90 years of dormancy, Ibu woke up in 1998, and since then activity has been frequent, even continuous since 2008. When activity started, the volcano had a deep summit crater that has since filled up with lava flows and also overflowed some distance down the north flank. The 2014 article shows two samples of recent lava and ash erupted from Ibu, they have a very evolved composition, a 67-68 weight % silica dacite. The lava sample looks like obsidian, it’s a black glass that lacks or nearly lacks visible minerals, according to the article it has no phenocrysts. Looking at caldera-forming eruptions of volcanic arcs, this is perhaps the most common type of magma associated with them.

Whilst reading scientific literature about volcanoes, I’ve come to notice that there is an important difference in crystal content between normal stratovolcanoes and caldera systems in subduction zones. Stratovolcanoes often erupt magmas like basaltic-andesites, andesites, or low-silica dacites (up to about 64 wt% SiO2), that have crystal-rich composition, very often as much as 40-50 vol% crystals. Such lavas can be mafic in composition but highly viscous due to interstitial evolved melt that is found in between the crystals that very often reaches rhyolite composition (the glass itself is rhyolitic and not the whole rock). For example, Merapi erupts basaltic andesite, but the small molten portion of the lava is rhyolitic which yields a high viscosity and development of lava domes instead of flows.

Volcanoes that produce caldera-forming ignimbrites have distinctive compositions and behavior. These volcanoes often collapse multiple times throughout their history producing energetic eruptions with pyroclastic flows that, as long as no mountains stand in the way, will cover a radius of around 30-40 kilometers in every direction from the volcano, producing the characteristic ignimbrite deposits. Subduction zone calderas above 3-4 kilometers wide are always or almost always ignimbrite calderas. The ignimbrite magmas tend to be below 20 vol % crystals in composition. The only important exception I know of is the Central Andes, where ignimbrites may come from crystal-rich dacitic magmas similar to those of regular stratovolcanism. Calderas are also generally higher in silica than stratovolcanoes.

The largest calderas on the planet, like Yellowstone or those of the Taupo Volcanic Zone, erupt crystal-poor rhyolite ignimbrites, the most silicic magmas on the planet, and also erupt these same magmas as lava flows and pumice during “smaller” eruptions in between collapses. Dacites like that of Ibu are probably more common though, since smaller dacitic calderas collapse more often and may also number higher in terms of total volcanoes. Examples of dacite calderas include the VEI 7 Mazama eruption 7700 years ago which erupted mostly 70 wt% SiO2 rhyodacite with less than 10 % phenocrysts, or the VEI 6 Rabaul eruption in the 7th century which comprises 64-66 wt% SiO2 dacite with 6 vol% phenocrysts. Another example is the Aniakchak caldera-forming ignimbrite which has a first half of dacite with 67-70 wt% SiO2 and 2 vol% crystals, followed by a second half of crystal poor andesite with 57-60 wt% SiO2 and 8 vol% crystals. The recent lavas of Ibu move in similar values as some of these volcanoes, it’s also crystal-poor dacite, so I think it can be considered a volcano with caldera potential. More mafic ignimbrite calderas also exist, although they are rare, like Hunga Tonga which is crystal-poor andesite or basaltic-andesite.

Having these magmas doesn’t mean Ibu is going to collapse. Volcanoes like Rabaul or Aniakchak have historically erupted dacites mixed with andesites, sometimes in substantial plinian eruptions without collapsing into ignimbrite eruptions. We don’t know what makes an ignimbrite calderas collapse exactly. We have only closely monitored Hunga Tonga which itself is a bit of an oddball being too much on the mafic side of such volcanism, and there’s not that much data anyway. The magma chamber probably needs to be ripe, which I think means having built a large enough amount of evolved enough magma. But it’s hard to know if this is or isn’t the case for Ibu, having erupted phenocryst-free dacite historically doesn’t necessarily mean it has a lot of it, most of its storage could very well be andesitic at present. But it does set apart Ibu from other volcanoes, meaning it has the potential to produce a caldera-forming ignimbrite at some point, maybe 10,000 years ago and it’s no reason to be concerned, but it could also very well happen in the short term. There’s also a potential for smaller plinian eruptions to issue from various parts of the caldera floor with little warning, as well as the main cone. Volcanoes like Aniakchak or Rabaul produce plinian eruptions from a ring of polygenetic vents inside the caldera that seems to match the location of the ring fault. Mount Ibu may be more rift-dominated I think, but there is still the same potential for large explosive eruptions from vents away from the mountain itself.

