Nyiragongo and its ultra alkaline magma – Part I


Nyiragongo is one of my favourite volcanoes and one of the most peculiar and most unusual of all active volcanoes on this planet. It’s also a very problematic volcano, close to a huge population center that is rapidly growing, and there is a lot of risks associated with its volcanism as well as with human-caused political issues and other hazards. I first got to know Nyiragongo as a 6 year old from the TV reports of the catastrophic 2002 eruption, when the magma column burst out into Goma city. I remember lots of people running from fast-moving a’a flows, and the burned shells of cars and busses floating in the river of molten rock. I remember hot fingers of pahoehoe dripping into the Kivu lake on the low quality TV image of the early 2000s. I developed an interest in Nyiragongo and its peculiarities. It is an interesting volcano in many ways. For many many years, I was completely alone with my volcano addiction, but with the invention of Volcanocafe Blog it is finally possible to put my volcano thoughts permanently on the internet. This will be my first post for Volcanocafe. Mt Nyiragongo is very unusual in many ways which is one reason to write about it.

Nyiragongo has a very unusual magmatic composition, basically one of the rarest magmas on the planet, and that is another reason that I write this article: I have an interest in highly ultrabasic magmatism.

Nyiragongo is also a very beautiful volcanic cone, eye stunning. That is also why I write about this volcano: Nyiragongo must be what most people imagine a volcano should be like – deadly gas pockets, hot fast lava, a lava lake, and a beautiful steep conical profile rising out of the jungle. Its fiery glow casts an eery shine over the night jungle far far away in a ”dark, poorly known” mysterious land. It is as stereotypical as a volcano can be on Earth. It is just like every child imagines what an active volcano would look like. This volcano is infamous for its fast-flowing lava and its unusual composition and is claimed to have the lowest viscosity of all silica-based lavas. In this article, I will have a close look at that. I myself have always been impressed by Nyiragongo’s perfect look, and perhaps only Shishaldin, Pavlof and Villaricca are even more perfect and stereotypical as steep mafic composition volcanic cones. Most people imagine volcanoes to look like Nyiragongo and the other examples, but that is clearly not the case with most volcanoes.

Nyiragongo is a relatively unknown volcano, and actually, despite frequent geological investigations since late 2000 it is not very well-investigated, but it is fun trying to write an article about a relatively unknown volcano. In other words, it is a very difficult volcano to write about. In this article, I will have a look at Nyiragongo and its peculiarities, like its viscosity and why it is so steep despite its composition and general geology.

Nyiragongo’s geological setting and a look at African continental rifting in general

Image from https://www.nature.com/articles/s41467-019-13181-7: O’Connor, J.M., Jokat, W., Regelous, M. et al. Superplume mantle tracked isotopically the length of Africa from the Indian Ocean to the Red Sea. Nat Commun 10, 5493 (2019). https://doi.org/10.1038/s41467-019-13181-7

Nyiragongo is a continental rift volcano, like a majority of the African volcanoes are. Here I will give a summary of what powers Nyiragongo. The volcano is in the slow-spreading Albertine Rift, the western arm of the great African rift system where Nyiragongo and Nyiramuragira form a very active volcanic center. Continental Rifting is divergent tectonics in the interior of large continents. There are many continental rifts in the world, some are very active and some are almost passive spreaders. Some are boosted by mantle plumes while other rifts are not. Most of the Albertine Rift is quite passive, with little volcanism. In places, the spreading has formed very deep almost Baikal-like rift lakes, as there is a lack of volcanic in-fillings. When you spread apart the continental lithosphere the warm asthenosphere will move upwards, since it is generally above its melting point it will undergo decompression melting and generate rift magmas. In the Albertine Rift, it seems to be relatively passive, but when we come to Virunga area, we have intense volcanic activity at only Nyiragongo and Nyiramuragira.

The Virunga volcanoes are Africa’s most active volcanoes and are the only place in Africa other than Erta Ale that are intensely and frequently active. The intense local activity in Virunga has given many geologists the idea that there is a local hotspot in that part of the Albertine Rift, an emergent mantle plume that just started to decompression-melt. There is a large local round uplift that has elevated the whole area to just over 1 kilometers above sea level. This ”lithospheric dome” seems to confirm the mantle plume hotspot idea in the Virunga area.

Volcanism in Virunga became intense only very recently. The Nyiragongo and Nyiramuragira volcanoes just started forming in the late Pleistocene. Nyiramuragira is thought to be 20 000 years old and Nyiragongo is between 15,000 and 12,000 years old. The young age of these two volcanoes makes the region very productive volcanically, perhaps the third most productive in the world after Iceland and Hawaii. The two volcanoes are built on a much older metamorphic basement and perhaps emerged as two islands in the deep rift lakes of Africa. Another theory from geologists is that the two volcanoes are fed by an arm from the African Superplume, the large mantle plume body that governs the East African Rift far east of Nyiragongo. The plume found its way up in the younger orogenic seams between the cratons, and initiated volcanism. Virunga magmas are all highly alkaline and many like Nyiragongo are very silica undersaturated. Such magmas form deep down by small amounts of partial melting of the mantle rock, so perhaps the emergent mantle plume is heating rock in the region which has just started to melt. In many geological textbooks, classic examples of continental rifting and break-up start with the arrival of a large mantle plume, doming of the lithosphere and an initial flood basalt. That may be the case with Pangea break-ups and the arrival of the Afar Plume far to the north of Virunga. But at Virunga it seems that the plume has only recently arrived, well after the Albertine continental rifting started 10 million years ago since the high levels of magma production at Virunga only started very recently.

