PlanetGeo: The Geology Podcast
PlanetGeo: The Geology Podcast
What Makes Supervolcanoes? With Professor Shan de Silva and Dr. Rachel Phillips
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What distinguishes supervolcanoes from regular or non-super volcanoes? How many supervolcanoes are on Earth today? What are the precursors to supervolcano eruptions? In today's deep dive, Dr. Rachel Phillips, from GeoGirl, and I we got to talk to supervolcano researcher, Dr. Shan de Silva, to answer all your supervolcano questions (and more)!
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Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you. Hey folks, we've got a great episode for you today. I am doing another collaboration with Rachel Phillips, aka GeoGirl, on YouTube. And in this episode, her and I interview Shan DeSilva, Professor Shan DeSilva, Professor of Volcanology Emeritus at Oregon State University. And Rachel, as usual, asked her listeners several super volcano questions, and we got some good ones. We do go into the weeds about volcanology here. And Shan DeSilva also gave a talk at Penn State recently that triggered some really interesting conversation, I think, in this podcast. So if you're interested in super volcanoes, we got one for you. As always, you can follow us on all social medias at Planet GeoCast. Download our Camp Geo mobile app. First link in your show notes there. We're excited about new developments on that platform. Go there and also we appreciate some feedback. So if you are interested in giving us some feedback and maybe meeting with us, running through what your thoughts are on the app, design, outline, things like that, shoot us an email. There's a contact us link on our website, also a contact us link on the app itself. Just shoot us an email there, say hey, I'm interested in giving you feedback, and uh you might be able to get a free audiobook out of it. Alright, Shan DeSilva, here we go.
SPEAKER_00Hi, I'm Sean DeSilva. My full name is Shaunica. I am or I was a professor of volcanology at uh Oregon State University, and I'm now emeritus. I've spent most of my career studying very large explosive volcanism. And so we're gonna talk about super volcanoes and super eruptions today. Very exciting.
SPEAKER_01Which I'm so excited about. And clearly the viewers were very, very excited for this one because we got a record number of questions, and we will not get to all the questions, but supervolcanoes. So I feel like we taught we hear the word super volcano. Really, the only thing I picture is Yellowstone, because that's the only thing I know about. But can you just start with just general, like what is a supervolcano and how are they different than regular volcanoes?
SPEAKER_00Yeah, so the key thing I think is uh scale and uh explosivity. You know, it's a the the term supervolcano has um a checkered history because there's no formal definition. Uh and there's two scales uh that are often used. There's what's called the volcanic explosivity index, which is a scale that is a logarithmic scale, but it's a qualitative scale. It's sort of based on the amount of material that was erupted, so the ash, uh what we call tephra. Uh and then um the explosivity is based on largely the volume that was erupted. So Mount St. Helens 1980, for instance, is a VEI 5. It was one cubic kilometer of Tetra that was thrown out. A supervolcano is a thousand times that, VEI 8. So three orders of magnitude greater than a VEI 5. So if you can imagine, you know, at least a thousand Mount St. Helens going off at the same time, that would be a super eruption. So that brings up the link between supervolcano and super eruption. So a supervolcano is a volcano that in its history has produced at least one super eruption.
SPEAKER_01Wait, so a supervolcano uh can produce non-super eruptions or yes, in fact, most of the eruptions from supervolcanoes are small eruptions.
SPEAKER_00So if you take Yellowstone, for instance. Yeah. So Yellowstone has had three big, effectively super eruptions, but it's had probably 80, 90 smaller eruptions uh between and after these uh super eruptions. Oh I mentioned that there are two scales, right? There's the VEI scale, which is the volcanic explosivity index, and that's kind of this qualitative scale based on how much stuff is out there. Yeah uh the other scale is um a more quantitative scale, it's the magnitude. So it's based on a calculation of the amount of magma that was actually erupted, and that's called the n or magnitude scale. And generally VEI and magnitude are correlated, but there are some nuances because you can have ash deposits which are very low density, which when you actually calculate the volume in terms of magma volume, what we call dense rock equivalent, then the magnitude actually goes goes down. So our preferred definition is that a supervolcano is a volcano that has produced at least one M8 sized eruption.
SPEAKER_02So can I ask a question on that, Shen? So this VEI versus the M scale, maybe you can explain what are the factors that control the difference? So I'm just imagining there's a whole bunch of volume of magma down in the crust, and that all gets turned into ash at some level. But basically, VEI is a the is an ash volume and m is a magma volume. Is that kind of the difference? Or or does it have to relate to gas amount of gas in the magma chamber? Or what are things that control differences? You know, and and are there any volcanoes that are categorized as a supervolcano on one scale and not categorized as a supervolcanic eruption on the other scale?
SPEAKER_00Yeah, great question. So the bulk volume. So if you imagine, you know, you go to an outcrop and you find this ash deposit, that is um a function of the density of the actual rock itself. And there's lots of pore spaces, it's permeable and stuff like that. So you can have a big volume, which if you collapse down to its original magma volume, ends up being a smaller magnitude than the actual volume itself.
