Talk:Volcanic Explosivity Index

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[edit] Fix

Than you for fixing the page. 164.64.161.97 17:51, 15 February 2007 (UTC)Dave Someone really messed with this page it is nolonger suitable for the academic use I need. 164.64.161.97 19:01, 8 February 2007 (UTC)Dave Freeborn New Mexico Office of Emergency Management

[edit] examples

Looking at both this article and the article on Vesuvius, it's difficult to imagine the 79 AD eruption (ostensibly a once-every-two-millenia event and a Plinian eruption) is not assigned a VEI in at least one of these articles.

Could someone who knows about this add a few major well-known eruptions to this page for perspective. For instance, Krakatoa, Mount St. Helens, Pinatubo, whatever. --rmhermen

Krakatoa was a 6, Mount St. Helens a 5.

I added some more "interesting" eruptions. However this list could get really big. I don't think this is the right page for this list. List of volcanoes is also not the right place since volcano and eruption are not the same (many volcanoes on the current list should be on it multiple times). I think there should be a new page list of volcanic eruptions. See also List_of_volcanic_eruption_deaths, Top_10_most_deadly_volcanic_eruptions. Maybe it should be list of largest volcanic eruptions. Jdorje 02:12, 21 May 2005 (UTC)
Honestly making a list by hand is probably not a good use of time. The global volcanism program already has a huge database of eruptions. Simply looking at this list of VEI 4+ eruptions [1] should be intimidating. Looking closely at the information for each eruption you'll see the amount of raw data they have is staggering. Jdorje 04:41, 12 July 2005 (UTC)
I agree that the eruption list is useless. As noted, the The Smithsonian Global Volcanism Program maintains a database of eruptions, constantly updated, for all volcanoes with eruptions in the last 10,000 years. Currently there are more than 9,500 known eruptions from over 1,500 volcanoes. Why try to reproduce any of that by hand when it will be out of date almost immediately? I won't delete it due to a "conflict of interest" though. GVP Webmaster 22:19, 26 December 2006 (UTC)
What about Cosiguina eruption (Nicaragua) of 1835 ? I think it should own a respectable VEI...(didn't it deposit ashes until Mexico/Jamaica/Colombia ?)

[edit] vei 8

The table in this article states that there has been only one (known) vei 8. However, in the article about supervolcanos about 10 examples are given. Either I'm missing something or one of these articles is mistaken. S Sepp 16:19, Oct 29, 2004 (UTC)

I think what they mean there is that, in human history, only one VEI=8 event, Toba, is known to have occurred. --Golbez 04:12, Dec 29, 2004 (UTC)

What it means is in human lifetime the toba eruption is the only one to have occured. This is wrong Lake Taupo erupted 26,500 years ago erupting over 1,170km3 making it a super-euption also. Also 7 other vei 8 eruptions have happened in the last 30 million years but these were not in human lifetime. The others are stated as supermassive eruptions (VEI7) not super eruptions like Taupo or Toba.

[edit] 1 and 2

Is the jump between 1 and 2 a mistake? The only authority I see for it is the USGS Glossary illustration which could easily be in error. No acknowledgement appears in the text, which is vague or even contradictory ("Each increase in number represents an increase around a factor of ten. The VEI uses several factors to assign a number", but "[in the figure] Each step increase represents a ten fold increase in the volume of erupted pyroclastic material"—except for #1!). Kwantus 01:24, 2005 Jan 5 (UTC)

[edit] power output

I know little about vulcanology (although I know more now:>), but from what I can determine, the power output of an eruption seems to be a significant measure of volcanic explosivity. The VEI classification does not consider this. I have preemptively added a statement on this issue in the article, but a section detailing the weaknesses of this classification might be better. Opinions?--ChrisJMoor 02:25, 12 Mar 2005

[edit] Megatonnage?

