Report by Jesper Sandberg

Forewords

2025 has so far been an exciting year with volcanoes, definitely so with Kilauea which is in many ways Earth’s most impressive volcano. It continues its caldera filling episodes at the previous Halemaumau crater area. If Kilauea keeps going like this for years the whole caldera will be filled. The whole historical summit topography will be buried quite soon if Kilauea’s rift systems do not open soon and divert the magma supply downhill. The lava rivers and fountains are simply magnificent every week now at Kilaueas summit. With its massive supply and accessible eruptions, it is my favourite volcano.

But I have many favourite volcanoes. In Europe, Etna produced its first ”tourist lava flow” during a few week’s long eruption. This allowed tourists to poke and go close to active lava flows. I think it stopped just a few weeks before this post was published. Stromboli has also had increased magma supply with lava fountains sending channelized flows into the ocean. In Iceland the Reykjanes fires are still ongoing, waiting for the next eruption there as well.

Most of the worlds volcano watching attention have been foucsed on the usual volcanoes. Kilauea, Etna, Sakurajima, Stromboli, Campi Flegri, which are easily accessible for visitors and well monitored, being in the developed part of the world. But we may forget that there are other very interesting volcanoes in less developed parts of the world that have huge needs of better monitoring. Very interesting things have happened in one such area.

Nyiragongo and Nyamuragira are an example of “neglected” yet very well known volcanoes, close to a major city center yet mostly only studied with space thermal instruments. These two are among the world’s most constantly active volcanoes which are nearly always erupting, with both often hosting active lava lakes together as is the situation now.

These two are among the world’s most problematic volcanoes too. They are ultra active and close to the very large population center of Goma which is home to millions of persons. Their activity may be fluid and gentle, being fluid-hawaiian in type, but with lava fissures with massive eruption rates being able to open up in the middle of Goma city and other nearby towns, these two volcanoes are perhaps the world’s two most dangerous effusive volcanoes.

Their alkaline lava flows are highly fluid and known to flow close to populated areas. The area is very densely populated, politically dangerous and is full of other hazards such as gas pockets, acid rain and diseases. Massive limnic eruptions from Lake Kivu from methane and CO2 are another major hazard. Because there is activity at both Nyiragongo and Nyiramuragira, Goma’s whole night sky is now red. It is lit up by two red orange gas condensation columns going up into a red cloud roof, which must be an unsettling sight indeed. Such sights have given rise to local myths that Nyiragoingo is the gates of hell.

I been reading about Goma’s local tales. Well behaved persons end up living in the bright clouds and snow at the dormant Karisimbi volcano, while the badly behaved persons ( criminals ) burn forever in the raging fires of Nyiragongo. Both Nyamuragira and Nyiragoingo are thought to be home to souls of the damned, evil spirits and demonic beings as well. That is a very different local mythology than the volcano-lady Pele at Kilauea.

Nyiragongo and Nyamuragira are together with Kilauea the world’s three most thermally powerful volcanoes on the planet. These three are the ones that over long term emit the most heat energy. At the time of writing Nyiragoingo is filling its summit caldera, having reactivated in autumn 2021 after the spring 2021 lava lake drain-out. Nyamuragira has gone full shield building. Nyiragongo and Nyamuragira must be what every child and video game imagines 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. Their fiery glow casts an eery shine over the night jungle far far away in a ” poorly known dangerous” mysterious land. They are as stereotypical as any volcano can be on Earth.

Virunga National Park which hosts Nyamuragira  is also a very beautiful place. For sure it is one of Africa’s top hidden gems where you can find astonishing natural beauty. The landscapes with glowing Nyamuragira and Nyragongo, lakes, other dormant snow capped volcanoes, glaciers, savannahs, rainforests and rivers makes Virunga really one of the top spectacles on Earth. Virunga’s natural scenery goes all way from Nyamuragiras lava lake to the misty Rwenzori Mountains. I have always loved Virunga because of its beauty, so think it is time to put up an article on it again after my first Nyiragongo series. Things are very interesting now at Nyiragongo’s larger sister volcano Nyamuragira, with the opening of a huge lava lake in the caldera in 2024 and the start of a shield building pahoehoe phase that has already been on-going for a few years.