SPEAKER_02So you have to adjust in the rock and the ash and all this stuff.
SPEAKER_00So you have to adjust for the porosity and the uh density. Okay. And you can have so if you took uh you know the same volume of magma and you erupted it as a lava flow, and you erupt it as ash, you get a bigger volume of ash than you do lava. Right? Because the lava doesn't contain it, it's not fragmented and it's not you know frost up. So that leads to um differences in classification of some eruptions. That's why I said uh Yellowstone has had two definite super eruptions, but a third one could be a super eruption on one scale, but not on the other scale. I mean, these are nuances, but you know, they're big eruptions. And so then the question right, then it goes to, you know, this question of what makes an eruption or a volcano super.
SPEAKER_01Yeah, actually, I was gonna ask on that. You mentioned like super volcano is a volcano that's had at least one M8 or like, you know, super eruption. So can a regular volcano become super if it has a big enough eruption?
SPEAKER_00So then we get now we get into um we have to think about how does the earth actually produce a super eruption and a super volcano, right? So if you go to somewhere like the Cascades where we have all these composite cones, none of them have ever produced a super eruption during, you know, the last 600,000 years since the cascade started. Could one of those become a super volcano? Um, from what we know, I would say no, because the size and scale of the system depends on the amount of energy that's brought into the upper crust where the magma sits before it actually erupts. In the case of a place like the Cascades, the thermal energy that's brought into the crust uh is only capable of producing and incubating small volumes of magma. In order to uh grow to the size of a much larger system, there needs to be a completely different thermal environment. And the simple way of looking at this is that the reason a volcano erupts is that the magma that's stored underneath reaches a certain condition where it can fracture the rock surrounding it and produce a dike towards the surface, and that initiates the eruption, right? So that depends on the strength of the rock, right? So if you imagine a magma chamber sitting in cold rock, if you pressurize that magma chamber, that cold rock is going to reach a point where it's going to break. What's called a sort of brittle failure. In order to grow that system, we have to somehow stop that failure. Right. So one way uh we think that that happens is if you bring enough heat and you warm up the crust, you create a ductile environment. So then it's kind of like a balloon, then, right? So then the pressurization in the magma chamber is in an environment where the rocks are plastic and they can move. So when you pressurize the chamber, the rocks actually flow rather than fracture, right? And you know, there are nuances to this, but essentially to a first order, if you can warm the crust where you're growing your magma chamber, then that leads to feedback that results in growth rather than eruption.
SPEAKER_02Coska, quick question on that. So um, if the this fracturing mechanism to sort of initiate an eruption, yeah, is that the same as is it the same dynamic that would have that would allow for outgassing from a magma chamber? And so, you know, in your model, does a supervolcano not outgas because it's got this like you know ductile surrounding area, and whereas a normal volcano, or let's say a non-supervolcano, maybe, like the cascades, does outgas a lot because the cool rock is fracturing around it, allowing magmatic gases out, or is it is that really not part of the equation? The the gas content of the magma and how it gets out.
SPEAKER_00To a first order, I mean, uh we would have to argue that uh the the ductile halo around the chamber does uh retard sort of any kind of um simple uh fracturing. But in in reality, yes, there's probably damage and there's probably pathways and there are maybe locations, but it's not pervasive enough to actually drive a um a major uh eruption. And you know, maybe you do create cracks, but they get sealed up. But the key is that you know, you just need enough heat. The difference between a normal volcano and a supervolcano is the amount of heat that is brought up into the upper crust where it um where the magnet sits. Interesting, okay.
SPEAKER_01So that makes pretty clear that location matters, like the what kind of crust is there, um, how much heat is being brought into that. So that brings up another viewer question was do supervolcanoes have to be continental? Because you know, the examples that we we think about are Yellowstone and even large ones like cascades that aren't even super volcanoes, but these are continental. So, but then we think of things like Hawaii, where there's also volcanism, but not super huge. So is that because supervolcanoes can't be oceanic or can they be?
SPEAKER_00So again, this goes to the link. Uh the term supervolcano is linked to super eruption. The super eruption is an explosive eruption of a certain magnitude. Explosive eruptions happened with silicic magma, so silica-rich magma. In the oceanic environment, it's very rare to be able to produce large volumes of silica-rich magma. So you need about 65% silica or greater. Most super eruptions are that composition. Where on the earth can you produce that? Well, continental crust is the most likely place. And it's no accident that most of the supervolcanoes that we know are in places where there's thick continental crust. So that goes to the question of uh, you know, are things like flood basalts and so on, which are huge volumes, are those supervolcanoes, are they super eruptions? Not by the use of the uh the definition of supervolcanoes, because it has to be silicic. Well, it has to be explosive. And explosive eruptions are typically uh silicic composition.
SPEAKER_01Yeah. Okay, okay. So you can have huge volumes of magma brought to the surface in a more flood basalt, like oozy type of eruption, but if it's not explosive, which if it's an oceanic crust and not silicic crust, it kind of isn't, then yeah, okay, that's not not super volcano. Okay, good to know. So it's funny, I just had somebody on who talked about how like 80% of volcanism happens in the ocean. Oh, yes, on the seafloor.
