Chris Bolhuis: [00:00:00] Welcome back. How are you doing, Dr. Jesse? Reimink.

Dr. Jesse Reimink: Christopher Bolhuis. What's up, man?

Chris Bolhuis: I am ready to go. I know. This is fun.

Dr. Jesse Reimink: This is a super fun one. Oh, I'm, I'm excited.

Chris Bolhuis: So today, this is chapter three and we're talking about the Yellowstone hotspot. And what we're gonna do is we're gonna talk about the Geology of what is a [00:00:30] hotspot. We're gonna talk about, whether or not that hotspot moves and, what makes the Yellowstone hotspot so unique. And then we're gonna finish up kind of by talking about the Snake River plane and the significance of all that. And, so that's, that's kind of the gist of where we're going today.

Dr. Jesse Reimink: And Chris, I think this is a great follow on from our 30,000 foot view that we covered in chapter two, where, you know, we're hovering above the landscape, watching, you know, geologic time go past us. That was a beautiful high level overview, but this is really the driving [00:01:00] force. I mean, this is the process we're getting into really the single thing that makes all of the features in Yellowstone operate is this mantle plume. All of the volcanism, all the hot springs, all of the geysers, everything that sort of follows on from that is driven by this thing we're talking about today. And we're talking about the deep, solid earth like Geology 1 0 1 basics. So it's something you and I are totally passionate about and, and good at teaching, I think. So this is a really exciting chapter.

Chris Bolhuis: Let's, let's hope we're good at it. Right. Let's, let's hope, [00:01:30] um, , so, you know, we're gonna begin today just by jumping right into image number one in your stack. And this shows the volcanic centers where the Yellowstone hotspot began down in the southwest part of this diagram, along what's called the Snake River plane. Which is kind of south and west of where Yellowstone National Park is today.

Dr. Jesse Reimink: Yeah, and depending on how you got to Yellowstone or how you planned to go to Yellowstone, you might actually drive through the Snake River plane. And if you do, it's a beautiful thing. We've got some stories to tell [00:02:00] about driving through that. So basically what we're seeing is in the background there, we have these different aged volcanic centers. They're different names, McDermott, Twin Falls, Helsey ends at Yellowstone. Those are time progressive. So they're starting old on the bottom left and going to younger by Yellowstone on the top right. And what we're really drawing your attention to is the correlation with the Snake River plane, which is the lighter colored field there, that extends from Yellowstone down to the southwest and the old volcanic centers match up pretty well with the [00:02:30] Snake River plane. And the Snake River plane is a morphological feature. It is a topographic feature. It's a plane and there's mountains all around it. And we'll talk about this a little bit more as we move forward, Chris, but I think what we should do right now, that's good description. Ready to, to move on??

Chris Bolhuis: Yep. yeah, let's talk about what a hot spot is.

Dr. Jesse Reimink: Yeah cuz this is Geology 1 0 1 and Chris, I'm looking at you over Zoom right now. You got the gray beard going on man. You've been doing this for a long time. You, you actually taught me about hotspots and [00:03:00] about basic Geology 1 0 1. What is a hotspot? So let's dive into that now, shall we?

Chris Bolhuis: Yeah. Well, okay. So before we talk about the Yellowstone hotspot specifically, I think we need to talk about it as a much broader topic because the, some of the coolest places on the planet are hotspot related. So there, you know, there are many hotspots throughout the world, right? And a lot of people don't realize that. They think of Hawaii. Okay. I think everybody knows that I, or at least most people do. Sorry. And then the [00:03:30] Galapagos Islands. And you've been to the Galapagos Islands, Reunion Island in the Indian Ocean, Iceland and Yellowstone National Park. These are some of the more famous hotspots, but there are, between 40 and 50 hotspots worldwide.

Dr. Jesse Reimink: Yeah. And Chris, I , I unfortunately don't work on hotspots. I I don't research hotspot volcanism. I mean, this is the biggest scam in Geology. The people who research these things, they just get to go travel and go do field work in Hawaii or Reunion or Iceland. I [00:04:00] mean, it's a total scam. And I think, I've done something wrong here, when I, I go up and do field

work up in Northern Canada with fight the, the flies, the black flies and the mosquitoes, and they're out, you know, snorkeling for research!

Chris Bolhuis: I agree. People that do this are definitely smarter than you and I. But that said, I, I do have to say this is one of the great scams of Geology, just in general. Geology is the best excuse on the planet to get out and go see really cool places. So we're doing okay. Cuz you know what, I have never ever [00:04:30] met an unhappy geologist. They don't exist.

Dr. Jesse Reimink: It's true. That is very true. And the happiest ones are the ones who study mantle plumes. Some of them are at least.

Chris Bolhuis: Right on. So let's talk, Jesse, I, let me jump in here a second. Okay. Because most volcanoes are associated with plate boundaries- whether that be divergent plate boundaries or convergent plate boundaries with subduction zones like Cascadia and Northwestern part of the United States.

Dr. Jesse Reimink: Let me just interject that real quick, Chris, and say, plate boundaries, the Earth's surface is broken up into [00:05:00] tectonic plates. I think a lot of people know this. This goes back to middle school or high school level classes. They're broken up into tectonic plates. There's whatever, 30, 40 of them. And what you're talking about is that where those plates, where the edges of them hit each other and interact, subduction zones, et cetera, there's a lot of volcanoes there.