It is quite difficult to write an article about a volcano like Nyamuragira. It is quite well known and famous, yet it is also very understudied and not visited very often despite a large city nearby. If it were not for the rather uncertain political situation in the Kivu region I would definitely recommend this area for tourists to get to see the immense beauty that exists in Virunga National Park and I think the area received a regular stream of visitors up to when the local war started. Both volcanoes were also visited by the famous volcanologists the Kraffts who got the first color footage from them in the 1970’s and 1980’s, but Tazieff was first with color video from Nyiragoingo.

There is much more to see in Virunga than just the gorillas. Nyamuragira has clearly formed a huge lava lake. Due to the rather limited information on the lake we will first have a look at what the volcano been up to in recent times, to explain today’s state of activity.

General facts and eruption history up to today

Nyamuragira is Nyiragongo’s forgotten sister. It is not known as much in the media, but it turns out to be Africa’s most powerful volcano when it comes to magmatic influxes and Africa’s most powerful in magma supply. It is the most productive African volcano and one of the most productive volcanoes on the planet. Virunga’s current supply is very vigorous with perhaps half of Hawaii’s historical average supply, or perhaps nearly a fourth of Hawaii’s current elevated supply. Due to Virunga sitting in a continental rift a lot of the rising magma may be trapped at depth so the deep supply maybe much much bigger than the output. The deep melt generation may be near hawaiian in scale.

Nyamuragira is because of that a pretty impressive performer, having erupted in the year 1865, 1882, 1894, 1896, 1899, 1901, 1902, 1904, 1905, 1906(?), 1907, 1907, 1908, 1909, 1912-13, 1920, 1921-38, 1938-40, 1948, 1951, 1951-52, 1954, 1956, 1957, 1958, 1967, 1971, 1976-77, 1980, 1981-82, 1984, 1986, 1987-88, 1989, 1991-93, 1994, 1996, 1998, 2000, 2001, 2002, 2004, 2006, 2010, 2011 (6 Nov) – March 2012 – 2015 – ongoing (summit lava lake). This ultrabasic shield volcano is estimated to be no older than late Pleistocene. Like its sister, it has a very smooth youthful profile despite the equatorial rains. It is a bit less alkaline than Nyiragongo but is still very potassic and low in silica compared to say Iceland and Kilauea. The lavas are basanites and tephrites so are quite similar to the Canary Island’s magmas and to Vesuvius’ odd lavas but Nyiragoingo’s odd nephelinites are even more alkaline. Nyamuragira is a very rare silica, undersaturated 40% SiO2 magma compared to most other magmas elsewhere. But its viscosity, just as Nyiragongo’s lava, seems to be no lower than Kilauea’s.

The active volcano closest in chemistry on the European mainland is the Vesuvius. but Nyamuragira’s lavas are much less evolved than Vesuvius’ phonotephrites, and are closer to the basanite parent melt. (Nyamuragira magma input is also far larger than Vesuvius or any Canary volcano.) Basanites ( very low silica potassic basalt ) evolve via basanite – tephrite, tephriphonolite/phonotephrite – phonolite. Nyiramuragira’s recent lavas ( tephrite ) are not very evolved. They can be seen as a lower-SiO2 and more-alkaline version of Etna’s trachybasalt. That is because basanites are richer in potassium and more silica poor than Etna’s trachybasalts. It is sourced from alkalic basanite and not from Etna’s alkali basalt.

Nyamuragira is nearly always erupting. It has two main types of activity: flank eruptions and constant shield building. The recent ongoing shield building has nearly completely filled the summit caldera with lake-tube-fed lava flows.

Nyamuragira is a magnificent beast. Its enlongated edifice or so-called lava field is around seventy kilometers long and thirtyfive kilometers wide with a large central cone resembling a larger version of Nyiragongo itself. This whole edifice (and Nyiragongo as well) maybe only 12 000 – 25 000 years old making them very young prolific volcanoes indeed. By long term thermal output it may be the world’s 2nd most thermally powerful volcano after Kilauea, at least in its current summit shield lava lake state. Among the worlds highly potassic volcanoes, Nyamuragira is the most powerful and productive.

It’s behaviour is cyclic, shifting between summit and frequent flank eruptions. Nyamuragira displays two main types of activity: short lived fissure eruptions that are common along the flanks and long lived slow lava lake fed pahoehoe fillings so called “ shield building”. It is possible to divide flank eruptions into fast and slow types. We will have a short look at eruption behaviour before we get into the interesting stuff.