SPEAKER_03Right.
SPEAKER_01And and yet, you know, the the other 20% is where we have the possibility of super volcanoes. So it doesn't seem like they're they're all that common, which I think leads us to the next question, which is where are the super volcanoes on Earth today? Like what are the other ones other than Yellowstone?
SPEAKER_00Yeah, so um the majority of them are around the Pacific Rim. And then there's a few odd ones scattered around. Now, some of that could be, you know, sampling bias that people have studied these things, and it could be that um, you know, the countries that have put effort into mapping these things are predominantly around the Pacific Rim and so on. But it's also no accident that, you know, subduction zones, uh convergent margins are the places where you have thick continental crust and lots of heat coming up from the mantle that then uh produces the conditions where you can kind of incubate super supervolcanoes. So it's interesting.
SPEAKER_01Sorry, go just Rachel.
SPEAKER_00Sorry.
SPEAKER_01Oh, I was just gonna say it's interesting that most of the super volcanoes today, as you just mentioned, are like along subduction zones, which makes sense for volcanology, right? You know, we get the subduction, the heat coming up, and it's under continental crust, so that creates explosive eruption. But then things like Yellowstone is a hot spot. So I'm curious if there are any other like hotspot supervolcanoes or if Yellowstone is unique.
SPEAKER_00Uh so Yellowstone is a hotspot that has hit continental crust. So, you know, there is heat and continental crust are the two ingredients you need. Uh, there have been similar volcanoes in other uh non-subduction zone areas. So in the Red Sea triple junction area of Yemen and so on, there are big uh super uh eruptions there. There's some in Ethiopia, um, but they're not not as well studied. But yeah, so anywhere you can bring enough heat and you have thick continental crust, uh, you can do that. But then the majority are along sort of convergent margins. Right.
SPEAKER_02So that that brings up an uh, I think a potential obvious question, Shan, is why are the cascades not producing supervolcanoes? Whereas the Andes or Indonesia, these other subduction zone systems have at least some supervolcanoes. What's different? Is there something different about the Cascades or the thickness of the continent crust or something that that you think doesn't allow for supervolcano production there?
SPEAKER_00So in the early history of the Cascades, there is some evidence that there were extremely large silicic eruptions before the current condition. So that then tracks to the evolution of the convergent margin, you know, what is the rate of heat production in the mantle and how does that propagate into so you know convergent margins go through cycles. There are times when, depending on the geometry and rate of subduction and so on, there are times when much more mantle productivity is um part of the system, and there you have what we call flare-ups. So, you know, sometime in the future, if the geometry and the uh rate of subduction changes in the in the uh western margin of North America, it may change to a flare-up system.
SPEAKER_02And then I want to maybe ask one follow-up question as well. Um, is Long Valley Caldera a super eruption by your definitions, the the big eruption there?
SPEAKER_00Yes, the Bishop Tuff uh does classify as um a super eruption, yeah.
SPEAKER_02So one I guess one part of that story, and I I only I know that well because we did a whole series on on Long Valley Caldera for our podcast, um, but was that this like pre the the essential sort of preconditioning of the crust, a lot of basaltic volcanism beforehand and then afterhand as well. Is that uh a necessary part of creating a super eruption? You need to like punch a bunch of basalt through the crust to heat it up such that you get you can build up a large magma chamber. Is that kind of the recipe for building a super volcano that you have to have like would you say if you're looking for old supervolcanoes, would you say, Oh, I have to find a bunch of early basaltic volcanism, then I might be in an area where a super eruption could happen. Is that a pre uh like a part of the recipe?
SPEAKER_00Yeah, I think uh that's certainly part of our model for uh super volcanoes is that you have to thermally condition the crust in order to sort of grow grow these systems.
SPEAKER_02So uh it's counterintuitive to that the you you'd think, I don't know, you kind of think, oh, you would want to store magma for a long time. Right. And then you create you would want no eruptions for a long time, then a big eruption. But you're you this preconditioning is kind of it's kind of non-intuitive.
SPEAKER_00This this the conditions that would allow you to store the magma for a long time have to be created over a long time. If you look at something like Crater Lake, for instance, right? There's the big 50 um the big eruption 7,000 years ago, but there's you know several hundred thousand years of activity before it got to the stage where it could actually incubate a uh very interesting silly volume.
SPEAKER_02Amazing.
SPEAKER_01Well sorry, I'm I need more clarification. What does the basalt eruptions, how does that condition for the super eruption?
SPEAKER_00So if you keep pumping basalt into the crust and it starts to focus in on a certain area, that whole area starts to get warmer, you start melting the crust, you start producing solicit magmas, and eventually that will lead to the conditions that you can grow larger and larger volumes. If the if the rate at which basalt comes up is slow, then you never reach those conditions. But if you get to a point where it goes above a certain threshold, then you you sort of flip the system into silicic systems. So the Valles Caldera in New Mexico is another perfect example. There's a you know several million years of basaltic activity before the big silicic system develops. And you know, there it's a rift. So it's not a convergent margin, but there you've got rifting of the continent, and that allows you know lots of basaltic magma to come up and um start processing the continent.