Chris Bolhuis: That's right. But hotspots we often refer to 'em in Geology as what we call intra plate volcanism. In other words, vulcanism within the plate. Far away from plate boundaries, or not associated with any kind of [00:05:30] plate boundaries. So we think, and Jesse, this is your opportunity and I will do my job of keeping Dr. Reimink out of the weeds here. Uh, uh, I, I promise. But we think that they originate at the core mantle boundary, and I think that we need to describe this. What does this look like as this material rises up from where it rises up. Why don't you go ahead and describe this. This is your thing,

Dr. Jesse Reimink: Yes, please keep me outta the weeds. So I [00:06:00] think Chris, we need to draw attention to image number two in our stack right now because this is a schematic view of the interior of the Earth, and it shows what we're talking about. It shows the modern ideas of where mantle plume volcanism originates from, like you said, the core mantle boundaries. So that gray layer in the inner part of the earth is the outer core. It's a liquid iron outer core. The tannish part, the bulk of the earth is the mantle. And right at the base there, we have this red kind of piled [00:06:30] up patch of stuff that's piled up. It's like a big mountain of material sitting on the, the outer core. And coming off from this, some people call it a super plume. If you read press releases of geoscience news, you'll hear these things called LLSVPs, which is very unoriginal acronym for a Large Low Shear Velocity

Chris Bolhuis: All right. Hey, Dr. Reimink. Dr. Reimink. We don't need to go into LLSVPs,. We, let's, let's, let's keep this kind of, simplify this for us.

Dr. Jesse Reimink: Fair enough. So these are piles of material that is either hot material or [00:07:00] chemically different in some way. And basically this is the, the breeding ground for plumes. Plumes rise up from here and make their way all the way to the surface.

Chris Bolhuis: Alright. The image is awesome. Actually, I, I think this idea of the super plume and how this kind of bulges off from the liquid outer core into the mantle is very well put in here. But I have a question for you. Why does this happen - where they happen? Like why is that super plume there? Do we know that?

Dr. Jesse Reimink: Not really, no. And this is a really active area of ongoing research. It's [00:07:30] sort of one of the big questions in the solid earth sciences right now is what's going on with these things. They are probably hot, so the material there is probably hotter than the surrounding mantle, which is

probably. Hence the name hotspot, which is probably why it rises up at, at least in part. And it is, we know it's chemically different, so there's some small or maybe large chemical differences there, which also could help it rise up and, and be buoyant, but we don't really know for sure. .

Chris Bolhuis: Bottom line is you have an area down there that is [00:08:00] hotter than everywhere else. That makes it less dense, which makes it buoyant and it rises up and goes toward the crust. So let's move on then. As that mantle plume reaches the base of the lithosphere, what does the mantle plume do?

Dr. Jesse Reimink: Yeah, and this is, I think, sets up the middle part of this chapter really nicely where we are going to compare and contrast Yellowstone, the main theme here with Hawaii, cuz Hawaii is the great other end member of what mantle [00:08:30] plumes might look like and there's some key differences here. So we're gonna get into that now.

Chris Bolhuis: that was a perfect segue to go in. So let's take a look at image number three.

Dr. Jesse Reimink: And image number three is contrasting really Hawaii, which is an oceanic hotspot. So on the left side of that diagram, that would be Hawaii with a continental hotspot, which is Yellowstone. Yellowstone's, a continental hotspot. Chris, is the main difference between these two? What's going on?

Chris Bolhuis: Yeah, I think we need to talk about why hotspots are not all the same. The contrasting examples is Hawaii and Yellowstone National [00:09:00] Park. I mean, imagine in your head what Hawaii looks like. Hawaii is an island nation made up of black rock. It's all, spectacular, beautiful pahoehoe and aa lava flows and, but it's all black rock and the eruptions are frequent and, you know, generally non-violent in personality. I mean, not these explosive things.

Dr. Jesse Reimink: I mean, every year there's, you know, there's an eruption. Hawaii's erupting all the time, sometimes catastrophically meaning, you know, a lava [00:09:30] flow. Just recently, lava flow kind of destroyed a bunch of homes and a lot of infrastructure, and that's really damaging. But on the scale of geological events, Hawaii eruptions are pretty small. And you can see this when you're walking through, right. You see individual lava flows as you're walking up the mountainside.

Chris Bolhuis: And Yellowstone is made up primarily, at least inside the Caldera is made up of this really light colored, yellowish kind of rock. Geologists actually like to think that Yellowstone is called Yellowstone because of all the yellow Rhyolite in there. But back at the [00:10:00] chapter one, we know that

Dr. Jesse Reimink: that's right.

Chris Bolhuis: that’s not the case, but we like to think that's the case. Okay. So they're very, very different. Yellowstone doesn't erupt frequently. We'll talk about that later in the episode in terms of how frequent this happens. And when it does, it can be a game changing event for the entire planet actually. These are big deals. Why is this the case? Well, the plume sits below the lithosphere, and if you refer to image number three and you're looking at this a second, you can [00:10:30] see that, beneath Yellowstone, there's much thicker crust that that plume is sitting below and within. And so it has to traverse that much thicker crust and it's continental. And continental crust tends to be made up of very different material than oceanic crust is. So Traversing through this thick continental crust to get to the surface. It's a much longer journey. It's traveling through different material, which [00:11:00] that material gets assimilated. It gets blended into the composition of that deep-seated plume. So evolving! It's changing its chemical makeup, and the net effect is when it traverses through this continental crust like Yellowstone, it makes the magma sticky, thick, viscous - and that changes the personality of the volcanism.