Nyiramuragira being more remote than Nyiragongo is very hard to monitor. It is rarely visited even if on site observations by volcanologists are done now and then. Because the volcano is not ultra well monitored, any news of direct observations rarely comes out in the media. OVG likely lacks resources and have few people due to the highly unstable, uncertain regional political situation. In the modern era it has been more and more possible to monitor volcanoes from space. Lots of Nyiramuragira’s recent doings have been seen from space using thermal sensors which is used as base information for the subject on this post. Observed from space, you don’t need to visit the volcano as often which is quite convenient. Today we can monitor Nyiramuragira in a completely different way than the limited ways that were available just forty years ago. But despite advances in remote sensing Nyamuragira and Nyiragongo remain hard to monitor from space due to the persistent deep tropical conditions. The Virunga is very cloudy making it hard to obtain clear space imagery for either Nyiragongo or Nyamuragira.

Flank eruptions 1950’s – 2012

Rift eruptions are a result of magma supply accumulating under Nyamuragira’s edifice when the summit conduit up to the caldera is sealed up or even collapsed. When Nyamuragira is set up like that the magma supply accumulates and sets up pressure in the rift systems. One rift system of weakness goes south east, one system of weakness goes north west. Increasing pressure from magma accumulating causes the rift to snap and an intrusion rushes towards the surface resulting in a fissure eruption. These types of eruptions are a spectacular sight: lava fountains up to many 100 meters tall roars along the fissure and a massive incandescent pyrocumulus steam cloud rises up to 30 000 feet making its own weather. Goma is lit by a terrifying red nightglow and the results of these types of eruptions make it into the global news. These fast rift flank eruptions can be a spectacular sight for the tourists that cherish the tall lava fountains. The 2011 rift eruption was visited by quite a lot of persons. Eruption rates range from 1000 s of cubic meters at the start to sustained at 100 s for a few days later, dropping fast to 10 s. For the local wildlife and nature every such flank eruption is local disaster. It is a terrifying burning apocalypse resulting in gorillas and chimps having to abandon their territories when the hell-flood burns everything in its path. After just a few days the lava fountains have made a cinder cone when the eruption focus on one point. The central fountains feed very fluid channelized fast moving lava flows that in turn downslope feed massive slow moving viscous Aa flows.

During large rift eruptions such channelized lava flows can flow for many 10 s of kilometers. The longest Aa lava flow in the early 1980’s flowed 23 kilometers from the vent. Every such rift eruption forms a monogenetic flank cone. Nyamuragira is full of flank cones from such eruptions. These types of eruptions typically last just a few weeks with the larger ones lasting over a year. Slower types flank eruptions can form tube feed pahoehoe flows like the very large long lasting flank eruptions in the early to middle 1900’s. Cinder cone forming flank eruptions at Nyamuragira are rather similar in behaviour to radial flank cone forming eruptions at Galapagos and Etna but with a ultrabasic magma that is much more alkali rich than these. Between 1967 and 2011 there have been 19 cone forming flank eruptions during the 44 years time span. That is an eruption almost every two years. This behaviour was the norm for decades during my lifetime until I was about 17 years old.

The largest of these types of eruptions result from the termination of shield phases at the summit caldera through collapse of the magma column. The summit caldera has during those years of frequent flank eruptions also been home to small summit fissure eruption events that laid down numerous small Aa sheets during short lived co-flank-eruption fissures. But other than that, the summit caldera morphology has likely been quite unchanged in appearance for many decades. The magma supply has been focused on the rifts and not on the summit caldera. Nyamuragira’s summit caldera are linked to its rift systems of weakness. The draining of large summit lava lakes columns into these rifts can collapse whole summit pits. The flank eruption that created the main 2.2 kilometers wide main caldera itself must have been an enormous spectacle, a few times bigger than the Leilani eruption perhaps.