SPEAKER_01Okay, interesting. What is the most recent supervolcano eruption?
SPEAKER_00So the one that is cited most is um uh the one that we know best is the Uruanui eruption in um in New Zealand. Uh-huh. About 30,000 years ago. There may be some younger ones in uh in Japan. Let me just uh check here. I do have a list of interesting. Let's see here. The youngest one. Oh, there's the 7,000-year uh eruption of Kikai Caldera in Kyushu, 30,000 years in um Ira caldera in Kyushu. So Kyushu has three very young uh eruptions, which are actually uh so the 7,000-year one is a bit younger than the Uruanui, which is in New Zealand. So that's the youngest one as far as we know.
SPEAKER_01And I'm curious, you know, I'm actually surprised. I don't think this was a question, but it just came in my head now because I know I was asked this when I when I went to Yellowstone earlier this year, people ask me, but is there any sort of periodicity or cyclicity with regards to the eruptions? Like, say, you know, we we know Yellowstone's last super eruption was however many hundreds of thousands of years ago. And so does that mean that it's you know any closer to a next one? Like, is there any telling when the next super eruption from a super volcano would be?
SPEAKER_00Yeah, so I mean there is this periodicity that's attributed to so some supervolcanoes are multi-cyclic, that they have several super eruptions, and Yellowstone has had three, and they're roughly six hundred and fifty thousand years apart. So some people have argued, oh, you know, it's six hundred and forty thousand years since the last eruption, uh, it's overdue, and you know, that's the press like to uh pull that up, and it's sort of a media clickbait type thing. Yes. But um there are huge uncertainties on those dates. So, you know, hundreds of thousands of years of uncertainty. It depends on the thermal conditions. You know, you get may get to a point where after three cycles of super eruptions, maybe the the continental crust underneath that area just simply can't produce any more silicid uh volcanism. So, you know, the system. Uh dies off. I mean, three big super eruptions seems to be the limit. I you know, Toba has had three big eruptions. Again, two super eruptions, but you know, a couple of smaller ones. Yeah, it it I think you get to a point where you simply can't process enough of the uh crust that the system just sort of uh dies out after a time, even if there's enough heat coming in. Whereas Yellowstone, because it's moved, because the continent is moving.
SPEAKER_01That was my question.
SPEAKER_00Yeah, so that's a special situation where you know for 16 million years you've been producing supervolcanoes as the continent moves over. So you're continually moving new material into that heat source, and so that can kind of process stuff. So that's a special situation, right? Yeah.
SPEAKER_01So Yellowstone's so you you have said a few times it's had three super eruptions as like in its current location. Does that not count all the other places it's been like the hotspot has been under?
SPEAKER_00No, that's not so Yellowstone is merely the youngest uh expression of the hotspot uh on the continent. And if you follow the Snake River Plain down to the southwest, you get to the Oregon Nevada border, and that is the sort of uh the there's the Bruno Yarbage Center, which is about 16 million years, and that's the sort of initiation of that uh super volcano trend.
SPEAKER_01Okay, so very far. What is Jesse? Do you have a lot of things?
SPEAKER_02Oh, I mean, I've got thousands, but but I feel like I'm I'm talking too much, though. You are No, no, no. I mean, this is all this is all super interesting. I'm curious. I think we'll we'll come to some questions, but I'd uh I'm curious to touch on this point of like how I mean what's the proportion of super volcanoes that produce more than one super eruption versus the ones that produce like the one-off? Like Long Valley did the one-off, I think, and then but is that a is that more frequent to do the one-off thing, or is it more frequent to do the Yellowstone or the does Toba have a bunch of have have multiple eruptions that are super eruptions?
SPEAKER_00Yeah, so I think it's scale, it it it seems to scale with size. So the biggest ones seem to have multiple super eruptions.
SPEAKER_02Okay, okay, interesting.
SPEAKER_00Uh the ones that are on the margin have one big one and then they sort of um uh you know blow their top. But uh and I think when you look at it, it's kind of depends on the regional magmatic history. If it's a um a large region of supervolcanoes. So in the Central Andes, for instance, there's a region which there's nine supervolcanoes in an area the the size of Texas kind of thing.
SPEAKER_02And uh is that the is that where that Laguna del Male, I might be pronouncing that wrong.
SPEAKER_00That's that's actually not even a super volcano, but uh yeah, that's not that's uh that's in the southern area. But if you if you go up north in Chile on the border between Bolivia, Chile, and Argentina, is probably one of the largest fields of uh super eruptions. Kind of like the Great Basin of the Western US, where there's many, many, many.
SPEAKER_02Is that the is that the part of the subduction zone or the Andes that is the super thick crust, the central volcanic zone or something where it's really, really thick crust? Okay.
