Pelean eruptions – the catastrophe of 1902 in the Lesser Antilles.

The recent eruption of La Soufriere volcano in Saint Vincent island reminded me of the events of 1902, of the tragedy that was unleashed by the two Caribbean volcanoes, La Soufriere and Pelée. Our current method of ranking explosivity, the VEI, doesn’t capture at all the violence of these two eruptions nor any of their kind. To avoid another disaster like this from happening it should be understood how these eruptions happen, how big they are, and how they deal their damage, and because our models and classifications do not make any justice to their real intensity, I decided to do an article that fully focuses on this style. This article is about Pelean eruptions.

The eruption of La Soufriere in Saint Vincent, 1902.

La Soufriere was a beautiful, lush, tropical mountain, topped by a large bluish-green crater lake enclosed in steep, verdant walls. But it also had a bad reputation. La Soufriere had produced major explosive eruptions in 1718 and 1812. It was probably for this reason that the local Carib people were very wary of the mountain in which they were living. When frequent earthquakes started to be felt in the month of April the people living on the western slopes of the volcano  prepared for evacuation.

La Soufriere before the 1902 eruption.

May 5th , the day before the climax, a column of steam rose from the crater, and soon the western slopes were being vacated at full speed, with the few available boats being sent to the northern coasts to carry the news and rescue people. It happened though that the summit was constantly shrouded in clouds, due to the trade winds, when seen from the eastern and northern slopes of the mountain, so they didn’t see any of the steaming nor the incandescence that could be clearly seen from the settlements on the other side of the volcano, and because  no earthquakes or rumblings were felt either, most people in these areas had no knowledge of any unusual activity until only 3 hours before the climax, and then it was too late.

It was May 6th. At 11 AM the volcano entered a phreatomagmatic eruption with the typical ink-black jets of mud shooting water from the lake onto the ravines around the crater and pouring in powerful lahars down into the Rabacca and Wallibu rivers. Explosions were heard and light rains of pumice and ash came down to the east. Only now did much of the population on the cloudy, windward side realize an eruption was underway. Many people at this point went into hiding inside houses or cellars.

A little past 2 PM those around La Soufriere heard a loud roar and an increase in air pressure which made their ears hurt. A gigantic explosion had sent a wave rippling through the atmosphere. The huge volume of ash and gas came down in a huge pyroclastic flow that within a few minutes swept down from crater to coast, engulfing a radius of 4-7 kilometres all around the vent, and leaving death and devastation in in its way. The flow burned and uprooted trees. As it came down to the shore, where most of the people were, it had lost much of its destructive effects and it did little damage to trees or buildings, but it was hot enough to kill every person and animal who was out in the open. Most of those who were inside houses and huts died too while a few survived. Instead, those who had previously taken refuge inside cellars all survived. There was one case where a men and his wife, who were hiding in a cellar with 70 people packed together, had decided to take a breath of fresh air only to die just outside.

Wallibu river valley filled with pyroclastic flow deposits, craters are from secondary steam explosions.

The 2 PM explosion and pyroclastic flows came to be known as The Great Black Cloud. This is the account of some survivors who had evacuated the area, but then returned to retrieve some of their belongings, and on their way back from their village were caught in the edge of the cloud:

“The sea was perfectly calm and the day clear, though there had been a few drops of rain in the forenoon. The boat had just rounded the point south of Richmond River and was on the north side of Chateaubelair Bay. The cloud struck them like a strong breeze, though, being under the shelter of a high spur of land, they did not feel it much. Still it came over the water with a strong ripple and a hissing sound, due to the hot sand falling into the sea and making it steam. In a moment it was pitch dark and intensely hot and stifling. The cloud was highly sulphurous, and this irritated their throats and nostrils, making them cough. The heat was terrible and the suffocating feeling very painful. They threw themselves into the sea to escape burning by the hot sand. It does not appear that the surface of the water was boiling as it was in some other cases. They all dived, and when they returned to the surface the air was still unfit to breathe and the heat intense. So they continued to dive repeatedly, but when they came up again the air was almost as bad as before. How long this lasted they cannot tell, but they thought it might have been several minutes.”

La Soufriere then entered a sustained plinian eruption that lasted for 12-15 hours. Darkness fell over the whole of Saint Vincent, and ashfall extended to neighbouring islands. As much as this stage frightened the population it was relatively harmless, and except for some of the larger raining stones which, falling at an angle due to the trade winds, broke crystal windows and injured a few people, and some lightning which set the vegetation on fire, the plinian eruption otherwise did little damage. In many locations the ash and pumice was soon washed away by the first torrential rains and everything was back to normal. It was the part of island hit by the 2 PM explosion that was destroyed, and it was because of this brief event that 1600 lives were lost. The culprit was a singular but terrifyingly powerful explosion.

Rabacca river valley. The trees were broken by the pyroclastic flows of 2 PM.

The eruption of Mount Pelée.

It is quite surprising that barely 18 hours after the eruption of La Soufriere, and on a nearby island, Mount Pelée would bring an even bigger volcanic calamity, even though there is no apparent connection between the two events.

Before 1902 the summit of Pelée was a horseshoe shaped crater. The crater was known as Etang Sec, it was bounded by walls 300 meters high except towards the southwest where it was open, in the general direction of Saint Pierre, the city that would be destroyed. The pyroclastic flows in May 1902 advanced much further in the southwest direction, 9 kilometres, than to the other sides of the cone, 3-4 kilometres, which was perhaps due to the topography of the crater.

Map showing the devastation area from the May 8 blast that destroyed Saint Pierre, and the even bigger August 30 blast that destroyed Morne Rouge. By NordNordWest.

Unlike with La Soufriere the people around Mount Pelée did get plenty of precursory activity. The crater had been in eruption for several days, and had sent some lahars through the breach into the Riviere Blanche. However Pelée had already erupted in 1851, and this eruption was small. While many in the villages closer to the volcano did flee, mostly to the city of Saint Pierre, it was considered that Saint Pierre was at a safe distance, and this would be true if the 1851 scenario was to repeat. However volcanoes like to throw some variety, and had they known of Pelée’s previous eruptions, in the geologic past, they would have probably reconsidered their safety.

The eruption was not showing much sign of escalation either, eruptions were frequent but remained relatively small. All of a sudden, at 8 AM on the 7th of May, the top of Mount Pelée exploded with a roar that was heard all around the mountain, pyroclastic flows shot through the breach in the crater towards the city of Saint Pierre and the harbour. The blast broke away trees, blew down buildings, twisted iron beams, sent statues flying, while the temperatures of more 300-400ºC set everything combustible ablaze so that the whole city was soon enveloped in flames. The destruction was much worse on the northern side of the city, than on the southern side, where farther away from the crater the buildings were less damaged, although there was not a roof intact. Several ships that were on the harbour caught on fire and sank. After the pyroclastic flow powerful winds blew towards the destructed area and there is a description reminiscent of a fire tornado.

Saint Pierre before the eruption. From Lacroix, 1904,
La montagne Pelée et ses éruptions.

 

Saint Pierre after the eruption. From Lacroix, 1904.

An observer from Morne Rouge stated that the “burst of rocks” rose no more than 50-100 meters above the crest of the mountain, a maximum of 400 meters from the crater floor, quite low, and as I will further discuss later shows how the eruption clouds of pelean blasts move low over the ground. Several witnesses of the event indicate that the pyroclastic flow travelled in 1 minute from the crater to Saint Pierre, at an speed of 400 km/hour. The destruction was terrible and practically everyone within the city lost their lives, an estimated 28,000 casualties. Because of this there are very few accounts of how it happened. This is the description from Captain Freeman of the Roddan, the only ship on the harbour that escaped destruction:

” At about 8.15 he was in the chart room; a good many of the sailors were leaning over the side of the vessel watching the distant mountain, which was emitting dense clouds of smoke and occasional flashes of light. Mr. Campbell was talking to Mr. Plissonneau on the deck. On a sudden he (the Captain) heard a tremendous noise, as though the entire land had parted asunder. Simultaneous with the noise there was a great rush of wind, which immediately agitated the sea, and tossed the shipping to and fro ; he rushed out of the chart room, and looking over the town and across the hills he saw a sight he cannot describe. He remembers calling out to Mr. Campbell, and saying : ‘ Look ! ‘ —then an avalanche of lava was upon them. It immediately caught the town afire as it passed over it, likewise the shipping. It struck his ship with the force of a mighty hammer, and the lava rained upon the deck. Everyone, as far as he could see, sought shelter at once, but the heat was so great, and the air so suffocating, that Mr. Campbell and many of the crew, among whom was the chief mate, threw themselves in despair overboard.”

