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. Big fountain now but the valley is getting hot too and starting to glow very dull red

    Is another fissure to the east or west due? The pressure at the one vent is high now.

    • Wow a sudden flare up in the area between the fountain vent and the old north cone. I have an uneasy feeling about this.

        • There have been 2 times I saw flaring up from this area and other people saw it. At the same time the camera gamma quality varied and you could see the infra-red at times and it showed a sheet of magma movement spreading in this region quite quickly.

          I had an uneasy feeling that there might be a sudden opening or tear in this region of the valley and sudden fountaining or a lava lake breaking open might occur.

          That is what I was uneasy about

      • 5:11 am nice overturning event front and centre in the lava lake that is deepening there. Continues intermittently to after 6am.
        There’s also a large degassing lavaberg getting rafted around the corner out of the eastern valley exit.
        On the north Langihryggur cam, it seems to collapse and cause a bit of a lava-jam before being inexorably swept away. About 9am.
        There’s also a lava drainage event around about the same time, I’m assuming it’s going down a tube or a channel out of sight of the camera to Meradalir. Would be nice to get some sort of visual angle on that.

  2. The lava flow is really fast where it flows out of the cone, way faster than it was before, it looks liek a set of rapids with a deep plunge pool at the base where the main channel starts and it slows down.

    • Was about to say something about that myself Chad,
      looks like the river has a nice hot flow, on the Geldingadalir cam
      some video of it would be marvelous.

  3. Is it likely that the original twin vents Smeagol and Gollum will be buried under lava coming from the newer vents? Smeagol is only emitting steam and Gollum seems to be extinct.

    • Probably still some open vent but no lava, all the lava is erupting out of Ragnar right now, as it is called on the livestreams.

      The effusion rate if anything is probably significantly higher than it was before, you dont get fountains and flows like that with 5 m3/s.

      • Not sure about that. Previously we had around 6m3/s from four vents together. Now it seems to be focussing on one vent so it is to be expected this one becomes more active. The eruption rate is better judged from the lava field but that is currently caught in the pond depression and is expanding more in volume than in area. I expect that the eruption rate is still pretty much what is was before. But wait and see tends to work best

        • More talking about the last few hours, theres a very clear increase in the power of the fountaining and how fast the lava is flowing out of the cone, its not like it was before where it flowed fast because it is falling, it was flowing fast because of the output.

  4. Mæg ic on Ængliscan wrítan hér? Ænglisc wæs séo spræc þara Ænglsican léoda in Englalande in geardagum. Séo spræc is gelíc tó Islendiscre spræce. Ænglisc ond Islendisc cumaþ fram EaldorGemaniscre spræce.

        • Eart þú fram Islande, Nell? Ic wunie in Niðerlandes norþeasternum dæle. Ic brúke þone Ieldran Fuþark tó wrítenne in húse, eac Rúna stæfræw genemnod.

          • No, I’m from north east england, lots of old norse preserved in the dialect and place names there. I’ve always been interested in my nordic heritage and know a little bit about the Futhark, but am by no means an expert!

    • Perfectly understandable for a Dutch native as well! (in fact there is still some debate if the oldest known written Dutch frase is indeed Old Dutch, or Old English)

      • Old English is very similar to modern German when it is about the Germanic inflection, which is inherited from Proto-Indo-European: declension cases, conjugation of verbs and the Germanic ablaut in strong verbs and in nouns and adjectives derived from strong verbs. The Dutch language has lost its declension cases, fossilized expressions excepted. And Old English and German have a simplified inflection system, when you compare them with the ancient East Germanic Gothic language.

        As a Dutch who lives in the northeastern part of the Netherlands, I am proud to be of Germanic ancestry and of speaking West Germanic languages (Dutch, English and German). I use the Elder Fuþark to write in Runic alphabet at home.

  5. Tuesday
    27.04.2021 04:57:03 63.932 -22.185 6.1 km 3.2 99.0 1.2 km SSW of Keilir

    • How long would the waves take to hit the lava field? Would we see this on the webcams?

  6. A few people on the stream chat have figured out that the lava fountain is about 120 meters tall if it reaches the top of the screen. The cone therefor is about 55-60 meters tall, and the fountain is more or less sustained at the height of the cone. It s abit less certain from the angles involved but the lava channel seems to be at least 10 meters wide where it exits the cone, and flowing about that far ever second too, which is a speed of 36 km/h if true, very fast.