Continental Rift Volcanism produces magma compositions according to the depths of melting, and the amount of melting in the mantle. It all depends on what stage the rift is in and how advanced it is in the process of becoming a real ocean. It also depends on if there is a mantle plume involved, and how thick the lithosphere is. Alkaline magmas like alkali basalts and the even more alkaline basanites, nephelinites require increasingly smaller amounts of melting deeper down the more alkaline these lavas are. Africa’s Rift System has a whole variety of magmas because of that. The rising magma also interacts with the continental crust that contaminates the mantle melts. Continental Rifting is very complex in magmatism and has a lot more magmatic variety than true oceanic ridge volcanism because of the thick continental crust.

Many continental rifts do not evolve into true oceans. The East African rift system has a chance of becoming a new ocean breaking the continent, but the future of the western part with the great rift lakes is much more uncertain. The rifting in Africa is trying to find its way between the old stable cratons. These are indeed stiff bulky behemoths to push aside, Nyiragongo’s rift is stuck between the Congo Craton and Tanzania Craton, a challenge for the Albertine Rift that is still far from being an ocean.

The geologically recent valley-forming rifting started around 25 million years ago in East Africa. Exactly what started it is unknown but is generally agreed to be convection currents in the mantle and the melting associated with the African superplume and other plumes that likely exist in the rift. There are maybe many mantle plume heads in the African rifts, even if most studies on this generally agree on a single large plume under Africa.

The Afar plume and the Virunga plume are the two sources of Africa’s most active rift volcanoes. In my mind, they look like two separate mantle plume upwellings, but they could be just places where the African Superplume sneakily found a way up between the cratons, in the younger seams between them. I myself believe that Nyiragongo and its sister feed from a separate emerging mantle plume in the Albertine Rift.

Continental Rifts are thought to be driven by convective currents in the mantle as well as extra heat from mantle plumes if they are present in a rift. Around 30 million years ago the Rift system experienced its first continental flood basalt that formed the Ethiopian Highlands. That was the result of the arrival of the Afar Plume whose remains still feed Erta Ale and other Afar volcanoes today.

In the East African Rift, the magma chemistry follows the depth of melting as the ABC figure below shows. In the northern-most parts of the rift in Ethiopia with thin continental crust, spreading has gone far and melting is shallow and amounts of melt are large, volcanoes like Erta Ale and Hayli Gubbi produce relatively normal oceanic tholeiitic basalts which is the same magma you find in Hawaii and Iceland and mid-ocean ridges. As we go south into Ethiopia the melting in the asthenosphere gets deeper, producing smaller amounts of melting. The amount of sodium and potassium increases in the magma chemistry and volcanoes like Korath range, Silali, and Olkaria are a lot more alkaline than Erta Ale to the north. The continental rifting has already gone far enough to form a well-formed rift valley and allowed the rise of quite normal basaltic lavas, but alkalinity dominates. When we travel south to Kenya, Tanzania, and Uganda, still with a clear rift valley well into Kenya, the melting plume asthenosphere runs into really thick crust and it’s partially blocked by the Tanzanian craton. Here the magmas get really strange as melting is deep down. Kenya and Tanzania are thick-crusted enough to stop the spreading from expanding southwards as it runs into the Tanzanian craton. Here you find extremely alkaline volcanoes like the snow-covered giants of Kilimanjaro, Mount Kenya, and Mount Elgon that grow into giants on the slow-moving thick crust.

The largest area of ​​the most silica-undersaturated extrusives (lavas) in Africa occurs west of the Kenya Rift. There exist large amounts of volcanic extrusives made up of nephelinite and carbonatite lavas, and some have built some large (now inactive) volcanoes.

These large (very sleepy) central nephelinite/carbonatite volcanoes include Mount Elgon, Kadam and Napak. The extrusives of these three volcanoes consist mostly of nephelinites and melanephelinites, among which are olivine- and melilite-bearing varieties. More evolved phonolites and trachybasalts, or trachyandesites also occur among the earlier flows. These volcanoes are largely built of pyroclastics, mainly as coarse agglomerates, which are mostly composed of fragments of gas-rich nephelinite. Many smaller polygenetic volcanoes with nephelinites and carbonatites occur in that area such as Moroto, Yelele, Toror, Ruri Hills, Homa Montain, and Kisingiri. Volcanic activity in this area has long died off. It seems that Tanzania is today the most likely location for future nephelinite eruptions in the world outside Nyiragongo, where we have a very thick lithosphere with a melting asthenosphere deep down. This is the area of Ol Doinyo Lengai and other nearby less active nephelinite and carbonatite volcanoes, both polygenetic and monogenetic. But Nyiragongo in Virunga is at the moment the only active erupting Nephelinite volcano

Carbonatite volcanism appears as well at Lengai. Other sites with previous carbonatite volcanism can be found in the thicker crusted parts of the rift system. Nyiragongo chemistry lavas can also be found in many volcanoes around Kilimanjaro and Lengai. Nyiragongos own rift, the Albertine, stops just north of the Rwenzori Mountains above Lake Albert when it runs into the behemoth that is the Congo Craton. The most unusual magma composition in Africa is found in Kenya and Uganda as well as Congo. The mantle has difficulty melting here and melts in small amounts deep down giving rise to highly alkaline sodium-rich silica-undersaturated lavas and even carbonatites like the the Ndali-Kasenda Volcanic Field and Fort Portal volcanic field. The nature of Nyiragongo’s silica-undersaturated magmas I will discuss much further down in my article.

