The VSI scale

Guest post by Tallis

Humans have always had some fascination with rankings, some of the most popular videos and articles on the internet have dealt with comparisons and rankings. However, this doesn’t mean that it is just another useless fad, on the contrary, a well thought-out “Top 10 list”  can be very informative. For disasters, we have created scales, and we are all very familiar with these scales, the Fujita scale, Safir-Simpson scale, Moment magnitude, and the VEI scale. Just like us, these scales are imperfect, they don’t factor in all of the variables, most of which you would only know right when the disaster is taking place or afterwards but they get the job done. We don’t need to understand all of the variables to understand that when an EF5 is coming, that means get into a basement. However, volcanoes aren’t like most disasters, we don’t really see disasters that produce such varied and extreme consequences on so many levels. For example the Laki eruption, a VEI 5, killed more than 30,000 people directly, and the explosivity of that eruption had negligible effect on the actual population. The VEI scale is a great scale for scientific purposes, easy to understand and easy to apply but when it comes to the effects that is where it’s reliability breaks down somewhat. For instance a VEI 7 can cause less direct death and damage than a VEI 3.

My VSI scale will have it’s focus completely dedicated to the consequences of eruptions, and will serve as an excellent way of estimating the scenarios born from volcanoes. What does it mean? VSI stands for Volcanic Societal Impact, and it’s focus is dedicated solely to direct volcanic impacts, so climate consequences are not a factor. Climate effects of larger eruptions are chaotic and unpredictable. When a large eruption takes place, by the time it takes to get a general idea of the volcanic winter, the eruption could have already ended. The damage done by a on-going eruption does not include subsequent climate effects (although it could be factored in for historic eruptions).

For the VSI scale, lahars, ashfall, tsunamis, landslides, shockwaves, gas emissions, glacial flood outbursts, and pyroclastic flows can all be factored in with relative ease. The two primary factors are range and impact. Both are split into 4 categories, Short range: 0-30 km away from the volcano, Medium range: 30-70 km, Long range: 70-100 km, and Distal: 100+ km. The impact categories are, None or negligible, Minor, Moderate, Severe, and Catastrophic. If climate consequences were to be factored in, they would go under the Distal range.

The scale goes from 0-12, but how would we discern whether an eruption is a VSI 1 or 12? We think about what impacts the eruption would cause over any of the ranges listed above. We convert the impact categories to the numbers 0, 0.5, 1, 2, or 3; we then add all the numbers to get where the eruption lies on the scale. For instance, the recent eruption of Fagradalsfjall would be VSI 0 as it has negligible consequences on all ranges, so 0+0+0+0=0 and a truly Catastrophic eruption be 3+3+3+3=12.

Now this is where the problem shows, the definition of a moderate, severe or catastrophic impact would vary depending on who is using the scale, which would lead to some conflict on where to place certain eruptions, the Enhanced Fujita scale has similar issues. Another issue is that the scale doesn’t tell you what the primary hazards are, a VSI 8 over land and VSI 8 over water will have different hazards. Another issue is that this scale focuses on impacts and with some good preparation, the impacts of a massive eruption can be reduced substantially and as such the eruption would rank lower on the scale then a smaller eruption that took place without good prep. The largest eruption of the 20th century, the eruption of Novarupta ranks at 1.5! Needless to say, the population and infrastructure surrounding the volcano plays a crucial role in finding out what it’s potential ranking is.

Now that I’ve explained the scale, I will rank some past eruptions and I know the perfect place to start!

The 1883 eruption of Krakatoa

The town of Anjer, after the eruption

This eruption is one of the most infamous in all of history, and it was the first disaster to grab global attention, so naturally it’s the perfect place to begin. The eruption produced several explosions that were more energetic than most nuclear weapons and while the cause of the explosions are fascinating, it doesn’t matter for the ranking. Most of the deaths were caused by the four massive tsunamis produced by the eruption. Each explosion also caused massive pyroclastic flows that reached distances of up to 40 km in some areas. This eruption is one of the deadliest in Human history killing more than 36,000 people. In Anjer alone, 7600 local inhabitants and 14 Europeans died.