Dr. Jesse Reimink: Chris, you used all the, the key terms there, assimilation and most people know that [00:11:30] assimilation, when we talk about it from like the human perspective, you know, you move to another country for a year and you kind of assimilate with the culture, right? your accent might change a little bit. You'll pick up some different foods that you like to eat. you'll assimilate into the culture. Then you come back and you're distinctly different from the way you were before you did that one year, you know, trip to a different country. This is kind of the same thing. The personality of the volcano is going to change dramatically depending upon what type of crust and how much crust it has to assimilate. So, continents are, first of all, they're thicker. [00:12:00] They're almost double, sometimes more than double the thickness of oceanic crust. And they're also different composition. They're richer in silica, aluminum, potassium, a whole bunch of elements that the basaltic magma will assimilate with as it goes up through the continental crust changing composition.

Chris Bolhuis: Yeah, let me interrupt you a second, Jesse. The bottom line is, the takeaway is that traversing continental crust makes the magma stickier because assimilating these continental rocks. The composition of that tends to make this [00:12:30] stuff sticky and thick. Hot spots that are beneath oceanic crust, it's a thinner traverse, so it's not gonna assimilate as much, and it's also assimilating this more mafic, dark colored, material that the ocean floor is made of. The takeaway with that is that that magma tends to be runny fluid, more waterlike, and so the viscosity and the fluidity of magma really plays big into the personality of the [00:13:00] volcanism.

Dr. Jesse Reimink: That Chris is a perfect segue to sort of move on to the next thing, which is really this personality thing. And the way you described this when you were teaching me and the way I describe it now to my students at Penn State when I'm teaching them the intro to Geology class is basically think of a volcano as coughing. You're kind of coughing up stuff and if you have a little, a light cough, if it's easy to get that stuff outta your throat, you don't need to cough very hard to get it out. You won't build up a lot of pressure inside. And that's a basaltic volcano, that's [00:13:30] Hawaii. Because this mafic lava is really runny. It has what we call low viscosity, means it flows really easily and so that you can cough it out really easily. It gets out onto the surface and it flows a long way. It makes these really runny volcanic eruptions with lava that flows for miles. Yellowstone, this stickier magma, this stickier stuff gets caught in your throat, so you have to take like a really big, deep breath in to really cough that out, and that's what's going on. You have much more violent [00:14:00] eruptions. They're less frequent, they're more violent, and they often have a lot more gas in them. You know, pressure builds up inside there a lot more because the magma is getting stuck in the volcanic plumbing system that you can see in image number three.

Chris Bolhuis: And I also want to highlight one thing we're throwing around words like mafic and felsic. It's not very complicated. When we say mafic, we're referring to dark colored rocks like Hawaii. When we talk about felsic, we're referring to light colored igneous rocks. The kind that you see all over [00:14:30] the place in Yellowstone National Park. Alright, Jesse, let's move on to this. The, the next question is, does the hotspot move, because image number one in the stack showed these different volcanic centers along the Snake River plane. Is the hotspot what's moving? That's where we're going now. So go ahead and answer the question, Dr. Reimink, does the hotspot move?

Dr. Jesse Reimink: No short answer is no, the hotspot does not move. Chris, and you have a great analogy for this, but I'm gonna introduce [00:15:00] image number four real quick, which is again, we're, setting Yellowstone in Hawaii. We're kind of juxtaposing these two against each other. Image number four is the Hawaiian hotspot track. And basically what this is showing is this is the topography underneath of the Pacific Ocean. And you can see in the bottom right there, there's a whole bunch of dots. And there's this big string that starts in the bottom right and goes up and then dog legs up to the north. So it heads up to the left and then dog legs up. And this is what's called the Hawaii Emperor Seamount chain. And Seamount is just [00:15:30] underwater mountain, basically is what it means. And so Hawaii, the actual active.

Chris Bolhuis: Under water volcanoes. Yes.

Dr. Jesse Reimink: underwater volcanoes and Hawaii where all the action is currently happening, the active part of the volcano is down in the bottom right corner of this plot. And so what this is showing is that as you head up into the left and then you hit that dog leg and head straight north on that. These are basically old versions of Hawaii. They're no longer actively erupting. Erosion has knocked the volcano down to just [00:16:00] below the ocean surface. And now they are seamounts, these underwater mountains. And this is showing us where Hawaii used to be. But not really where the hotspot used to be, it's showing us how the plate has moved over the hotspot. And Chris, you have a great analogy for this that just really nails this, it drives it home. So what do you do in class and uh, have you ever harmed a student while you're doing this exercise in class?