Image: by myself. Cratons are nasty neighbours for a young aspiring rift. The poor Albertine Rift. Nyiragongo and her sisters are themselves stuck between the behemoths that are the Congo and Tazanian craton. Cratons cannot be penetrated, they cannot be cracked, but they can be pushed aside. It is difficult to know if the Albertine Rift will succeed to form a new ocean. The young orogenic seams where past continental collisions happened seem to not stretch or connect this rift to the other rifts in Africa. There is a younger very tight border between the Congo and Tanzanian cratons that may be possible for continental rift propagation of the Albertine rift. If continental rifting is successful, then the whole Somali plate that holds the Tanzanian craton will be torn from the Albertine rift’s east side.

The future of the Albertine Rift is still uncertain as to how far continental rifting will go in this area, but Virunga as discussed above seems to have an emerging mantle plume. The high levels of neodymium and strontium in Nyiragongo’s magmas are identical to ancient asteroids, which suggests that the partial melting that feeds Virunga is occuring very deep down, well below the continental crust. Other great rift volcanoes with quite similar chemistry and setting as the Virunga volcanics are Lengai which is partly made of Nyiragongo-type magmas. Others are Visoke, Meru, Homa Mountain, Bufumbira volcanic field, Katunga tuff maar, Bunyaruguru volcanic field, Katawe Kikorongo volcanic field and Fort Portal volcanic field. These examples are rift volcanism on thick crust with a setting similar to figure A in this graphic https://www.nature.com/articles/s41467-021-27166-y/figures/3 . They all have highly unusual magmatism and we are going to look one such chemistry much later in this post.

a href=”https://www.nature.com/articles/s41467-021-27166-y”>https://www.nature.com/articles/s41467-021-27166-y https://www.nature.com/articles/s41467-021-27166-y/figures/3 Excellent graphics showing an active volcanic continental rift at different stages of its development. Its magma production is determined by the depth of the hot asthenosphere. The eruption composition is determined by the depth and amount of melting as well as the residence in its crust.

At the start (A) melting is deep down and in small amounts. This produces the ultra alkaline magmas such as nephelinites, basanites, phonolites and even carbonatites that we see in Nyiragongo, Lengai, Kilimanjaro and others in slow rifts with thick lithosphere. Virunga Volcanoes and Kilimanjaro area are in this early stage of highly alkaline rifting under a deep lithosphere.

At B continental rifting and thinning of the lithosphere continues, and the asthenosphere moves closer to the surface, which results in more melting and less alkaline magmas. Shallow magma chambers form evolved melts. Alkaline basalts and evolved trachytes are common. This is typical of most of the African rift north of Kenya. A whole variety of volcanoes forms depending on supply and crustal residence in the magma chambers.

At C, the asthenosphere is getting very close to the surface, boosted by a plume head. Melting now becomes very extensive indeed and that forms normal oceanic tholeiitic basalts. Volcanism is common and often intense. Such places are Erta Ale on the Afar Triangle. At this stage alkaline volcanism has completely vanished, replaced by normal basalt, Andesite, dacite and rhyolite, because melting is extensive in the asthenosphere. The process of replacing continental lithosphere with oceanic quickly begins at this stage of rifting. Voluminous basaltic eruptions happen if a plume is involved at this stage.

Cropped from https://www.youtube.com/watch?v=3jpbArY2L78 and modified by myself. Nyiragongo and Nyiramuragira are probably fed from a local emergent mantle plume, to explain the high levels of activity for this local area in the Albertine Rift. There are continental rifts with mantle plumes and some without only powered by extensional tectonics.

In conclusion, Nyiragongo and Virunga volcanics represent the very early stage of continental rifting over a thick semi-rigid lithosphere with a mantle plume involved. Now I have explained to the Volcanocafe readers what large-scale tectonic forces are behind Nyiragongo, it is time to take a closer look at the volcano itself and its magma in the next part.

Jesper Sandberg, July 2022

107 thoughts on “Nyiragongo and its ultra alkaline magma – Part I

    • The other parts are more or less completed .. and Just needs to work with Albert to edit them .. : )

      Part one became Very good for soure and was the most easy to write

    • Absolutely fantastic job Jesper!

      I actually knew quite little about Virunga aside from tidbits mainly picked up by your comments over the past year.

      So this article went down nice and smooth and helped me get a much better understanding of the area.

      I hope you continue writing, this was wonderful!

      • Yes will be more soon .. its a 3 part series … the whole series was written by me this winter

        Fun you enjoyed it!

        • Well done Jesper!

          Rifting and the unusual volcanoes it produces is so fascinating.

  1. Finally.
    I congratulate you on your courage and comprehensive article.
    I hope you continue like this.

    • Thank you .. and this is just part 1

      The other parts are already completed
      They will be posted later soon enough

  2. Jesper,

    Still reading your article — enjoying it — though your “the low quality TV image of the early 2000s” comment did bring me up short. The TV image my six-year-old self viewed was strictly in Black and White. We thought it was a miracle. Imagine that.

    Going to continue reading now.

    • Fun you likes it.. the other parts are already completed.. and I Will improve them togther with Albert .. before publish them as well

      • Jesper, nice job with your first article in this series. I admire how you qualified some of the information you present, when the science is uncertain, with phrases like “are thought to be”, “is generally believed”, and a simple “perhaps.” That’s good writing.

