Cumbre Vieja and the San Juan eruption of 1949

The volcano Cumbre Vieja in the island of La Palma has been showing signs of unrest. The question on everyone’s mind is, will there be an eruption? Maybe, or maybe not. This is always hard to know.

The Spanish National Geographic Institute reports inflation, a total of 10 cm of deformation. As such it is evident that there is magma on the move under Cumbre Vieja, it has intruded underneath the volcano.

There have been multiple swarms of earthquakes since 2017 in Cumbre Vieja, a total of nine. Previous swarms were probably magma intrusions too, but which did not reach the surface. The recent swarm however is more shallow and more intense than its predecessors which raises the possibility that the outcome may be different.

The current swarm started on September 12. A total of 4530 earthquakes have been detected at depths of mainly around 10 km, although there are a few which have been very shallow. The swarm commenced under the summit of Cumbre Vieja, where a magma conduit probably exists which is supplying the intrusion. Earthquakes have propagated to the northwest. This probably represents the propagation of magma filled fractures, possibly sills, radially from the centre of Cumbre Vieja. However the earthquakes only show a but a blur of what is going on down there. The exact shape and pathways used by the intrusions cannot really be known with much precision. It is somewhat similar to the prelude to the eruption of El Hierro in 2011 which also seems to have commenced with a sill that later propagated a crack towards the seafloor.

Image from the NASA.

The location of the earthquakes suggest a possible eruption in the NW sector of Cumbre Vieja. However there is a factor of unpredictability. The exact path that the intrusion takes may or may not connect with the surface, such being difficult to know if there will or will not be an eruption . The precise location where the intrusion will breach the surface is also difficult to know. The fissure could open in the middle of a town, in a forest, or it could open underwater, which are wildly different situations with wildly different consequences.

We can know however the style that the next eruption of Cumbre Vieja will take, whenever and wherever it happens. To do this we must look at the past history of this volcano.


La Palma

La Palma is one of the Canary Islands. It was formed due to volcanic activity. The oldest rocks of the island are 3-4 million years old and belong to a submarine volcano. These submarine lavas are now found at heights of up to 1500 meters above sea level in the Barranco de las Angustias, in the old northern part of the island, which shows the enormous uplift that the island has undergone. Probably numerous sill intrusions have pushed the volcano upwards.

La Palma. From the NASA.

La Palma is shaped like an arrowhead. The northern part is formed by the old Taburiente volcano. Deep gullies dissect the ancient lava flows exposing the overlapping layers of volcanic extrusions and the frozen dykes and sills which cut through them. The volcanic edifice was destroyed by a series of giant landslides, the last of which took place around  560,000 years ago. Activity continued inside the landslide scarp until 530,000 years ago. Afterwards activity died out in the northern half of the island.

Large scarp formed due to erosion of Taburiente volcano. Some sills and dykes are visible on the left. From Wikimedia, by Zyance.

Volcanic activity in the southern half of the island has been ongoing for at least 125,000 years and has constructed another volcano known as Cumbre Vieja, or also simply as Dorsal Sur, “Southern Ridge”. It is a shaped like a ridge in a N-S direction. Despite being different edifices it seems that Cumbre Vieja is part of Taburiente’s structure. Taburiente had 5 subtle radial rifts. This is much better appreciated in submarine shield volcanoes which are often shaped like ridges or like three to six-pointed stars. Knowing well the shape of submarine volcanoes I can see that Taburiente displays the same five-pointed star structure, although being subaerial it is not so easily visible. The longest, dominant rift goes southward, known as Cumbre Nueva. It can be seen that Cumbre Vieja is the southern continuation of Cumbre Nueva.

Topography of La Palma. Note the northern volcano Taburiente which is cut by deep gullies and a central erosional crater, and the southern volcano Cumbre Vieja which is dotted by young volcanic cones. There is a bow-shaped ridge connecting both volcanoes, this is Cumbre Nueva, the ancient rift zone of Taburiente, partly destroyed by a landslide. From


The main magma erupted in La Palma, as well as in the Canary Islands, is basanite, which is relatively fluid, but not as much as say Hawaii. The fluidity is comparable to the more frequently active Mount Etna in Sicily. The magma is not so fluid that all of it would flow away upon landing on the surface, but it is not so viscous that it is entirely blasted into light pumice and ash carried away by the wind. The eruption style is known as “violent strombolian” or “violent hawaiian” depending on whether it produces explosions or sustained fountains. It is the middle ground between the blazing rivers of lava and the billowing columns of ash. This style is ideal for producing pyroclastic material that rains around the fountain, rapidly constructing a mountain around the vent, known as a scoria cone. These conical mounds of ejecta are everywhere over Cumbre Vieja. Because the volcano doesn’t have any central vent that erupts repeatedly, then it makes a new fissure each time it erupts. The pyroclastic material rapidly oxidices. This gives the terrain various hues ranging from black to red, which together with the abundant canarian pine trees gives the characteristic landscape of Cumbre Vieja.

