Dr. Jesse Reimink: [00:00:00] Do I have excited Chris for this

Chris Bolhuis: You always have excited Chris!

Dr. Jesse Reimink: are you particularly excited?

Chris Bolhuis: Well, uh, is there any other version?

Dr. Jesse Reimink: No, that's true. That's true. But Chris, this one is Old Faithful. like, this is the big dog. This is, you know what Yellowstone National Park is branded on, I think is old Faithful Geyser,

Chris Bolhuis: I would agree with that. Yeah.

Dr. Jesse Reimink: This episode, I'm gonna give just a little overview here cuz we're not just talking [00:00:30] about Old Faithful cuz there's so much other stuff to see. Like it is the main attraction, it's the main event, but there's a lot of other stuff to see. So what we're gonna do is we're gonna kind of introduce some of the high level scientific things you need to remember for the next several episodes as we work through a bunch of different famous hydrothermal features. Then we're gonna talk about Upper Geyser Basin, old Faith was a part of. Then we're gonna get into the details of Old Faithful, so like the last half of the episode's gonna be all about Old Faithful because it's a really cool thing and we understand it pretty well [00:01:00] scientifically.

Chris Bolhuis: so refer yourselves to image number one. This shows where Old Faithful and the Upper Geyser Basin is located,

Dr. Jesse Reimink: me just say Chris, the name is very confusing here. The upper, middle, lower geer basins, like these are confusing. They don't match the map view, so, so this is what we're talking about, right? Remember that when you're driving around?

Chris Bolhuis: This is so true because they're actually named, they're, you have the upper geyser basin, the Midway Geer basin and the Lower Geyser Basin, and they are flip flopped from geographic [00:01:30] up versus down. And they do this based on elevation. So the upper geyser basin is at the highest elevation. The lower Geyser basin, which is furthest to the north, is at the lowest elevation, and that's why they're named what they're named. So that is a really good point because it is, it leads to a lot of confusion actually.

So image number one shows the location.

Dr. Jesse Reimink: In image number two shows Old Faithful. This is what we're, we're here to talk about. It's showing interruption of Old Faithful, and one thing to note, I think, is all the people around the boardwalks that you see [00:02:00] on the other side of the geyser on the near side of the geyser, on the right side of the geyser. Like there's a lot of people watching this thing because it is the marquee event, and we're gonna talk about why it's the marquee event here. So

Chris Bolhuis: Can I say one thing though about viewing old Faithful, if you do want to get away from some of the people, it can be viewed, like you said, all the way around it, but one of the best places is actually across the Fire Hole River on top of Geyser Hill. You'll get a more secluded and, uh, just as spectacular view in my opinion. And [00:02:30] so that's a, a recommendation that I have.

Dr. Jesse Reimink: That's a, a good tidbit, Chris. So, okay, we're gonna talk this chapter and the next several are all about hydrothermal features, right? And so there's some really broad classifications that matter a lot when we talk about these and explain some of the differences. Chris, what are those? Guide us through the high level differences that will stay with us. And so remember these things over the next couple chapters.

Chris Bolhuis: Sure. I like to lump things into, into categories, and

Dr. Jesse Reimink: are a lumper, and [00:03:00] actually there's, you told me this, that there's a term in high school you worked as a lumper, which was in college. Okay. College you worked as a lumper, which was what, like stacking watermelons in the bed of shipping trucks or something like that. What? What was it?

Chris Bolhuis: Unloading trailers is, there's a term for that, semi-trailers, and it's called lumping. And one of the things that I did, in college all the time was I lumped watermelons, which means they just had the watermelons stacked up in the bed of the trailers, and I would pick 'em up and put 'em into bins. So these are the bins that when you go to the grocery store and you, you know, you reach [00:03:30] in and you, they've got like 40 or 50 watermelons in there. That's what I did.

Dr. Jesse Reimink: You were a lumper. You were a lumper back then and you're a scientific lumper today. So what are we lumping?