Chris Bolhuis: I've not, I've not harmed a student. What you're describing is the scorched earth, the plate moving over [00:16:30] top of the hotspot. So what I do is I take a lighter and ask a student to come up to the front of the class, you know, or if we're in Yellowstone, you know, we'll do this in a safe place, but I'll have a student stand up and, hand the student a lighter. Say, okay, well light the lighter. Your hand that holds the lighter, that's the hotspot. And this is not gonna move. And then I take, so I've tweaked it a little bit since you were one of my young students, Jesse, I I take…

Dr. Jesse Reimink: you've modified it in the last 15

Chris Bolhuis: I have, I have. Yep. And I think this is gonna work. [00:17:00] You just wait because you're gonna be impressed. You don't know what I'm gonna say. I take one piece of paper and I, put the edge of the paper near the, the lighter. So I'm sliding the paper very slowly and gradually over top of the lighter at a distance distance that's gonna scorch the paper or leave a track, you know, and then, I'll stop it and then it'll, I'll let a, a hole burn through the paper and, and then I'll keep moving it and so on. Well, when you're done sliding the entire piece of paper over top of the lighter, that [00:17:30] shows the plate moving over top of the stationary hotspot, and flip it upside down and you can see that scorched part of the paper. You can see the track of exactly where that paper went over top of the hotspot. And that's a perfect analogy of at least I think it is, you know,

Dr. Jesse Reimink: It is. No, you're exactly right. It is a perfect analogy for this. It is exactly what we're after here.

Chris Bolhuis: But what I do then that one single piece of paper represents the Hawaiian hotspot. Okay. What I do to represent Yellowstone is I take a [00:18:00] stack of papers and I slide it over top of the lighter! That works.

Dr. Jesse Reimink: Yeah, That's a good modification. Absolutely. Nicely done, Chris. Nicely done. Christopher Bolhuis, eh? Yeah. Nationally renowned high school teacher. I can see why now.

Chris Bolhuis: It is not going to have an easy way to burn through all those papers. Right? It’s gonna happen less frequently. It has to traverse a much thicker stack, so it's gonna change the composition of the magma, and that's what we have going on with Yellowstone. Yellowstone [00:18:30] represents a thick stack of paper sliding over top of a stationary lighter, and that's what we have going on.

Dr. Jesse Reimink: Chris, I, I'd love that analogy. Great modification, . I'm gonna use that next time I teach intro to Geology in class too. I'm gonna just steal that right from you. But I think it's a good time to transition into the geological representation of this. And we introduced this as the Snake River Plane. What we're gonna talk about now is the Snake River Plane. And Chris, I think I really got turned onto Geology on this trip, the summer [00:19:00] science trip that you lead. And you've led for, what, 25 years now? When I was on that trip, I remember we were actually leaving Yellowstone National Park. This is like emblazoned into my memory as one of the more frustrating and exciting things I've done in, in a time that really turned me onto Geology - why I'm a geologist. And so we were leaving Yellowstone, I don't know if you remember this or not, but we were leaving Yellowstone and we were driving from Yellowstone to I think Craters of the Moon. So we were going through the Snake River Plane, and I was pretty bored in the back of the bus.

Chris Bolhuis: Actually, we were leaving the Tetons. Yes.

Dr. Jesse Reimink: We're okay. [00:19:30] Tetons. Okay. Well we're, we were driving through the snake of a plane, like, you know, big highway right down the middle of this big valley. And I walked up to the front of the bus and, you know, there wasn't a lot going on, so I just sat on the steps right at the front of the bus there and I was just like, I'm just gonna talk to Chris and annoy him or something. And I don't know what you were thinking, like what you was going through your head, I'd be curious to hear, but you basically just ask me, Jesse, what are we driving through right now? I was peppering you with Geology question cuz I was interested and you were like, Jesse, hold on. [00:20:00] What are we driving through? Like, look to your left. You see big mountain ranges. Look to your right, you see big mountain ranges. Look ahead and look behind us. And it's just flat. What are we driving down? And I don't know how long I was up there, an hour maybe, and I just could not figure this out. I couldn't get there. You had to finally give me the answer. And it was so frustrating to me that I couldn't answer the question. You know, I, it just drove me crazy, but then you gave me the answers like, oh, that is so cool. And it really just turned me on to, [00:20:30] all things Geology. So

Chris Bolhuis: Yeah, I don't remember that. I, I do remember the conversation. I don't remember the result. I don't remember that I had to end up giving you the answer because.

Dr. Jesse Reimink: uh, it was so frustrating.

Chris Bolhuis: That didn't happen very often because we had just left the Tetons. We were hiking down from a beautiful place called Amphitheater Lake. It was a longer hike. We had a six mile walk down and you just were sitting in my hip pocket as we hiked down, asking me questions about the Tetons. And by the time we had gotten all the way down to the parking lot where the trailhead [00:21:00] was, you had worked through by answering my questions, you worked through the entire geologic story of Grand Teton National Park. And so I didn't remember that, you didn't get the answer of the Snake River Plane. Alright, well, Jesse, what is the significance of that? Let's talk to that then. What was going on?

Dr. Jesse Reimink: you described it in your visual perfectly, and this is the answer you had to give me. Is it's the scorched earth. This is where the super volcano of Yellowstone traversed, and basically it just blew a [00:21:30] massive scorched track through the crust. So there's a big valley there because the mountains got blown away by, Yellowstone, like eruptions, right?