Desertic volcanic landscape near the southern point of the island. San Antonio volcano visible in the centre formed in the 1677 eruption, The brighter cone to the left of San Antonio is Teneguia, which formed in 1971. From Wikimedia by Tony Hisgett.

Other magma types present in Cumbre Vieja are the tephrite and phonolite groups which are more silicic and viscous. They are  present in trace amounts making small lava domes. A small volume of phonolite was emitted in 1585 producing tiny cryptodomes and domes, although the eruption was mainly basanitic.

Types of volcanic rocks depending on silica and alkali content. From Wikimedia by Woudloper.

Cumbre Vieja last erupted in 1971, 1949, 1712, 1677, 1646, and 1585. It is the most active volcano in the Canary Islands. Eruptions have taken place at intervals of 20-60 years. The exception being the remarkable 237 years long dormancy between 1712 and 1949. Why did this happen? It is possible that the volcano follows cycles of more frequent eruptions separated by long dormancies. Another possibility is that the enormous 6-year long eruption of nearby Lanzarote Island, occurring in 1730, induced a long dormancy in Cumbre Vieja.

It would not be unexpected that now, 50 years after the last eruption, there was a new one.

The eruption of 1949

The eruption that took place in 1949 is an interesting example of a typical Cumbre Vieja eruption.

Swarms of earthquakes had been frequent since 1936 and leading until the eruption. The morning of June 24 some fumes were noticed, and soon afterwards a towering black column of ash was rising hundreds of meters, if not more, into the sky. A new volcano had formed along the crest of Cumbre Vieja. The fissure had opened a small distance north of the highest point of the ridge. The vent is known as Duraznero.

During the following days Duraznero continued to erupt, belching out ash and rocks. Earthquakes frequently rocked the nearby communities and steaming fractures opened in the  ground around Duraznero. Magma must have been making its way into growing fractures. Over the days the erupting fissure progressively grew to a length of 500 meters and developed 5 main vents, of which Duraznero 2, at the southern end, was the most active, creating a 170 meter-wide crater. The activity was entirely explosive but of a low intensity that must have been little more than a slight annoyance to the local population. The erupted lava was tephrite. Earthquakes were more impactful, they damaged houses, cracked roads, and occasioned rockfalls. On July 6 the ash was carried downwind over the island of Tenerife where it wrapped around the summit of El Teide in a menacing black cloud.

Fissures of Duraznero. Image by KrisNM.

On July 8 a stream of lava came out from a new location known as Llano del Banco, 3 kilometres north of Duraznero, and from the other end of a system of cracks that had opened up. It did so quietly with no explosive activity whatsoever. The lava must have been degassed by Duraznero, gone into cracks, and found an outlet at a lower elevation from Llano del Banco. The lava erupted was tephrite, same as that of the earlier phase of the eruption. The initial fissure died out at about the time the new vent opened.

It is common for eruptions of Cumbre Vieja to have some vents which are dominantly explosive while others are effusive. In the eruptions of 1646, 1677 and 1712 it also happened that the vents which opened at the highest elevations had explosive activity and built large cones of scoria, while other fissures opened at lower elevations, sometimes offrift, and even at sea level, producing solely lava flows. The eruption of 1949 shows how the process works. A vent that is high up degasses the magma and then it is carried laterally through fractures towards openings downslope from which it emerges effusively.

Lava descended in fiery tongues from Llano del Banco down the flanks of the mountain. People were being evacuated as the flow headed for populated areas. It took 10 hours for the lava to reach the main road of the south of La Palma. Later that day the flow had destroyed 20 structures, including houses, cellars, and barns.

On July 10 lava cascaded over a cliff into the ocean. From this day on the entry of lava into the sea became continuous, and a lava delta was gradually constructed. Cloud of steams rising over the waters were illuminated by the convoluted streams of incandescent rock.