SPEAKER_00Yeah, so you know there's a parallel between there and the Great Basin because it was thought that during the time of super eruptions in the Great Basin, the crust was really thick, and you had equip it was sort of equivalent to the Andean structure that we have today. Okay. Fit continental crust.
SPEAKER_01Yeah.
SPEAKER_00Yeah, yeah, yeah.
SPEAKER_01Okay. Lots of material to work with. Okay. So what um another viewer question was what are the kinds of signs or precursors that we would expect to see leading up to a super eruption?
SPEAKER_00Yeah, this was a tough one. I mean, you know, the problem is that the time scale over which these things develop is you know, way beyond anything we have experience with. So what we do know about super super systems is that um they just state over hundreds of thousands of years. You know, what the expression of that uh building of that magma system, the model suggests that you know there's probably going to be topographic doming of some sort. But the time scale of seeing that is you know beyond anything that we would see. I think as you come closer to the eruption, then we'll sort of get into the type of things that we see in a in a normal, normal volcano where there's uh you know, I'm curious too, on that, you know, when you go to Yellowstone, you see, and I know geysers aren't uh, you know, analogous, but you sometimes see like a tiny little vent uh of a geyser next to a huge one.
SPEAKER_01So I'm curious if a super volcano was coming within the next, I don't know, 10,000 years, let's say like a relatively short time on geological time, would you see like smaller volcanic eruptions in and around the region before the big one went off? Like, is that would that happen or no?
SPEAKER_00I would say Or do we not know? Well, I mean, you know, again, we don't have experience, but uh again, what we do know is that you have to destabilize that otherwise stable system, you know. So it the conditions that actually grow these magma chambers are they retard eruption. So how do you actually erupt these things? Well, they have to grow to a certain size where simply the crust can't hold it anymore, so the roof just fails and it collapses in. So once you're at that threshold, then you would expect some instability in that system, and you know, you start propagating fractures and things start escaping. And I would expect that you do have to have initial eruptions that then kind of you know, you get this runaway effect. But um the the super volcano movie on Discovery Channel, I think does a really good job of um showing how right. Oh, interesting. Okay, well, that's good to know.
SPEAKER_02Well, one of one of the few that does a very good job.
SPEAKER_00Yeah, no, I I I I use it uh regularly. I mean, you yeah, there's very few places where I wince in that um in that movie. Okay, well that's good.
SPEAKER_02That's that's a good met that's a good metric. Um so I've seen some work uh from Yellowstone, from some of these the eruptions at the the the current volcanic center of Yellowstone that uh are looking at oh the ones I was looking thinking of are zircon geochemistry, and they're looking at zircon action isotopes and things like this. But basically their argument was that the Yellowstone eruption is tapping at various points in time different parts of or different magma chambers, different kind of chemically distinct areas within the crust. I mean, uh, what do you think of that model? How does that fit with super volcanoes? Is that a requirement of super volcanoes to have multiple, like multiple storage areas for magma, either vertically or laterally across their center, and then they they kind of tap those progressively through the eruption? Because I think is it Long Valley too that has this story of a six-day eruption that people can track by looking at the phenocrists assemblages in the in the tufts in the Bishop Tufts and kind of see oh it came from over here and then it moved west and throughout the eruption. Is that a common feature of these huge eruptions that they I don't know, they're kind of grabbing stuff from a bunch of different locations in the crust over time?
SPEAKER_00Uh yeah, almost certainly. I mean, I I think the exactly how things are organized are up for debate. Okay. But there's no question that the material, the magma that's erupted is not homogeneous. It's homogeneous maybe on a major element scale. But when you start looking at uh the crystals and you know trace elements, there has to be heterogeneity in that volume. So yeah, this idea of a big blob of magma that is homogeneous throughout is uh something that has uh gone away in the last 30 years or so. Um Okay.
SPEAKER_02Okay. Yeah. Interesting.
SPEAKER_01Yeah, I'm hearing more and more about that, about this uh you know, our typical textbook figure of a big balloon of magma underneath volcanoes, not well, you know, I mean necessarily.
SPEAKER_00The geophysics basically shows us, you know, blue and red. And red is you know areas with lots of melt, and um blue is cold rocks. So how things are organized in that red zone, we don't really know. And it's most likely that there's different melt contents and different crystal contents, and some parts are very crystal rich, which we call mush, uh, and other parts are not so crystal rich, which we call eruptible magma. And so, you know, then you get a lot of.
SPEAKER_02And what is the scale? What what is can you what is the percent magma in there of the differences between those? Of the mush. Broadly. Uh mush to eruptible.
SPEAKER_00Well, I mean, geophysically what we what we see is um underneath these systems is not much more than 20, 25 percent melt, but then you're integrating over the scale of the geophysical observation, right? So you could have pockets which are much more melt-rich than others, but it's a convenient way to think about it as mush. Yeah. And sometimes the eruptions will only tap melt, so you get crystal poor eruptions. Other times it will tap the crystal-rich portions and you get crystal rich uh eruptions. And you know, the prejudice in the system uh in in the community is that uh if you have fifty-sixty percent crystals, the magma is uh immobile, and so you have to kind of uh make it mobile in order to erupt. Got it. Okay.