Chris Bolhuis: And what didn't get blown away got consumed as the Caldera collapsed. It just got swallowed by the collapse down into that evacuated magma chamber from these tremendous explosions. What we're talking about, Jesse, is basically the 500 mile scorched earth of the plate. [00:22:00] The North American plate over top of the hotspot that sits below the continental crust. This began 17 million years ago, and refer back to image number five in your stack. This shows the scorched earth. The Snake River plane is below all of these volcanic centers. You see seven different volcanic centers on this, and 500 miles worth of scorched earth. What we're talking about, those seven different volcanic centers, we're talking [00:22:30] about a hundred caldera forming eruptions along the Snake River plane. So we're talking about massive amounts of magma coming out of the magma chambers. After these eruptions, they would collapse down in and what wasn't destroyed would be swallowed, and then lava flows would come out and fill in the caldera and flatten everything out. So when we were driving through and I said, Jesse, look to your right. You saw mountains. Look to your left, you saw mountains. We're driving through flat area. We're driving through [00:23:00] those old Calderas. It's amazing. It's such a cool story.

Dr. Jesse Reimink: It is so cool. I think Chris, it brings up one final question here, which is, you described the paper moving over the lighter and you were moving the paper continuously over the

lighter. Correct. So you would get a, a sort of a straight and relatively consistent track through that. Which we see in the Snake River plane in most cases. But the Geology is not that. We have seven volcanic centers that it's broken apart [00:23:30] into. And the way that these tectonic plates move, the way that the continental plate of North America is moving over the hotspot is continuous. It's moving at a rate of about the speed your fingernail growths. So pretty slow, but pretty consistent. But yet it's broken apart into these seven volcanic centers. So why does that happen? Well, I guess the question is why is it not just those a hundred eruptions are broken apart from 15 million years ago, 500 miles away, and they just occur linearly till Yellowstone today?

Chris Bolhuis: I like to think about it this [00:24:00] way. Magma takes the path of least resistance, just like water does. And so if you refer to image number six, you will see this deep-seated mantle plume at the base of the lithosphere. And it finds this way, this network, this plumbing system, if you will, up toward the surface where it in places shallower in the crust. And this does a great job. This gif here does a great job of showing the plate moving from right to left over top of that stationary plume, [00:24:30] and then you get shallower, smaller magma chambers that emplace in the crust below those volcanic centers. So basically, the, the answer to your question, Jesse, is that it just finds the path of least resistance and it exploits that until it moves past the hotspot to the point where it's now detached. It's not connected. It won't get injected with any more fresh heat from the deep-seated, super huge plume at the base of the [00:25:00] Lithosphere.

Dr. Jesse Reimink: The perfect description. I love this gif. I love image number six cuz it really shows this exceptionally well - why this is broken apart. And so Yellowstone right now, current Yellowstone is sitting over the mantle plume and so it's got this magma supply. It will not always be the case. Pretty soon the plate will continue and will pull the current Yellowstone National Park away from the plume and that'll kind of shut off Volcanism. The magma supply will run out and a new one will pop up to the east somewhere.

Chris Bolhuis: So when we drive through the Snake River plane, we are [00:25:30] driving through old Yellowstone National Parks. I wanna make one other point to throw back to chapter two. When we talked about the 30,000 foot view of Yellowstone, we noted that mountains are all around Yellowstone National Park, except in the southwest corner of Yellowstone National Park. It is flat. There are no mountains, there are no volcanoes there. And that is because that's the scorched earth over top of the hotspot. Any mountains that were there, and there [00:26:00] were mountains there, either got destroyed by volcanic eruptions or swallowed by a collapsing caldera.

Dr. Jesse Reimink: And if you're driving through the snake airplane, if you are headed that direction on a trip that you're going, or you took that route to get to Yellowstone. It really conveys the scale of Yellowstone. I mean, I, I think Yellowstone, as we talked about before, it's hard to really get the scale of the size of this volcano while you're there in Yellowstone. But driving through the Snake River, a plane where you see mountains on your right, mountains on your left, and flat in front of you and behind you, it conveys the scale of the [00:26:30] scorched earth really, really well. So I think Chris…

Chris Bolhuis: Yeah. Because it's 60 miles wide of a scorched earth. I mean, that's, that's amazing. That's the size of these calderas.

Dr. Jesse Reimink: Chris, the next thing we're gonna move into here, and I think now's the time, is we're gonna zoom in a little bit more on the magma chamber that exists underneath of Yellowstone. So now we're, kind of moving away from the mantle plume part of this, and we're zooming up closer to the earth's surface in the crust, looking at this assimilation process. What's going on as the magma [00:27:00] traverses the continental crust.

Chris Bolhuis: Buckle up everybody cuz Jesse's excited now he's sitting on the edge of his seat cuz he gets to talk about what is a magma chamber. Real quick, a quick story. You joined me in Yellowstone, I think back in 2019, uh, when I was teaching my field course. You know what, Jesse, I was thinking about this. I, the amount of time in my life that I have spent in the field teaching young students, Geology - I've spent probably the better part of two years of my entire life, 24 [00:27:30] 7 teaching Geology in the field. Um,

Dr. Jesse Reimink: two years out of the last 25 years probably. What are you?

Chris Bolhuis: yeah,

Dr. Jesse Reimink: It’s like one 10th of your life up till this point,

Chris Bolhuis: It is. I know, I know. It's crazy. Anyway, um, yeah, you joined me back in 2019 when I was teaching the summer field course in Yellowstone National Park. you flew out, spent about a week with us, and you got to talk about what is a magma chamber. We had this beautiful spot. We were back off the trail. [00:28:00] There was no trail where we were in a place called Crater Hills. And we found this like shady you know, meadow to to, yeah to sit in and, and it maybe was a little too comfortable because some of the students were, uh, lulled to sleep by Dr. Reimink

Dr. Jesse Reimink: It was, too, it was, uh, too comfortable. And also you put them asleep. But

Chris Bolhuis: uh, well, no, I didn't, Uh, anyway, that's beside the point. But all of the diagrams, all of the analogies that you see in a typical Geology class, [00:28:30] show a magma chamber incorrectly. So you wanted to set the record straight about what is a magma chamber. So here's your 30 second chance. That's all you get by the way, to explain why all of these diagrams and analogies are wrong. What is the magma chamber? What's it look like?