        This is a fascinating topic and I learned a ton from your article. Favorite fact: “The high levels of neodymium and strontium in Nyiragongo’s magmas are identical to ancient asteroids…” That’s wild.

    • Yes it contains rare Earth metals so partial melting is occuring deep down in a hot but very deep ..and pressurized astenosphere thats slowly and steadly decompressing. Nyiragongo Maybe getting its magma from 85 to even 150 kilometers below perhaps … too deep to produce normal basalt .. and with small ammounts of melting .. the mantle is tought to be cO2 saturated as well

      In other words a very long pipe under Nyiragongo and Nyiramuragira.. they both feeds from diffrent melting areras of same melting area ( diffrent compositions ) ( Nyiragongo is deeper )

  3. This is very good Jesper. I was worried it might end up being like our wall of text commen posts but this is very professional and well articulated, much better structured than my first post 🙂

    • Thank you! Yes it became much better than I first tought… it became excellent. Part two and three are already finished, I and Albert will start to edit them soon enough …

  4. It’s interesting to compare the rift valleys like this, I didn’t know that these two rifting areas could be seen as in different stages of development, that graphic is excellent. Nearly as excellent as those big hostile cratons, which I absolutely expect to see in a textbook someday.

    I’m always a little torn with my excitement around the workings of fascinating volcanic systems like this, when the volcano is also such a terror for the inhabitants of Goma.

    Great article!

    • Exactly .. continetal .. rifting produces fascinating magmas and strange volcanoes .. and specialy If the litosphere is very thick

      Fun you enjoyed Part 1

    • If you look at what happened along the Kenya/Tanzania rift when volcanism began, then you will see that Nyiragingo and Nyamuragira are going to have a very bright future. Goma not so much…

      Kenya Rift opened with large alkaline volcanoes and has continued to produce them up to the present, but in the mid Miocene it also produced an alkaline flood basalt. Was not quite a proper trap formation liek happened in Afar but I dont really think that would matter so much if you were there at the time, these eruptions would have been far larger than anything we can dream of happenning in Iceland today.
      Samburu volcanics was around 50,000 km3 of phonolite flood lavas as well as large volumes of primitive magma of several types, basically a land Hawaii. I expect Virunga is going to become something like this in the next few million years. Alkaline volcanics dont necessarily mean lower rates of melting, if enough of the mantle is hot enough… 🙂

      • Current rate of magma production under Virunga actually is already as high as the time average for the Samburu volcanics (~1 km3 per 10-20 years), about half that of Hawaii.

      • And because of their very deep origin and many are monogenetic and not comming from shallow stoorage either

        Many highly alkaline magmas coud perhaps be hotter than many normal ocean basalts .. ( Althrough plume picrites and superheated basalts coud be hottest )

        But many emerge as cool strombolian melts as well

        But Hualalai and La Palmas hot alkalines .. confirms that alkalines haves high temperatures as well …

      • You coud be right, Nyiragongos magma source coud be melting at large rates very very deep down and allows only a small ammount of the mantle to melt But at the same time at large ammounts

        But magmas as very alkaline as Nephelinites and Melinilites ( Melinilite are even more alkaline and coud be the parent magma of Nyiragongos Nephelinites ) they do require small ammounts of melting

        Nyiragongo is indeed producing unusualy large ammounts of Nephelinites and Nyiramuragira is producing unusualy large ammounts Basanites .. magmas that are mostly seen as monogentic ..

        The mantle under Virunga is Probaly vigorously melting .. but melting far too deep to produce ”normal lavas” and instead you gets large ammounts of alkalines if you haves vigorous melting very deep under pressure

      • Being realistic, I think these alkaline lava floods would have been visually a lot more impressive. If Mars and Venus are valid comparisons it looks like most of the eruptions associated with LIP provinces are nearly entirely effusive, maybe a lot like the lava lake draining events at Kilauea, rather than massive fire fountain events that present large basaltic eruptions usually are. That is, the lava literally wells out of the ground, in enormous volumes but rather quietly, probably cutting deep canyons in the ground as the top of the dike erodes under the flow.

        The majority volume of the Samburu volcanics was actually phonolite, not basalt. I think phonolite is quite misunderstood, it is in the middle of its series and is an evolved magma, but it is evolved in respect to having an extreme alkali content and still has only about 45-50% SiO2. The examples of it erupting as viscous magma probably are where there is a large crystal content, basically a trachyte with a lot of crystals. True phonolite melt especially if hot is probably a fluid magma, even trachyte seems to be quite mobile if it is hot and crystal poor. Erebus is a bit more viscous than Kilauea or Nyiragongo but its lavas still flow easily and it would probably not be that different from Etna if it was more active. Based on the colour of the lava too, Erebus also seems to be very hot, so whatever process of evolutiuon to create its lava is going on, doesnt seem to require cooling in any significant degree.

        These massive flood volcanics probably would have looked a lot like the first stage of a Hekla eruption, a massive fast moving a’a flow field with gigantic fountains at the vent. The extent of some of these flows is larger than the combined area of all of the Holocene lava in Iceland, and that is after 12 million years of erosion…

        Of course to get magma that composition there must have been some sizable magma chambers, Nyamuragira is not yet big enough to compare, its chamber is probably refreshed every couple of years, but if the volcano keeps growing it can evolve and things could get a lot more interesting.

        • Phonolites of the Kenya dome area generally have 52-58 % silica, so they are somewhat silicic. Probably not as viscous as trachytes, but more viscous than basalts and basanites. The volcanoes that produced the phonolite plateau flows probably would have looked similar to Mount Kenya before being dissected by the rift and eroded. Two of them are still visible on the east edge of the rift. Other volcanoes probably collapsed into the rift axis.