    • Its flowing very quickly indeed now
      Faster eruptive rates also puts more strain on the supply .. faster than supply draining itself. Big fast fountains rarely last more than a few months before they drain the themselves dry

      We can only Hope that This is the
      ”Hell Mantle Decompression Machine” Thats started up and that we gets a more larger conduit melted and opened up and a shield later there

      • That is the normal case but this is the first eruption of this cycle, there is going to be a lot of magma accumulated. This time the magma is accumulated very deep but it seems otherwise to be the same.

        Normal Krysuvik eruptions are fast and probably in the range of 0.1-0.3 km3, but the dike complex might be several times bigger, probably each eruptive episode involves several km3 of magma with only maybe 10-20% of it erupting, the longest dikes probably go underneath Reykjavik even, but stay underground at that distance because of the terrain getting higher in elevation.
        The slow eruptions though probably dont form a massive rifting dike complex before the eruption, just a small one under 10 km long like we observed in March. Theres way less rifted terrain at Brennisteinsfjoll than at Krysuvik for example and lava flows at Brennisteinsfjoll tend to be larger.
        With this in mind a larger volume of the total will probably erupt in this scenario, just that it will take a lot longer. I dont know exactly how fast the effusion rate for Ragnar is now but even doing this sort of fountaining it could go on for several years I think.

        This also doesnt include that this particular area has skipped most if not all of the Holocene cycles so could be particularly voluminous in storage.

    • I estimate the current height of the fountains as ~ 30 meters above the lava base level (within the cone)

      • RUV says the fountains are about 45 meters high and that the flow rate has increased, though it doesnt say by how much, though for them to report it the change must have been at least significant, a doubling or even more, which would bring the flow rate in line with the supply to the dike in March.

      • Hmm, I make peak height to landing in the 3sec to 4 sec range, which would be (ignoring air resistance) 44m to 80m.

        • It varies. It is more active now and taller than when I looked at it before. A quick count confirmed 4 seconds landing time for moderate height fragments. It is not ballistic: you can see that the speed stops increasing around half way down. I assume that the hot rising air slows the fall. Measuring the first half of the fall for the highest fountains gave me 3 seconds or 40 meters, and a total height of 80 meters at this moment.

    • You were discussing the effusion rate earlier. If your flow speed estimate is fairly accurate, then if you can make a reasonable estimate of the depth of the discharge channel you could probably get a reasonable estimate of the current effusion rate.

      • The depth of a lava channel is not so relevant. What you need is what the speed of the lava is below the surface. It is like runny honey: only the top layer moves at full speed, anything below goes much slower. This is because the viscosity is much higher than that of water, and you can’t compare it to a river. In practice, the full speed may only be the top 50 cm. You can see this from the lava boats, which tend to move much slower than the top lava.

  7. I just saw the cone in the MBL camera cave in on itself. That gave the vent pause for thought.
    Then, it cleared its throat and went into fountaining overdrive!
    There must be some serious pressure driving it.

    • The levels have been up and down like a yoyo this morning, with a major drain, as you say, at about 10:50. There are at least 2 terraces which seem to drop and raise slightly with the flow. I reckon there’s a tube going down to Meradalir, that may get a sudden rush when the flow gets high enough. There’s still an awful lot of thickening going on in the mildly moist boggy bit, though. See how it’s sneakily inflating at lower left.

  8. Flow rate yas increased to 6.3 m3/s

    http://jardvis.hi.is/eldgos_i_fagradalsfjalli

    Also from Iceland Uni regarding activity and fountain hight.

    G´day
    Just before 20:30 last night (26 April) there was a phase change in the activity in vent #5 – the southernmost vent of those that opened and have been active since 13 April. The intensity (and vigour) of the explosive activity jumped and began to support 40-50 m high lava/fire fountain. At the time of writing the eruption continues to support the more vigorous fountaining. Consequently, the flow of lava into the “Valley with no Name” has increased substantially. Also, the activity in the northernmost vent (#6) from 13 April appears to have dwindled significantly, but the one just south of him (#4) is still active. Not easy to judge the state of the original vents in Geldingadalir, but there was still some glow in “Norðri” last night.

    • Yes 3 and 4 are still active but its very low, basically a spattering pond. All the activity is at 7 with the high fountains. 6.3 m3/s really just doesnt seem high enough for fountaining like that though, Pu’u O’o was erupting at a rate not much lower than this and it rarely fountained at all, and even when it did it was never anything like this after 1986. Maybe the volume is reporting the DRE, in whivh case the actual lava effusion might be over 10 m3/s which seems more plausible for the fountain we see.