A new change in the eruption took place on July 12. The composition of lava erupted from Llano del Banco changed from tephrite to basanite. It became less silicic. At a similar time a new vent opened 400 meters north of the initial vent of Duraznero in the location known as Hoyo Negro. Black cauliflowers of ash pierced with flashes of lightning rose rhythmically from the Hoyo Negro vent. It erupted various magma types including basanites, tephri-phonolites and phono-tephrites. Once again the vent uprift was explosive while the vent downrift was effusive. The basanitic magmas must have released their gas into the explosions of Hoyo Negro and then come out laterally through the opening in Llano del Banco.

Hoyo Negro projected bombs to a distance of 1 kilometre from the vent snapping the trees and setting portions of the pine forest on fire. Clouds of ash frequently dusted the western part of the island. The explosions excavated a 400-meter wide crater on sloping ground. This created a spectacular 200-metre cliff against the higher side of the slope, which exposed the many layers of ejecta painted in a variety of colours.

Hoyo Negro. Image by Rafael Medina.

A raging stream of lava continued to issue from Llano del Banco and cascade towards the coast. Despite erupting continuously for 18 days the vent produced no distinguishable ejecta, and shows how the gas had been entirely removed from the melt before erupting. The ground above the fissure collapsed among loud noises, the rocks fell into the stream and were carried away, a length of 150 meters of rock above the conduit was eroded away and disappeared leaving behind a deep chasm in the forest.

On July 22 the activity of Hoyo Negro was down to a solfatara. Llano del Banco was also dying down. By July 26 the eruption had fully stopped.

Early on the morning of July 30 the eruption suddenly resumed. Duraznero and Hoyo Negro exploded simultaneously. An hour later fluid basanite lavas emerged from the location of Duraznero 1 and poured into an old crater where it formed a lava lake which then overflowed and formed a narrow stream of lava that rapidly sped down the steep slopes of Cumbre Vieja, cutting the road of Santa Cruz de la Palma, and nearly reaching the sea after 11 hours of advance, when the eruption came to a stop. This was the last episode of the 1949 eruption.

The flow of July 30, although of rapid advance, it was fed at a rate of only 10 m3/s, which is very low. It was also similar to the mean eruption rate of Llano del Banco, which was approximately 14 m3/s. The explosive activity was of little volume so it probably does not change the overall numbers too much. As such the eruption of 1949 was of very low intensity, in both its effusive and explosive counterparts. Slow eruptions are typical of the Canary Islands. Such low intensity eruptions do not pose much of a hazard to the people, in fact no one died in the 1949 eruption, despite 120 houses or so being destroyed, and people having approached the eruption in order to view it. This doesn’t mean that the hazard is inexistent.

If someone stands very close to the vents he/she could be asphyxiated by the noxious gasses or may be impacted by a lava bomb or by lightning. Rarely when lava flows reach steep slopes they collapse into blistering landslides resembling small-scale pyroclastic flows that could potentially kill someone. Conditions around volcanic eruptions can change suddenly in unpredictable ways and become hostile to humans. Safety is not guaranteed.

If Cumbre Vieja erupts in the future it will probably resemble the 1949 eruption in many ways: an earthquake prelude to the eruption that may deal damage to structures, unpredictable opening of fissures, some vents producing mainly explosive activity while others feeding mainly streams of lava that destroy human properties, and also the likely entry of lava into the sea.

Of course if the current earthquake swarm will culminate in an eruption or not cannot be known for sure. Swarms before the 1949 eruption occurred as early as 1936 and did not culminate in eruption until 13 years later.


San Martin volcano, formed in a 1646 eruption. Image by Rafael Medina.


Interesting links

Eruption of 1949 (in spanish).

IGN news (spanish).

GRAFCAN visor (includes geologic and topographic maps).


1,260 thoughts on “Cumbre Vieja and the San Juan eruption of 1949

    • Its front coud be as tall as 16 meters when it hits the ocean at coast

      I doubt it will get much thicker
      The huge mass of Aa insulates itself too. .. it coud probaly flow quite a distance If this continues

      Its so Viscous for being a basalt

    • Yes. If the eruption stays in “episodic surface flow” mode, it’s basically game over for that wall within days. Path B will be disabled long before the Natthagi Dam / Path C will be overtopped.

    • Uh… As much as I am fascinated by volcanoes – it is more enjoyable to watch nice tourist eruptions that burn a bit of moss or a camera here and there, than watching houses being reduced to ashes, live and in slow motion.

      One can only hope that those houses being hit are “only” second homes of the rich. Might work here to some extent, but certainly not for Taal.

      • Oh, come on, Groundhog. The “rich” don’t even own houses there, there is just one single decent beach in Puerto Naos, the rest is rocky, volcanic. And the beach in Puerto Naos is dark, volcanic.
        The “Rich” own poperty in London, Paris, Côte d’Azur, Courchevel, Florida.