Chris Bolhuis: right. So let's lump. Here we go. All of the hydrothermal features in Yellowstone can be lumped into three categories. The first category they're slightly basic, which means they have a higher pH than normal water. These are called alkaline chloride features, and these are gonna be areas like the Norris Geyser Basin, old [00:04:00] Faithful, Grand Prismatic in the Midway Geyser Basin. That's one category. The second category, Is the calcium carbonate features, calcium carbonate is limestone. It's a form of calcite. These are features like mammoth hot springs and terrace hot springs and so on. And they involve hot water that's flowing through limestone. So it's a completely different feature that you get there. And the last one are very acidic features. So the opposite of the old [00:04:30] faithful area, the alkaline chloride. These have a very low pH and these are called acid sulfate features like what you get at mud volcano or fountain paint pots or artist paint pots. Those are the famous acid sulfate features that you get. So Jesse, we have a little image. Image number three. Can you go ahead and walk us through this image and why this is important in the context of the types of thermal features that we have.

Dr. Jesse Reimink: Yeah, Chris. So really the differences between these three [00:05:00] water types, the ones that you just laid out here, that are alkaline chloride, calcium carbonate, and acid sulfate features. The source of the water is pretty much the same. It's how they interact with the rocks, what rocks they interact with on their path to the surface that defines these in this image. Image number three in your stack shows two of these. It shows the alkaline chloride ones the acid sulfate waters, and really the difference here is what types of rocks they're interacting with. So if the water interacts a lot [00:05:30] with Rhyolite or tuffs, it's gonna dissolve silica from those and it's gonna become an alkaline chloride, brine or water. If it interacts with limestone, like you said, it's gonna become calcium carbonate. That's not on this image. We're gonna talk about that with regards to Mammoth next chapter. And if the water contains a lot of interaction with deep fluids and a lot of basically magmatic gases that are coming out, it'll have this acid sulfate feature to it, and that will form various features we'll talk about in the next coming chapters, Chris. So it just shows that [00:06:00] the path the water takes and therefore the rocks it interacts with controls the chemistry of the water, which controls exactly what we see, what the feature is on the surface, and it's a really cool phenomenon. So that's all we need to point out with this image.

Chris Bolhuis: And everything in the Upper Geyser Basin, which is what today's chapter is all about, and refer to image number four in this, it involves

the first type, this alkaline chloride water. Okay. Slightly basic, and this is an important thing to bring up, I think, because I think most [00:06:30] people would assume that the water that they see in these hot springs and the water coming outta the geysers, they think it's acidic. Actually, the water is slightly basic, so neutral water has a pH of seven. It's not acidic and it's not basic. The water here has a pH of about 8.3, which means it's slightly acidic. Examples of basic fluids, like everyday fluids, would be baking soda and water. Ammonia is basic and lye. [00:07:00] These are just common examples of basic kind of fluids.

Dr. Jesse Reimink: Chris, that's, a good point that we often think of these things as, as acidic. I mean, you think of reactive fluids as acidic, that's just kind of what everybody's default is. And, but we have to separate acidic in basic waters cuz what happens to them and what they do at the surface when they hit the surface is dramatically different. So, why is it not acidic? Everybody assumes it's acidic. It's not. It's basic. Why is it not acidic?

Chris Bolhuis: The main reason why it's not acidic is because [00:07:30] this water is flowing through Rhyolite, which is rich in silica, SiO2. So essentially it has a lot of quarts in it, but at depth it is acidic because it has these gases that are dissolved in it. It's got carbon dioxide in it. It has H2S in it, which makes the water acidic deep, deep down below the surface. But as this water rises up, that water begins to Degas. So it's losing the carbon dioxide, it's losing the hydrogen sulfide, that rotten egg smelling gas, and[00:08:00] Therefore, as the water loses these gases, it's raising the pH of it, making it. By the time it comes out at the surface, the water is actually slightly basic.

Dr. Jesse Reimink: Yeah, and Chris, that's a really good point that you just made, that it starts acidic down at depth because we need that acidity to interact with the rhyolite or the Tufts or any of the very silica rich rocks down beneath, and it needs to dissolve that silica, then it out gases and it becomes basic, right? So this. Water chemistry is quite complicated down at depth, [00:08:30] but the point here is that it's interacting with these tufts, these rhyolite flows. Those are fine grain minerals that are easy to dissolve when you have slightly acidic water around the fine grain minerals, the obsidian, these things are really reactive rocks actually, when you introduce hot acidic water. That's pretty reactive and it drives these fluids to become more basic. So when you're looking at Old Faithful erupting, you can think of the path this water took and where it's coming from and how it's interacting with rocks at depth before it gets to the [00:09:00] surface. And the chemistry we see at the surface tells us that story. It's really cool.