Pelée continued to erupt until 1905, producing occasional explosions with pyroclastic flows, and grew lava domes including a 300 meter high spine known as the Tower of Pelée, which later crumbled into rubble.

Pelean eruptions

The explosion that destroyed Saint Pierre and The Great Black Cloud of La Soufriere at 2 PM cannot really be classified as plinian eruptions. The two events did not involve tall eruption columns at first, instead the material travelled horizontally from the vent over the ground in the form of pyroclastic flows, or pyroclastic density current that is how they are now being called. The volume of material that is erupted within a brief span of time in the explosion is so large that can’t possibly mix with surrounding air fast enough and become buoyant, instead the heavy, dense volume sweeps over the ground at enormous speed in a devastating blast, and it is only now as it advances over the surface and mixes with atmospheric air, which becomes heated and expands, that the pyroclastic flow inflates up into a buoyant plume known as a coignimbrite cloud.

Scientists of the time understood that the two eruptions of La Soufriere and Pelée deserved to be made into a class of their own. This is when the term pelean was coined.  The eruption of Lamington in 1951 was also classified as pelean. After Lamington the term became somewhat forgotten and little used, and the type of eruptions that it had initially been created for remained little studied. Pelean was replaced with the term lateral blast, that stands for the same thing more or less, but seems to imply that the explosions come out laterally which is not true most of the times.

This is the exact way that pelean type eruptions were defined for the first time:

“Eruptions of the Pelean type are distinguished by the occurrence of one or more discharges of incandescent sand, which rush down the slopes of the mountain in the form of a hot-sand avalanche, accompanied by a great black cloud of gases charged with hot dust, which sweeps over the country with a very high velocity, mowing down everything in its path. All living beings within the zone nearest the crater are killed ; all plants reduced to charred and broken stumps. At greater distances men and animals are scorched by hot sand or mud ; plants are burnt, eroded, and stripped of leaves and branches ; but beyond the limits covered by the great black cloud no effects are produced, other than those consequent on the rain of ashes which precedes or follows the avalanche.”

This basically means eruptions with pyroclastic flows. While it is true that many types of eruptions can have them, which the authors were not aware of at the time, the 1902 eruptions of La Soufriere and Pelée do stand out for the massive scale of the flows, and the style in which they were erupted is distintive. A huge violent burst. It is similar to vulcanian explosions but much bigger. Vulcanian grades upward into pelean so it is just a spectrum between the two types.

What drives pelean eruptions? The sudden expansion of gases within the magma column or the flashing of groundwater into steam is what ejects a large amount of dense material. For this it is required that the pressure acting on the gas suddenly drops. Why this happens is not obvious in most cases. I am tempted to say that a clog seals the vent which causes magma pressure to rise in the conduit below, then when the clog is breached it explodes. In reality many volcanoes that have gone pelean were erupting just before the big blast came, so that it doesn’t look like the vent got plugged in any way, suggesting that it is more complex than this, and that such a simple reasoning would not be useful in any way.

Maar-type eruptions have a more obvious trigger. For example during the eruption of Tarawera a dyke of basalt lava intruded below Lake Rotomahana, which was a geyser field, and as the water came into contact with the magma it became superheated. When this natural, gigantic pressure cooker found a way out through the cracks, that the dyke itself was opening up, it simply blew up the whole lake in a very pelean way, and blasted away the famously beautiful Pink and White Terraces. It left behind a huge crater with a lake that was larger than before. This is called a maar crater.

Another obvious trigger is a dome collapse, or a landslide like how it happened to Saint Helens in 1980. There are suggestions that a landslide was also what started the eruption of Lamington in 1951. The lithostatic load is suddenly reduced which frees the gas to expand violently, and blows the conduit from within.

The eruption of Mount Saint Helens was closely monitored and is an insightful example. The pyroclastic flow it produced was so immense that it blasted down forests up to 20 kilometres from the volcano, which is an area far more extensive than in La Soufriere and Pelée eruptions. There are many photographs of the disaster that were taken from multiple angles around the mountain, even from a plane flying above its summit, and also the famous series of photographs taken by Gary Rosenquist from the northeast of Saint Helens.

Physical models created after the eruption together with the photographs captured during the event show how quickly the material is ejected. Saint Helens discharged 0.19 km3 of ash into the pyroclastic flow, or pyroclastic density current, that later swept northward, and this was within the span of 20 seconds This means Saint Helens reached VEI 4 in less than 20 seconds.

Mount Saint Helens erupts on May 18th. 1980. Photos from Gary Rosenquist.

VEI means Volcanic Explosivity Index, and while it is meant to measure explosivity it would still make no distinction between Saint Helens, and any other eruption that took hours or days to produce the equivalent volume, because VEI considers only the total amount of ejecta, whatever the eruption rate or style. Seems absurd doesn’t it? But it goes beyond the VEI, because the overreliance on this way of classification also reflects the aspects that we give most importance to, the total volume, and the column height, both very poor indicators of the destructive consequences that powerful brief explosions unleash. It does turn out that the vast majority of pelean eruptions are VEI 3.  The eruption of Lamington in 1951, which flattened the tropical forest over a radius of 12 kilometres around the volcano, had a volume of “only” 0.025 km3, and the same is true for the eruption of Taal in 1911 and many others. Often a pelean event reaches VEI 4 or more only when there are other stages in the eruption that produce a greater volume. The Volcanic Explosivity Index is so flawed that there are fire fountains which can be watched safely from up close, in the same VEI 3 slot as eruptions that could blast away whole cities.

Sparsely a single short explosion can have a volume of >0.1 km3, like with Mount Saint Helens, and even more rarely they may reach a much greater scale during caldera-forming eruptions. Krakatau volcano erupted in 1883 with an initial plinian stage during the afternoon of August 26.  The following morning came a series of 4 powerful explosions, I’d say pelean type, that produced massive pyroclastic flows, tsunamis, and killed 36,000 people. The largest of Krakatau’s explosions was heard 4800 kilometres away, and is estimated to have been 8 times more energetic than the blast of Saint Helens.

Pelean eruptions the most dangerous for many reasons, mainly: pyroclastic flows, lahars and tsunamis. A crater lake can be ejected into lahars during the initial explosion. The massive pyroclastic flows that ensue can generate lahars when they move over a glacier, like with Nevado del Ruiz, and can displace the water of a lake or the sea into a tsunami, like with Krakatau. Tsunamis and lahars extend the damage of the pyroclastic flows to greater distances.

The coignimbrite cloud

Initially the pyroclastic cloud is way too dense to rise so instead it flows laterally over the ground like a sheet. As it advances it mixes with external air increasing the temperature of the later, which becomes buoyant, so that the top of the flow inflates with hot air and rises in a powerful updraft, known as a coignimbrite cloud or plume. This creates an area of low pressure, drawing air inward, and often this inflow is strong enough to reach hurricane wind speeds that can deal damage on their own.

The eruption of Pinatubo in 1991 had a series of precursory eruptions before the climax, the first four of which were plinian, which were followed by thirteen pelean explosions with shockwaves and giant pyroclastic flows. The following image shows the coignimbrite cloud of one of the explosions, 8 hours before the climax. The line of mountains is 1 kilometre tall as a reference. The photo was taken only 6 minutes after the eruption started, which shows how fast the pyroclastic flows and coignimbrite cloud grow.

From USGS.

The shockwaves allowed the precursory explosions of Pinatubo to be identified. Pelean erutions make powerful shockwaves. This is why measuring the infrasound waves generated by volcanic eruptions might be the only way to accurately detect the individual pelean explosions, which otherwise are very sneaky, they happen quickly, often shrouded in the darkness of ashfall, and moving very close to the ground, as shown by people that were caught in the edges of Saint Helens’ pyroclastic flow, who often didn’t see it coming until it was upon them because it would be hidden behind trees or hills. The coignimbrite cloud then shoots upwards from the pyroclastic flow and would be detected by planes or satellites, but even then it can’t be distinguished from a typical plinian column unless you have a visual of the broad base, which probably isn’t the case.

Conclusions

There is too much attention being paid to the plinian style, a sustained jet of pyroclasts, gas, and hot entrained air that rises up into the air into a lofty umbrella. The VEI is appropriate to measure the impact of a plinian eruption in such aspects like aviation or climate. However pelean explosions, also known as lateral blasts, are far more dangerous to the immediate surroundings of the volcano, as well as very important to understand how volcanoes work, and to how ignimbrite deposits are formed, so should be given as much attention as plinian and the VEI doesn’t rank them properly.