Several of the articles linked to or from this one mention explosive power in megatonnes. It would seem that adding a column to the table giving ranges would be very useful. Anyone know of such info? Maury 19:25, 10 Apr 2005 (UTC)

I have my doubts about the megatonnage calculation. I don't know the original source -- the 200 megaton number is replicated all over the Web.
I'm uncertain about these numbers. Consider Krakatoa. The amount of energy to lift 10 cubic kilometers of material with a density of 3 gm/cm^3 to a height of 25 km is about 7 x 10^18 J. A megaton of TNT is (somehow) calibrated to be 4.2 x 10^15 J. So, my rough computation is that Krakatoa would be 1600 megatons! Well, maybe not all of the material was lifted all the way to 25 km, but 200 megatons would imply it was lifted an average of 3 kilometers. Maybe we need to divide the plume height by 8, to get an average height?
I hope an expert on computing the energy of volcanic explosions will chime in. -- hike395 20:42, 10 Apr 2005 (UTC)
Making up numbers like that isn't a good idea since there are too many variables for us to take into account. However 7 x 10^18 doesn't seem that high; the 2004 Indian Ocean earthquake is estimated at 2.0×1018 joules. I'd agree that the measurement of energy would be the most accurate method of assessing a volcano's explosivity, but I have no idea how a volcanologist would go about calculating that. The Moment magnitude scale might be useful here - naively I would assume a VEI 6 volcano would be similar to a magnitude 9 earthquake. Jdorje 02:22, 21 May 2005 (UTC)

[edit] Problems with VEI

I'm no volcanoligist, but simply trying to explain and categorize existing volcanoes on Wikipedia shows up several major problems with the VEI system. (All numbers below are for the purposes of argument; most are from memory and may not be accurate.)

  • Quantization. While earthquakes are measured using a continuous system (to one or two decimal places) most volcanoes explosivity measurements have only one significant digit. This is a major problem when comparing volcanoes of near-equal explosivity that happen to fall on different sides of the boundary, or for very different volcanoes that happen to fall in the same category. For instance Tambora (80-150 km³) was a minimal VEI 7 volcano while Long Valley Caldera (750 km³) was a a very large VEI 7. This is also a problem when there is uncertainty about the eruption size. Consider Santorini (50-200 km³), Taupo (85 km³), and Tambora (80-150 km³). Should Taupo be a VEI 6 while the others are VEI 7, even though Taupo could have been the largest of them? Very rarely I've seen decimal places used in the literature (one source claimed Santorini was a 6.9), but almost all sources stick to integers (sometimes with caveats, like "6-7" or "6+").
  • Different measurement techniques. From what I've read, geologists looking at ancient eruptions usually measure in "dense rock equivalent". Thus Toba erupted material equivalent to dense rock of 2800 km³. By comparison modern eruptions are usually measured using whatever scale is handy. Pinatubo erupted 10 km³ and Mount Hudson 6 km³ of ash, but this would be the equivalent of only a small fraction that amount of dense rock. By comparison Laki released 14 km³ of lava (dense rock) and another 12km³ of tephra (mostly ash). Looking at the weight of the ejecta can help in comparisons here, but most sources don't include the weight. It seems obvious that the best solution here is to look at the amount of energy released in the eruption rather than in the amount of rock released (see "megatonnage" discussion).
  • Explosivity isn't a good indicator of effects. In many eruptions it's not the explosion itself that causes effects. Pinatubo, Hudson, El Chichon, and (presumably) Tambora and Toba's largest effects were from the release of sulphur dioxide, which may itself not have been at all explosive but had the largest global effects (in particular El Chichon was only a VEI 4 but had a larger global impact than any recent VEI 5 eruptions). This is true of earthquakes as well to some extent - location and type of the earthquake play a big role in how much devastation it causes, as the two recent Sumatran earthquakes have shown - but this isn't really the same thing since earthquakes don't have global or long-lasting impact.
Sulfur dioxide emissions by volcanoes.
Sulfur dioxide emissions by volcanoes.