This volcano ranks pretty high for a low end VEI 6. The Short and Medium range impacts were all Catastrophic due to the tsunamis and pyroclastic flows, Due to the tsunamis, the volcano produced severe Long range impacts, and the ash fall and the tsunami would’ve produced moderate distal impacts. So this eruption would a VSI 9 (3+3+2+1=9)

The June 1991 eruption of Pinatubo

The most recent VEI 6 eruption, this eruption was one of the most important in the history of volcanology. It was the first VEI 6 and volcanic winter to be analyzed with modern technology, and this event greatly broadened our understanding of large volcanic eruptions. The response to this eruption was a triumph, as the preparations prevented 1000s of deaths. Still, this volcano killed more than 800 people due to falling ash. This eruption did substantial damage to the Philippine economy and it produced lahars for years but consequences for the country were nowhere near as bad as it could have been. As such his volcano ranks a bit lower on the scale. Short and Medium range impacts were severe, long range and impacts were moderate, distal impacts were minor. So Pinatubo would be a VSI 5.5

The April 1815 eruption of Tambora

This eruption was one of the largest and deadliest of the past 4.000 years, killing more than 75,000 people directly and causing global famine. All life surrounding the volcano was destroyed by the massive pyroclastic flows. Despite being 10s of km away from the coast, the pyroclastic flows still displaced enough water to cause a moderate sized tsunami that would kill over 7,000 people, the ashfall was so severe that it plunged several major islands into famine and the extensive rafts of pumice would hinder sea travel for years.

The short and medium range impacts were catastrophic, with severe consequences for Long and Distal ranges so this eruption would be a VSI 10

There are several big candidates for VSI 12 eruption, some you already know about but there are some that don’t get talked about but that’s an article for another day and in fact I would like that series to be a joint venture.

With this scale we can have a better gauge of the societal effects of major eruptions but it’s not perfect. If you have any suggestions on how to make the scale better, I would like to hear them in the comment section. No scale can be perfect, since the scale makers aren’t perfect. Perfection should be sought after but never expected.


380 thoughts on “The VSI scale

  1. These fountains at Geldingadalir….are we absolutely sure they are not new vents from the rift? Cracks from the conduit(s) coming up west of the main vent?
    I’m watching them on Randall’s video (above – thanks Randall) and the three of them often fountain in unison, suggesting a common gas supply.
    These to me look like a radial arc around the main vent – rather like Tallis’ ring faults…
    And I continue to stick with my theory the main conduit collapsed. This new and weird phase might be the result?

    • And I’d add the sheer quantity of hot, liquid lava in the ‘lake’ could only come from a fresh supply, like in new vents.

      • On early videos you can see they are detached, before the vent at the bottom of the cone turned into a raging torrent the lava lake was already there and the vents in it have only gotten bigger since then too 🙂

    • All I can say is where there is smoke(plumes) there is….

  2. Lava now flowing thrue the bottom of the crack in the crater
    Watch the latest video from GutenTag postet 1 hour ago

    • Wow. perhaps a glimpse of what the great flood basalts looked like! Albeit on a very small scale.

  3. On Nátthagi (mbl) are dots up on left side.
    Is this lava or people?

  4. Anyone got a current live cam? Langihryggur has that blank black syndrome again, though it was working half an hour ago. If it’s facing the cone from across Geldingadalir, so much the better.

    And why is there this sudden preference for Facebook over Youtube? Several people here have reported that it’s harder to access them there, at least without signup, though I was able to watch that one last night for a while before encountering difficulties.

    • Its because none of the livestreams on youtube are on the side where the eruption is happening. Also the cam is still working it is just in the clouds.

    • I share your preference for youtube over facebook. However, youtube’s obsession with adverts makes watching it without an addblocker tiresome. Facebook is big brother making its money not by selling you products but by selling you. Pick your preference

      • Facebook dont store everything you write and message anymore..