Pelean explosions are brief but powerful and they may occur isolated, intercalated in plinian or phreatomagmatic eruptions, or at the onset or the end. They generate massive pyroclastic flows that will most living beings in their path, so the area should have been evacuated by the time they happen or else the loss of life can be terrible. And lets hope that no large city is ever found in the path of a large pelean blast, again.

Further links

History of La Soufriere and Pelée eruptions in 1902, definition of the pelean term, by Tempest Anderson and John S. Flett.

Gallery of photographs showing the ruins of Saint Pierre after the 1902 eruption of Mount Pelée.

Some photographs of Mount Saint Helens, including the devastating blast of May 18th, 1980. 

Another photo of the blast, Mount Saint Helens.

 

514 thoughts on “Pelean eruptions – the catastrophe of 1902 in the Lesser Antilles.

  1. Looks like I beat the post to the new article!

    Including Mnt St Helens, the eruption which marks the start of my romance, which still continues to pressent…

  2. And lets hope that no large city is ever found in the path of a large pelean blast, again.

    Managua chuckles, ‘I’m in danger.’

  3. That’s a scary article, Héctor. Scary in the consequences of these blasts. Thanks for such an eloquent and fascinating description!

  4. I expect some of these result from eruption through water, e.g. a crater lake. Before the eruption starts, the floor of the crater separates the water from magma; there’s no vent yet. When it does start, a vulcanian to plinian eruption column, or even a lava fountain, punches through the water and then holds it back with its own pressure. But when this weakens sufficiently, water that is no longer held back can drain down into the vent. Water lower down becomes superheated, weighed down by the water higher up behind it, until the superheating gets high enough (convection will readily transport the heat upward within the water) or water ceases arriving from above, and then kablam. This mechanism is likely responsible for the 1902 event in St. Vincent, and (occurring not once, but four times) for Krakatau’s violent climax, as well as the 1790 “footprints ash” eruption at Kilauea — thus showing that even normally-effusive basaltic volcanoes are not immune, if they have developed crater lakes.

    A sudden removal of overburden, as at St. Helens, likely accounts for most of the remaining instances, and all explosive caldera-forming events, including VEI-8 supereruptions. When the roof tips down or breaks up and its cold, dense rock sinks into the magma chamber, so long overburden pressure and hello violent degassing on a monstrous scale.

    Every one of these scenarios is some species of scaled up boiler explosion, with either the magma’s volatiles or externally-supplied water providing the steam.

    • I do think water plays a very important role in some pelean explosions. The best evidence is that some powerful blasts from basaltic volcanoes, like Fernandina in 1968, Taal in 1911 or Kilauea in 1790, eject mostly pulverized old rock, with very little fresh magma, showing that external water flashing expanding into steam and not magmatic gasses drives the force of the explosion.

      Regarding caldera collapse events, these usually enter an ignimbrite phase which is very violent and probably involves huge explosions like those of Krakatau. One possible mechanism that might start the explosion is the piston collapse of the roof. Piston collapse will increase the pressure acting on the magma chamber but it will do the opposite on any magma that is intruded in the ring fault, because one side falls down the weight of the rock from this side on the magma will be reduced. Additionally the magma in the ring fault will be pushed upwards by the sudden increased pressure in the magma chamber and combined with the decrease in lithostatic load, the magma may suddenly decompress and explode.

      • In Krakatau, the first explosions were on land, and involved the eruption sites there. But the final and largest (by far) explosion happened off the island. We know this because the tephra rain from this was wet (from undersea mud) while all previous ash falls had been dry. It seems to me that the final explosion was driven by a flank collapse on the west side of the island. This doesn’t say how exactly it occured. A collapse may have opened the magma chamber to water, or the removal of the bulk of the island caused the decompression. Roof piston collapse feels less likely in this case than flank collapse. But obviously we do not really know. It is a pity that in the weeks before the big eruption, no one had a chance to inspect the west side of the island.

    • I imagine when Crater Lake in Oregon had its cataclysmic eruption it likely had pelean explosive episodes. Glad it happened thousands of years ago, and not today.

  5. I just determine that Furnas is one of Europes most dangerous volcanoes

    Furnas in Azores is an potentialy extremely dangerous volcano. It Maybe a sleepy and tired and very stale volcanic system, 1440 persons stil live in this caldera, thousands of persons visit every week. Furnas is capable of infrequent large VEI 5 s plinians and much larger. It generaly produces gassy stale trachyte magmas. But Furnas is indeed a very stale magma system with very low productivty.

    With a small magma supply, it means that eruptions are very rarely infrequent and large amounts of magma can accumulate over many thousands of years. The Pleistocene pyroclastic events there where quite big indeed

    So big old stale magma reservoirs are able to form under the calderas. So the eruptions can sometimes be really big plinian and other types of pyroclastic events.

    The year small VEI 5 1630 Subplinian killed over 200 persons. The entire arera was showered by trachyte pumice and pyroclastic currents spreading in the valleys. Furnas eruptions are very rare, but if something happens, it will be dangerous. ”Invisible” volcanoes like these are often the most hazardus. Saõ Miguel is not very productive in volcanic materials, its on a superslow transform fault spreading, and partial melting is small. But the volcanoes gets full of gassy old stale magmas, and haves huge explosive eruptions sometimes. Both Furnas, Sete Cidades and Auga De Pau volcanoes are dangerous

    • Its the stale and ”invisible” and
      populated calderas that are the most dangerous volcanoes

      Campi Flegeri tops to list as most dangerous in Europe …

      Furnas is hiding itself as a inviting Subtropical Valley depression

      • there should be some law to not build towns near volcanoes, unless you are 1000% it’s extint

      • Campi Flegeri, Taupo and Furnas are good example of populations living in areras in risk of pyroclastic events.

        Furnas is specialy dangerous since there is
        No good fast escape as well as in Flegeri

        Pyroclastic events specialy a groundhugging boilover type woud be catastrophic in these areras. Even a small peleean event woud be a mess indeed. But the historical settlers did not knew any volcanology

        • The Marsili shouldn’t be underestimated either as its collapse would lead to a giant tsunami, and because of Etna, the Aeolian Islands, Vesuvius and Campi Flegrei it is a bit neglected.

      • What is latest news on Flegrei? Most news is in Italian and I hate google translate.

      • human nature is such as to ignore it, like it won’t happen in my life time or a volcano here, I cant see it, so it doesn’t exist

    • A Pelean eruption in Furnas or Sete Cidades woud be absoutley terrfying!
      Everyone in the calderas are trapped But luckly modern montoring systems exist .. in chase of activity

      • Campi Flegrei often goes for pelean too, its eruptions are almost always maar-type which gives powerful steam blasts with extensive pyroclastic flows and tsunamis. It is very dangerous to Naples, even when it goes off small.

    • The 1630 eruption is written as it was a real disaster “year of the ashtray” “total devstation” “valley made unlivable for a few years” and it was one of the largest post – glacial holocene eruptions of SaO Miguel. So it was almost certainly a very powerful eruption … with 200 persons killed it was perhaps a ground hugging boilover PDC when the eruption started … that later evolved into a plinian eruption phase. In holocene its been around 11 trachyte pyroclastic phases in the caldera… so about every 1000 years Furnas erupts. Then an eruption is not likley for many 100 s of years to come

      • There were 2 or 3 VEI5 eruptions in Sao Miguel, Azores, within a highly active volcanic period of 200 years, one around 1444 (Sete Cidades), 1563 (Agua de Pau) and one in 1630 (Furnas). They were close to each other in the same island.

        GVP assigns VEI5 to the latter two eruptions. In the first eruption, the reports are of a blown up tall mountain giving way to a large caldera. Historical reports are in Portuguese. It is consistent with a VEI5 eruption although GVP ranks that one at VEI4.

        Some centuries earlier there is evidence for other big ones. Azores, like Reykjanes, could follow also a cycle of volcanic activity.

  6. A further note on the wet-vent mechanism: once the explosion and renewed volcanic activity weakens sufficiently again, if there is water remaining near the vent it will happen again. This will continue until either the water or the magma is depleted. In the crater-lake case, the volume of the crater lake is likely to be the limiting factor. All of it probably went in the first 1902 blast at St. Vincent. But if an island volcano opens a vent below sea level it’s Katie bar the door. The limiting reactant will be the magma this time. Surtsey, being newborn, had no magma chamber so it produced a few explosions of moderate size and then became effusive once the debris from these had raised the vent above sea level. Krakatau was less fortunate, and so it went caldera: all of its magma chamber contents were converted into ejecta, mostly pyroclastic flows, until nothing remained and the edifice collapsed into the resulting void. Thera most likely suffered the same fate, taking the Minoan civilization with it when it went. So, if an island volcano opens a vent below sea level it’s finito. What might otherwise have been a moderate VEI4 or 5 vulcanian or plinian eruption becomes a massive caldera-forming VEI6 or 7 event and the edifice is no more.