I think it’s a volcano worth studying further. Maybe research could go into figuring out when and how the caldera around Ibu formed. Also, what was the chemistry of the eruption that formed it? It would also be interesting to know what the main stratovolcano of Ibu is made of, which would help understand if the silicic stuff is a new thing or not. Images and videos of Ibu show narrow layers of hard material exposed in the walls of the crater resembling lava a few meters thick or less, I think spatter actually, and they are separated by red and black colored tephra, probably oxidized scoriaceous material that is possibly andesite or basalt, but it would be best if there were studied samples. Combined with the steepness of the cone I think Ibu used to be a basaltic or andesitic stratovolcano, prone to lava fountains that built a steep cone, the fountains covered the cone in alternating layers of spatter and scoria. The flanks probably saw effusion from the summit or flank vents. The large crater could have formed in either a large plinian eruption or non-explosive collapse like the twin pits of Ambrym.

The volcano is populated and even a regular plinian eruption could be life-threatening. I’ll just say that there are over 10 small towns inside the caldera itself, within reach of anything that might come down the slopes of Ibu (lahars, debris avalanches, or pyroclastic flows). If it ever goes caldera (hopefully something that will wait thousands of years), there’s no need to say that these towns would be no more, and destruction would also extend beyond the caldera due to pyroclastic density currents and tsunamis.

Mount Ibu in 1999. The image is probably taken from within the caldera. Image from the Volcanological Survey of Indonesia.


Saing, U. B., Bani, P., & Kristianto. (2014). Ibu volcano, a center of spectacular dacite dome growth and long-term continuous eruptive discharges. Journal of Volcanology and Geothermal Research, 282, 36–42. https://doi.org/10.1016/j.jvolgeores.2014.06.011

C, K., K, C., & C, B. (2002). Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon. Bulletin of Volcanology, 64(7), 486–501. https://doi.org/10.1007/s00445-002-0230-5

Fabbro, G. N., McKee, C. O., Sindang, M. E., Eggins, S., & De Maisonneuve, C. B. (2020). Variable mafic recharge across a caldera cycle at Rabaul, Papua New Guinea. Journal of Volcanology and Geothermal Research, 393, 106810. https://doi.org/10.1016/j.jvolgeores.2020.106810

Dreher, S. T., Eichelberger, J. C., & Larsen, J. F. (2005). The petrology and geochemistry of the Aniakchak caldera-forming ignimbrite, Aleutian Arc, Alaska. Journal of Petrology, 46(9), 1747–1768. https://doi.org/10.1093/petrology/egi032

78 thoughts on “Ibu, an overlooked caldera

  1. Great article on a volcano not talked about Hector.
    Is this volcano, like Ruang, likely to build a sticky dome which could then be exploded away? The composition is slightly different, but the hazard would be similar even in case of a lower end eruption.

    • Thanks Andy.

      Ibu does very gentle explosive activity, with small explosions and jets which erupt from small spots over the conduit rather than the whole thing blowing at once:


      That said, I think recent explosions have escalated in violence. I’m not sure if it can do something like Ruang. It may be more likely for it to happen if Ibu goes inactive but continues to get supply and erupts several years later. Some volcanoes seem to erupt more violently when this happens. The lava that has filled the crater could in the future act as a plug that helps build gas or pressure, instead of the porous deformable breccia that was there before the current eruption period.

      • Ibu is my new favorite volcano ever since I’ve seen the “controlled quarry explosion” type eruptions.

        Albeit this article and the video you linked make me wary of a potential for something bigger.

        The kind of eruptions in this video reminded me of this fireworks storage that caught on fire … and just as you are like heyyyy ohkay, wow, this was actually kinda nice firewoooaahfuuuuu…

        That sort of thing. Scary.
        It was around that time I started to feel uneasy about all types of fireworks too.

  2. That’s fascinating. thanks, Héctor. I had a look on Google Streetview (isn’t it amazing we can do this), and the villages are poor but almost idyllic. Pyroclastic flows from the current cone would be ruinous.