        In 2014 my School bullies broke into my Account, flooding it with very unacceptable stuff

        I deleted everything… and changed password, cleaned walls, chats

        In September 2021
        I downloaded my Facebook Account history from Facebooks Servers to have a look If its still on the platform

        Absoutley nothing coud be found in the files that Facebook sent to me, the message and post files where empty that Facebook sent to me from 2014

        They changed ..
        They dont steal and store your photos or messages anymore

      • My Facebook Account works well .. and I think the 2014 stuff is its gone from the platform

        Facebook is moving towards more comfortable storage policies.

        In the future Only the stuff Thats reported will be stored on the servers .. and the algoritms will be improved

        The rest of the content is truely yours .. althrough not there yet

      • Albert You can be pretty comfortable on Facebook
        They store very little now of you

        Dissapearing messages exist too! That are gone instantly from servers after your friend sees them

        Facebook is very diffrent now than it was in 2009

      • You should try Facebook
        Its very diffrent now than it was in 2010 ..

        Big Brother .. but they are moving to more comfortable systems .. the content photos, commentary messages, will be entirely yours soon

        If you delete a post .. it will soon never be possible to get it back

        I joined in 2012 and did not like at all their policies back then .. But I think they are changeing now

        • I have never liked, nor felt comfortable on Facebook. It’s kind of creepy. I have an account to keep in touch with family but I very seldom use it.

          I call it “Faecesbook.” 🙂

        • Then its good that they are changeing their ways

          In 2008 they where very bad with storing all your information

          But now most of the content is never stored Once deleted

    • Wow!

      I learned a lot from that, thank you! One thing it showed me was that the lave field was still largely fluid under a very thin crust; we started to see sloshing motions moments after that lava started to splatter. And that’s the kind of thing people have been walking on, ugh…

      Another thing that cought my eye; the camera panned right briefly, showing is the “shore” of the lave field, where it appears there’s a new moss fire. My guess; that means the level of the lava field had increased right around that time, probably due to flow feeding those vents.

      It will be fascinating to see what the area looks like in daylight now.

      • Well, might be a while before the fog clears but that whole area is a lava lake now. These vents got very powerful before the fog set in though, they are not just holes lava is flowing into and displacing air or would have died out in minutes, also this entire video wouldnt exist at all. Lava tube skylights dont fountain like this either let alone there is no tube here to begin with.

        There were fountains in a lake like this in the beginning of the month too, and the failure of the cone was very abrupt and actually pretty violent as it saw a lot of fountaining from the crack, which I wouldnt expect from a simple hole in the side. Seems there was a diversion in the conduit a while ago, and it was just not recognised at the time. What this means long term I dont know though because the shields in Hawaii once flank vents formed they turned to sustained slow effusion, that has not happened here.

        • The height difference between the crater and the flank vent was much higher in Hawaii though. In this case there is not a huge difference in pressure between the two… So I would not expect a change based on that – but the behavior itself of course has changed, so anything might happen…

          • Actually not really, it is close to 100 meters here.

            Might be 200 when talking about Kupaianaha to Pu’u O’o when it first formed in 1986, but it almost leveled off by 1992 and all the flank vents were in equilibrium to lava in the main crater after that.

      • That could have been fresh lava though, pushed out of the ground. Also, that part of the field was the youngest part, just a week old. Hopefully people only walked on the older parts… Emphasis on hope.

  5. Recent small quake swarm not far from the eruption site (the blue ones). Don’t know if this has any significance.

    Meanwhile the high freq graph refuses to drop. That’s unruly.


    Made this, the location of the vents and lava from the ongoing episode. I expect the flow has advanced well to the south by now though, it is a bit of a depression there but more downhill further to the right.

    • Thanks, this made things clear again!

      I am just wondering.. how far can the lava advance towards the northwest? There is a little ditch there but mostly I wonder how far the lava has to rise before it flows towards vent 2 (the left side, so the plateau-area).
      I cant finds the altitude-maps anymore, it has been a while since we had an update on this (especially for the geldingadalir valley, meradalur I kinda know how high the lava is/has to been).