    Lost overburden pressure seems to have the same result if it allows the top of the magma chamber itself to start to degas: the magma chamber will now be so buoyant that the whole of it gets barfed out of the hole, and then the mountain falls in. Goodbye St. Helens.

    • Iwo Jima is very very scary. It has the capability to do a VE7. If it does a summit eruption, it could top out below that, such as VEI4; if it does go all the way to VEI7, expect everything on the island to be obliterated and expect major climate impacts ala 1816. The mountaintop will be gone; it will look like an island St. Helens. It will basically be Tambora all over again.

      If it does a flank eruption that opens a vent below the waterline, on the other hand, it’s pretty much guaranteed to reach VEI7 and the island itself will be reduced to a broken ring of rocks resembling Santorini. Other nearby islands may be devastated by pyroclastic flows and the tsunamis will clobber mainland Japan as well. And, again, the climate effects. Tambora-sized but Krakatau-type event.

  7. Thank you Hector for this excellent article.

    The pictures from St. Vincent show quite a lot of destruction and it is not finished yet.

    I do have a question though: the current eruption of St. Vincent has rather light colored ash. Is this often the case?
    You mention black ash.

    • Thanks!

      I mention black as the colour of the eruption cloud during the initial crater lake explosions of La Soufriere. The cloud is black, from the mud, and white, from the steam, typical of phreatomagmatic/surtseyan activity where the magma erupts through water.

      But when the ash settles in the ground, in silicic magmas, it is white or grey depending on how much bubbles the rock contains, white usually meaning more bubbles and that the magma rose faster.

  8. just saw an idiot actually get up on the lava on cam K100. and they did it twice… looks alone. Don’t You have to be helicoptered in there now??

    • and You don’t have to fall into a “burning ring of fire” to get hurt….. just breaking thu can give You a nasty infected cut. Like shattered glass.

  9. Great piece, well written. 29.000 people died in St. Pierre (nearly 100%).

    • Thanks!

      It would be very hard to escape alive from Saint Pierre. Many people were probably buried under the collapsing buildings, others would have died from burning or asphyxiation due to the pyroclastic flow, and those who still survived would have been caught in the firestorm that ensued. Some sources cite as little as 1-2 survivors, although this doesn’t seem to be entirely clear.

      It is usually estimated that 28,000 people died in Saint Pierre on May 8, while 1,000 people died in Morne Rouge during another eruption on August 30. I don’t know much about the later event so I didn’t write about it.

      • Clive Oppenheimer writes in his book “Volcanoes that shook the World” that 29.000 died corresponding to 99,997%, so I took the number from there. He further mentions that one person survived because he was in prison. It must have been a good prison 😉

  10. Héctor, we need to find the scientific paper that a woman scientist did on explosive eruptions of the Caribbean. I had read the paper once, but did not archive it, and when I try to find it today, it seems inaccessible.

    Basically there was a powerful explosion from the volcano on (I believe it was) Montserrat which was totally unexpected, but her hypothesis was that there was a certain type of volcanic magma mixing which took place and the lower basaltic lava empowered the rhyolite to cut loose in an enormous gas decompression event, similar to the large explosion of La Soufriere that you write about.

    It would be a good thing to track that paper down and have it posted.

    While steam is very powerful and we can see Anak Krakatoa after the slide in Dec 2018 erupting enormous phreatic clouds with much lightning, due to sea water interaction there is a trigger which gets pulled to start this activity.

    I also did come across this interesting paper https://www.lanl.gov/orgs/ees/geodynamics/Wohletz/LaSoufriere.pdf titled “Phreatic Eruption Clouds: the Activity of La Soufriere de Guadeloupe, F.W.I., August – October, 1976” which is another Carribean volcano. It suggests heating started vaporization which then drove the pelean eruptions.

    Finally, thank you for a very insightful article. I guess if you are on a Caribbean Island and some ground starts pushing up, it is time to find another island.

    • I am reporting that volcano for having a dodgy catalytic converter, £200 fine, 3 points on licence!
      It is interesting that there is no background pollution just the volcano, must be a pretty strong mix.

    • They ran out of solar. It’s been cloudy the past few days. They are going to fill up on power today if gas pollution permits.

      • Basically their solar panel size and/or battery size is not adequate for the conditions and should be increased.

        • Perhaps every tourist taking a selfie in front of the camera should be charged for the privilege, by connecting their phone to the solar panels to charge up the panels..

  11. https://www.opentopomap.org/#map=15/63.88342/-22.26246

    I hope this link works as it should show an interesting map conflicting with most of the others I have seen for the Fagradafsfjall eruption. If you follow the 190m contour line East of Geldingadalir it closes off to the North but doesn’t to the South. This would mean the pass to the North is over190m but to the South it’s under?

    If the map is to be believed then the lava when it exits Geldingadalir would be considerably more likely to flow South rather than North into Meradalir as it is the lower exit point.

    Also the height of the rim of the hollow is higher in other maps I have seen. The most common estimates I have seen is the rim at 200m high exiting North and 202m exiting South.

    • resolution may be different between different maps. If I read this one correctly, it has the current exit from the valley at the right place, with the flow bifurcating after the exit, one part going south into the pond but no further and the other north. If the eruption continues at a decent rate, it should now or soon be flowing into Meraldalir. There is no camera covering that area, sadly

      • You are right the 3D model from 21st April does show a small flow from the top of the hill into Meraldalir which I am sure will have been added to since then.

        Based on the map I posted though surprisingly the N exit is higher than the S, something I had not seen before, so once the hollow to the south fills it is more likely to continue on its way south into Natthagi.

        Other maps I have seen suggest that the N exit is lower than the S which should lead to a flow back N into Meraldalir.

        Thanks for the feedback and belated Happy Birthday.

        • I think a lot of it is down to very subtle differences at a level of detail that none of the maps show. That has probably pushed the flow more to the north due to differences of a couple of metres or so, partly due to where the flows have exited the vents. This then pushes it into hollows that make it harder to turhn back south. If the flows change slightly though, then it could start to run south more preferentially.

      • So glad that others are seeing a similar topography which I thought was a distinct possibility weeks ago… 😉

    • do not forget that the elevation in the pass is around 200m, so it is dependent on the angle of the flow coming through the gap if it would run north into Meradalir or towards the south. Then there is the question of distance, the current flow rate has a range limit of about 1 – 1.5km before the lava becomes too heavy for the craters to keep pushing on it.

  12. Another fascinating and insightful account, thank you Hector.

    I’m a long time lurker with no academic experience in the fields of volcanology or geology – but I wondered whether the dissatisfaction that I read here with the VEI scale is reflected across the discipline? If so, is there a case for another scale to be developed, potentially along the lines of the Enhanced Fujita scale measuring destructive force as opposed to mere ejecta and debate rock equivalent?

    • And autocorrect seems to have replaced “dense” with “debate”. You know what I meant…

    • Thanks!

      I think that creating an alternative scale that measures peak ejection rates or the size of individual explosions, for example from measuring the shockwave it generates, could prove very useful to rank how destruction that it can cause to the surroundings of the volcano, and also to distinguish properly between pelean and plinian styles.

      Maybe not to replace the VEI scale but rather to work alongside it, while VEI measures the overall size and some distal effects, the other scale measures the intensity and the proximal hazards.

      • We may even need two scales.

        One: VII, Volcanic Intensity Index. Suitably shifted and scaled logarithm of peak ejection rate. Applicable to any eruption type, including rootless maars, as any ejected material, whether fresh or preexisting rock, will count. St. Helens would be huge on this scale, having ejected 0.1km^3 in the first less than a minute. The Skaftar Fires would exceed Holuhraun and Leilani, which would exceed Fagradalsfall and Pu’u O’o. Mauna Loa 1950 might exceed any of those, and rival St. Helens.

        Two: VDI, Volcanic Destructivity Index. 4x the logarithm of estimated minimum safe distance to avoid being directly killed by the volcano, if on higher ground (so lahars could extend further than this along river valleys). So a VDI 8 will kill nearly everything within 100 km, about commensurate with estimated lethality of a VEI 8. St. Helens would be a VDI 7 though, despite only being a VEI 5. You could be over 60km from it and if it was in the north direction still get clobbered with very little warning, and even on a ridge top. The eruptions that are the focus of the article would be VDI 6s, nearly as bad, and also with quite high VIIs. The two part ways for effusive eruptions, as high ground a km or so from the worst Skaftar vent would have been relatively safe, giving that one a VDI of one or two despite the huge VII.