  3. Dukono is weird, erupting continuously but it doesnt really actually ‘erupt’ just have constant degassing and incandescent glowing vents. Also strange it seems to be a rifting volcano in a subduction zone yet has no caldera. To me it also looks like possibly two parallel systems, rather than a single huge system, but I havent looked into it.

    Have often seen stuff about Ibu show up recently, mostly drone footage of small eruptions on its dome. That it seems to be a VEI 7 caldera is concerning given it hasbeen very active the last 20 years.

    • Yes, it’s curious. Most videos just show a noisy incandescent spot in the bottom of the crater, but the eruption seems to have been permanent for nearly a century and it’s also one of the top volcanic sulfur dioxide sources on the planet.

      I have also considered Dukono to be two separate systems, but because “stratovolcanic” behavior (typical polygenetic constructions and degassing) only happens in one spot I believe the whole thing is one shallow magma architecture with magma being supplied under the active crater of Dukono and extending into a sill to the southwest, and dikes to the northwest and southeast.

      • I’d be concerned that Dukono is a caldera volcano that simply hasn’t had its first caldera-forming event yet. There are several craters of up to a few km side nearby that might, along with the big maar and the arc of cones in the northeast of the high-elevation portion, be on a developing ring fault.

        Dukono’s lavas are not as silicic as Ibu’s, or typical calderas, with upper 50s percent SiO2, so it might have a ways to go yet … unless, of course, caldera systems’ magma chemistry changes after the first caldera collapse, perhaps because of it. I could not quickly find data for Dukono magma crystal percentage.

        As for Ibu, the central cone reminds of Nyiragongo and likely formed the same way. As with Nyiragongo (and Ambrym, mentioned above) it may at one time have hosted lava lakes.

        Both systems should be regarded as extremely dangerous, given the setting and Ibu’s past history.

        • Not sure if it would be a volcano with magma that fluid, but something like at Etna SEC complex maybe. A magma that fluid would be very hot and the current lava dome complex is pretty blocky and viscous especially for being low crystal. The dacite lavas at Aniakchak and rhyolite at Cordon Caulle are felsic lavas which formed thin sheet flows so it can be done.

          Maybe a more likely case is that the stratovolcano of Ibu is not formed under the same conditions as the present. It looks young but maybe there was no molten dacite back then, and it erupted from the deeper source, and later changed to evolved magma as the rest of the chamber was warmed back up. I cant think of any way a volcano can be hot enough to have a lava lake and then erupt a blocky dome in the same place without a wide interval between.

          • I wasn’t meaning to suggest that it was like Nyiragongo yesterday. 🙂 It is hard to explain the cone looking the way it does if it wasn’t at least much of the way to that extreme in the past. And as you say that likely means a lot of time has passed since the cone first formed — and even longer since the last caldera-forming event.

            Which may mean the next such is (and I know some here will hate that phrase) “statistically due” …

  4. Ibu seems to be a case of a reheating of an old magma chamber. The lack of crystals indicates that the magma chamber had become stratified, and now the new heat is sufficient to melt the rhyolite layer but is not hot enough to melt the rest. If that remains the case, you would expect small effusive eruptions but nothing major. what is sthe source of the heat?

    • I’m not sure that lack of crystals means there will be nothing violent. I’d say the opposite. Half the Aniakchak ignimbrite from 3400 years ago, some 14 km3 DRE of dacite, is nearly crystal-free at only 2 vol% crystals (in one of the articles referenced), while the andesitic rest is not much higher. Generally low crystallinity is a characteristic of caldera volcanoes lavas and tephra.

      But for the time being the volcano behaves quite gently. Hopefully, nothing will chance that. And caldera volcanoes do erupt “small” most of the time.

    • Seems to start flaring up at the south end of the caldera, then go across to the ERZ connector. Before February it was the same but it went down the SWRZ connector. I wonder if the lack of seismicity to the southwest us because the area rifted so tension has been released there, which hasnt happened on the ERZ yet. SWRZ stations still show significant uplift after February so arent starved of magma.

      I wonder too if a repeat dike in the same place would be so noisy. Svartsengi just about woke up all of Iceland with the quakes in November but now it is pretty stealthy, even nearly silent. I believe the same was true for the eruptions in the 1960s on Kilaueas ERZ, breaking open the rift is noisy but later intrusions go less far sideways and more up, and go faster.