SPEAKER_01Okay, so I want to move now to another question that's more on post-eruption processes or what happens after eruption. And so one viewer was curious how do super volcanoes affect climate?
SPEAKER_00Yeah, so you know, that's that's sort of a sin eruptive and a um yeah, uh what is the long-term global effects? Um essentially it's uh how the sulfur content of the magma is distributed into the atmosphere and depends not only on the sulfur content, but what happens is uh sulfur becomes sulfur dioxide. So it oxidizes, and that essentially acts as um an uh interceptor of uh the sun's radiation and cools cools the planet. But the effectiveness of that depends on uh the scale of the aerosols, you know, how small the uh aerosol bubbles are and so on.
SPEAKER_01Would carbon dioxide and methane and other like carbon compounds from the volcano from the eruption compete with that cooling effect from the sulfur to to have a warming effect, or is that a different time scale?
SPEAKER_00Um CO2 is uh limited in uh silicic systems. So, you know, water is the most abundant gas, and then yeah, maybe CO2 and SO2. The impact of SO2 is has a big, huge multiplier in the atmosphere. So that's the primary primary effect.
SPEAKER_01So I've talked a lot on my channel about mass extinction events in the pat, like millions of years ago, and a lot of them are associated with huge, like large igneous provinces, big volcanic provinces, or you know, things we call like Deccan traps, Siberian traps, these these traps. And so one viewer was curious what's the difference between these traps or these huge igneous provinces versus supervolcanoes? Like were they super volcanoes or were they not? And how how did they affect climate differently?
SPEAKER_00Yeah, so that goes to our definition of uh supervolcanoes and super eruptions. So lips, these bit large igneous provinces, they're primarily basaltic, they're non-explosive. Okay. So even though they're huge volumes, much larger than super eruptions in some cases, they're not considered uh super eruptions because they're not explosive. Okay. And also the the time scale over which the magma is ejected is much longer than in a super eruption. So there's the intensity and the explosivity that is an important part of uh super eruption and super volcano.
SPEAKER_01Okay, so it's a lot, it's not explosive, but it's a lot of material. It's different material, so it's not silicic, so it it affects climate differently. Okay.
SPEAKER_00Yeah, I have a bunch of slides actually that says these are not super uh volcanoes and walls. I mean, these are common questions that uh come up.
SPEAKER_02Do you find that this is a major part of your job, Shen, is going around saying, you know, no, Yellowstone will not erupt soon, and or maybe we don't know that it will, or at least soon, and no, this is not a super eruption. Is that a common a common line in your talks?
SPEAKER_00Uh yes, but uh, you know, there's an official voice for Yellowstone. So, you know, um the USGS are the official voice for that. So uh, you know, I may give my opinion, but I always say it's uh you know, go talk to Mike Poland first. Exactly. Yes, exactly.
SPEAKER_02That's not go watch him in his YouTube videos, yeah.
SPEAKER_00But in terms of I mean, you know, even in our professional uh community, there's problems with the terminology, and not everybody uses these things correctly. And as I said, you know, there's VEI and there's the M, and some people use VEI and some use M.
SPEAKER_02Yeah. Back to your process, because I, you know, the the number that whatever it's VEI or the M number is somewhat arbitrary by def like somewhat arbitrary there, that definition, but your process is probably not arbitrary. This you you described as like tipping point of going from like a thermally uh you know, thermally processed crust that could produce a super eruption, that tipping point. Do you does that match? Does your tipping point process broadly match with the like super versus normal definition and the VEI or M scale? Or is there like a decent amount of latitude here that you think your your process could be active with lower VEI eruptions or or are you saying does your your process align with the scale pretty well, or is there like a lot of room for right?
SPEAKER_00So, you know, that goes to the fact that uh super volcanoes don't only produce super eruptions, right? So you know, you've got a system which is which fits all the criteria for producing a super eruption, you know, thermally and so on, volume, but it only produces uh a very small eruption. And you know, that you go to Yellowstone, that's probably the most likely thing that's gonna happen uh next is something like the last 7,000-year eruption, which is uh a big lava flow or something.
SPEAKER_02Gotcha. Okay. And why what's going on in the magma chamber to do that? To go from this place where you've got a how how do you go from like a really ductile crust that can build up a big super eruption, then you erupt through that. How do you not go back to building another superp? How does it go to brittle where you can do a little eruption? How how does that work?
SPEAKER_00Well, the the supereruption evacuates most of the eruptible part of the system, and what's left is the the the sort of non-eruptible mush, which either becomes a granite pluton or you know, it grows towards the next cycle. And what we see from Zircon studies is that you know subsequent supereruptions are cannibalizing old leftover material. And actually, so um one of the things that we've done at Toba is look at what happened after the last major supereruption, 74,000 years ago, the biggest supereruption we know, the youngest Toba tuff. But then what happened since 74,000 years ago? Well, there's a whole history of how the system recovers from that catastrophe. The structurally, the whole uh caldera um readjusts and the floor gets pushed up in what's called these resurgent dome, but then the leftover magma is also leaking up through so there's you know 30,000 years of eruptions after the 74,000 years, and those are just leftover bits of magma which are kind of poking through. And that's similar to Yellowstone, right? Since since the last super eruption there, you've had 80 lava flow eruptions, huge things, but they're tiny compared to the and a lot of it, some of it is new magma that comes into the system, and some of it is just the leftover dregs. So until there's a big enough thermal kick to really push the system to the next threshold, the system will either die out and become a granite Pluton, or it's going to um go to the next super eruption cycle. Got it.