      • It can flow directly into Natthagi, Geldingadalir is a bit of an extinct name now as there is no longer a valley at that location 🙂

        I think because of the slope though it will be slow, if it builds a shield up here though it will become a lot faster with time. If this turns out to be sustained flow it will tube over and flow a long way. The end of the valley can flow into Natthagakriki, if it does that it ends up in a drainage towards Grindavik, which is only 10 km away. It is dead flat but remember Pu’u O’o sent flows 12 km to the ocean with ease at only half the effusion rate we see at Fagradalshraun…

        • “…Pu’u O’o sent flows 12 km to the ocean with ease at only half the effusion rate we see at Fagradalshraun…”

          That is a very useful piece of information; really puts things in perspective. Do you know how similar or different the gradients are as between the two eruptions? Also, I wonder how flow varies over different surfaces: to the N of F’fjall, near the sea and just S of the road, there are some pretty blocky lava fields. How might this compare with the relevant bit of Hawaii?

          • It is very flat, just like the coastal plain on Kilauea. Lava tended to flow slowly there but still never really had trouble. It did start to have trouble in 2012 but actually retrospective analysis has found that was not a supply stagnation but because magma was beginning to leak downrift of Pu’u O’o even back then, ultimately to initiate the 2018 eruption. So flat surfaces see the flow spread out but it wont really sto it, just slow it down. Fast flows can be stopped but sustained pahoehoe is more tenacious.

            I think it will be a long time before Grindavik is at risk, it is not directly downhill. But it is certainly not ‘too far’ to be at risk. The same is true of Vogar, lava can easily flow the 20 km to the north coast, but at present there is not a direct path that direction so it has not done so. If (probably when) the growing shield overflows Fagradalsfjall things get very interesting.

          • Thanks. It sure will get interesting if F’fjall gets much bigger.

            I am familiar with Reykjanes but not with Hawaii. It’s about 14-15kms down the fall line to the sea from where the gradient eases off beneath Langhóll. The altitude at that point is about 250m. I was interested in the comparison with Hawaii.

            Gríndavik? Well, I think the Icelanders are concerned that if the lava runs out of Geldingadalur, overcomes the berm, and flows down into Nátthagarkriki, then Svartsengi and Grindavík could be threatened.

        • Fagradalshraun is very hot 1240 C been confirmed
          So it will be able to form very nice lava tubes When the effusion goes constant. Been yellow white in daylight some flows

          Puu Oo – Halema’uma’u coud have lasted forever since they are connected to the decompressing plume hell machine in Hawaii 🙂

    • If my rocky memory serves somewhat correctly, the original RUV camera that we watched the birth of the Twins would be somewhere near the tail of the arrow you drew on the image?

      One wonders if the powers behind MBL would be moving a camera over towards that area? It would be in a great position to cover all the new action and the potential flow (only “potential” since volcanoes do whatever they please) over the saddle and/or southwards towards the west Natthagi hill.

      I’m definitely in the camp of ‘these are new vents’ in the Geldingadlir W/NW valley. Also enjoy your analysis as well.

    • Hmm – those vents remain on the north and west side of the MAR that runs roughly west to east @where Theatre Hill lies.

      What seems like a thousand years ago, Albert presented a diagram that showed the the line of the intrusion as it butted up against the MAR, and the main “Ragnar” vent lies just a bit north of that meeting.

      With regards to my earlier picture of the empty main vent, I remain personally 100% convinced we had a conduit blockage on/after 3 September. The thing is, the new primary conduit that forms the gusher on the main edifice could shake down the west side of Rangar resulting in a very messy eruption site!

      Untidy volcanoes!

  7. Post by the University just under half an hour ago on Facebook. The referenced videos are all separate Facebook posts. I’ll try to find non Facebook links and add them.

    My interest is where they call the fountains secondary vents, and say the lava was still flowing underneath the crust while the surface activity was paused.