        Anyone want to go propose this through whatever the proper channels are, which I a) don’t know and b) likely lack any access to, whilst also having words with RUV about their terrible QoS? They could obviously stand to learn some things from mbl, whose cam has been far more reliable of late than either of RUV’s.

        • That is an interesting discussion. Although the 1950 eruption of Mauna Loa I think is getting overly hyped up, the peak eruption rates of Saint Helens must have been 10,000 times or so higher than Mauna Loa, there is a huge leap in between the intensity of lava flow eruptions and explosive eruptions. This is in part because lava flows are only formed slowly, even if fluid magmas came out very fast it would explode and make an spatter ignimbrite.

          It is true that lava flows with the highest effusion rates, 5000 m3/s for Nyiragongo, are the ones that can potentially overrun people. Intensity is a good proxy for how dangerous an eruption is, although for a full hazard estimate external factors that do not depend on the eruption characteristics are also important, like the steepness of the slopes, how much people live nearby and the presence of glaciers or bodies of water that might become lahars or tsunamis.

          • Mauna Loa 1950 woud be extremely scary If you where on the upper slopes. The initial opening is as close as we can get to IO on Earth.
            You woud have a hard time to escape from the raging fountain Aa sheet flows

          • Im sure you have information on this but the Mauna Loa 1950 eruption was very intense, probably a lot more than Nyiragongo in any of its eruptions even. I read the original report from HVO in 1950 that says the fissure, all 22 km of it, opened within the first 2 hours of the eruption, and it was erupting on its entire length for about 3 hours with fountain heights ranging from 50 to as high as 200 meters. The full half of the fissure at highest elevation was entirely in that first 6 hour period. Probably at least half the total volume was erupted in that first night.

            For an eruption as violent as St Helens I dont even think it counts as an actual eruption rate anymore, that requires a vent to erupt the magma, but in this case the entire mountain and the magma body inside it just blew up, its really a whole other beast entirely. The plinian stage afterwards can be calculated but is probably pretty unremarkable, most of the volume was the lateral blast.

          • I don’t think there is any estimate on the peak eruption rates of Mauna Los’s but I doubt it is as high a Nyiragongo. If a 8 km row of lava fountains at Krafla is ~800 m3/s, then a 22 km row of lava fountains at Mauna Loa might be ~2000 m3/s? This is a guess.

            Mauna Loa did have an impressive eruption that was Nyiragongo-type in 1877, it erupted 0.5 km3 in less than a day offshore, can’t remember how long exactly. I think it was a catastrophic draining of a large lava lake that had been growing inside the 1868 caldera of Mauna Loa, I was planning to investigate and make a post about it at some point. Kilauea has also had some Nyiragongo-type lava lake drainings.

          • The eruptive speed eruption rate of St Helens peleean blast in the first secondsaafter the landslide must have been Impressive

            But very short lived.. thats what Hector is trying to say

            Mauna Loa 1950 was a mini Laki

          • 1877 was very fast yes, I think HVO said it lasted longer than a day based on morphology of the vents but it was very fast for an eruption of such volume. Its really very lucky it didnt happen just inland or in shallow water, that area was and still is populated and theres reports of glowing cracks on land, this would have been like a lava tsunami… Theres also two small fissures with the right orientation close to Mokuaweoweo, they arent dated but might be from 1877 too.

            HVO has 1950 at 2500 m3/s, but that might be for the flow that reached the ocean in 3 hours where the source fissure was active for about 7 hours at large volume, and for much longer near the southern end. The upper part erupted a flow to the east that is just as long as the flows which reached the ocean and was active for only 3 hours. I hope HVO releases the updated map of that area soon 🙂

            Would guess the 1823 eruption is what you are referring to for Kilauea, as well as 1840. Really makes you wonder, the current activity at Kilauea is much like the early 19th century, an eruption like one if these could happen in the near future.

          • I think that the 1877 eruption of Mauna Loa started very early in the morning, then later that same day it was already over and the glow from the top of Mauna Loa gone, the glow from the lava lake, presumably the draining complete. I would need to read more about that particular event although I imagine there is not much information.

            It would be quite dangerous for an eruption like 1877 to happen subaerially in Hawaii. luckily it seems to be something extremely rare. The Keaiwa flow of Kilauea is the only subaerial example that I know, it lacks any sort of spatter cones, pumice or any kind of ejecta, like the upper fissures of Nyiragongo in 2002 and 1977, shows the lava was degassed and drained directly from the summit lava lake. The Upper Kealaalea flow, formed sometime 1790-1823, too, but it erupted from the same height as the summit lava lake so that it was a slow small event. I have searched for other fissures that completely lack spatter ramparts in Hawaii, but there are none that I could find, which makes me think that whenever a catastrophic lava lake draining happens it finds its way into the sea.

          • I have wondered also if the north flank of Kilauea could be prone to these events too, the area of Volcano Village and Fern Forest. This would be the continuation of the Kilauea Iki dyke swarm away from the summit. In 1832 Kilauea cracked multiple kilometres eastwards in this direction, it wasn’t specified exactly how long. But this would only be a concern if the lava lake that right now exists on the summit of Kilauea would continue to grow for years, as of now it is too small, and even if it drains at some point it will probably be slowly back into the magma chamber because of the East Rift undergoing some eruption or intrusion.

          • I didnt know that there was an actual rift zone east of Kilauea Iki in 1832, I thought it was a part of the summit complex with rifting mostly being at the southern edge of the caldera, the outer caldera fault is about where the east edge of Kilauea Iki is.
            Directly east north east of Kilauea Iki though does go on the same axis as the southwest rift, and the south ring fault/Keanakako’i area does sort of merge a ring fault and a rift zone mechanic that also follows this axis, like a single long fissure swarm from Kamakaia hills to beyond Kilauea Iki, parallel to the one from Halemaumau. Will be very interesting when the caldera fills more, which at base supply rate will not take that long at all.

          • I had this idea for quite a while now, might be a bit different to yours and its also not very good on small scales, but I think this is close enough, the fissure swarms on Kilauea.

            https://imgur.com/a/Kt5ngiT

          • I do have quite a similar map! Although there are differences of course too. Circles are the location of magma chambers that feed dyke intrusions.

            Some of the fissure swarms have been active many times historically, while some of the others have had very little or no activity and it is up to guessing where do they start and their exact paths…

            Here it is for comparison:

          • And we both chose red for Halema’uma’u, of course! 🙂

          • Thinking again about Nyiragongo-type eruptions, it is interesting that they often make characteristic trenches and wide cracks, sometimes 20 meters wide or more, which I call great cracks after the one of 1823-32. A great crack forms when the lava flowing at shallow depths carves out a subterranean canyon through thermal erosion and then its roof collapses.

            Mauna Loa doesn’t have any great cracks except for a small feature on the southwest side of Mokuaweoweo.

            Kilauea instead has a lot of great cracks. A bunch of them can be seen leaving the southwest corner of the caldera, near Crater Rim Drive, and then travelling down the southwest rift, some of them beyond the coast probably although they are intermittent features that only show up in those places where the roof collapsed. So Nyiragongo-type lava lake drainings are probably very common down the southwest rift and originating from the Halema’uma’u area.

            There are two parallel great cracks that run down the Middle East Rift Zone, and probably discharged somewhere in Lower Puna. One of them can be traced up to the lip of Napau Crater, the crater was probably filled at some point will lava up to the brim and then drained catastrophically downrift, perhaps engulfing rather violently some lands populated by native hawaiians downslope. The other Great Crack may come from Napau Crater all the same. They are best seen in historical images because Pu’u’o’o has buried much of the place:

            https://uhmagis.maps.arcgis.com/apps/webappviewer/index.html?id=f6672e31727d49468a37b7bb3ab77d77

            One of the cracks though has survived many historic eruptions, swallowing up magma and never filling up. The Kamoamoa eruption among others sent huge cascades of lava into the Napau crack that disappeared into the darkness and still today it stands there, ready to take on the next eruption.

          • Lava canyons is a name that would suit them too.

          • The base map actually has topography of Pu’u O’o 🙂

            https://imgur.com/a/KZwBBCK

            I dont know if this is what you mean but this is a massive lava flow, if it was a lava lake draining event even more so, a lava flood for sure… It is a shame that no official maps actually show these older flows properly, they are all very young, part of the flow in the picture (yellow dot) is only from the early or mid 18th century although I cant find the exact source I read that from.