      • Erebus is more viscous than Etna. Erebus lava its about 980 C to 1020 C in its lava .. yet Erebus as is fluid as it is
        The sodium rich sillica chains are less polymerized

        So right .. a really hot Phonolite woud probaly flow very easly .. and its high alkalinity lowers the viscosity. An 1100 C Phonolite woud probaly flow very much like a basalt flow

        Phonolites are more alkaline than Trachytes

        Heated in a furnace to over 1200 C a Phonolite woud probaly be highly fluid ( like Fagradals)

        • Based on videos, the Erebus lava lake is not too different from Etna, but much less explosive. More viscous than Kilauea for sure but it is still a fluid lava by comparison to most other places. It looks a lot like the lava from Hekla in recent eruptions.

          Now imagine 100 km3 of it erupting from a fissure, massive fountains and fast moving a’a flows going for 100 km in both directions.

      • Yes these where massive Phonolite eruptions .. and magma that alkaline also haves an insane gas content
        Yes where are talking of plinian fountain columns going into the tropospause 🙂

        A Phonolite haves a much higher gas content than a andesite / ryholite

        Erebus haves a viscosity a bit higher than Etna and that makes it even more fountain friendly combined with a high gas content

        These massive Miocene Phonolite eruptions happened in a Tropical rainforest btw .. the climate was more humid and warmer back then

        Our Miocene Ape ancestors probaly experienced it 🙂

        • Maybe that area was not a rainforest though, quite high in elevation and inland, probably was a lot like the abrupt treeline on Mauna Loa or Kilimanjaro. Given the large heating such a rift would get I think the lavas here would be hotter than Erebus, probably same range as most basalts. The sheer extent of the flows would require low viscosity.

          Gas content is actually variable, Erebus is only 0.2%’ the same as tholeiite basalt, while Vesuvius is 6%. So the violence of these eruptions might not be so extreme.

          • Erebus is indeed surprisingly gas poor. I’ve been looking it up on GEOROC. The water, chlorine and sulphur contents are the same as tholeiite, and the carbon dioxide is only slightly higher. But Erebus does have 0.2-0.3 wt% F, which is 20-30 times the amount contained in mid-ocean ridge tholeiite (normal mantle). It is possible that Erebus has such a low volatile content because of the lava lake which degasses continuously lowering the volatile content in its shallow storage. This would explain why it has a high F content, because the gas formed from fluorine, hydrogen fluoride, is very soluble in magma. This speculative though, but interesting,

            “Furthermore hydrogen fluoride, being one of the most soluble
            gases in magmas, exsolves only partially (< 20%) during volcanic activity."


          • Generally phonolites are water rich. For example Tenerife phonolites have about 4 wt% H2O. Vesuvius phonolites from the 79 AD eruption have 4-5 wt% H2O. So Erebus contrasts strongly with its 0.1 wt5 H2O.

          • Well, that is quite curious as Mt. Erebus’s lava lake is infamous for being explosive to where people close to the crater has to watch out for lava bombs whizzing by. Quite odd for a low-gas lava (unless water is involved… ?)

          • *from an external water source. It is weird enough for a lava like phonolit to be low in gas there but also weirder to have it be explosive (strombolian).

          • It is maybe the way spattering happens with viscous magmas. Very large bubbles build up and are released in a large strombolian blast. Even gas poor magmas can still explode sometimes. There are many videos of rockfalls into the lava lake at Halema’uma’u that was active until 2018 and then the whole lake exploding.

          • I keep forgetting that Vesuvius is highly alkaline and produces phonolites aside from big booms.

        • Erebusian Phonolites are quite viscous ( so perfect for Strombolian gas slug flow )

          But They are far more fluid than many other lavas like Dacites that are ”evolved”

          • If you consider that Phonolite has about the same SiO2 as basaltic andesite and andesite, being a more intermediate rock, Erebus is not very viscous at all. I guess 1000+ C andesite with low crystal content is not a viscous magma, just that situations where that actually happens is not very common. Kilauea fissure 17 was the first time an andesite was clearly visible flowing as a liquid but I expect that is just from video coverage. I think all of the eruptions from Hekla in the 20th century after 1948 were basaltic andesites only, so doesnt quite count, there is some very nice footage of lava at Hekla in 1947 or 1948 which might be andesite.

            Phonolite is probably also less viscous than andesite compared equally. Trachyte is also probably less viscous than dacite compared equally, there are some lava flows that look quite liquid at Menegai and Longonot that are trachytes, not exactly a river of lava but closer to that than a lava dome. There were also trachyte flood lavas in the area before the rift valley formed.
            I guess evolved magmas will tend to have crystals by default in most situations, which will make them more viscous as a liquid. Erebus has maybe got low overall crystal content.

        • Exactly Vesuvious base magmas are very sillica undersaturated Basanites .. so its a highly alkaline volcanic system

          Vesuvian base lavas are even more gas rich and more fluid than Etnean lavas I think

          • Vesuvius when it has an open system is very fluid, pahoehoe lava and a large open lava lake, really it is very similar to Nyiragongo, some of its flank eruptions in the past millennium were probably quite similar.