        The people who own vacation homes on La Palma are medium-sized folks who have worked for that dream and mostly let the houses for holiday rental, thank God as there are not too many decent small hotels. They often got inammorated with the place while hiking. Decent people, believe me. Germans, Dutch and Scandinavians mostly, the British are more in Tenerife.

        Aside from that I consider this kind of social envy cheap.

    • And much much much more fluid
      Also Las Palmas is tiny compared
      To Mauna Loa .. and Mauna Loa is much much much younger than entire Las Palmas 🙂

      Hawaii hotspot Maybe 10 times stronger than the Canary Hotspot

      • I don’t care for corrections, but here it seems important, sorry Jesper. Las Palmas is the capital of Gran Canaria, whereas La Palma is a single island. Hope you don’t mind. So flights for Las Palmas go to GC. The other airport is Santa Cruz de la Palma.
        Just worried you climb into the wrong plane one day.

        • The best way to get to Santa Cruz de la Palma (in my experience) is via Germany, where there are (were?) direct flights. You can also fly via Tenerife but international flights end to arrive in Tenerife south and the onward flight is from Tenerife north, and that is a long way apart. You can take a bus or rent a one-way car – taxis not cheap. A ferry can be considered between the islands, less sensitive to volcanic ash. Santa Cruz de la Palma is a really nice town. There are good roads on the island but beware of blind corners and speeding drivers. Same as everywhere but it is more obvious on the mountain roads. Don’t drive up to the observatory at night.

          • My friend lived close to the observatory. So, you were there, great.
            I met the stars there, studied them every night. The flight is easy from Germany, right. Unfortunately it got very expensive, even pre-Covid.

  1. from RTVC’s site:

    📌 The lava that is managing the #VolcandeLaPalma is expected to arrive in the coastal zone this Monday afternoon, around 20:00 p.m.
    📌 According to information administrations have received from scientific agencies monitoring the behaviour of the volcano, laundry is expected to enter the sea off the coast of #Tazacorte, possibly in Playa Nueva, in Los Guirres
    📌 ULPGC Geology professor Jose Mangas has warned that lava rivers will bury terrestrial, electric and phone communications and create acid rain when they arrive at the sea
    📌 The #VolcandeLaPalma is streaming from 6.000 to 9.000 tons per day of sulfur dioxiode (SO2) and has formed a laundry with an average height of six meters advancing to 700 meters per hour, killing its passing houses, crops and infrastructure

  2. The place north of the lava stream where the cam was located in the morning has now the lava closing by (from behind). This can be seen occasionally on: …

    • This is a pity. The stream from TV LA PALMA was the best so far. Clear pictures and not so much talk.

  3. Looks like this coud grow even more if the volcano is still inflating

  4. It appears that a lot is going on in the North Atlantic icluding its side oceans Mediterranean and Caribbean this year, Soufrière St.Vincent, Fagra, Etna, Cumbre Vieja.
    Is that a wrong impression? If not I wouldn’t be surprized if Sete Cidades or Furnas were next.

  5. In the meantime in Iceland, Fagradalsfjell Volcano is ramping up for a comeback….

    • Do you anticipate further eruptions along this trail of quakes? That would be pretty nasty for the folks there.

      • There is a possibility of future eruptions or new vents occurring, but I am not trained well enough in volcanology to give a % range. I am sure that the geological/volcanlogy scientists are watching this with intense interest.

  6. Being a rather sad person I always have an urge to find out exactly where webcams are placed. (Sorry).
    I’m pretty sure I identified the one being used in this video stream:

    It’s on the top of the Castillo de la Virgen in Parque Gomez Felipe to the north west.
    Co-ordinates 28.656472079919645, -17.914874139280354.

    There we are. Got that off my chest. And I have to say the zoom quality on that camera is impressive.

    • Yes, wild spattering now. At least 3 vents. Looks like more fluid lava is ariving now!

  7. Just glanced at the feed below at about 2:15 EST. They were looking at the front of one of the advancing lava flows. They then pan up and left to the main cone. At the bottom right corner of the cone it looks like there is some fresh lava moving down the hill. There was also what I thought a slight glow in the emissions from the cone. We need a time stamp on these feeds.

  8. I can’t see it mentioned above, but prevailing winds are currently WNW ~~ NW ~~ NNW at different heights, so plume is headed for Africa. I’ve no doubt La Palma’s astronomers, their instruments still safely up-wind on NW flank of Roque de los Muchachos are watching with keen interest…

    • Seem to be, as watching the last 15 mins shows lava increasing in production coming from both the main fountain vent and the new vents, at least to me, guaging by the brightness in the camera.