          • Actually I did think about that there was a lot of slow lava lake activity at Mauna Loa after 1868 as you say, apparently several eruptions but it looks likely it was a continuous lava lake with overflows of varying intensity, although it also could have been secondary fissures opening too with fountaining and faster flows. Then in 1877 it all drains out, and eruptions on the rift become common again.

            This all sounds very similar to the situation we are in now, a caldera has formed at Kilauea in 2018, it is now filling in with a lava lake and it is filling as a single unit instead of as a lava shield. It took 9 years at Mauna Loa for that lava lake to eventually drain, so we might be a while off from something like that at Kilauea now but its interesting. That sort of timescale is long enough for the 2018 caldera to fill up, so it might get to that point very quickly and then drain out.

          • Yes, it is those 2 fracture systems that I was talking about, they continue down to just north of Heiheiahulu, although it not entirely clear if it’s the same two or not. I had assumed they probably erupted below, in the LERZ, but I don’t know that, maybe the flows that you outlined did come from the lava lake in Napau that drained, there wouldn’t be much of an altitude difference then.

          • Might not have just been an overflow from Napau, there could have been a proper eruption derived from the deeper system that opened a fissure through that area with a curtain of fire eruption, that then also acted as a drain for said lava lake.

            Also (probably most likely) it was a number of eruptions, though it does look like the pahoehoe surface goes quite far downslope before turning to a’a on the pali which is indicative of a high effusion rate. There were villages along that area back then, and the flows underlyign are a lot older around 1000 years or so from Kanenuiohamo shield, must have been pretty scary to see a lava flow rush down. The episode 48 a flow that went down this exact path flowed as fast as walking speed.

          • I was taking inspiration from the draining of Alae crater in 1969, the volume of Alae is negligible compared to the volume that Napau would be able to store up, but the process is similar. Alae opened the rift up all on its own with no help from below, it drained at 5500 m3/s and thermally excavated a “canyon” 10 meters wide and several tens of meters deep, and this happened in only 30 minutes.

            The lava was not able to erupt immediately because the Alae Crater rapidly run out of lava so just a little oozed out later some distance downrift. In the past Napau Crater may have held a much more substantial volume of lava, up to ~200 million cubic meters, that could easily send a dyke several kilometres downrift and still produce a largish eruption. Of course a lot of this is speculative, it may not have taken place the same way.

          • I guess that means there would have been some sort of eruption at or near Napau, maybe not like Mauna Ulu but probably something that would have been recalled in a story, especially if it made a lava lake which would have glowed bright at night during foundering, as the modern one did back in December.

            Looks very much like the lake now is destined to drain too in this manner, if it reaches the lowest ledge it will have a volume of about 0.1 km3, if it reaches the big downdropped block it will be well over double that, and bigger than your hypothesised Napau lava lake, and the ones in the early 19th century. 0.3 km3 is a massive volume of liquid lava to have sitting at a high elevation.

            One can only imagine the biblical lava flood that would result if the entire 2018 caldera was to fill with a single lava lake, nearly 1 km3, that is the effusive version of a lateral blast…

          • Unless it doesn’t drain, or it recedes slowly back into the magma chamber due to an eruption in the East Rift lowering the pressure. We will see, any of the possibilities seem just as likely right now.

          • I think any situation where the 2018 caldera actually ends up filled to the brim with a lava lake will end in a massive lava flow, be it a lava flood or a repeat of 2018. The fact this could happen within a few years potentially… HVO is going to be busy, between this and Mauna Loa waking up.

  13. Yes finally an article on why the VEI scale isnt perfect 🙂

    Way too much focus is placed on volume when that is only important for really big scales, like climate effects. The real killer and thing most people actually think of is the intensity, but it gets merged into volume for some reason by even a lot of volcanologists talking about the subject let alone anyone else.

    That is why there is the never ending metric of Hawaiian eruptions being small and St Helens being just a firecracker. Mauna Loa in 1950 I found had a higher effusion rate on its first day than literally every single eruption of any sort in the 21st century with the exception of Kelud in 2014, and that is without conversion of the volume to tephra for a fair comparison. All of the 20 km long fissure was actually open at the same time for a few hours and opened within 2 hours of the eruption beginning, before any of the lava flows had reached the ocean even. 20 km long and almost 100 meter high curtain of fire… 🙂

    Im also one to say that I have always though St Helens was vastly underestimated in its magnitude by placing it as the little volcano next to Krakatau or Pinatubo, it was only a VEI 5 because the mountain itself was not big enough in volume to do anything larger. A whole mountain gone in seconds, if it was not caught on camera no way anyone would seriously consider such a violent eruption to be possible.

    • The VEI scale is an explosive energy scale. It has long been recognized that a small volcano in the wrong place can do much more damaga than a large one far from anyone.

      • Yes but it isnt presented that way, even by a lot of volcanologists. Its just ‘1 small 8 big’, more or less.

        The VEI scale really needs to be measured based on the magnitude of the explosions, not the volume. Maar craters are small mafic eruptions usually that would be a tiny harmless lava flow in a dry area, but the biggest maar craters are as big as small calderas, we have set off a 5 megaton nuke underground (Cannikin) and it didnt escape, that says enough about the colossal power of eruptions like this, yet this is only a VEI 3.

          • A VEI 6 is really big indeed, and they are highly dangerous almost always, even so there are some differences in how hazardous there are that the VEI doesnt consider.

            For example the Masaya Tuff and the 1932 eruption of Quizapú are equivalent in VEI, they are ~10 km3 borderline VEI 5-6 events, but they are completely different in their destruction capabilities.

            The Quizapú eruption was almost fully plinian and did not produce any sizable pyroclastic flows anyone watching from a few kilometres upwind would have probably been fine and enjoying the show.

            The Masaya Tuff instead sent pyroclastic flows reaching a distance of up to 40 kilometres, most people ~10-40 kms around the vent would be scorched to death and the forests blown to muddy broken stumps.

  14. well that was fun… watched the cone from one of the youngest vent destroy it’self over a couple of hours… from the K100 cam. It’s almost 1:30..am… in alaska… must to bed… bleary eyed but more fun than a night out. 🙂

  15. This thread brought back memories.

    Back in the 1980s I was a member of the Association of Speakers Clubs (what used to be known as ‘Toastmasters International’), and one year, I was our area’s representative in the semi-final of the National Speech Contest. I gave a ‘Word-pictures’ (descriptive narrative) speech entitled “Out Of The Lungs Of Hell” about the 1902 Pelée eruption, as told from the viewpoint of Ludger Sylbaris, one of the few survivors out of the 30,000 or so killed in Saint-Pierre.

    It didn’t win, but I was at an unfair disadvantage. The winner was Welsh (with a wonderful lilting accent).

  16. Thank you for the insight Hector. A good read.

    The last ~12 hours La Soufriere seems to be smoking or steaming(?) visibly in sat imaging towards west wo. any indication of SO2 in it (windy). Probably at very low altitude. The was one small puff to ~1 km altitude at ~05.50 UTC but the thin line of white? smoke has been visible on GOES-16 ABI for quite some hours.

    Could this be steam? And has anyone noticed this before during the eruption?

    • So magma is becoming more alkaline? That is very strange, usually the opposite happens. Its going from tholeiite basalt to high Ti basalt. That is the magma that is erupted at Katla, its similar to Etna basalt and a bit more viscous than tholeiite, so the future eruptions at Fagradalsfjall could be more strombolian in character, or possibly intermitent high fountains like at Etna or Pu’u O’o. To have that at the same time as the normal Reykjanes cycle, where you get lava flood eruptions at the other volcanoes, and all right outside Reykjavik, that would be quite a sight 🙂

      Is there any information on the temperature?

      • Note that alkaline lavas can also be very fluid, see Nyiragongo. An increase in alkalinity doesn’t mean higher viscosity. All the lavas of Reykjanes are quite fluid from what I’ve seen, noticeably more fluid than those of Katla, or even Grimsvötn.

        High fountains would require magma to rise rapidly through wide open conduits, this isn’t the case here where the eruption rate is very low, it can’t accelerate to the speeds it needs to decompress fast and carry gas from great depth.

        • Viscosity of alkaline magma seems to change a lot with temperature, Nyiragongo is also very hot around 1200 C. That is why I am curious on the temperature, if it is still 1220 C like before or if it is now lower.