            It is basically what happened ladt year at La Palma but if that kept going for a lot longer. It has some phonolite when long dormant, like in 79 AD, but generally Vesuvius seems to be a mafic volcano, and phonolite is more like andesite than anything properly silicic as discussed earlier.. Quite ironic given its importance in explosive eruption terminology… 🙂

      • Yes .. and in Early 1900 s up to 1944 Vesuvious had ”shield building” Althrough very slowly .. or more like summit ”caldera fillings” with Basanite filling the summit crater cone, spatter cones, lava lakes, pahoehoe, it was an excellent lava Tourist destination. Looking at Photos from activity before 1944 https://www.mindat.org/gl/145740?page=2 very fluid Basanites

        Is there any eyewittness accounts of open lava lakes at Vesuvious? Pre 1944 activity .. was mostly pahoehoe and spatter cones filling the summit caldera

      • Exactly most Andesites in subduction zones erupt well below .. 1000 C and that makes them crystal rich mushes forming blocky flows and even domes

        High temperatures breaks down the Sio2 polymerisation effectivly as seen at Fissure 8

        • I mean Fissure 17 that even had Etna looking Andesite Pahoehoe !

          ( well Etna is not an andesite .. But same viscosity as Etna )

          • Not sure, I think Etna is a lot less viscous than the early F17 lava, although the later lavas probably were about the same (after the rest of the eruption took off and F17 started to fountain much higher). I saw something that lava from that point was more basaltic andesite, and that actual true andesite was only erupted from the upper end of the fissure and only for a couple days, but it is not entirely clear.

            Etna lava is much faster flowing, just that most cases it erupts at low effusion rate and is cold and degassed, paroxysms make huge very fast flows that go several km in a couple of hours, up to 8 km, and some flank eruptions went further still.

          • It can flow fast at higher viscosities as well.. given slope and eruption rate
            Etnean summit lavas at least in my lifetime are not as fluid as Hawaii or fagradals… But I do seen cow pie bombs on my visit up to Etnas summit craters an indication of really runny lava so you maybe right… its just cooled alot in the fountains

          • Etna is probaly so very gas rich… that everything just becomes tephra and Aa in form of large lava fountains, but most etnean flows are quite visocous even this years from the summit. I buy your idea of cold lava in the upper throat of the volcano. But in early 2000 s and latest 1990 s there where some extremely fluid flows from SEC and the areas below SEC

        • Etna is about as fluid as the late .. Fissure 17 basalt

          The Early was probaly as fluid as Erebus Phonolites

  5. Thank you! That’s an excellent and well written article, and I’m learning a lot from it. Good stuff, Jesper!

    • Thank you! And you will find the other parts fun as well ( Myself and Albert will edit and I Will improve them soon )
      They are more or less complete

      Nyiragongo is souch an unusual volcano thats why its worth a series about it 🙂 .. its possible to write a whole book about it

      will be a 3 part series

    • Lots To think about When talking about continetal rifting and its magmatism. Africas Great Rift haves pretty much every single type of magma and type of volcano possible
      Depends on crustal residence and supply to the volcanoes and depth of melting and you can get almost every kind of magma

      In the later parts we takes a very close look at Nyiragongo

  6. Thanks Jesper for an excellent article! I really enjoyed reading it and I’m looking forward to the next part.

    • Thank you and more of that soon enough

      Yes this is one of the worlds most fascinating and most unusual volcanoes

  7. Thanks Jesper. Great article. It was fun to read and richly illustrated.

    • Thank you! Me and Albert Will edit the other parts soon .. they where written this winter as well

      • We helped with the English language editing and added the first figure but all the content and the style is Jesper.

      • Hi Albert When will we start to edit the other parts ? So I can add information that I feels missing .. and a photo or two.

        But the other parts are more or less complete overall ( was written this winter )

  8. congratulations Jesper, what a fascinating place. I can’t wait for 2nd part.


    Adriano Nobile
    The coherence is finally back, I had to wait only 10 months 😜. #Sentinel_1 interferogram between Sep 1st 2021 and Jul 10 2022 shows that the uplift (~10 fringes – ~30 cm) at #Askja continued during the winter.

  9. Jesper, I am very proud of you, son! Your first installment on Nyiragongo exceeded all of my expectations. All of us are looking forward to your upcoming posts!

  10. Finally some fresh competition! Interesting article and I looking forward putting my retort down.

    • Fun you liked it! Im also editing the last parts before I sends them to Albert

      Nyiragongo is fascinating yes

  11. Nice article Jesper, simplified a lot of mechanisms I hadn’t previously understood for creating this type of magma. If only we could exist beyond a 100 years or so, we’d see if this truly is the birth of a mantle plume…

      • Imagine witnessing a flood basalt in real time? What is the ‘normal’ yearly eruptive rate, 100km^3? I know it’s something like that, and it’s insane. Impossible to think about. Year after year, endless effusion.

        • Depends on the event. Columbia River basalts would have been big in scale but very far apart, maybe tens of millennia, magma generation rate was not really more than Hawaii or Iceland today, just eruptions were nit constant. Some others might have looked like a cluster of normal volcanoes all linked to a common source, like Hawaii but bigger. But some probably really were like actual floods of lava, shield building but where it makes a shield the size of Iceland, basically an Olympus Mons on Earth.

          Virunga probably will not be that extreme but all the evidence would suggest the area will have a big future.

  12. O.T.,…but I’m seeing that England may well set a new all-time record hi temp in the next few days…with 40C (104F) being mentioned as entirely possible.
    Holy mackerel.
    While 40C is actually pretty normal for my neckadawoods (in Summer), for those not used to these temps, this heat wave could be potentially deadly. Sure hope not. I’m pretty sure air conditioning is not a “regular” appliance for the general population in GB.

