When a mountain blows its stack, most of us lose our cool.
Massive erupt at the Lewotobi volcano in Flores island, Indonesia 🇮🇩 (07.11.2024) pic.twitter.com/4EBmGZ1mwj
— Disaster News (@Top_Disaster) November 7, 2024
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Residents react to an unexpectedly strong eruption at Mount Lewotobi, Flores Island, Indonesia, on November 7, 2024.
And when a whole mountain explodes —
— well, can we even think rationally?
Of course we can (from a safe distance in time; the caldera that Crater Lake occupies formed almost eight thousand years ago, and there haven’t been similar VEI 7 eruptions — that experts know of, anyway — since 1815).
Park rangers and other experts in the Crater Lake video are serious, and they know the audience is, too.
We are part of that audience of rational people.
Wonder and other emotions are certainly there, but so is the knowledge that 1815 isn’t all that long ago.
We have some serious questions about the “big ones,” but it’s hard to find answers.
- Those sensational articles and videos online are fun when they try to be factual, but they don’t really get much beyond the “Wow! That’s BIG!” stage.
- Volcanologists and other knowledgeable authorities have many of the same questions as ours and more besides, but the boffins can be hard to follow.
I’ve read a few of the many scientific papers on VEI 7 eruptions for this blog post (see source list) and believe that some of the simpler points sank in.
What little I’ve learned is worth sharing. High-end eruptions like Tambora’s in 1815 are serious business, wherever they occur, not only because of the local devastation but also because they have global effects if circumstances are right.
I don’t know about Crater Lake — it happened before historical record-keeping (although some of today’s descendants of local survivors remember the old stories) — but circumstances definitely came together at Tambora, as you can read in this paper, a rare blend of readable popular science AND a highly cited research paper.
Among Tambora’s effects were the infamous “Year Without a Summer” in 1816 and the deaths, both directly and indirectly, of tens of thousands of people. (Oppenheimer, 2003; 2011)
🌋🌋🌋
Let’s ask, and try to answer, just three basic questions about VEI 7’s (two of them concerning Crater Lake):
- Exactly how big was the Crater Lake blast — a supereruption?
- Will Crater Lake erupt again?
- When is the next big one due — and where?
Crater Lake
Second question first, because it has been answered by the US Geological Survey (USGS):
The long history of volcanism at Mount Mazama, the volcano that houses Crater Lake, suggests that this volcanic center will be active in the future…
They don’t give any information about the scale of possible future activity — and couldn’t, even if an eruption was on the way (it’s not: Mazama is sound asleep, reports the Cascades Volcano Observatory, and most of the park is open, weather permitting).
Also, Colucci and Papale note that expert monitoring today can pick up early signs of awakening at a volcano, but geoscientists have no way yet to accurately forecast how big an eventual eruption might be.
How large was the Crater Lake blast?
Mount Mazama’s caldera-forming eruption 7700 years ago — the caldera that now is filled by Crater Lake — was big, but it wasn’t supersized.
To see a “super” crater lake, you’re gonna need a higher satellite:
That arrow on the left points to Lake Toba, and the blue seas at the top and bottom of the image are washing opposite shores of the big Indonesian island of Sumatra. (Image: Overview, CC BY 2.0); Samosir Island, in 62 x 19-mile Lake Toba, is a resurgent dome, as is the much smaller Wizard Island in 5 x 6-mile Crater Lake. (Image: kris, CC BY-SA 2.0)
Based mostly on the geologic record of material that fell out of the eruption plume or was deposited by pyroclastic flows (Cashman and Sparks; Crossweller et al.; Mason et al.; Newhall, Self, and Robock), many experts have classified the Crater Lake and Toba eruptions as a 7 and 8, respectively, on the Volcanic Explosivity Index (VEI).
What does that mean?
A picture is worth a thousand words: Geology.com has a nice image, in their article on the VEI scale, that shows relative sizes of some famous present-day and prehistoric eruptions, including both Crater Lake and Toba.
Since geologists are ingenious, this isn’t the only eruption scale out there, but VEI is the one that we laypeople have heard of and it’s also the scale most widely used in scientific papers. (Crossweller et al.)
It ranges from VEI 0 “gentle” Hawaiian-style lava flows up to the VEI 8 “colossal” ash hurricane that is a supereruption.
That’s quite a range!
They do it with logarithms — with certain low-end exceptions (which don’t concern us here), each level is ten times larger than the one before it.
So Toba’s VEI 8 activity was ten times bigger than Crater Lake’s VEI 7 blast and came through a sizable chunk of northern Sumatra, while Crater Lake involved a single mountain.