          You can get episodic high fountains if magma can accumulate somewhere, Pu’u O’o was very high fountains fed by a magma supply much lower than its eruption rate, its like a geyser. Fagradalsfjall is a hyaloclastite mountain that is basically a massive gravel pile, so it should be pretty easy for magma to spread at a shallow depth and make a shallow magma chamber, something that could allow for this geyser-like activity.

        • Fagradalshraun is a hot eruption.. almost 1220 C so close to liquidius temperature
          Yet quite close to the vents the pahoehoes haves troubles of forming smooth shiney flows outside the fluid lava lakes.. The pahoehoe seems fluid… yet it seems to have diffuclity to form really smooth flows outside vent lava lakes and channels…
          Its incredible.. that at over 1200 C and its still quite not yet as fluid as Hawaii

          But it coud be that this lava is so rich in olivine microlites that it adds some viscosity
          At full liquidus temperature…things get super smooth

          • And Puu Oo at 1160 C measured inside pahoehoe toes and tubes was superfluid and alumimum smooth! … yet cooler… than Holuhraun and Fagradalsfjall!
            There is something extremely smooth and unique about Hawaii even when its at below 1200 C.

            But a few weeks ago Fagradalshraun did look as fluid as Hawaii in its lava ponds

          • I would guess its because Hawaii actually is the volcano, where in Iceland the volcanoes form inside crust that was already there, like a continent except its still mostly basalt. Bardarbunga is probably the most extensive volcano on earth by the size of the fissure swarm but the actual volume of the central volcanoes is not very big at all compared to Hawaii, maybe 1000 km3 for all of them combined, maybe more if Tungnafellsjokull volcano is actually an older central volcano on the same system instead of its own thing, which is what I think is the case, but its still total way less than any Hawaiian volcano.

            I would guess there is a lot of deep olivine crystal mush, millions of years worth of it, sitting there, Mg fractioned to the point that it just cant melt into the lava anymore and so it makes it look more rough from the crystals, though the melt is as fluid as it is in Hawaii.
            Hawaii I also suspect is probably a much more powerful source of heat than Iceland. If there are crystals recording 1300-1400 C temperatures that were actually erupted in Hawaii in 2018 then there must be magma at that temperature not that far below the surface, shallow enough to be involved in eruptions even if the lava doesnt actually erupt at that temperature. In this case it is probably in the deeper summit system, which is only 5 km down or so, very shallow to find magma at such a high temperature.

          • Not so fast… there are many.. beautyful superfluid pahoehoe examples in Iceland… Reykjanes is acually full of Hawaiian fine pahoehoe with small breakouts and delicate toes… The large Icelandic Shields contains some of the most beautyful pahoehoe lava on the planet.

          • That video is pretty old now, it was back before fissure 2 died and fissure 3 was still small, fissure 4-7 hadn’t opened yet. These little flows came from 3 it looks like.

            Seems something to do with lava tubes, theres no proper lava tubes in the eruption so far and it might be those never form if the vents arent stable, so longer flows will be channels that form a’a.

        • Nyiragongo is really low viscosity because its a rare example of a low sillica alkaline melt thats also really hot. Nyiragongo is quite hot as chad say…around 1180 C and that togther with 36% sillica makes it very fluid… But Thoelitic melts like Kilauea 1959 and Wolf 2015 maybe just as low in viscosity..

          Most other alkaline melts and Nephelinites erupts quite cool and crystal rich

      • Alkaine magmas have alot of K2O plus most important Na2O) relative to silica (SiO2).
        Na2O content of Fagradalshraun is low. The increasing Ti content suggest this stuff is getting extremely primitve… high Ti thoelitic/ picritic basalts are stuff of hadean … like the early moon basalts. If we are lucky… Fagradalshraun may produce lunar like ancient looking maare lavas.
        Still a quite to go in temperature… to reach the 1400 C moto oil fluid like Moon maare lavas… and that wont happen here.

        Whats the Na2O content of Fagradalshraun?

    • LG,

      Skimming through your twitter link, I saw a short video of someone sampling the lava with a plain, run-of-the-mill, wood-handled spade. given the extreme temperature of the lava and the small sample size, what is the likelihood of the sample being contaminated by the metal in the spade?

      • Thats a pretty standard way to collect lava, most common metal objects are iron alloys which are in the 1300-1700 C melting range so even the extreme hottest lava is barely enough, and metal also has higher heat capacity so you would need to completely submerge it. Probably you could even use an aluminium shovel to collect lava if it is in a small pahoehoe flow.

  17. I have taken a look at the MBL camera, and the nearest ‘cone’ is now fountaining steadily. So far as I can see the next cone along is still just ‘belching’ so to speak. It’s hard to see other cones with the cams down and the bad weather.

  18. I should mention that I started being drawn into this stuff by Albert’s piece about Hawaii and the Pacific. The beautiful map, the vanished plates (Farallon, Izanagi, Phoenix), the brillant explanation ignited a love for plate tectonics, and since then it never faded, neither the fascination, nor the interest for this site, the writers and their style with a lot of background knowledge and the readers’ comments. It’s probably plate tectonics that make such a beautiful unique planet. A very lucky planet in case the Grand Tack Hypothesis is right. A miracle. And I think the other miracle is the knowledge that was accumulated in short sixty years. Harry Hammond Hess’ theory of Seafloor spreading, confirmed by Matthews and Vine are one year younger than Albert. And that must have helped Volcanology.

    • The theory was published in 1962, the magnetic reversal in 1963. So Albert is the same age as my big sister… Unless the date refers to the proposal of the theory, 1960, in which case Albert is 1 year older than my big brother…

  19. And now the mbl cam’s view has gone to shit. Because of course it has.

    Time to get to doing something productive, I guess …

      • Very correct … Lucifer once again crawled inside the camera 😈.. I can see his red tail and red face laugther He is in joy that it does not work … IMO team is working hard to get out that red thing from the camera electronics : D

    • Are we finally back to the original view of Smeagol-Gollum? too much gas…

  20. well i hope someone caught a timeline for the cone collapse. Don’t normally just sit and watch but i needed some quiet timeout. Generally, the small sides fell in and then flow increased with help from the next cone. Slowly the near side started to disintegrate and move toward the vent.A new flow started to ooze from near the lower section of that side toward the camera. It started as a bright spot and i thought it might be a bomb and waited for the color to die. Instead, it grew brighter and larger and lava began to flow out. i couldn’t tell where it originated; which vent? It increased reaching the larger flow below and seemed to undermind the whole side. The side of the cone seemed to squeeze the vent and increase the spray like a thumb over a garden hose. All the while…. the whole vent had been lowering and now more inside wall could be seen on the opposite side. A large flow from the next vent joined the new flow and seemed to ‘float’ the near wall and it crumbled and came to a heap resting at the lower level… i did the same… coming to a resting heap and headed to bed. Much better than i can describe…. i did wonder if the lava had changed somewhat as it seemed different… more shine but i was tired and distrusted my eyes.

    • I had to stop gawking at the eruption cams and do some work (happens from time to time) … by time I got it was completely different. Thanks for the great description, now I know what I missed.

      On the topic of Hector’s great post, as a child in the 1970s my first adult level book about volcanoes was “Volcanoes” by the late Peter Francis. I read and reread that until it fell apart and my mum had to rebind it. Amongst many other things it had a very detailed chapter about Peelean eruptions and the destruction of St Pierre. In that book PDCs were referred to by the French term “nuees ardentes”, glowing clouds, as they also were in contemporary reports of Mt Lamington in 1951. Interesting how the terminology has evolved over decades.

      • I think it is a very good term, a pyroclastic surge is really like an actual blast wave, its ash and other really night stuff with no real volume but a lot of power and is very hot. A pyroclastic flow is basically a volcanic landslide, so a different sort of thing. The flows probably are not actually very dangerous as they would be predictable and flow in valleys or other low points, just the same as a normal landslide, but the surge is going to go over anything at all until it dissapates, its not really governed by gravity at all.

        Not universal obviously but its I think a very nice descriptive word, one that should be used today I think 🙂

        • Actually a flow and a landslide are different things. See this video which is part of a talk delivered for the Geologists of Jackson Hole earlier this month which covers landslide classification:

          https://youtu.be/WqZVR2Yl7tQ?t=940

          The overall talk is about a census of land movements in Grand Teton National Park using LIDAR and I’ve got it to the point where the presenter talks about slides and flows and falls etc.

          • Probably a dry debris flow is a better non-volcanic comparison, or a powder snow avalanche, the last one being quite relevant.