SPEAKER_02Okay.
SPEAKER_00Now there was a question about ancient supervolcanoes. So those are actually really useful because we can go back to um these ancient uh systems which have been exposed by erosion and mountain building. In fact, in the Alps, there are fantastic old Permian supervolcanoes where we can see the entire uh system from the caldera down to the mantle. And there's a place called uh Val Cessia in in northern Italy, where you can literally go walk from the from the Moho up to the caldera. You walk through the granites and you walk through the lower crust, which is producing the silicic magmas, and it's an amazing place. And then um there's uh place in Bolsano in uh northern uh Italy as well, which you can see these big sections through these old super uh super volcanoes. So we use the ancient systems to tell us what's going on underneath these uh young, young systems. Very interesting.
SPEAKER_01The ancient systems we just were able to recognize that they're super volcanic systems rather than regular volcanic systems because just pure volume? Is that right?
SPEAKER_00Yeah, pure volume and uh the structure. So the other thing um I guess that we should say that's different between supervolcanoes and normal volcanoes, are supervolcanoes and negative volcanoes, in the sense that they're big basins where the entire crust, you know, the size of a large city or more, just essentially collapses down into the space that is created by the well, sometimes it acts like a plunger where it actually falls into the chamber and pushes magma out, but you produce a large depression rather than a conical volcano. Right.
SPEAKER_01Yeah, yeah. But not all calderas are super, right?
SPEAKER_00Right. So you can get calderas in normal volcanoes. Super volcanoes are calderas, basically, very large calderas.
SPEAKER_02Okay, yeah. So there have you um if we're going back to how how would you identify some of these? Because there's this place in uh in Pennsylvania, in southeastern Pennsylvania, South Mountain Baffilith. Have you heard of this, Shen?
SPEAKER_00I have heard of that, yes.
SPEAKER_02Uh okay. They're like 570 MA or something like that. It's you know the original initial rift, and there's a rhyolitic center, I think it's Mount Rogers. I might be getting that wrong, but somewhere down in Virginia. But um, there's a recent proposal by somebody who who spent a bunch of time mapping this thing. He proposed that this was a caldera complex, and it was that it was really thick, I mean, you know, kilometers thick of of rhyolite deposition, and it's complicated, the structure's incredibly complicated. But like, is there a path forward to in places that have been tectonically deformed? And uh can you can you do this geochemically? Is there any way to kind of go in and say, how big was this volcanic eruption when you go back that that long ago? Or is it just is that a tough hypothesis to test?
SPEAKER_00I think you have to be careful how you scale, you know, if you have a large volume, let's say 10 cubic kilometers of uh material and it looks homogeneous, how do you scale that to you know thousands of cubic kilometers? Certainly, you know, if if there's granites and there's rhyolites, that tells you that there had to be a large silicic system there, but um, it could have been a you know a small silicic system versus a super eruption. Um if you have a region like that, you know, in Missouri, you have the St. Francis Mountains, which are protozoic granites and their associated erupted materials. The granites are huge. Uh the amount of erupted material that remains because it's protozoic is relatively small, but you could speculate that yes, this was probably a region. Okay, but you know, you can't be more definitive than uh than that.
SPEAKER_02Can you can you do the same thing again in the East Coast in the Appalachian Basin? There's all these bentonite layers, and some of them are really thick, and we can, you know, they get thicker as they head down to the southeast. Can you do the same thing? Can you kind of calculate the volume of ash preserved in a basin? That's this is all ash fall deposits, like very far flung, presumably. But can you can you relate that to the the volcanic volume or the magma volume as well, or or less?
SPEAKER_00Yeah, so the the problem with uh as you get into bentonites and deep sea ash layers and so on is what's primary and what isn't. So if you take the Toba, uh the 74,000 year eruption, uh Toba, and you go into the deep sea record, there are records of that ash layer over a 10,000 year period. Now, some people want to interpret that to say, well, the 74,000 year eruption occurred over 10,000 years, but when you start looking at those layers, they're reworked. So you have to be really careful about what is you know the primary thickness versus. What's a secondary thickness? So, yes, I mean, almost certainly these big bentonite layers are telling us that there will be gryolytic eruptions, probably super eruptions, but um, you know, how you get back to the uh the truth is not so easy.
SPEAKER_02Yeah, sure. Okay, fair enough. All right, yeah, yeah, yeah. Yeah. No, that's really a tough, tough thing. So do things like Yellowstone and Toba, they they put out these what will become bentonite layers eventually. There's ash falling. Oh, yeah, I mean the seafloor. Okay.