Nyamuragira, like other volcanoes with fast or very fast or constant supply such as Kilauea, Nyiragongo, Erta Ale and Ambrym, goes through cycles of summit lava lake fillings and flank intrusions which drain out their lava lakes. Nyiramuragira perhaps shifts between these over many decades. After more than 60 years of flank eruptions the volcano changed after the large 2011 flank eruption. After that eruption the magma supply went up the summit caldera’s central conduit, meaning a temporary end to decades of flank eruptions. With the central magma conduit once again visible as a convective open conduit lava lake, the volcano has entered a ”shield lava lake phase” fillings its summit caldera. This behaviour it shares with its sister Nyiragongo with the difference that Nyiragongo has mostly been focused on summit conduit activity rather than rift activity.

2012 – 2025 today summit lava lakes, lava ponds and ”slow shield building”

 

To understand the current huge lava lake that resides at Nyamuragiras summit it may be worth to summarize the events that led to today’s overflowing lava shield. Nyiramuragira belongs to a group of very few open conduit volcanoes that host lava lakes that are basically convective magma columns that are open to the Earth’s surface. This ultra rare phenomenon requires both a constant magma supply and open conduits. Due to the size of the current new lava lake I guess that Nyiramuragira has a very powerful thermal influx.

Nyiramuragira summit lava lake reappeared in the caldera in 2012, in the smaller intra caldera pit ( 500 m wide ) that had been there for many decades. The formation of open conduit lava lakes has only been seen a few times in recorded history. Good examples are Nyiragongo 2003 and Kilauea 2008 with Kilauea ( Halemaumau 2008 ) being the most interesting. The rising magma column simply ate its way through the roof that began collapsing with a steaming hole where circulating lava later became visible. The same happened in Nyiramuragira on 16 April 2012 when Dario Tedesco spotted a new collapse pit in the pre-existing intra NE caldera pit. The new conduit steamed heavily and a deep glow could be seen at night. On 1 July 2014 a violent rolling lava lake was seen in that pit. The rolling convection sent up a huge sulfur plume. Pele’s hair and ashy particles produced by the lava fountains fell all around. This was a clear sign that the magma column had access to the surface. Volcanologists could once again observe the formation of an open conduit circulating lake.

This was the first time since the early middle 1900’s that a summit lava lake was visible. The magma column rose and fell and by 2016 it had mostly fallen out of sight. When 2017 came, lava reappeared in the pit as spatter cones and the pit crater began to fill up by pahoehoe fillings. After that it slept until 2018 when the inner caldera pit started to fill again with pahoehoe lava fillings and a small lava lake was present (nothing compared to the giant lava lake that is present today). By the end of 2019 the inner pit crater had been filled to the brim and in spring 2020 the lava flows had filled the pit to the rim. Throughout 2018 – 2019 at least on on-site observation there was a small lava pond feeding tubes. By then pahoehoe lavas tube-fed by the lava pond and spatter cones was flowing over the main caldera floor for the first time since the late 1930’s. Up to this point there was no large open lava lake, unlike in 2015, but rising magma was always present in the central conduit of course.

From 2017 to 2023 these ponds, hornitoes and sporadic lakes was the typical behaviour that filled up the caldera, perhaps because the magma column was narrower than today’s giant lava lake. In December 2020 pahoehoe flows spilled over the SW portion of the caldera, filling a depression that had been there for decades.

Its very interesting how the current activity and how the post-2012 summit activity leading up to today have all focused on the same pit: the NE pit in Nyamuragira summit caldera and pretty much nowhere else in the caldera. That is of course a clear sign that at the current time the central conduit resides in the NE pit making that pit perhaps what Halemaumau is for Kilauea’s outer summit caldera. Effusive activity kept going and on 29 September and 1 October 2020, a team of scientists from OVG doing fieldwork at the summit caldera observed that effusive activity fed by the lava pond and spatter cones between March 2020 kept going.

Magma conduit columns are heavy and unstable phenomena, very much so in Nyiragongo and Nyamuragira that are rift volcanoes with weak structures. In 2021, roughly at the same time that Nyiragongo had its 22 May flank lava-lake-drain-out eruption, Nyamuragira did a smaller similar collapse event in its NE intra caldera pit. I strongly remember OVG volcanologists flying over the caldera pit in a helicopter, which found drain-out with no lava visible in the crater pit. So it drained out and I don’t know of any known flank eruption that resulted, likely due to the small scale of the intrusive event.