Dr. Jesse Reimink: To describe, if you've never seen a Geology textbook to describe what this is typically shown as is basically a red blob. And we've shown schematics in this chapter that have just a red blob. And [00:29:00] immediately what everybody's mind jumps to is a ball of liquid, a big body of liquid down in the earth. And that's definitely not what is going on in a magma chamber. A magma chamber is instead much

Chris Bolhuis: Wait a minute. What? What are you telling me? Everything I've ever taught and learned in, in class is wrong. What's going on?

Dr. Jesse Reimink: I know, I know. This is crazy, right? The, there is no big chamber of liquid down in the earth. And what you have to envision is, it's what we call instead a crystal mush. [00:29:30] And so a big network of interlocking crystals, that are solid, that make a really solid framework, and there's little bits of magma distributed throughout there. So that's really what a magma chamber looks like. So it has strength, like you can't, squish it and move it around because the crystals give it this network of strength.

Chris Bolhuis: So a magma chamber is mostly solid, is what you're saying? It's mostly solid with a little bit of liquid in it, but it's super hot. Right? I tend to think of it this way. It's more like, if you [00:30:00] envision a vase sitting in your kitchen table, and you fill that vase up with marbles, and then you can pour a little bit of water and the water sits in, between the marble spaces in, the poor space there. That's more what a magma chamber really looks like. Mostly solid…

Dr. Jesse Reimink: That's a really good analogy, Chris. and you know, a vase or a vase if you prefer sitting on your table with, with marbles in it and liquid poured in between. That's exactly what's going on. This liquid is stable there because it's so hot. But it's right on the margins. It's kind of on the [00:30:30] margins of either crystallizing or erupting. And, so if we go to image number seven in a stack, what we're trying to convey here is that if you went down beneath Yellowstone, and there's actually two different quote unquote magma chambers beneath Yellowstone. One shallow one that's like three kilometers deep and then one deeper one that's 10 to 15 kilometers deep. And if you looked at these, if you could get a visual of what these are, they are small amounts of melt distributed over large regions. So huge volume has a tiny, tiny amount of melt [00:31:00] in it. And so there's actually a lot of melt down there, a lot of magnet down there, but it's distributed over really wide area. And that area is mostly crystal. So Chris, the…

Chris Bolhuis: So then can I interrupt you a second then? So what would precipitate an eruption maybe then is fresh injection from the deep-seated plume. Magma, then getting injected up into that shallower chamber, causing a more significant amount of melting. Right. and then you, combine that with maybe bulging and like [00:31:30] swelling up of the magma chamber, cracks develop and you have now a path to the surface and there's an eruption.

Dr. Jesse Reimink: That's exactly right Chris. And so if we go back to image number seven, we can kind of see that here schematically. The darker colors, the purples, the dark ones down below are the more mafic, the black rock, the basaltic magma. Down below that is more like the mantle plume, the original mantle plume composition. As that stuff goes up, you get this injection of fluids and it ends up being the lighter [00:32:00] colored stuff, that area that's labeled rhyolite partial melt. This is the stuff that has assimilated a lot of continental crust around it that has changed composition

Chris Bolhuis: and it can kind of float to the top, right? I mean, it's less dense than the mafic magma. They don't really mix well because of their very different densities. And so you have this very, very different composition of magma that has evolved this way.

Dr. Jesse Reimink: the thing that connects us to what we're gonna talk about next, which is talking about the eruption sizes - you, might be thinking in [00:32:30] your head if you're listening to this, thinking, wow, there's only a couple percent of magma down there in the crust. So a volcanic eruption does then is it draws magma from a huge volume of stuff, little bits of melt over a huge volume actually makes a huge amount of magma if you can draw all that stuff up through the surface in one volcanic eruption. And that's exactly what happens in Yellowstone. In the past eruptions, we can see evidence for a bunch of different little magma [00:33:00] chambers, disaggregated magma chambers, all being caught up in the same eruption cycle and erupted onto the surface in the same lava flow.

Chris Bolhuis: So Jesse, let's transition then into Yellowstone specifically - where Yellowstone is right now. The three massive Caldera forming eruptions in the last 2.1 million years. What do you think? Should we just go through each of them in order? I think that's the best way to do this. 2.1 million years [00:33:30] ago was the first eruption in what is now Yellowstone National Park. If you refer to image number eight in your stack, this visual is fantastic for showing the scale of Yellowstone eruptions. You can see in, you know, the first, two blocks in this gif they show the size of a Mount St. Helen's eruption. They show the size of Mount Mazama, which is Crater Lake in Oregon. And then you start looking at the three Yellowstone eruptions in terms of their magnitude. This gif is [00:34:00] really good. It does a great job. Because I think a lot of people have seen, you know, footage and, seen this in the news and so on about Mount St. Helens in 1980. We're gonna compare Yellowstone eruptions to Mount St. Helens because I think it's like the best analogy. So 2.1 million years ago, the first big eruption, this was 2,500 times bigger in terms of the volume of material that was ejected out than Mount St. Helen's. That's hard to wrap your mind [00:34:30] around in terms of how much larger that is