SPEAKER_00Toba's ash is found all over the South China Sea and the Indian Ocean, as far as Africa. Um Wow, really. Yeah. Wow. Okay. So um, you know, the calculations that have been done by um the people that worked there, Bill Rose and Craig Chesner's that the whole earth was covered in at least some ash from the um from the Toba eruption.
SPEAKER_02Interesting. Okay. Wow. Yeah, that kind of brings our like one of the climate questions back to the climate questions, Rachel.
SPEAKER_00Of uh, yeah, but climate is not so much the ash, it's the aerosol. In fact, it is the aerosol rather than the ash. And then it becomes, you know, how effective, how finely comminuted that aerosol is. And one thing I should say is that uh there's a big debate whether you can simply scale the climatic impact to the volume of the eruption. And there are those who think that, you know, Toba, even though it was hundreds of times bigger than Tambora, the effect of Toba on the climate may not have been much bigger than the uh impact of uh Tambora.
SPEAKER_02Okay.
SPEAKER_00But then there are others who argue for volcanic winter and a bottleneck in human evolution and so on. So, you know, that's the great thing about our uh our discipline, right? We can speculate wildly. Yeah. Yeah, yeah, yeah.
SPEAKER_01This is storytelling.
SPEAKER_00Right.
SPEAKER_01Um and I and I know Jesse, you're uh have to go soon. But last couple of questions, really quick ones. So we did actually have, and this might be a laughable question, but I'm I'm curious because again, I talk a lot about mass extinction events, and so I've talked a lot about the Chick Saloop impact. And so I always say no to this question because that's my understanding, but you might have more intricate knowledge about it. But they often ask, could the impact have triggered any sort of volcanism? I mean, we know the Deccan traps were already erupting, so like they didn't necessarily the impact didn't necessarily trigger those, but could an impact like that trigger volcanic eruptions or super eruptions uh anywhere across the earth?
SPEAKER_00Aaron Powell There is some debate as to when the Deccan traps were initiated or when the big pulse of the Deccan trap. And there's been models that have been done showing that, you know, what is the antipodal effect of big um asteroid impacts or uh big bolide impacts on the earth. And certainly, you know, you can geophysically model the focusing of the seismic energy and you know, disrupting perched magma chambers, so chamber systems that are essentially close to eruption, they just need a little kick, and seismic energy might be one way to do that. There's an interesting study we've done is um so that the Toba eruption 74,000 years ago is antipodal to another supereruption, almost exactly the same age in Guatemala. And so we've argued that you know the the the seismic energy associated with a super eruption could potentially focus in on the other side and tip the other system.
SPEAKER_02Yeah, and this is a model that I've seen proposed for uh for large igneous provinces as well, that you sort of induce the eruption of uh there there is some relationship between impacts and an antipol large igneous province. I mean it it gets pretty arm wavy, but there are some ideas out there about that.
SPEAKER_01And I've always been very like hesitant to say anything because it sounds like conspiracy-ish. But that's really cool to know that.
SPEAKER_00It's it's not the deck and trap, it's it's the reunion hotspot, right? Because the decans were where the reunion hotspot was at that time, and that's antipodal to Chicksaloop, so it's it's kind of you know, it's a nice coincidence. Yeah, yeah, yeah. Yeah, it may be more, yeah. Interestingly, yeah. So I wouldn't categorically say no. Uh I I you know it's certainly something.
SPEAKER_01So more research required. Yes. Okay.
SPEAKER_00Yeah, and it's a fair.
SPEAKER_01And that that brings me to my last question, which was, or the last viewer question, which was what are the major unanswered research questions still left in our investigation of super volcanoes?
SPEAKER_00Yeah, I mean, you know, many of the things that I've uh I've uh talked about here are not necessarily debated, but there are nuances that uh, you know, the sort of third, fourth, fifth order things that we we don't know. We know that heat is important, we know that continental crust is important now, why they develop in certain areas. You can kind of look at um the geologic history and sort of see that there are certain things that need to come together to do that. But you know, what triggers an eruption and some of the questions about what are the what are the uh precursory signs? You know, there's two things we don't know in volcanology, right? There's when it's going to erupt and how big it's going to be. You know, even if we know that there's lots of magma down there and it's showing signs, we can't really say exactly when and then how big it's going to be. Same issue with uh with these super systems, is what tips them.
SPEAKER_01Okay. So we need all new uh more students in volcanology and super volcanology.
SPEAKER_00Yes, yes.
SPEAKER_02That's that's super interesting. Well, thank you, Shen. This has been super uh this has been super fun. I uh and thank you for your great talk you gave at Penn State. And uh, hope the emeritus status is uh is is serving you well right now.
SPEAKER_00Oh, it is. I'm I'm living the dream now.
SPEAKER_02Yeah, that sounds great. Awesome. Well, I've got to go teach, so I I'm gonna take off here. But uh but thanks very much.
SPEAKER_00I think we got yes, we got what we need.