As we’ll see next time, supereruptions are amazing!
In case you’re wondering, there is no VEI 9.
Theoretically, it’s possible: the scale is open-ended. However, Newhall and Self, who first proposed the Volcano Explosivity Index in the early 1980s, noted that eight was the maximum number of categories they could distinguish in their study of eight thousand past and historic eruptions.
As we will see next time, there can be “size 9” eruptions, using a slightly more precise magnitude scale.
For now, though, let’s just stick with what we’re familiar with and see if we’re overdue for another VEI 7.
When will the next VEI 7 happen, and where?
Newhall, Self, and Robock wrote in 2018 that it could happen at any time.
Thus far, thankfully, it hasn’t.
A scene from the climactic VEI 6 phase of Mount Pinatubo’s 1991 eruption. Now upsize it x10. (Image: NOAA via Wikimedia, public domain).
They also gave odds that, globally, one or two VEI 7 eruptions could occur every thousand years.
So that takes the world up to 2815.
But what’s the actual risk we’re facing today?
When?
It all depends on magma, which comes up from the planet’s mantle and moves through the outer crust; available storage spaces and paths for that magma; and various other factors.
Boffins know very little about all that because there is so much rock between them and what they need to study.
This is where the heavy-duty science comes in — statistics and computer modeling, as well as all the relevant geoscience (chemistry, physics, thermodynamics, fluids, etc.)
Eeek! 🤯
But still, it’s an interesting question, and we all are stakeholders.
Let’s leave technical details to the boffins (and their many, many papers) and instead focus on a point that Poland and Anderson, among others, make: the largest eruptions occur after very long rest times.
They catch us off guard. As Crossweller et al. note, these big ones thus have the highest death tolls in historical times.
This was true of Tambora, as mentioned — the biggest blast on record. (Oppenheimer, 2011)
People thought it was either dormant or extinct until it woke up in 1812 and, three years later, shook the world.
It was also true of Mount Pinatubo, as this video shows:
Yes, that’s the same Newhall who coauthored papers listed in this post.
He and, I think, all of the other USGS people in that video were also involved in the Mount St. Helens eruption of May 1980, and that was intense, too. (Thompson)
In these pressure-cooker circumstances, volcanologists need to always be on top of the hazardous and rapidly changing situation as well as in constant communication with civil authorites and the media, yet it’s difficult to think clearly — that’s just human nature.
So Newhall, Hoblitt, and others worked up a statistical tool called an event tree and applied it to their short-term forecasts of the volcano’s next move. (Newhall and Hoblitt)
This layperson knows nothing more about it but apparently they had good results.
Volcanoes, like cats 😉 , are very unpredictable, but the event-tree approach now seems to be in fairly widespread use, judging by Google Scholar results.
As the hypothetical next VEI 7 eruption approaches, event trees probably will be constructed. Their databases, hopefully, will contain enough information from all the ongoing twenty-first century research into VEI 7’s to identify a possible VEI 7 tree branch.
Then talk about pressure!
The scale of pre-eruption emergency response needed for a Tambora or Crater Lake-sized eruption would make a false alarm disastrous in terms of public trust in scientists.
Yet if the forecasting tools did raise that possibility but the experts didn’t warn people, thousands to millions of people could die.
Well. Let’s hope such a trial for all concerned, scientist and layperson alike, never comes up in our lifetime.
🌎🌏🌍
Anyway, this layperson guesses that event trees and other such tools could tell scientists an idea of the “when.”
However, the intensity of the coming eruption might not be clear until just before it occurs or even during its start, which is too late to take emergency measures.
Newhall, Self, and Robock write:
Because uncertainties will be high at all but the final steps to eruption, scientists will need to set aside their usual conservatism, and their usual high standards for certainty, and simply make the best calls that they can in close coordination with civil defense officials who will manage mitigative measures. Risks of false alarm may be high, but risks of not taking precautions will be even higher.
And we laypeople need to be as forgiving as we can when there is a false alarm.
The volcanologists and emergency managers are doing the best they can — and one day, for sure, the forecasted big one will happen.
Where?
A thousand years is only a byte of geologic time, and since we’ve got until 2815 (theoretically), it’s safe to assume that no VEI eruption will happen in North America’s Great Plains or in the ancient mountains along its eastern coast.
Most of these big events occur in subduction zones (Newhall, Self, and Robock), so the western coast of North America — home of Crater Lake/Mazama — is a possibility, as are most locations along the Pacific’s “Ring of Fire” and elsewhere on the planet where active volcanism exists in a subduction zone.