In December 2021 the magma rose again in the NE pit forming a lava lake that slowly filled the pit. Between 2021 and 2023 many lakes came and went in the NE pit and pahoehoe kept filling the areas around it. On 20 May 2023 the whole caldera had filled by pahoehoe flows so the lava began to pour out from the caldera and down the western slope, with large silvery fluid lava rivers pouring from the filled caldera. The summit caldera was not filled by open lava, but the lava was pouring from perhaps an underground lava pond that flowed out from the pahoehoe shelf that had filled the caldera. Lava effusion continued but was confined to the summit crater. Crater incandescence was seen from Goma. It was perhaps the first time in nearly or over a century that lava flows spilled over the caldera rim and the first time since 1938 that Nyamuragira entered a lava lake shield phase again.

In 2024 slow pahoehoe ”shield building” continued from the lava lake source at the NE pit feeding the caldera filling of pahoehoe. A series of tube-fed pahoehoe flank flows were formed. Images from space in the Summer 2024 recorded a long tube fed pahoehoe flow called the NNW flow. It had advanced nearly nine kilometers downslope by early August 2024, fed by a long lava tube that was in turn supplied by the lava lake in the NE pit. The caldera was by late 2024 nearly completely in-filled by pahoehoe with the northwestern wall completely gone under tube fed shield type flows. The summit caldera was already quite full before the shield ”phase” started but the filling rate is impressive anyway even if it is much slower than Kilauea’s current filling.

In 2024 there were many tube fed flows that advanced kilometers downslope from the caldera. There have been many episodes of pahoehoe lava flows from 2023, still ongoing today. That is very likely how Nyiramuragiras steeper upper edifice formed in the first place: through many short episodes of tube fed lava flows supplied by high standing overflowing lava lakes. Nyamuragira’s densely forested slopes are full of smooth hummocky ”pahoehoe geography”, so-called shield building. Such activity can last decades when the volcano’s deep magma system is open towards the surface. Lava lakes are dangerous because they tend to collapse when the column gets too heavy.

At the end of 2024 the current large lava lake ( that is the article subject ) became well established in the NE pit, which is now one big open vent lava lake. I was looking at sulfur dioxide layer setting in the windy app a few months ago and noticed over a couple of weeks frequent very strong emissions of sulfur dioxide from Nyamuragira. I suspect that could have been because the magma column is now exposed to the surface atmosphere, and can fully convect and de-gas itself. The situation resembles 2015 again only this time the lava lake is even bigger and has higher elevation.

The latest thermal imagery from remote space tools shows continuous lava lake activity from a nearly 400 meters long lava lake NE pit thats been presistent since 2024. Pahoehoe lava flows of basanitic/ tephritic composition continue to be active at the time of this writing. Tube fed lava flows, likely fed internally by the lake, By march 2025 are very busy building up the caldera floor ground around the NE pit and a strong thermal anomaly is visible on one of the 2023 south west overflows that could perhaps be a large skylight where a lava tube roof has caved in.

Sentinel Playground (where you can access space imagery) has been very useful to monitor this, even if the cloudy tropical climate often suppresses both visual and thermal satellite instruments. Tropical cumulus clouds often block instruments but this year has been a true treasure trove for remote monitoring of Nyiramuragira so far. A recent Satellite photo shows that the strongest thermal source was Nyiramuragira due to the new large lava lake. A much smaller but persistent thermal source was also found in the nearby Nyiragongo, which has also been present for some years. Nyiragongo, according to thermal data, likely hosts a smaller lava pond in a large spatter cone rather than a large lava lake, as it did the last time there was a clear shot in 2024. Both volcanoes produce rather huge condensation plumes. Although the Goma residents on the ground have been busy with M23 squabbles, the Nyamuragira acid cumulus plume was particularly impressive in photographs by locals on 21 March 2025, published on Facebook.

With this information in mind it is clear that Nyamuragira has changed its activity behaviour back to open vent degassing at its summit. Lava output has been pulsating with increases and decreases of supply to pahoehoe flows building up overlapping lava fields.

The current new large lava lake at Nyamuragira 

The large open circulating lava lake present at Nyamuragira summit shows that the volcano has entered a new eruption cycle of open conduit summit-centered activity. The last time the volcano was like this was back in the 1930’s. To say the truth: it is better to call this a shift in eruptive behaviour rather than a shift in an eruption cycle. A lot what Nyamuragira does is random and has no timetable or exact forecasting, even if high standing lava lake columns in Nyiragongo and Nyamuragira can be correctly forecasted to lead to collapse and drain out in the rifts. Lava lakes being exposed deep magma columns are long lived and this one could last decades. But with the lava column building itself higher and heavier through ”shielding” a drain-out into the rift systems is a serious possibility quite soon.