    • Met Office forecasters are saying 80% chance of the current record being broken, and 50% chance of 40°C being recorded somewhere, as the models are inclining more towards higher temperatures. Of course, the media imply it is a dead cert instead of only a possibility.
      It’s also the first time a red warning for extreme heat has been issued.
      I don’t think I’ll do a roast dinner this weekend. Our forecast in mid Sussex is for 33 on Monday, and 35 on Tuesday. I think I’ll go and research awnings for the windows.

      • The forecast for Manchester is 35 and 36C, with one model suggesting 40C on Tuesday (yes, this is the right Manchester, not the one -by-the-sea). No need to roast the dinner.

    • Other than Visoke, has any of the other Eastern Virunga volcanoes had historical activity or been dated?

      • Karisimbi has Holocene eruptions but not well dated. There are probably also monogenetic eccentric eruptions that are not a part of any of the big volcanoes, the last was in the 1950s so presumably they are not incredibly rare, given the short official record of the area (mid 19th century).

        I do kind of wonder if the rest of the chain might be functionally dead though, they are outside the rift and now that the active volcanism is within the rift valley proper it should stay there. Nyiragongo is sort of on the edge of the rift and doesnt erupt much by volume, seems more a very big fumarole, Nyamuragira is within the middle of the valley and erupts more lava than every other volcano on the continent combined.

        • Most of the features of the Virunga Province are very young-looking, they have little erosion, probably most volcanoes are active to some degree. The stratovolcanoes of Mikeno, Muhavura and Sabinyo are heavily eroded and possibly extinct. That said one volcanic system can give rise to multiple stratovolcanoes, Nyiragongo has three stratovolcanic structures plus many monogenetic cones. So probably all volcanic systems continue to be active, either from their central stratovolcanoes or from flank monogenetic vents.

    • Im writing up ( improving ) the last article sections… before I sends them to albert
      Nyiragongo is a very diifcult volcano to write about, and takes time to figure out the answers to the questions in the article.

      Well probaly been lots of unseen undated momogenetic eruptions of Melilities, I doubt they dated all the cinder cones in the Virunga Area and they grow over quickly in the tropical climate

  13. https://www.flickr.com/photos/130650384@N02/27335984836/in/photolist-wQJ6wH-y2REcM-uWvvPd-xAXYx9-tCFVNW-sSdEH3-24BoVH-oK52X8-yn6AxJ-HSCAK6-edtUK8-25ocMX-WEzc6N-pq2RKD-2m4pEJ1-5sEZEE-5uB3Wg-8GrF8f-tnupiU-7jucmZ-HTofB4-ee7Gig-c5akij-edQmHj-cRP5qw-oErZj-SEu5cY-2we5vx-c29CxE-76ZfoS-HDA4Vo-7QavNE

    Another shot of Etnean pahoehoes
    Whatever if the magma was more gas poor or more fluid than Todays Etnean lavas .. this is real pahoehoe. Etna also haves a massive pahoehoe field near bronte. I guess this is the deep lava of Etna

    • I wonder if maybe there was a lava lake before 1669, to allow degassing of the summit system. Etna is a bit like Nyiragongo in that it doesnt seem to have much of a shallow storage just a wide open conduit from deep levels. Nyiragongo must be wide enough (or that lava is more liquid there) so that it stays passive, but Etna seems to have some sort of branching in its upper levels that lead to 4 conduits, so there is no way for a lava lake to form at any single spot and instead is just building a tall cone. I would expect at some point though that the summit conduits will merge and become a lava lake, or maybe even several lakes like at Ambrym.

      Etna erupts at a temperature of 1080 C and 50% crystals during effusive eruptions, and during large paroxysms the crystal content is lower and the temperature is at least 1125 C, possibly a lot more.
      The fact it flows pretty easily still with 50% crystals and under 1100 C probably means the actual melt has a very low viscosity like the stuff erupted at La Palma. The extreme fountaining is probably from the high water content of the magma and the huge eruption rate, the SEC is the final form lava geyser, it is what Pu’u O’o or Fagradalsfjall would have turned into if they had more favorable conditions. SEC is probably where a lava lake would form last, it is the youngest, and has survived numerous lateral eruptions that are what killed the fountaining at other volcanoes.

    • Right .. Etna haves a high crystal content .. and Maybe thats as well why its lava flows are not smooth
      But at 1080 C most basalts are quite viscous .. and perhaps Etna is crystal rich because of that. The 1960 s eruptions Peaked in temperatures of 1140 C … 1997 – 1999 also had fluid lava in voragine and bocca nouva

      Nyiragongo acually probaly have at least two magma chambers connected by an open pathway .. Geological investigations have found signs of a shallow stoorage at Nyiragongo. One shallow chamber just under the edifice and a much larger deeper one .. at 20 km depth .. the summit caldera of Nyiragongo must have formed by the drainage of a previous large shallow chamber and that happened very recently, knowing how fresh Looking the caldera is. The magma pipe in Nyiragongo is deep as you say probaly going down 100 km or more .. the supply is constant but not extremely large, and lots are probaly going into rift stoorage deep down

      • The eruptions last year were supposed to have been high temperature too, was at leas mentioned that the composition indicated a fresh batch of deep magma.

      • The other thing is too that some eccentric eruptions are not fluid at all, the eruption on the west flank in 1974 was mostly explosive and made only a short viscous flow, probably was mostly old crystalized magma. Several other eruptions in the same general area had very similar characteristics, maybe a small flank magma chamber that can cool down a bit.