I guess my conclusion would be that the VEI measurement is immature, much like the Richter scale measurement was before it. A more advanced measurement would probably give two numbers. An explosivity magnitude would be measured from the energy release of the eruption and could be calibrated either to use the moment magnitude scale or to correspond roughly to the current VEI system. Meanwhile the climate effect value would approximate the global climate effect by measuring the amount/effect of different climate-effecting gasses (SO2, NO2, CO2) that were released by the eruption (see sulfure dioxide figure, right).

Also, I wonder if the problems with the VEI system should be put into the article (the measurement techniques issue is already mentioned).

Jdorje 05:32, 12 July 2005 (UTC)

[edit] last-10000-years numbers

These numbers need some sort of disclaimer because they are known to be incomplete. There are 4 VEI7 eruptions, one every 2500 years - the last one happened to be just 200 years ago but this is coincidence. There are 43 VEI6+ eruptions, one every 250 years - but there have been 4 (Tambora, Krakatoa, Katmai, Pinatubo) in the last 200 years alone. Further down the list there have been 4000 VEI2 eruptions - one every 2.5 years - but these are listed as weekly occurrances. My point is just that many/most eruptions of the last 10000 years are not known, particularly for the smaller volcanoes. Someone looking at these numbers expecting to get something out of them will be rather mislead. Jdorje 16:00, 21 September 2005 (UTC)

Is it that evidence of VEI-6 can usually be found, VEI-5 if one looks close enough? For smaller eruptions I guess the number will always be inaccurate, as the evidence is destroyed in later eruptions. —Preceding unsigned comment added by 91.153.52.32 (talk) 04:55, 23 September 2007 (UTC)

[edit] km³ versus m³

someone was asking about these comparisons...1 km³ = (1000 m)³ = 109 m³ = 1 billion m³. — jdorje (talk) 17:52, 9 February 2006 (UTC)

[edit] The Fish Canyon Tuff (La Garita Caldera) was not a VEI-9 eruption

Someone has stated that the Fish Canyon Tuff from La Garita Caldera was a VEI-9 eruption and that the volume was 18,000 cubic km. Both are inaccurate. Nowhere in the article [2] does it state that the FC Tuff had a high volume as this. In fact, it's still stated as 5,000 cubic km in that article by Mason et al. [3]. Because the volume erupted is less than 10,000 cubic km, it is still a VEI-8 eruption. If you read the article carefully (see first link in this paragraph), you will notice that "Magnitude" is really a separate scale, and it is important to note that VEI and magnitude measure eruption sizes differently. VEI measures eruption sizes based on volume of magma erupted in cubic km and eruption column height. Magnitude, as used in the article by Mason et al, measures eruption size based on mass of magma erupted in kilograms. NorthernFire 06:10, 26 July 2006 (UTC)

Sorry, that was me. I misread the article. Thanks for fixing my mistake. -- Avenue 08:58, 27 July 2006 (UTC)

[edit] Date of Taupo eruption (holocene)

Now what is the exact date of the Taupo eruption, that supposedly caused red sunsets in Rome? I've seen anything from 177 to 186 AD thus far. So what is the latest? I think 177 is, dated via Greenland ice-cores by Zielinski (Science 264 [1994], p. 948f.). I am right? --Bender235 20:14, 13 December 2006 (UTC)

[edit] Flood Basalt vs. Tephra

It seems that some Flood Basalt events have been added with very large VEI numbers due to the volume of the products. But the definition at the top of this VEI article says that VEI is based on the volume of Tephra. To the best of my understanding, Tephra is airborne matter whereas a Flood Basalt is floods like a liquid.