I became suspicious that there was a large open active lava lake present in the summit of Nyamuragira as early as January 2024. I clearly remember photos on social media, especially one seen from Goma at night showing a huge glowing red pyrocumulus column rising from a yellow base at the caldera. Such condensation columns are pretty much always present in both Nyiragongo and Nyamuragira, two glowing columns, but the condensation column over Nyamuragira is by far the strongest and densest these days. It makes sense that it was an open magma column that is convecting and degassing itself. For the Goma residents it must be a terrifying sight for many, the night skies ( that are nearly always cloudy ) due to lava lakes’ illumination of the clouds have nearly always a sickly twisted red color. Remote monitoring from space was hard for weeks due to the equatorial cloudiness but I remember thermal shots from space showing an intense thermal source from the NE pit sitting right below the condensation plume. It was much bigger than any other open lava lake thermal signature that I seen earlier in SWIR instrument images. The thermal area was at least 400 meters wide so it was sizable indeed compared to other convective lava lakes. I struggled for a long long time with satellite tools getting a clear shot in the caldera. In the deep tropics clouds are pretty much ever present and they mixes with the steam column from the lava lake making it hard with monitoring.

I really wanted clear weather shots of the NE pit but the tropical humidity turned out to be annoying and it was hard to find clear shots from space. My luck came true on 21 February 2025 when using Copernicus space imagery from the Sentinel Playground, a clear day offered a good shot on the NE pit that indeed had become one huge lava lake. I was quite surprised by what I saw. The whole NE pit was filled by a convective open lava lake. I used the measurement tool and got almost 400 meters wide! That is nearly twice the diameter of Kilauea’s old summit lava lake as it was in 2015. More clear imagery came on 21 March 2025 showing the lava lake to still be there. The SWIR thermal instrument showed a very strong persistent thermal signature 380 m long at the same spot. Lava lakes are not common on Earth. During this type of activity magma circulates constantly between the surface and the deep magma system, as hot fresh incoming magma rises and cooler degassed magma sinks back into the conduit.

A lava lake acts very much like a lava lamp with its convective currents. A massive heat influx and constant supply is needed to keep the whole thing running and to keep it from solidifying. This explains why lava lakes are so rare on Earth. The whole buried floor of NE pit may have simply collapsed into the magma chamber itself that is now visible at the surface as a lava lake. It is a rare phenomenon having a circulating magma system open to the surface. At 350 – 400 meters wide it is at the current time the world’s largest open conduit lava lake. It is much larger than the small lava ponds in Yasur and Masaya. A lava lake’s size may be correlated with the strength of the magmatic influx. Nyamuragira and Kilauea have the highest magmatic influxes on the planet as individual volcanoes and together with Nyiragongo tend to form the largest lava lakes. Kilauea is stronger, which is why I imagine Kilauea may be able to far exceed Nyamuragiras new lake in size in the near future. But by these days ( at writing ) this is the world’s largest circulating lava lake.

Nyamuragira’s new lava lake is roughly bean shaped with rising lava apparently welling up in the southern part of the lake and sinking down back in into the conduit in the northern part of the lava lake as a part of its natural convection cycle. The scale of lava lake activity is quite impressive, I measured the glowing parts in the lake at different dates at 130 meters wide for many spattering upwelling and downwelling regions. The specs were especially impressive for 20 February 2025 showing a glowing red surface in visible light over 200 meters wide! The lava lake must have had a very fast surface flow to allow it to glow like that because lava cools very quickly on the surface forming an insulating skin that otherwise restricts a high thermal flux. Between them there is a calmer region where a thin crustal “scum” can form. Lava lakes tends to have a violent formation and they tend to calm down when they grow larger and the system degasses. It will be very interesting to see just how large this lava lake will be able to grow before it gets too heavy and drains out. This very vigorous convective activity is driven a lot by rising gases that come from way below Earths crust. Sulfur dioxide emissions have been especially vigorous from Virunga recently. Near the crater rim, underneath the volcanic plume rising from the lake, the rain that sometimes condenses out from the plumes from both volcanoes can have pH as low as 2. Low pH values and high fluoride contents has been measured as far as the village of Rusayo, 10 km from the summit (sourced from Albert’s information on local acid problems).