      • The magma here can be more gas-rich than Pu’u’o’o, that also influences the height of the fountain.

      • They are calculating the flow rate by the ΔV(t) of the lava fields, derived by aerial measurements of the total area and comparing current surface height with high res elevation mapping of the same area.

        I currently remember only 2-3 occurrences where they specified the time frame of the measurements at all, and in one instance they had mentioned two flow-rate figures ΔV(72h) and ΔV(YTD)

        So their 6.3 m³/s might be derived from the last 24h, 72, 5 days, kinda depending on how long between their last overflight mapping

        • And I just checked the article, the flow rate posted is mean flowrate for ΔV(5 days)

          Heildarrennsli frá öllum gígum síðustu 5 daga hefur að meðaltali verið rúmir 6 m³/s. Þessi tala er svipuð langtímameðaltalinu, en þá 38 daga sem gosið hefur staðið reiknast það 5,6 m³/s.

          The total flow from all craters in the last 5 days has averaged just over 6 m³/s. This figure is similar to the long-term average, but during the 38 days that the eruption has lasted, it is calculated to be 5.6 m³/s

      • If I’m reading the graphs correctly, that is the estimated rate up to 25/4, so two days ago. The graph title references 26/4. Either way though, it wouldn’t be including the last 12-24 hours or so.

    • I call the Valley With No Name the mildly moist boggy bit, maybe I should capitalise it

      The Mildly Moist Boggy Bit

      😉

  9. Nice series of cone collapses on the mbl cam, from 11:09:40 to 11:11:40, with the biggest at 11:11:25, which blocks the vent, leading to some lovely fountaining at it clears its throat.

      • I’m not really up on the names, but it’s the one that’s currently fountaining madly on the mbl cam. I think it’s vent system 5.

    • Check out the view from the RUV cam. You can just make out the collapse, and the resulting fountains are immense!

    • Ye gods, but it went a bit bonkers after that! It explains that channel drainage event downstream; the lava drained away temporarily as the supply was limited for a few minutes. There will be a few bergy bits floating down the river soon enough.

    • Well, we just need to pitch in so that they can get chopper access instead. 😉

      • Considering that there is quite a bit of equipment from IMO on the same hillside, I doubt that they’ll have a hard time hitching a ride with a chopper 😉

    • They seem to be a tad unlucky in their choice of locations; we’d better keep an eye out for the next venue!

  10. It strikes me that if the conduit opens wider then the flow will increase but if there is a constraint at the top (likely the last place to melt) then widening the exit may reduce fountaining.

  11. Hmmm, posting a reply seems quite a endeavour nowadays. Not only the logging in thing, but also the fact that you do not get a refreshed window showing your post…. I am not so sure that I want an account here @volcano café. Hesitant at least.

  12. New vent on the Mbls cam in the (more to the side really) middle of the tourist field.

      • as of 19:06 pm, two new spots a bit north of this zone are also slowly emitting smoke.. fair to say that the ground is really hot in this area

  13. New vent looks to be forming on the mbl cam. There is steam emitting from non lava-covered ground and I think I see bits of lava every once in a while.

    • Nova… we saw it first… we make a good team… how i love the smell of new vents in the morning.
      We should get browie points… 😉

    • I wanted to ask earlier: Are they actually adding noise to the video to make it more impressive? Is this a possibly low paid person forced to produce random noise 24/7? By fizzling into some mike…?

      • Good catch. The sound sounds awfully sophisticated for a single mic. Wide stereo and very soft. Could be some type of red/brown noise, artificially generated.

  14. Well, things can change in a hurry. I wake up to find that the crater of the most active vent has widened considerably. I did see a chunk of the wall fall into the fountain around 15:20 pm local time and fountaining went very vigorous at that point. Then at 15:22 the whole thing almost calmed down to a pond, very quiet, but 8 minutes later vigorously fountaining again.

    I agree that some kind of vent seems to be forming in the ground in the mbl cam view.

    There has been some explosive fountaining, 3 or 4 bursts, where the upwelling lava spray is quickly hit while still on its way up, but I would not say that this is occurring regularly. The night that the original north cone did this, about 8 hrs or 9 hrs later the northmost fissure opened up.

    It will be interesting to see what new fissures open up, as there also has been around mag 3 quake near Keilir and aftershocks.

  15. Question: Has the exit point of the active cone risen in height the past few hours? I remember this being lower, but now it seems to have risen another 10 meters or so. Or did the lave channel sink, which is to the left and it seems like the exit point rised?