  9. LP 03 and LP 04 have a clear uplift. It is interesting that LP 04 moved ES pushed away, LP 03 stayed at the spot.

    But what do you think about LP06? it is quite far but still getting marginal uplift?

  10. For your info, the neighborhood of Tacande is being evacuated, not sure if it is because more vents are expected to open to the north, or due to gases or something else

  11. Spanish news is reporting the lava slowed down, it used to travel at 700m an hour, they were expecting the lavaflow to hit the sea tonight

    • Did they gave any indication what time it will enter the ocean? I picked up something like ‘it travelled only half the distance we expected”, but I may have misunderstood.

      That being said – One of the volcanologists with RTVC said yeesterday that the lava would slow down the further it comes, because the terrain is somewhat flatter and the lava cools down.
      I understood it slowed down to a speed of 300 m/h.

      Does anyone has a picture/image or idea of where the lava tongue is now?

      • They probably went on the 1949 flow reaching the ocean in 10 hours, but that flow was more fluid, erupting only several days into the event, where the current flows are stage 1. Even at Teneguia in 1971, which is basically perched on a steep cliff above the ocean and way closer to it than the eruption now, still took a day to create an ocean entry. When more fluid lava erupted it would reach the ocean rapidly. Fluid lava could be erupting now, and probably more is on the way, it will probably enter the ocean soon.

        • The flow of Duraznero of 1949 almost reached the sea in only 11 hours, but note that the distance was much shorter than here and the slopes much more steep. Llano del Banco took 2 days and the distance was also shorter than now.

          • 1949 vents actually in both cases are further from the ocean than today, the current eruption is only 2 km from Llano del Blanco. it is probably just that 1949 didnt make much lava in stage 1 so no flows developed. 1971 is probably more similar to the eruption today, though being so close to the ocean it is hard to tell how far lava would have gone otherwise.

  12. That is a MASSIVE amount of Lava coming from that vent for hours on end now. Where is it all going? It looks to be going behind the vent as the lava flow in the usual direction isn’t greatly increased from this morning. Could this be this what is causing the evacuation, that it is flowing in a different direction?

    • Or perhaps they are only showing the vent and not where the magma is flowing now. All I can find on live feeds is the vent erupting huge fountains.

          • I have been watching the main vent and an eruptive center is moving down to the right slowly but surely. Timestamp 22:48 UTC (there seem to be 2 main vents, but definitely something is moving down the slope to the right)
            (dogs barking constantly too, while watching this)

          • what is your link? I have two and neither one has a time stamp.

          • Now a small hot spot glowing bright yellow to the left of the fountain, 23:43 UTC timestamp. in an area which was previously black. This is not spatter.

          • When I take a snapshot from this video display, I refer to my system clock which I translate to UTC. I have NO idea if the video is real time or not, but I assume that it is.

          • Las Canarias have the same time zone as the UK – if that helps?

  13. *Fagradalsfjall has tourists all but play with its little lava flows and from time to time gushes a bit around*
    *Cumbre Vieja fires lava jets in the air like a broken oil well spits oil, and burns half of the municipality down*
    Cumbre Vieja: @Fagradalsfjall, Errrm small hint: You’re doing it wrong.

  14. I’ve lost track of the La Palma situation. Last night and this morning we had somewhere between 5 and 7 vents. Last night’s video showed spectacular lava fountains all over the place.

    During the afternoon today I could see 1 active fountain and lava flows. One flow hit a water main and went up in a big cloud of steam. Not a new vent.

    Tonight there appears to be only 1 smaller vent active? Both TelevisionCanaria and Sixty Media are focusing on this one vent?

    My head hurts.

    • The past hour I have carefully been watching the fountaining, and a hot spot appeared between the active fountain vent and the 2nd lower vent, almost in a line about 1/’2 in between. I believe that we have a fissure underneath which is NOT too far below the ground from the active cone to the 2nd venting area.

      This hot spot was very faint and could hardly be picked up by the camera, nevertheless it is real. I took a snapshot to document it.

  15. Fountaining looks really intense tonight. Almost looks like a Strombolian eruption.

  16. When I watch the stream at 60 media. From a great distance, this morning, the lava flow didn’t move much further towards ocean entry. New vent? Not a single pic.

  17. The lava flow didn’t get very far either. The stream just showed the house with the green wall (it still exists) after that there was the burst water pipe. I don’t think more than 100 meters this night.
    The big white house above the first camera location also still exists.

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