As already told the scale of lava lakes surface activity is quite impressive and it looks and behaves very different from other past large lava lakes in Kilauea and Erta Ale that are typically more placid in surface behaviour. This lava lake is nearly raging, at least near the edges. Highly potassic volcanoes like Nyamuragira and Nyiragongo have a lava chemistry and gas ratio content that differs from normal basaltic volcanoes so gives both lava fountains and lava lakes a distinct look. The gas rich nature of the magma from water and carbon dioxide may be the cause of the spectacular surface lake activity, combined perhaps with an increase in magma supply. Alkaline magmas tends to be gassier than sub-alkaline ones perhaps explaining why Nyiragoingo and Nyamuragira have more active lava lake surfaces than Erta Ale and Kilauea. That said, because of Kilauea’s massive supply at moment and very high sulfur gas content it may too be able to form a similar lava lake in the coming years and it maybe able to grow much larger than this.

Lava lake activity continues non stop at Nyamuragira and it appears ( seen from space ) that between February and January 2025 there may have been a slight decrease in lava lake levels. It does not mean that the lake is about to disappear. It has not been as high since it formed in 2012 – 2015. The magma column may have degassed itself a bit and the lava sunk a little. Lava lake surface activity ( degassing ) anyway remains incredibly strong compared to pretty much any other open lava lake that I have been studying in videos and space imagery. This is the most violent really large lava lake that I ever seen.

I hope that OVG goes up to this lava lake by helicopter very soon to take lava samples and gas samples that can be compared with earlier Nyamuragira eruptives. As with Nyiragoingo, Nyamuragiras magma chamber morphology is poorly known. The presence of a caldera is of course a strong indication of a shallow chamber. The geologist Hamaguchi (1983) found an aseismic zone between 3 and 7 km beneath the 1981-1982 eruption site, suggesting that these signs were indicative of a magma reservoir at this depth range. Other geophysical modelling of ground deformation through InSAR suggests a shallow magma reservoir sitting at a depth range of 2-4 km. The current lava lake pipe is connected to this system and new samples could be useful to track changes in the central magma system related to magma supply and magma storage. A convective lava lake is a manifestation of the very deep magma system that goes all way down into the asthenosphere, something that is rare indeed. I guess that we will get fresh direct footage quite soon.

The emergence of such a large lava lake at Nyamuragira summit gives extra potential hazards which the population at Goma that are dodging disasters all the time have to live with. The nearby villages are put at risk as well. The rising magma into the summit could end up feeding a large flank eruption. Nyamuragira and Nyiragoingo are prone to catastrophic drain-outs if their magma columns get too tall. This is a very likely scenario if Nyamuragira’s lava lake keeps getting taller and making itself a shield around it, which will increase pressure around the magma column. I assume that a lava lake column this large will put more pressure around it then a more narrow magma column would do. A small weakness along the volcano’s base could allow the magma to come rushing out through the side like it did at Nyiragongo in 1977, 2002 and 2021. A large drain-out has terrifying eruption rates with many thousands of cubic meters of lava a second. This is a serious risk for smaller isolated villages that are close to the volcano. Goma’s center, due to geography, is fairly safe from large lava flows emitted from Nyamuragira but Goma’s sub towns towards the west are at risk from being buried by future lava flows. Large lava flows have flowed there before in the early 1900’s where they entered Kivu lake.

The largest fear from the locals is a large intrusion down under lake Kivu that sets up an underwater eruption in the lake floor and stirrs up this volatile lake. Experts estimates that there is 72 cubic miles (300 cubic kilometers) of CO2 and 14 cubic miles (60 cubic km) of methane sitting at the bottom of Lake Kivu, and it can be stirred up by a lake eruption. That said, it is an extreme scenario that is not very likely on a human timescale.

It will be interesting to see how long this particularly large lava lake will survive before it drains out. A drain-out will likely happen in one of the two rifts where zones of structural weakness are.

 

 

Jesper Sandberg March 2025

Source links: GVP, volcanodiscovery and various including social media and https://browser.dataspace.copernicus.eu/?dateMode=MOSAIC is a very good site to remote monitor volcanoes.