    Any ideas? Is the cone slowly building a containment pool, but at a higher elevation?

  16. on th other hand….that small smoking points does show a future landslide? that lava volume that has been build on top of hill doesd press…i guess….and heat….

    • Not a landslide, but I have been watching carefully and the slowly smoldering ground picked up two new points north of the zone showing that some type of underground intrusion of magma has taken place. The pressure seems high at the active cone from the height of the spattering.

      I wish someone had a Flir camera to see the hot zones in the ground so as to know what to watch.

      • good point…i saw some videos with such a device pointing that black lava is hot in fact…..and i always wonder how come that they are not use such tools to check the lava temp…

        • My mbl.is feed got cut off around 19:35 and I’ve been unable to update to now at 20:04 pm, but you can definitely see the ground steaming in two zones. One is close to the lava flow margin, but the 3 new ones seem to be in a more northern location about 50 meters of so. I wish we had someone live at the eruption site to speak to what is happening here.

    • it has built quite a steep rampart. One would not be surprised to see more collapses. I wonder if he could measure the height of the fountains..

  17. MBL camera. Ground smoking nearer the camera from the active cone. Might be just burning undergrowth, but it has been so wet recently.
    Interesting…..

    • I think is is over-subscribed. I can get a minute of viewing before it seizes up.
      People may be hoping for a new vent. But it could be just water in the ground rock getting heated up.

      • Most likely it is steam, but I have noticed that the extent of this has been slowly broadening. Nothing to worry about, but just keeping an eye on it.

        • I watched it earlier on, around the time Motsfo (Hello again!) and others reported it, and I thought I’d noticed a small spurt of lava in addition to the steam. Then when I didn’t see it again, I thought I must have been seeing things. However, the spurt is clearly visible in the video that Hopper posted at 20.37 (a few posts above).

          What’s puzzling me is that if the lava is close enough to th surface to produce steam, show itself occasionally, and scorch the ground, why haven’t we got a new vent – especially when it’s only a few hundred metres, if that, from a vent which is fountaining so freely?

          • To clarify: I mean, the pressure must be significant in the area to produce the fountaining we’re seeing. But, on further thought, perhaps that is relieving some of the pressure from the scorched area and preventing the lava breaking through…

    • Wow. That really shows how big the Mildly Moist Boggy Bit is growing. Getting ever closer to the southern col.

      It’s late here now and DH has got home having had a hospital procedure earlier today, so the administering angel role is now mine for the night. I’ll look at the scale and size of this tomorrow.

      If some kind person could tell me how I can link photos and diagrams here, I cannot figure out how to do it, especially since my main IT support technician is out of sorts.

      • copy your image.
        set up an account with imgur.com
        sign in
        click on your name and select “images” from the drop down menu .
        paste your image (I use Ctrl-V)
        There will be a list of options on the right. Go to the second from the bottom, I think it says BBCode, and select COPY.
        Paste that into your volcanocafe post.
        Remove the last part, [/img] and the first part, [img]
        that’s it!
        It may sound complicated, but after you’ve done it a couple of times, you get it and it becomes easy.

        • Can be done much easier than that. Just right click on any image and copy the image link, as long as it ends in .jpg or .png it is good to go here.

          Skip the drop down menu in imgur, just copy/paste-drag-import the image straight into the imgur front page, and just go straight to right clicking on the image, when it has loaded, which now will have the appropriate code. It will rarely take more than ten seconds (depending on how fast your connection/computer is)

          • Thank you Bill G and Bjarki. I will take a deep breath and have a go.

            My very Dear Husband has just this evening upgraded my hamsters (it’s a very long story) into a box that isn’t much bigger than a box of tissues. It’s called a Shuttle. Apparently it will help speed things up and I can play nice games like Stellaris, and Age of Empires 4 when it is released. Dear Son is off to play Rome Total War again, it’s like being back in the Noughties!

            Also, we have a new ‘internet’ (NAS store, for backing everything up, that’s about the sum of my knowledge.)

  18. i think they start to move the equip they’ve got on the peak of that hill, weather station and of course mbl cam. for time been they move it down at about valley level…for farewell last shots…that hill will be soon enclosed in lava field

  19. So, are we down to one active vent, now? The one on the MBL camera? The others appear to be zoomed into it.
    One vent to rule them all
    One vent to find them
    One vent to bring them all
    And in the darkness bind them….
    (Sorry, Jesper, could not resist it! Perhaps the vent should be called: Sauronogigur)

    • I think the others continue to trickle lava into tubes, though many are not even producing much visible vog anymore.