  14. I have found an old video recording.. of what I think is Nyiragongos lava lake .. in one of David Attenborughs old videos with a nice pit wall falling into the lava lake, Probaly is the Kraffts or even Hauron Tazieffs old videos that BBC added in

    It shows of a pit wall Falling into a lava lake
    The lava is extremely fluid .. but also not as hot or bright Looking as Hawaii is.. so it haves To be Nyiragongo.. look 21:11 – 21:22 https://www.dailymotion.com/video/x2i43qc

    It haves To be Nyiragongo.. it looks alot like its lava, very fluid yet perhaps not as bright as basaltic lavas ( nice lava waves anyway )

    I will send the remaining articles materials To Albert today later

    • Not sure, Life on Earth was made in 1979, so the colour might be from the camera. I think that footage could be from Hawaii, from Mauna Ulu. It also could be Erta Ale, which was quite active in the 1970s.

    • Chad how do you know its not Nyiragongo?

      Hauron Tazieff took many many color videos from Nyiragongo

      Or is it an old video from Mauna Ulu eruption?

      • I dont know, it could be 🙂

        I do remember that a lot of old videos of Hawaiian eruptions have that colour palette though, so trying to identify on the colour alone probably wont work for anything not made this century. Probably more than colour is if there is steam, Nyiragongo being so tall has a lot of steam coming from the spattering sources as the gas condenses, which Kilauea doesnt have so much at least not so close to the lake.

        My first thought looking at it was actually the kupaianaha lava lake, until I saw that Life on Earth was made before Pu’u O’o started.

  15. I have now more or less competed the next part of this series .. so I sent Albert the next part 🙂

    I do perfer the docx files as Albert sent me.
    As they are less buggy than Open Office ( I sent two )

    Anyway Hopes the VC friends haves a nice weekend 🙂

    • Is this the one where you talk about what happens if a Chicxulub size meteor slams into Virunga during the beginning of a small flood basalt?

      Can’t wait!

    • Something more realistic the next part will have a look at Nyiragongos behaviour and the later parts will have a look at its magma chemistry. And the last part we will try to examine the behaviour of this lava

  16. I think I might have found a piece of the Hunga Tonga pumice on a beach not too far from me 🙂

    It is very light and part of the surface is very smooth and glassy in texture, and rather dark but not quite so much as basalt in Hawaii. Would seem to have come from a gas rich and relatively fluid magma, which is what Hunga Tonga is supposed to have, crystal poor basaltic andesite with 54-58% SiO2, so relatively mafic.

    The beach does face south into the Southern Ocean and I am rather a lot further south than where pumice is supposed to wash up, but it is worth mentioning. I have seen scoria in a garden as well as at a vent, and lots of it in Hawaii, this is very similar but a lot lighter, and not oxidised to indicate it being from a local origin on land. The glassy surface on one side as well as what might be something growing on it leads me to believe it has been in the ocean a while and is not particularly old.

    • What magma composition yeilds the darkest rocks ?

      I know that Basanites are pretty dark
      And Hawaiian thoelites can be quite dark too with their high iron oxide content

      Well depends on the content of dark minerals and crystal size as well and If its glass or not

      • Not sure, probably rocks with more dark minerals compared to silica content, rather than necessarily lower silica content. Kimberlite is not that dark, and carbonatite is basically white because it is made mostly of metal carbonates which are not coloured much.

        Probably some sort of basalt is the darkest, or maybe obsidian. I dont actually know why obsidian is so black when it is the same as rhyolite, maybe it is transparent and the small concentration of dark minerals in the glass is able to shine through.

      • Basanites can be super dark
        Lacking the white minerals of normal basalts .. yet not full of white Nepheline like a Nephelinite

        Basanite is a sillica devoid basalt .. one may say

      • I have more buit this shows what I am talking about most clearly. I did wash it off, it is still slightly wet in this picture so the shine is a bit exaggerated. I expect it is slightly altered by the ocean, whatever its original source was.

        • The timing seems right. There is a current running north to south along eastern Australia. That is the right direction from Hunga Tonga. The difficulty is the last little bit as it goes against the current along the southern coast. Wind may have played a role: the low pressure systems along the east coast may have caused easterly winds? Are there other local effects? New Zealand must be best placed to collect the Hunga Tonga pumice.

          • Location is on a beach maybe 20 km southeast of Hobart, facing the open ocean. There was literally no other rocks around, realistically it looked like someone put it there, but if that was the case I didnt see them.

            The colour is though pretty perfect, pumice that washed up in Tonga was dark grey or black, although a lot of the floating stuff looked white. I think the white is coming from alteration by seawater than magma composition. It might not even really count as pumice, which is meant to be silicic, and this stuff is more mafic-intermediate.

            I might go back some point this week to see if there is more but there isnt even supposed to be any pumice from the eruption south of Brisbane, let alone far south where I am, so in the dark as far as reports go…

  17. There are quakes under Brennisteinsfjoll just east of Kleifarvatn. Brennisteinsfjoll seems to erupt the same way Fagradalsfjall did last year but a lot bigger, maybe going up to over 1 km3 volume, probably several years long eruption.

    The swarm has already stopped and isnt that big, but shows something going on. Perhaps because the eruptions are not fast there is no pre-eruptive intrusions like there seems to be at Svartsengi (and probably also Krysuvik and Hengill), so things might just keep going andget more intense before erupting. The eruptions seem to be episodic, maybe overflowing lava lakes.

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