There are some exceptions, notably, Changbaishan on the China/North Korea border.
That isn’t obviously located on a tectonic plate boundary and yet it’s there. In fact, its VEI 7 Millennium Eruption is one of the two biggest post-Ice Age eruptions in the LaMEVE database. (Brown et al.)
LaMEVE stands for Large Magnitude Explosive Volcanic Eruption. The database contains records of all known or potential VEI 4 events upwards, going back into the Pleistocene.
This link should give you their list of all volcanoes known to have had a VEI 7 eruption.
There is much other information in the listings, too, including eruption magnitude, which is another scale that roughly corresponds to VEI and sometimes can be more precise.
For example, Tambora’s VEI 7 eruption has a magnitude of 7, but Crater Lake’s was magnitude 7.1 — a little bigger than Tambora’s blast.
We’ll get into that more in the next two posts, which are on VEI 8’s (superuptions) and magnitude 9’s (🤯).
Frankly, I was a little intimidated by LaMEVE at first but it and other databases, especially that of the Smithsonian’s Global Volcanism Program (GVP), are enormously helpful to volcanologists.
Brown et al. note that these records help identify high-risk locations and they also show gaps in knowledge that perhaps some fieldwork and other research might fill.
All of this improves our ability to get prepared, but it still isn’t possible to say for sure where the next VEI 7 eruption will occur.
Newhall, Self, and Robock used data and other criteria (like a past history of VEI 7’s) to speculate on likely candidates for another big one, but it’s only speculation.
And as Oppenheimer (2011) points out, there’s no reason why such an eruption couldn’t come from an unsuspected or simply unmonitored source.
Surprisingly few of the world’s known active volcanoes are monitored today (Newhall, Self, and Robock), and as far as I know, there is no hunt on to find unrecognized dormant volcanoes.
Why should there be? It’s hard enough to keep track of the active ones.
But recall that just one seismometer was there, more or less by chance, when Pinatubo began to stir.
As things turned out, that was sufficient — but what if there had been no warning?
Today, many dedicated earth scientists are hard at work in the hopes of collecting data and developing procedures and plans that will see us through a big one regardless of how much warning it provides before shaking the world once again.
Next time: The really BIG ones.
Featured image: Nadia Yong/Shutterstock
Sources:
Brown, S. K.; Crosweller, H. S.; Sparks, R. S. J.; Cottrell, E.; and others. 2014. Characterisation of the Quaternary eruption record: analysis of the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database. Journal of Applied Volcanology, 3: 1-22.
Cashman, K. V., and Sparks, R. S. J. 2013. How volcanoes work: A 25 year perspective. Bulletin, 125(5-6): 664-690.
Colucci, S., and Papale, P. 2021. Deep magma transport control on the size and evolution of explosive volcanic eruptions. Frontiers in Earth Science, 9: 681083.
Crosweller, H. S.; Arora, B.; Brown, S. K.; Cottrell, E.; and others. 2012. Global database on large magnitude explosive volcanic eruptions (LaMEVE). Journal of Applied Volcanology, 1: 1-13.
Mason, B. G.; Pyle, D. M.; and Oppenheimer, C. 2004. The size and frequency of the largest explosive eruptions on Earth. Bulletin of Volcanology, 66(8): 735-748.
Newhall, C. G., and Self, S. 1982. The volcanic explosivity index (VEI) an estimate of explosive magnitude for historical volcanism. Journal of Geophysical Research: Oceans, 87(C2): 1231-1238.
Newhall, C.; Self, S.; and Robock, A. 2018. Anticipating future Volcanic Explosivity Index (VEI) 7 eruptions and their chilling impacts. Geosphere, 14(2), 572-603.
Oppenheimer, C. 2003. Climatic, environmental and human consequences of the largest known historic eruption: Tambora volcano (Indonesia) 1815. Progress in Physical Geography, 27(2): 230-259.
___. 2011. Eruptions That Shook the World. Cambridge: Cambridge University Press. Retrieved from https://play.google.com/store/books/details?id=qW1UNwhuhnUC
Poland, M. P., and Anderson, K. R. 2020. Partly cloudy with a chance of lava flows: Forecasting volcanic eruptions in the twenty‐first century. Journal of Geophysical Research: Solid Earth, 125(1): e2018JB016974.
Thompson, D. 2002. Volcano Cowboys: The Rocky Evolution of a Dangerous Science. St. Martin’s Griffin (this edition: https://www.goodreads.com/en/book/show/178244.Volcano_Cowboys)
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