      On the other hand, there is that new activity, whatever it is, near fissures 3 and 5. The one someone is actively trying to hide, to judge by the fact that shortly after people started commenting upon it on Youtube and here, they jammed the mbl cam’s signal (the only one that had a good view of the smoking spot) and then physically moved it to a new vantage point that lets it show off fissure 5, but puts the smoking spot out of view on the other side of a piece of fissure 5’s associated lava bed. What I can’t figure out is the motive. Were they worried it being visible on the mbl cam would attract people to endanger themselves? They didn’t react like that to earlier new-fissure openings and other events that could have conceivably had such consequences.

    • Anybody watching the northernmost vent (RUV2)….appears quite active. There are still two!

    • Maybe not RUV2? The Langholl Cam and the vent just to the right of Mordor.

  20. When the drones of Bjorn Steinbekk went over the lava fields today, I noticed that the lava level had greatly dropped in the space between the active cone and the original north cone. In fact the flare up area was almost exactly where this pit now was, I would estimate some 20 meters deep.

    Question? Has anyone figured out the shrinkage of the liquid magma, per volume, into the solid form? It would seem that we have significant shrinkage, based upon the crinkled look of the lava fields after an eruption passes by a week or so.

    • Interesting question about shrinkage. I tried to find any usefull info, but didn’t get much.
      Most of the volume change during cooling would be caused by the loss of vesicles soon after the magma surfaces. Surfacing lava can be vesicles rich, basalts sometimes have more than 70% volume, sometimes lower than 10% (Etna and Kilauea samples). Large differences. I don’t know what vesicle percentage the Fagradalfjalls lava has.

      I don’t know if lava is that liquid enough that vesicles can escape, it would cause some shrinkage then.

      The crinkled look is mainly caused by the lava moving during cooling rather than shrinkage, you can watch this proces in the vids posted here in VC. The lavafront breaks and tumbles, flows, breaks and tumbles over again.

  21. And now the RUV cams have failed again: blank reddish blurs. The mbl cam is working, but Youtube has screwed something up. Every time I bring up the mbl feed it plays for about a minute and then Youtube gets stuck buffering, even if I put it at 480p or lower. I can reload the page, or seek to a random spot and then click “live”, and watch fissure 5 fountain for forty seconds or so, and then bam, Youtube gets stuck buffering again.

    edited. admin

    • RUV1 is working again and shows a nice spatter-fed lava flow drooling down the flank of the vent 5 cone.

      I’m still at a loss to explain simultaneous failures of two cameras that are located kilometers apart and a server (or network cable, perhaps) in a Google data center thousands of kilometers away from either. That’s generously assuming that frequent buffering in 1 video out of 3, with adequate bandwidth at my own end for any of them, is because Google stores them on different servers and the affected one is on a server that is having bandwidth problems at its own end.

    • Nice Spatter cone and If fountains get taller .. it will build a cinder cone
      But most cinder cones are formed by more viscous lavas than this

  22. big gush out the side of the south face of the active cone at almost exactly 2:00:00 am, it seems to have possibly opened up something?

  23. Do we safely assume that the active vent has stolen the hydrodynamic pressure from the other vents on this fissure?

  24. There are concussive bursts now in the active cone, around 4:01 am, they make a unique sound sort of like big lumber boards hitting each or a high pressure hose spray hitting a returning stream. I interpret this that the hydrodynamic pressure in the vent is very high, and would not be surprised to see a new fissure(s) soon.

    • I find fault with my reasoning, if pressure is high, all vents would be erupting, so that reasoning is incorrect. But we cannot deny that very vigorous activity is occurring, so did very high temperature melt a preferred conduit?

      I think the tiny fissure this afternoon needs more investigation and I noticed that Bjorn Steinbekk apparently captured a steaming area not in the fissure zone a couple of weeks back when the northmost fissure was active.
      I intend to ask him about this.

      • I think it seek the easy path. And can be that conduit/s are so narrow that the pure weight of dome lava field press it down so it force it to stop and open at another aria. But that i think Albert or some with better nowhow about this can answer better than me 🙂

      • That steaming area a few weeks ago was a normal fire started by the lava river coming from fissure 2, I think that was determined quickly. This new one seems more likely to be an actual magmatic effect, like a fumarole above a shallow intrusion, but it also could be spatter that flew off and started a fire. Its not in the fissure line so if it is a new vent its a shallow satellite, and it isnt lined up well to the fountain so probably wont do too much.