    • Also, it must be said, this is pretty extraordinary.

      UWEV-CRIM have moved 10 cm apart in the span of 3 GPS points. I noticed it the other day but assumed it to be noise but now it is pretty clear the signal is real. The ERZ connector also is active further than before, going strong to past Pauahi crater and nearly to Mauna Ulu where the real ERZ starts. But still inflation is dominant further west, I think the ERZ connector is just reflecting high pressure rather than being indicative of where magma wants to go. Although the ESC tiltmeter is responding…

      Even though it hasnt reached a point equal to the 2018 pressure on the instruments I think Kilauea might well be fully recovered from that internally. Most of the deflation was a physical collapse, HVO recently said the 2018 caldera was about half the volume of the lava erupted so maybe 2/3 of the DRE, the rest was elastic deformation, 0.4 km3. With a supply rate of 0.15 km3 a year that is 0.9 km3 of magma since 2018, with 0.2 km3 erupting and 0.5 km3 filling underground. Its curious that the amount of time to intrude 0.1 km3 of magma at 0.15 km3 a year is 8 months, and 8 months ago from now was in September just following the last eruption and when the SWRZ started to get really active…

      There are too many small variables to consider for this to be anything other than a rough guide but I think we are going to see Pele at her healthy self again. It will still be probably decades until the actual break even point of 2018 but the volcano has recovered to a normal pressurized state and we should expect much more activity than has been seen in many years. Possibly even since the 60s.

      • Reading back a few number errors. I didnt state that I think the 2018 lava DRE is 1.2 km3 leaving 0.8 km3 for the collapse and 0.4 km3 as elastic deformation over large areas of the volcano. Supply of 0.15 km3/year is 0.9 km3 in 6 years, with the volume erupted so far being 0.2 km3 above ground and leaving 0.7 km3 intruded, where I had said 0.5 km3 before.

        Still, I think after September the volcano had reached a point of positive pressure and that is why it has not erupted at the summit but is pushing so much magma into the SWRZ in particular.

  5. Ibu and Santa Maria seem to be very similar in a lot of ways. Both are stratovolcanoes that are probably originally mafic but which are now erupting dacite slowly. Ibu is more active and not as explosive while Santa Maria woke up from a long dormancy with a major eruption but they are very comparable now.

    Maybe Ibu will just keep filling its crater with lava over time and eventually just overflow all over. Maybe over time the magma will get less viscous too, as it seems might be the case at Santiaguito. Given that Santiaguito has been going over a century without anything serious I think maybe Ibu could be pretty safe as long as an open vent is present somewhere to relieve pressure. But then there are always unknowns, and there seem to be a fair share of those at this volcano…

    • Not that timeliness is surprising, of course, given that the Indonesian Volcanology people are excellent at their jobs and it was their elevated warning that prompted Hector’s post. Hopefully the warning has also meant the locals could all evacuate safely – and from my very non-local distance, I do appreciate being able to find the geology and history here that the news articles can’t give.

      • In the 2020 eruption, lava covered half the distance to the villages on the slopes. They are too close to a re-activating volcano. Even rhyolite can flow well if it has no crystals

    • Went to link and at the end of the guardian video it said that this was one of the most active volcanoes, erupting over 21,000 times last year.quick back-o’-envelope calculations says this equates to 2,100 eruptions every 36 days (approx.) or 210 eruptions every 3.6 (approx. 4) days, or over 50 eruptions a day. I’m no volcanologist but is this correct? if so, how do they define an eruption? every little burp and spittle of gas?

      • They did that for Sakurajima too, every vulcanian eruption being considered a full eruption. Properly it would be a single eruption from when it starts to whatever point there is a 3 month gap

  6. Dukono looks like it has a large Pleistocene caldera on satellite but it doesn’t look that way topographically.
    It does appear that there is a NE lineament from Gamkonora through Ibu towards Dukono, and into the sea where there is another edifice. Is Dukono younger than Ibu?
    Todoko-Ranu has quite a large explosion crater too, but densely forested.

  7. Looks like an earthquake swarm is happening off the southwestern tip of the Reykjanes peninsula. Just stress quakes caused by the ongoing inflation at Svartsengi, or something else (possible new intrusion)?

    • Strangely there has often been increased activity there prior to the eruptions in Svaetsengi area but this time it is really pulling out all the stops. It would be really interesting to understand what is happening below the sea but the quakes are still mostly more than 5km depth so nothing to see there yet.