So is the definition of VEI wrong in this article, is it an error to include Flood Basalts in the table, or is my understanding in error? -- Cjensen 02:54, 17 January 2007 (UTC)

  • It is probably an error to include flood basalts in the manner it was done in this article, thus I've removed the VEI-9-11 info in both tables in the article. Also, the uppermost limit of the VET is apparently 8 according the the Smithsonian Global Volcanism Program (Smithsonian GVP) - there doesn't seem to be any such thing as a VEI 9 or higher. You are correct in that tephra is airborne pulverized volcanic rock. It's really another name for volcanic ash. The VEI is not without its flaws, and I believe they take into account more for explosive eruptions of tephra. Take for example the Eldgjá fissure eruption in Iceland in the year 934 CE. It erupted over 18 km2 of basaltic lavaa - the largest known eruption of lava in historical times, yet Eldgjá erupted only 4 km2, so it mostly effusive/mildly explosive in nature and was assigned a VEI of 5. In comparison, Krakatoa was over 20km2, made mainly of tephra and was assinged a VEI of 6. Speaking of flood basalts, a flood basalt does not just form from a single huge individual eruption of lava. Rather, a flood basalt is made up of hundreds or thousands of individual eruptions of fissure-fed lava flows over a period of several million years, and they would have been mostly effusive, although there is evidence for some fairly large steam-generated eruptions in flood basalts perhaps prior to the actual fountaining of lava as the magma hit groundwater. But many of those individual eruptions of lava in a flood basalt can still be quite huge, generally anywhere from 100 km2 to over 2,000 km2 - about the same volume range for large caldera-forming eruptions like Yellowstone 640,000 years ago. The only difference is the kind of magma that comes out. NorthernFire 22:19, 21 January 2007 (UTC)

I Agree maybe a new system is needed so that it judges both tephra and basalt eruptions. Wiki236 14:19 25 January 2007 (UTC)

[edit] Tenerife

Does anyone know if the Caldera on the Island of Tenerife (Las Cañadas) is a supervolcano or not?. All I know is that it was most likely created in a VEI 7 explosion 150,000 years ago, could anyone help me out? Wiki235 18:15 31 January 2007

[edit] Discontinuity between VEI 0 and 1

This topic had already been mentioned some time ago, and maybe a solution has been found meanwhile (but not mentioned in the article). There is a discontinuity in the amount of ejecta that increases by a factor of 100 between VEI 0 and 1, but by a factor of 10 in the rest of the table. Apparently, this table (and probably most of, if not all other VEI-related web sites) is based on this USGS page. As can be seen there, this discontinuity could easily be caused ba a simple misprint in the labels within the diagram since it is never mentioned elsewhere. If this discontinuity is a feature, what is the reason for it? Since this discontinuity is obvious, it should be mentioned in the article (at least the fact, that the reason is unknown).--SiriusB 08:51, 29 May 2007 (UTC)

The original paper proposing the scale (Newhall and Self, 1982) is cited in both our article and the USGS page you linked. It would probably be the best place to look for a reason for the discontinuity. I agree it would be useful to at least note the jump in our article. -- Avenue 14:22, 29 May 2007 (UTC)
Unfortunately, I have no access to this paper (probably there is no scanned version online according to the ADS). If anybody has access to it via a library of a geological institute or so, it would be nice if he or she could have a look into it. Meanwhily the USGS page appears to be the only public source, and therefore the possibility of a simple misprint in the figure (as fas as I can see it is the only source for all public available data including this WP article) is not ruled out.--SiriusB 12:41, 5 June 2007 (UTC)
It is not the only online source. For example, the tables in this definition from the Smithsonian Institution give the same cutoff, twice. I don't think the suggestion that it's an error has any credibility, and I've deleted it from the article. -- Avenue 03:22, 6 June 2007 (UTC)
However, I cannot see any explanation for this discontinuity, and unless one of us gets access to the Newhall C G, and Self S (1982) paper (which seems to be the origin of the table) we cannot rule out the possibility of an error (errors of this kind happen much more often even in fully refereed papers than most people think). I think that this discontinuity is so striking that an error seems to be more probable than a real feature (that otherwise would have been discussed somewhere). On the other hand, if it is intentional then it casts doubts on the usefulness of such a definition of the VEI unless explained plausibly (not only in a non-free paper but also on the public web pages). Therefore I suggest to mention this possibility in the article.--SiriusB 17:21, 7 June 2007 (UTC)
Personally, it doesn't surprise me that smaller eruptions would be treated differently by the scale, but that is not the issue. Discussing your personal speculations about possible scale errors in our article is not appropriate. Please do not add them unless you can provide an external source mentioning at least the possibility of an error. -- Avenue 22:29, 7 June 2007 (UTC)
Unfortunately, the Newhall/Self 1982 article is not available online (even to university subscribers), so I'll just go and photocopy it from the library tonight. But I think it's likely that the factor of 100 was done intentionally so that VEI 0 would contain only non-explosive eruptions. Incidentally, I think the table at Volcanic Explosivity Index#Classification may have an error, in that the VEI 0 ejecta volume should say "<10,000 m³" instead of ">1,000 m³". This is what both USGS and GVP imply. But I'll wait to make any changes until after reading the original paper. --Seattle Skier (talk) 22:49, 7 June 2007 (UTC)