Dr. Jesse Reimink: and that is the red cube in image number eight there, the red cube…

Chris Bolhuis: Yeah. And that is to scale. We made sure that these were accurate to scale when we created these gifs here. So that was the first one. The second eruption that happened at 1.3 million years ago. This is 800,000 years after the first one that we just talked about. This was the small Yellowstone eruption. This one was only 280 times larger than Mount St. [00:35:00] Helens. So I say that sarcastically. I mean, it's still really, really massive. However, it doesn't fit the criteria of what we call a super eruption. Um, in order for it to be a super eruption, it has to be on the order of about 1000 times larger than Mount St. Helen's. So let's fast forward again to the most recent Caldera forming eruption in Yellowstone. This is 631,000 years ago, and this one was 1000 [00:35:30] times larger in terms of material ejected than Mount St. Helen's was. By the way, I wanna mention this, these estimates are on the low end. Okay? We're not exaggerating the amount of material. These are low end estimates, so it was a minimum of a thousand times larger than Mount St. Helen's.

Dr. Jesse Reimink: Yeah. so Chris, let's sort of talk about what was going on. Let's paint a visual for what was going on during these eruptions, because these are kind of eruption events, I would say and [00:36:00] there's a lot of things that precede them and postdate them typically. So think of these Caldera forming events, and we're gonna talk about, really, it's image number nine in your stack shows a schematic of what would happen during one of these events. And so we're gonna kind of walk through this slowly, um, and paint this visual. But caldera forming events are the big ones where you're evacuating a magma chamber - that disaggregated magma chamber is getting evacuated. You're losing huge volumes of stuff out onto the surface. And then the land collapses back down in [00:36:30] on itself because it's, there's empty space down there now. But before this and after this, there is often other volcanic eruptions - much smaller volcanic eruptions, but, the magmas moving around like the magmas moving in Yellowstone today even. And so as stuff kind of moves around, you get little pockets of lava that come out here and there. And these kind of occurred before and after all the big ones. And Chris, you always described this as think of taking a deep breath and [00:37:00] then exhaling and think of how your chest moves. Your chest really rises when you take in a big deep breath and then it falls when you exhale out, you slowly exhale that out. That's kind of what's going on in the magma chamber. It's kind of just breathing. It’s sort of pulsing up and down. Exactly. And that kind of implies that the magma is losing gas. There's gas escaping, the magmas shifting around underneath, and it's moving from side to side as the stresses in the earth change a little bit. But when you build up too much pressure, [00:37:30] you get this cycle of really, really explosive eruptions with big ash flow deposits everywhere. And these are these catastrophic things we described in chapter two where we would wanna move our hot air balloon out to space or very far away from Yellowstone as it was erupting. Right. so this is

Chris Bolhuis: I wanna see it. But you gotta get away.

Dr. Jesse Reimink: exactly, and then after this collapse, after the Caldera collapse, the, the kind of area has more Rhyolite eruptions, smaller eruptions that kind of ooze out onto the surface and fill in the landscape and kind of flatten out that Caldera center.

Chris Bolhuis: I think that's a very [00:38:00] important point to emphasize. The most common kind of volcanism in Yellowstone National Park are these lava flows that happen after the Caldera collapse. There have been over 40 lava eruptions, lava flows that have happened since the last 631,000 a year ago eruption the cataclysmic 1000 times larger than Mount St. Helens. There have been several dozens of lava flows that have happened since then. So this is, I think that's an important point to [00:38:30] emphasize. The most common kind of volcanism that happens at Yellowstone is actually rather nonviolent lava flows.

Dr. Jesse Reimink: And we can see a schematic of that in image number nine. The last frame or two kind of shows this stuff extruding back up onto the surface. And Chris, image number 10 shows where you can go see these actually. And so this is actively going on in Yellowstone today. Some of these things are not erupting now, but we can see where they did erupt relatively recently - and where are the best places to see these?

Chris Bolhuis: There [00:39:00] are two, what are called resurgent domes, and that's what this gif shows on Image number 10 is the Sour Creek Dome - resurgent Dome, which is just north of Yellowstone Lake by fishing bridge. It's a huge, broad area. It's hard to, recognize unless you kind of take a, a step back view of this. And then, more towards the old faithful area, the Mallard Lake Dome. Those are resurgent domes. This is where beneath the surface, magma has [00:39:30] been injected up toward the surface, shallower and caused a doming or bulging effect there. So they're called resurgent domes because It's this breathing in taking air into your lungs and your chest expanding. That's what's happening below these two resurgent dome areas.