    • First time comments are always held back by the spam-deamon-in-charge, sadly for good reasons. It takes an admin-dragon to approve release into VC-world, and this took longer than average in your case because of sleeping dragons. Further comments should now appear without delay!

  8. Hector what wonderful timing, I have been wondering what is going on with Ibu.

    A couple days ago, GeologyHub mentioned some crazy (Australian? New Zealander?) posting videos under the name Extreme Pursuit showing rather up close footage of Ibu’s lave dome, or domes, nearly filling the crater, also a lot of seismic activity. Blocky blackish-grayish rock.

      • This is exactly the kind of plot I was asking for in a comment that probably got lost when a new article was posted. I questioned if the model should really be reset to zero after each event. I have to agree that this looks a lot like the inflation pattern during the Krafla fires.

        • Also suggests just how huge that original dike was. About 4X the drop of any subsequent eruption/dike! I guess as things get more pressurized underground with dikes, the closer the needed pressure will get to at start.

          • Pretty normal with rifting events, the first dike is filling in the whole rift while later ones have less space. Krafla was the same and this also happened at Kilauea in the 1960s.

            Its not a rule though, Mauna Loa doesnt seem to do this. It just goes full power immediately. Its last eruption was a nearly 20 km fissure that opened and stopped mostly within 12 hours, and this is very typical, some eruptions there have done the same in only 1-2 hours…
            Mauna Loa is very elevated, sequential repeated rifting seems to happen on flat ground above the source with a lack of a tall central volcano.

      • Those links that are supposed to go to a translated version of the page never seem to work very well. I prefer to get the original link and run it through the translation myself using the built-in functionality in chrome.

  9. Trying to write an article on SaO Miguel volcanoes but will take some time

      • That map is crazy. All those houses and infrastructure. Brings home again that even tiny eruption will be massive problem.

        • 165,000 people live within 5km or so of the earthquake sites. Which actually isn’t a terrible site for an eruption as that number is going to be at least 100k pretty much anywhere on the caldera. The worst place would be on the eastern side closer to Naples, there it is closer to half a million within 5km. On the bright side it has been fairly quiet the last few thousand years and even Monte Nuevo wasn’t very big.

      • Still ongoing


        INGVvulcani @INGVvulcani
        Alle ore 23.00 locali del 20/05/2024 è stato registrato un evento sismico nell’area dei Campi Flegrei di magnitudo Md= 3.6 ± 0.3.
        Info: banca dati GOSSIP: https://buff.ly/4bpZXpF
        #CampiFlegrei #INGV #OsservatorioVesuviano

        Translated from Italian by Google
        At 11.00 pm local time on 05/20/2024 a seismic event with a magnitude Md= 3.6 ± 0.3 was recorded in the Campi Flegrei area.
        Info: GOSSIP database: https://buff.ly/4bpZXpF
        #CampiFlegrei #INGV #OsservatorioVesuviano

  10. Thanks for writing this Hector. My thoughts on this volcano perked up when I read that it was dominantly Dacite, and also after simply looking at the profile of the volcano on Google Earth.

  11. @Hector,

    What is your opinion regarding the many caldera volcanoes that originate from Andesitic magma? Do you think those volcanoes may evolve to become progressively less crystal-rich over time before they would make a caldera-forming eruption?

    While Rhyolitic eruptions are common for the large-caldera producers, clearly there are a plethora of non rhyolitic volcanoes that have whopping huge calderas.

    And on a separate note, If what Albert said higher up is true regarding lack of crystals indicating stratification of the magma chamber, wouldn’t that align with a lot of the observed eruption dynamics before major eruptions that sees stratified magma chambers start to mix or overturn?

    • I don’t know many andesite caldera events. There’s Hunga Tonga which is borderline andesite/basaltic-andesite. Caldera-forming events that involve andesite usually start with high-silica dacites. Basaltic-andesite and basalt calderas are more common, like Okmok, Gaua, Yasur, Tofua, Masaya, and Ambrym and Ambae maybe. I think they are likely to keep crystal poor compositions all the time. Basaltic shields like those in Galapagos I think always erupt crystal-poor lava regardless of how close they are to a caldera collapse and same should apply to subduction zone calderas I’d say.