Well, I photocopied the Newhall/Self 1982 article (BTW, the reference to it was wrong, now fixed), and I have read through it twice. The VEI scale is now correctly presented in the article: VEI 0 is < 10,000 m³, while VEI 1 is between 10,000 m³ and 1,000,000 m³. The paper provides no explanation for this, but the authors spend much time and effort discussing the approximate nature of the scale and the difficulty of categorizing eruptions below VEI 2. So it appears likely that this extra order of magnitude was done simply to ensure that truly non-explosive eruptions would fall definitely into VEI 0, while the extra-broad VEI 1 classification could accomodate all borderline exposive eruptions (that's my own opinion based on reading the paper). I don't think there's any legal way to post the Newhall/Self 1982 article online, so others will have to track it down in their local university library and draw their own conclusions, if they wish to do so. --Seattle Skier (talk) 06:46, 8 June 2007 (UTC)

[edit] VEI-9

shouldn't the article mention VEI-9? 70.51.9.197 05:28, 13 August 2007 (UTC)

No. There is no 9 on the scale. — jdorje (talk) 23:04, 25 September 2007 (UTC)

[edit] Eruption count

According to the cited Global Volcanism Program page, no VEI-8 or "super-eruption" has occured in the past 10,000 years (which the table says it lists when it give 1 for VEI-8). The most recent eruption of that size was the Lake Taupo event around the end of the Last Ice Age 26,000 years ago. I think that whole erution count given for each category may need to be reassessed. -- §HurricaneERICarchive 03:00, 23 December 2007 (UTC)

[edit] Santorini

Hasn't Thera(Santorini) been reconsidered as a VEI 7 volcano?.

--Triou —Preceding unsigned comment added by Triou (talk • contribs) 23:00, 20 March 2008 (UTC)

Isn't that still a bit uncertain? The Smithsonian database says the Minoan eruption was "7?" on the VEI scale; this site reports it as 6.9. I'd be happy to see sources that confirm it. -- Avenue (talk) 13:08, 21 March 2008 (UTC)
The highest estimations for the Minoan eruption are 70 km3 tephra, which is still VEI-6 (a large one, tho). However, 30 km3 tephra is more likely. --Bender235 (talk) 19:31, 24 April 2008 (UTC)

[edit] VEI 9 and 10

Since the VEI is actually "open end", we might add a 9 and 10 on the scale, since there have been eruptions of the magnitude: Deccan Traps (VEI 9), Emeishan Traps (VEI 9) and Siberian Traps (VEI 10). ––Bender235 (talk) 19:31, 24 April 2008 (UTC)

None of those were formed in a single explosive eruption, so the VEI doesn't apply. -- Avenue (talk) 01:23, 25 April 2008 (UTC)
Even if they did form in a single eruption, none of those eruptions appear to be explosive; they're flood basalts. Black Tusk 01:40, 30 April 2008 (UTC)