    “12 september 2021
    (English below)
    Takið eftir að myndböndin eru hvert og eitt sett inn sem sérstakar færslur.
    Note: The videos are uploaded as individual files.

    Sæl öll sömul
    Í gær var eldstöðin á Fagradalsfjalli en á ný með sjónarspil þegar yfirborðsvirknin tók sig upp á nýjan leik eftir 8.5 daga langt hlé. Ferð sem farin var seinnipartinn í gær inn að gosstöðvum við Fagradalsfjall náði góðu yfirliti af þessari yfirborðsvirkni gossins og þar kom margt athyglisvert í ljós. En fyrst er rétt að geta þess að það eru góðar vísbendingar fyrir hendi, að gosið stöðvaðist ekki í þessu 8.5 daga langa hléi. Það er þó augljóst að gosrásin upp í gíginn (#5) hefur stíflast og þessi stífla varnaði því að kvika flæddi inn í hann. Þetta kom einnig í veg fyrir myndun og streymi stóru gasbólanna og þess vegna var óróinn svipur hjá sjón. En veikir óróapúlsar, stöðugt gasútstreymi frá gígnum, glóandi kvika í himnaljóra ofan við innri rásir hraunsins og nýjar sinur við hraunjaðra í Geldingadölum sýna að kvika var að streyma upp um gosrásina til yfirborðs í þessari pásu yfirborðsvirkninar.
    Athuganir gærdagsins staðfesta þessa sýn á hegðun gossins, og er þar helst að nefna:
    (i) Kvikan sem flæddi inn í gíginn kom upp um gígop sem er undir norðvestur gígveggnum (myndband 2021-09-12A) og síðar kom hún einnig upp um minni gígop ofar í gígveggnum og féll niður í gíginn í myndarlegum hraunfossum (myndband 2021-09-12B).
    (ii) Á sama tíma sprautaðist hraunkvika í bogadreginni bunu út úr gígopi á norðvestur gígveggnum utan verðum (myndband 2021-09-12C) og er greinilega beintengt gígopunum sem eru innan í gígnum. Frá þessu gígopi rann hraun í nokkrum álum út yfir hraunið sem var fyrir í Geldingadölum (myndband 2021-09-12D).
    (iii) Vestar í Geldingadölum rann einnig hraun, en það kom frá „kvikuhverum“ sem mynduðust á nokkrum stöðum í hrauninu vestast í Geldingadölum (myndbönd 2021-09-12D og 2021-09-12E). Þetta hraungos er augljóslega ekki afleiðing yfirborðsvirkninnar sem var í gígnum á þessum tíma, því að hraunbreiðurnar eru aðskildar (myndband 2021-09-12D) og hluti hraunsins sem kom upp um þessa „kvikuhveri“ flæddi í austur (þ.e. á móts við hraunálana frá „sprautunni“). Sem sagt, eins og glóðin í himnaljóranum og sinurnar í Geldingadölum bera vitni um, þá hefur óafgösuð kvika streymt niður í og safnast fyrir í Geldingadölum undanfarna 8-9 daga. Í gær var innri þrýstingurinn í þessari tjörn nægilega mikill til þess að brjóta sér leið upp í gegnum hraunskorpuna þar sem „kvikuhverirnir“ mynduðust (myndband 2021-09-12E). Kannski er þetta gott dæmi um „svæðisgos“, eins og þau voru hugsuð af þýska eldfjallafræðingnum Hans Reck upp úr 1910? Það er hugsanlegt að einhver aukning á kvikuflæðinu efsta hluta gosrásrainnar hafi átt þátt í því að koma virkni gærdagsins af stað.