    • I seem to recall (from the research I performed before the speech contest I referred to earlier) that the snakes in question were ‘fer de lance’, a particularly venomous pit viper. It was said that they deserted their usual habitats and found their way into St Pierre a couple of days before the eruption. Of course, snakes are highly sensitive to movement, so it’s quite likely they detected the volcanic tremor some time before the humans did
      .

      • I can’t like this as it involves danger noodles, but I’m glad that they tried to escape…

        • Fer de lance/Golden lance heads… Very nasty, very aggressive pit vipers. I’ve lived in Africa, have been confronted with puff adders (twice), and a mamba was killed just yards from me once… I’m not too bothered by most “danger noodles”… But Lanceheads ?
          Don’t blame you… I’ll pass.

          • Bothrops lanceolatus, Fer de Lance. Endemic to Martinique. Didn’t know. Different rock than the other islands, endemic snake. Interesting. The main problem here is though, when it’s dark and chaotic and the hospital gone. Poor people.

        • Working. We should thank these men for being out in the smoke and cold doing this work. Seeing them try to start the generator reminded me of my Dad’s old lawnmower… Would he ever get it replaced? Nope. Anyhow. Thanks, guys! Camera is running.

          • My dad had a 1950s lawnmower that you started by winding a rope around the flywheel and pulling hard. He could get it going on the first or second pull. I never mastered the thing although I’m quite good at hand starting tiny 2 stroke compression ignition engines used in control line model planes.

    • It’s wonderful people like this Gutn Tog who know the importance of stitching the whole landscape together that really help us to form our mental 3D maps correctly.

      It shows so many temporary strange and exciting small-scale features that rarely survive the end of an eruption, being such fragile, glass-like structures. The contrast between the cooler a’a and the hot, smooth fluid pahoehoe lava is fascinating.

      And also show the human, social side of this eruption. Very endearing. Because, teens will be teens…

      • The Human eruption indeed.
        I have said this all along, there is a “Vital Spark” about this.
        Its natural for us to go there, right next to the fissure and experience …
        Most Icelanders will go there in the end.
        If I were there, I would move heaven and earth…etc.

      • This is very much a “volcano for the people”, harmlessly bringing enjoyment, entertainment and education. It will be a rich source of academic material in future years too … no doubt a thesis or two will be written.

  21. Did some sketching based on map.is
    While the topping over into Meradalir in the north of the “bowl” is the lowest exit, and the one to the south-west is the highest, the northern one however has to contend with having the deepest point of the bowl closest, and thus having to climb the most. While the SW one has a reasonably shallow rise, but a longer distance to travel.
    It all however seems to be a moot point, as it looks like the lava has stopped flowing into the bowl and is now filling up Geldingadalir again, and the next time it leaves Geldingadalir it is reasonably likely to just go straight north into Meradalir.
    Hope that made some sense.

    • So many factors influence this. The first exit hit the northern side of the col and was turned to the south, which helped it spread that way rather than the more logical, lower, northern path. Once established that turn continued; quite funny to see all the big lumps being rafted around the bend and heading off, exit stage left (don’t all rush to groan, folks).
      No doubt, if the eruption continues, lava will again flow this way and we will see what happens then. It’s so much fun to follow!

    • It’s in the description. Not related to the current eruption and 40 km away. Probably a permanent feature that has been there for years. Looks hydrothermal.

  22. Great Article.
    No scale can be perfect, the more variables you want to factor in, the more convoluted the scale becomes. There is nothing wrong with simplicity, Similar issues exist with the Richter scale, Saffir-Simpson scale, and Fujita scale. Factoring the climate effects, Intensity, duration, all into one scale doesn’t seem practical. Haetpe was an intense VEI 7, there doesn’t need to be anything else. We know how much damage smaller eruptions can do, and a complex scale would just make the layman confused.

      • I noticed in mapping all the vents at Krysuvik there are sort of 3 valleys. Maybe if these quakes mean something this time around the active rift will go under Kleifarvatn which could be interesting, like Tarawera but with a lava flood…

        I also noticed that Krysuvik and Brennisteinsfjoll seem to erupt at the same time, rather than one after the other. Its going to be exiting to live in Reykjavik this century 🙂

  23. https://www.ruv.is/frett/2021/04/21/a-home-for-the-soul-of-iceland
    A new Icelandic Studies building to house a magnificent manuscript. Reading this reminds me that evidence for volcanic eruptions can be found in the strangest of places. My local family history group was given access to a farmer’s son’s diary, to preserve and interpret it. It covers, intermittently, 1814-1822, but with 1816 fully covered. The weather during the year without a summer is currently being compiled.

  24. Saturday
    24.04.2021 11:38:30 63.918 -22.021 5.1 km 3.1 99.0 4.0 km NNE of Krýsuvík

    • First to the west of the current eruption and now to the east. Are the neighboring dykes planning to take over?

  25. Saturday
    24.04.2021 12:32:52 63.916 -22.018 5.0 km 3.0 99.0 3.9 km NE of Krýsuvík

  26. Really impressive quake rate today. Krysuvik quakes in green. They come in waves… Let’s see if the mag 3 get corrected later.

      • Looks like it is oriented lengthways along the peninsula, so not a shallow dike yet. Probably will be obvious when that happens if its like what happened in March, but it could be much larger and faster than that too.

        I guess if Krafla is an analogue the first activity will be a long dike that might even go under Reykjavik, probably will not erupt, and will be called a failed eruption. Probably though there will only be a few big events instead of lots of dikes and small eruptions, there isnt mention of lots is eruptions there in the middle ages, just 3, only one being small. Maybe there is more magma available here than at Krafla, so the rift is overfilled much quicker and erupts faster.

    • I am wondering if the next fissure breakout will occur in the Krysuvik area. I think it is only a matter of a few weeks before another new fissure opens up.

      • Probably not in a few weeks, an eruption at Krysuvik proper is going to be a major event with all the same precursors as we saw in early March but even more so, it wont be silent and slow. Also definitely not safe to go close to, and no way will the opening sequence be mistaken for the moon rising or a car 🙂

        Most likely more fissures will open around the current eruption in the next few weeks though, theres been reports of warm fissures south of the first cone, presumably a vent will open here soon.

      • Not likely at the moment. The current magma is in a different location, so a new dike would need to form. That would show up on the GPS’s. If uplift is seen, that is the time to bring out the tourist trade

  27. looking on mbl.is could be seen that the lava pool in front of new twins has drained out and drop level. that’s the second time i see that, where has gone?

  28. Thank you Hector for a post that gives food for thought and many comments particularly about human fascination of things volcanic. Please bear with this old lady as she remembers a 3 week camping holiday touring Italy. I am not sure ow our small, primrose coloured Ford Anglia carried four of us and all the camping equipment, but it certainly took us on a Grand Tour. It was 1960 and Dad was determined to experience something Volcanic. Mum couldn’t manage the climb up Vesuvius as she was very asthmatic, but during our trip to Pompeii someone told him about Solfatara on the other side of the bay of Naples. It was a good place for people with asthma he was told. So the following day saw us arriving at Solfatara. I recognised it as a caldera from my Geography lessons at school and my deep interest in geology. we drove into the flat area that contained a building and a camp site. We planned to stay the night . We parked up and decided to take a walk round. We followed a path and found the pool of boiling mud..It was fascinating to watch as it blubbed and splattered like a pot of boiling grey porridge, Around the low cliffs there were small alcoves where some people were sitting. On asking what they were doing there, we were told they were asthmatics, sitting and breathing in the sulphurous fumes to aid their condition, Mum decided that she didn’t like the smell of rotten eggs and passed on taking an hour’s treatment! Probably a very wise decision. I did notice and we wandered from fumarole to fumarole that my rubber flip-flops were getting rather hot and felt the soles becoming tacky. I could feel the low vibrations of magma hitting the crust. I also made note how thin the crust of the crater was. I told Dad I wasn’t happy about camping there, It wasn’t just the smell but I had a nasty feeling about hitting tent pegs into the ground! He too had reservations and we decided maybe it wasn’t a good idea to stay the night there.
    Watching the clips on You tube now, the safety aspect of the guided tours there is more prevalent. The boiling mud is fenced off and danger signs have been placed. I don’t think there is a camp site there now!
    It was an experience. I have since learned more about Campi Flegrei . The eruption of this area is stuff of nightmares but Solfatara di Pozzuoli is well worth a visit. Locals say if Solfatara is active then Vesuvius will stay quiet. If it stops then Vesuvius will erupt. I am not convinced this is a good method of prediction! What is being monitored closely is the uplifting of the area as seen on the Roman pillars in Pozzuoli. These show the sea level dropping over the years.

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