Dr. Jesse Reimink: and Chris, it's called resurgent because it's kind of resurging up from the caldera floor. So, you know, the calera claps back down in, and this is resurgent, it's resurging up. These kind of things are uplifting [00:40:00] out of the catastrophe. That was the calera down drop event. And so you often get little lava flows that come back up. And this happens in other volcano types too. This happens in the Cascades. Mount St. Helens had resurgent dome. this just happens more because the volcano is bigger in Yellowstone. So we get these a lot around the place. And this is where the hydrothermal activity…

Chris Bolhuis: Can I interrupt you a second, Jesse? I want to, uh, just point out where you can go and see one of these lava flows on the west side of Yellowstone Lake. [00:40:30] One of my favorite places, actually, it's called Elephant Back Mountain. It's a short four mile trail. moderately difficult. It's just an amazing hike though. When you get to the top of Elephant Back Mountain, which is just a lava flow. First of all, you'll see all kinds of obsidian there. That's one of our favorite rocks. And this is the kind of rock that is indicative. It is. It's the kind of rock that is indicative of very, very toothpaste, [00:41:00] like lava flows. You're gonna get obsidian that forms out of that kind of material. Anyway. You're on top of Elephant Back Mountain. You have. Stunning view of Yellowstone Lake. You can see across the lake to the Absaroka volcanoes. It's just, it's, amazing. And so I highly recommend that. And that is a perfect example of one of these lava flows that happens after the caldera forming eruption. One other thing, Jesse, that I wanna mention about all these lava flows is they play a very [00:41:30] important role in many of the lakes that are inside the Caldera. I'm talking about lakes like Lewis Lake, Shoshone Lake, Yellowstone Lake. These lakes were formed by rivers that are dammed in by these lava flows. And something that you can also see as you look across from the top of Elephant back mountain. You can see how Yellowstone Lake is hemmed in by those lava flows. And then just to kind of finish off this story, the hydrothermal [00:42:00] activity - all of the geysers, the hot springs, the fumaroles, the mud pots and stuff that we're gonna talk about in chapter four, which is coming up next. All of that stuff is driven by this hotspot that you described before the heat for that the engine that drives all this activity that dominates what everybody thinks about Yellowstone now is driven by that hotspot that still exists below Yellowstone National Park.

Dr. Jesse Reimink: so Chris, I think that's a great [00:42:30] place to end because we have one frequent last question that we're gonna come to, that, that might take us a little bit to get into. But, um, let me just summarize where we went this chapter and just review. So we started off by talking about what a hotspot actually is, that they're sourced from the deep mantle, these huge sort of super plume type things down in the mantle, are basically the source for hotspots around the world. we talked about the difference between Hawaii and Yellowstone, and we talked about how in Yellowstone that hotspot material that Basaltic magma has to traverse [00:43:00] this big section of continental crust. And it assimilates that continental crust and changes really the personality of the Yellowstone volcano and makes it very different from Hawaii. And then we, we talked about the hotspot track, the Snake River plane, the scorched earth that as you're driving through the Snake River plane, tells you where the ancient Yellowstone hotspot used to be or where the crust used to be on top of the hotspot. And then we, we finished it off Chris. What a magnet chamber looks like as we go down deep, beneath, the crust a couple kilometers deep, what this thing [00:43:30] actually looks like, what it physically is, and tidied it up with resurgent domes, the discussions of how the resurgent domes, sort of play into the current structure of Yellowstone and what's going on on the surface today. So let's just talk about this, which is the FAQ for this chapter, which is one of the more common ones, Chris, and one of the more frustrating for geologists. And the question is: Is Yellowstone National Park due for an eruption? That's the, the faq, and it's a very very common [00:44:00] misconception. So let's keep it short, like one or two minutes here, but what's the

Chris Bolhuis: I will try. no, it is not overdue. Do the math on this. You know, 2.1 million years ago, 1.3 to 631,000 years ago, these cataclysmic eruptions, the Yellowstone is not overdue. The time span between these is, you know, several hundred thousand years. And so no, it's not overdue. So that, that leads into this whole series of [00:44:30] questions. Right. will it erupt in the next several hundred years? Um, probably not. It's not likely at all. It will probably erupt again. But the next one from a historical standpoint is much more likely to be one of these lava flows that have filled in the caldera. Those are much more common than these cataclysmic biblical kind of eruptions. So it's far less likely that we will see a fourth super eruption [00:45:00] anytime soon.

Dr. Jesse Reimink: Anytime soon. That's exactly right. And this is what we call sort of the statistics of small numbers. We have two intervals to work with and they're very far apart. And so just cuz we're “overdue” based on the average of those does not really mean anything for predicting when it's gonna happen again. And Chris, this is part of a broader conversation about volcano prediction, which is really, really hard to do. And the volcanologists, the people who study volcanoes use the term forecasting, which is trying to do exactly as what you just did is say probabilities of an [00:45:30] event occurring in the next a hundred years or the next 100,000 years and adding some probabilities onto that instead of saying Yellowstone will erupt, you know, June 10th, 2028. You know that's gonna be wrong. Right. And, and it doesn't work that way. That's right. Volcanoes are way too complicated for that. So that's the short answer. And we could go into this in a lot more detail, but the short answer is no. You just gotta do some simple statistics to figure out why. So when you're in Yellowstone, when you're going around, you don't need to worry about [00:46:00] a big super eruption occurring while you're there. Right?

Chris Bolhuis: That’s right. you are good to go. You can take your family, your loved ones,

Dr. Jesse Reimink: That's right.

Chris Bolhuis: The people that are most important in your life. You can take 'em there. I do every year

Dr. Jesse Reimink: And so, hey, coming up next is chapter four. We're talking about hydrothermal activity, an overview of hydrothermal activity, and then chapters after that we get into more specific regions. So

Chris Bolhuis: That's right.

Dr. Jesse Reimink: Stay tuned.

Chris Bolhuis: Cheers.

Dr. Jesse Reimink: Peace.[00:46:30]