        I think now that there is a single big vent it will stay at this location for a little while or maybe a long while who knows, but likely now there is focussed outflow and probably also an increase in effusion rate we will see longer flows.

        • If more of the eruption comes out in a single point then the flows may indeed get longer. Whether total effusion rate has increased is not so clear. The fountaining is impressive but the exit flow seems quite small in comparison.

          • My thoughts precisely, unless there are lava tubes from other vents below the surface, which does not seem unlikely to me, the rate looks much lower.

          • It varies a lot, I think at the moment the channel is pretty deep, it was shallower yesterday and still flowing fast, also the camera is now further away.

            The fountains reach over 100 meters at times, it just really doesnt seem like that can happen with only 6 m3/s effusion rate. The data so far doesnt show this lava to be exceptionally gas rich, a 1-2 thousand tons a day SO2 which is very comparable to Kilauea during Pu’u O’o, and there was no fountaining like this at Pu’u O’o after 1986 at any point. Not saying its impossible just it looks improbable.

    • Looking at the webcam Jesper posted below, at 9.10 ish the flow is really slow coming out of the main fountaining fissure. Do we have a name for this one? F5? This may be part of the reason for the drainage of the channel, not enough supply to keep the levels up. But it is a remarkably quick, dramatic drainage. It seems to be bull-dozing the a a lava further into the Mildly Moist Boggy Bit.

      • Flow in the channel seems to get stuck behind the lava boats, so backs up into a big lava lake in the channel which drains out, its done it a few times now I remember seeing.

    • And at around 9.25 the amount spilling out of the vent seems to pick up a bit, accompanied by some high fountaining that almost reaches the top edge of the camera view. And at 9.41 there’s a definite pick-up, lots of lava sloshing over the lip and incising down into the lip slightly.
      9.45 and 9.46, LHS wall mini collapses.
      10.53, there’s a RHS wall collapse. The camera jolts sharply at that one. Eq caused?
      10.57, and one of the rear pinnacles drops.

      I won’t try to calculate the velocity of an unladen lava-bomb, as I was watching double speed. 😉

      • The camera shook twice. Based on the time delay between the rock fall and the shake, I’d say the second shake was the sound wave. That would put the camera at 300-500 meters from the cone which seems reasonable. The first shake could be a ground wave but I am on shaky ground here

        • Measuring on the map makes it about 450 meters (as I am not 100% sure of the exact spot of the cone, the MBL camera is however visible in the RUV camera, so it is easy to find the exact location of as it is on the ridge).

    • It’s been a while since I saw a wide-angle view. From the last view I saw and from what is visible from the Langholl camera, I would say that the vents associated with the fifth fissure opening are the only ohes actively fountaining (may only be one of them) and the vent associated with the third opening is still showing visible lava. The vents from the first and sixth openings were smoking the last I saw, but didn’t have any visible signs of lava. To me, it looked like 2 and 4 aren’t showing any signs of activity.

  25. Huge cone collapses into the pit starting about 13:05:30. Again at 13:09. Wish I was there, looks like a lovely day for lava-watching.

  26. It is certainly extremely beautiful. I tend to compare it to birth, whereas Pelée or St. Helens is more like death.

  27. Based on official estimates from March the valley volumes before overspill are as follows:-

    Meraladir 44.7Mm3
    Geldingadalir 6.8Mm3
    Natthagi 4.3Mm3

    How big do people think the “Valley with no name” the (mild moist boggy bit) is, given the experts ignored it and didn’t give it any estimated volume.

    It has been filling up now for around 13 days with a couple of small leaks north so isn’t quite full yet.

    • Surely Natthagi is bigger than 4.3 ??
      The Mildly Moist Boggy Bit (MMBB) is, or was, like Geldingadalir, flat bottomed with no contour line on it that I can see:
      http://www.map.is/base/@339369,379551,z8,0
      And I think it is shallower to the exits than Geldingadalir, so not as big as that. I couldn’t hazard a guestimate though.

      • Thank you for you supportive comment on the Ballareldar chat.

        Alas I couldn’t reply on there because the reply button wasn’t available.

        Let’s hope the moderator doesn’t bounce this message

        • No Admin is bouncing your messages.
          For some reason our spam-filter really seems to dislike you. It happens on occation. It will slowly learn to not bounce you, otherwise there is a trick that we have up our sleeve that usually fixes things.
          But, for a little while we will have to manually release your comments.

      • Your estimate of 4.3 sounds very reasonable although I would come in more around 3.5

Leave a Reply

Your email address will not be published. Required fields are marked *