  12. Seems something happened here.


    There was a similar signal after the last quake swarm too, I wonder if it is artificial. If not then maybe it reflects a short lived flood of magma down the SWRZ connector, not a large volume but high rate of flow.

    • It does appear to be local to the south caldera area, so probably not magma going downrift. Maybe it is a rockfall from the caldera rim.

        • Yes I thought about that right after commenting… It just seems odd for this signal to actually be a magma movement tremor without any of the other signs. Even really small intrusions at Kilauea make actual earthquakes on the map, and dikes at the summit which actually erupt tend to last about an hour and are obvious though very fast. This has nothing. It was somewhere in the area though as it barely shows at all more than a few km away.

          Its also more surprising to me that Kilauea didnt erupt the other day, the UWEV and CRIM stations moved 10 cm apart in under a week and both are now recovered to beyond what triggered the last intrusion. I guess maybe magma did intrude, perhaps into the caldera fault and without breaking anything…

    • If you mean the signal after 8 HST, that’s just noise, maybe traffic, note it’s rush hour in Hawaii.

      The second signal at 22:40 is a Pahala tremor event. It’s faint and has not been located by HVO but does have the characteristic shape of a Pahala spasmodic tremor: sudden onset and several pulses inside continuous shaking for 15-30 minutes or so. Note that the tremor shows up identically in many stations over the island.

      • I’m not sure the episode around 8 HST is traffic. If so, it would always being showing up every day around the same time…which it didn’t yesterday…and I don’t remember seeing it before (but then again I infrequently look at all the drumplot…just a few).
        Only possibility might be a convoy of construction equipment over unpaved terrain?
        The drumplot is often noisy, but at various times it is also quiet for extended periods of time in the middle of the day when traffic is most likely.

        • Not sure what it is. But the signal is different in RIMD and WRM, which shows is something surficial.

  13. It is the 8 HST signal. Although there is no rush hour near Keanakako’i, it is only accessible by walking and RIMD is beyond the legal viewing area anyway. My best guess is a HVO vehicle or maybe from the park, there isnt evidence of the signal near any major roads.

  14. MBL reporting that HS Orku have noticed a pressure change in the Svartsengi Power Plant and have therefore evacuated staff. Blue Lagoon of course happy to stay open 😉

    It seems that this change occurred several hours ago, and of course the pressure change has preceded every eruption thus far. It’s slightly bizarre that there has been very little seismic activity in the last few hours, however if I’m not mistaken, the tremor has been showing on the SVR charts since around 12:30pm. Can we take it that this means Sundnnukar is more likely than other locations?

    • IMO has already addressed this in their latest update from today. Roughly, they say that no earthquakes were detected along with the pressure change, so the change doesn’t signal an eruption in this case:

      “This morning, a minor pressure drop was measured in the borehole of HS energy. No seismic activity or change in deformation was observed with these measured pressure changes. Therefore, the Norwegian Meteorological Agency did not activate contingency plans for possible magma flow.”
      Translated from https://www.vedur.is/um-vi/frettir/jardhraeringar-grindavik

  15. The IMO posted the latest today May 21st on the inflation at Svartsengi. See for the trend. If you want to read the article, go to the Iceland webpage, copy the Grindavik URL and put it into Google translate. I won’t flood you all with Greek language as Google seemed to want to do the last time for some odd reason.

  16. Some of largest ignimbrite/caldera eruptions like Fish Canyon, Wah Wah Springs, and other monotonous intermediates, are so crystal-rich (~40-50%) that they nearly borderline uneruptible mush

    • Yes, that kind of volcanism still happens in the Central Andes. Calderas often erupt very crystal-rich rhyodacites and dacites in the Andean Altiplano. Nowadays, it’s very rare to have these ignimbrites outside the Central Andes, though.

  17. I guess shallower parts of the suns mantle ( convective zone ) where the plasma density is similar to earths sealevel and much higher than that further in, woud be similar to be inside a ligthing bolt or electric arc, which says something how extreme it is as an enviroment. Further down it quickly becomes as dense as water… white hot blinding water that destroys a human in seconds .. infact gets so dense further down you cannot even sink through it. I finds it incredible how sharp and well defined the photosphere is but thats only because there is denser gases below that, the photosphere itself is only 1/1000 th of Earths surface pressure

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