    Hi all
    Yesterday the eruption at Fagradalsfjall ones again put on a show as surface (visible) activity resumed after a 8.5 day-long pause. A visit to the eruption site yesterday late afternoon not only captured a good overview of this activity, but revealed several interesting features. However, first it is useful to point out that the eruption did not stop despite this 8.5 day pause in surface activity. It is evident that the opening that fed vent 5 clogged up, which prevented magma from entering the vent over this time period. This also halted formation of very large gas-bubbles, which explains the drop in tremor intensity. Yet, periodic but weak tremor episodes, steady outgassing from the vent, incandescent lava in skylights above lava tubes and newly scorched vegetation along the lava margins in Geldingadalir is a testimony that magma was streaming up through the conduit towards the surface during this 8.5 day-long pause in the surface activity.
    This is further confirmed by the observations made during yesterday’s visit and below are the key points:
    (i) The magma that was flowing yesterday into vent #5 did so through an opening at the base of the northwest crater rampart (Video 2021-09-12A) and later it also flowed out of openings higher up on the rampart, falling to the crater floor in impressive lava falls (Video 2021-09-12B).
    (ii) At the same time the lava issued via sideways jet from a vent on the outside of the northwest rampart (Video 2021-09-12C) producing a few lava streams that flowed onto preexisting lava in Geldingadalir (Video 2021-09-12D) . This opening is clearly linked to the openings on the inner wall.
    (iii) Lava was also spreading out in western part of Geldingadalir, but originated from several “secondary” vents (Videos 2021-09-12D and 2021-09-12E) that had opened up through the surface crust of the lava already residing in this part of Geldingadalir. Also, it is clear that the formation of this lava is not a direct consequence of the lava issuing from the opening at vent #5, because these new surface flows are distinct identities and clearly issuing from separate “vents” (Video 2021-09-12D). In other words, as is evident from the incandescent lava in the skylight and newly scorched vegetation in Geldingadalir, undegassed lava was flowing via internal pathways down into and accumulating in Geldingadalir during the pause in the surface activity. Apparently, yesterday the inner pressure in this ponded lava exceeded the strength of the overlying crust and lava began to bubbling up through the “secondary vents” (Video 2021-09-12E) and producing the surface flows that covered the western part of Geldingadalir. Perhaps, this activity can serve as an example of Areal eruptions mentioned by the German volcanologist Hans Reck around 1910?”

    • So basically the vent was blocked so it formed a sill at a shallow depth which is now erupting in multiple locations. Would seem the conduit relocated a bit north under the north wall to me, the lava is not flowing completely horizontal but there is fountaining up, like a fissure trying to fountain through a moving flow and being partly diverted over. Will be interesting when the wall fails, it looks powerful, we might see a return of high fountaining.

      • We have 12 hours now of constant highest tremor. Did the assumed blockage produce the on/off regime we saw until now? (Just a thought)

        • Now a storm is coming, all readings are going to be unreliable for the next 12 hours or so.

          • The wind wouldn’t influence the blue high frequency graph that much, would it?

            The volcano is active at 1400:

          • The blue high frequency graph is so high during eruption that weather is insignificant. The visible rise in low frequency purple one however is due to weather.

    • Secondary vents? Okay, so plugging the main vent led to sill activity (and some type of rock cracking is visible in the FAF high-pass seismogram the past few days) and finally the fresh gassy lava finally had to erupt on the surface. I guess the question is whether or not the internal pathways connected with the main conduit. The change in location of the conduit to about midpoint of the cone wall is an interesting phenomena. Now it’s been foggy for several hours, but I am sure that lots of lava has been emplaced in Geldingadalir itself.

  8. Oh, no Natthagi cam doesn’t like work on sundays, hope mbl fixes them again .
    Only the still cams work but it’s foggy today, …. tomorrow?

    • My link to the MET Natthagi still camera stopped working about a month ago. Do you have a working link?

      • At this moment, not one cam is working.
        I go to yt, find mbl, then select in the overview the cam.
        I think links are changing.

  9. Quinauberon
    (No reply button on your last post above). I went back a bit before 14:00 – you can see lava popping up in the crater at around 13:53 or so. Interesting that it is still filling up. Not that we will be able to see any consequences anytime soon.

    • There is a thread in the newest article about this topic…I give you my condolences for your ignored comment

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