Chris Bolhuis: So image number four shows where you can go and see this kind of hydrothermal feature, the alkaline chloride. There are many, many different locations in the park that, you can view these things and this shows where they're located. Jesse, let's move on and talk a little bit about the Upper Geyser Basin. In particular, and then we'll dive into the Geology of Old Faithful specifically, where we'll kind of get into the weeds on that.

Dr. Jesse Reimink: Okay, Chris. I, [00:09:30] okay. That's a great plan. I think Upper Geyser Basin is so amazing, in part because of the concentration. This is the highest concentration of geysers. In the world. It's not a huge basin. Like our, our circles on image four are all the same size, but it, this is a smaller geyser basin, but it's heavily packed with geysers. More than 200 geysers in 1.5 square miles. And that is, 20% of the world's geysers. So just walking around Upper Geyser Basin, you have to keep the stat in your head because it's mind [00:10:00] blowing. You can look at 20% of the world's geysers just in a, a relatively short loop. Right. What do you think?

Chris Bolhuis: Uh, well, I think that you should devote time to explore this area. Okay. it's not very big, but there's so much to do and see here, it's, it's amazing. So I would say explore it, but if you can't, and I know that not everybody has time to do this, right? Watch Old Faithful. And then maybe drive to the Lower Geyser Basin where you can see some geysers and hot springs and the fountain [00:10:30] paint pots. So you get to see two of the three hydrothermal features at the lower Geyser Basin then, and I just think that you get more bang for your buck if you don't have time to adequately explore the upper Geyser basin.

Dr. Jesse Reimink: And so one point and then a question for you, Chris, go to the old Faithful Visitor Center. They have these timetables predictions for the geysers. Those are really useful. We can't convey that information right now because you know you need to be there at the time you're there and you'll get the timetables right. It's a really useful thing. You can pick up a walking map and the geysers do change all [00:11:00] the time. So go in there and get the updated, numbers and predictions that'll really help you kind of plan your experience. But Chris, the question for you is, When you're teaching students out there on this summer science trip, what do you do in the upper Geyser basin? Do you do the same thing every time, or does it depend on this timetable of, of, uh, you know, which geysers are erupting when? Because I'd imagine you don't arrive there at the exact same time every trip. And the geysers have changed year to year. So what, I don't know, how do you plan for this or how do you guide this school trip on this?

Chris Bolhuis: That's a, that's a good question. What I actually [00:11:30] do is maybe a little unconventional, maybe surprising. It's so busy at Old Faithful and it's hard to keep your students attention when you have all kinds of people walking past, and they're all talking and they're, they're saying some things about what's going on,

Dr. Jesse Reimink: and you catch a lot of hangers on following your group around the boardwalk afterwards, probably within 5 minutes.

Chris Bolhuis: We do. That's right. So I try to talk about the Geology of Old Faithful someplace else. And then we go there. And then I'm like, okay, go [00:12:00] watch it with this understanding. So that's the way I do it, kind of the way that this is designed. Right. Hopefully our listeners are, you know, driving to the area somewhere nearby or they're on their way out to Yellowstone and they're learning about this, and then they can go see it and view Old faithful through this lens. That's the way I do it.

Dr. Jesse Reimink: Okay. That, that's, that's really good that, that's interesting approach. I think you're right. It is a very busy place and it's worth it. There's a reason it's busy. Like that should not detract you from going to see Old Faithful, cuz it is spectacular. You [00:12:30] gotta go. But go in knowing that. Right. And so, Alright, let's do what you do then and let's get into the Geology of Old Faithful when you're not sitting there right in front of it and there's a bunch of people around. Let's get into some of the weeds here, as it were, on how Old Faithful Works. Because we understand this geyser in part because of the famousness of the Geyser. We understand it really well scientifically. We have a pretty good grasp of how this thing operates, arguably the best in the world as far as understanding a particular geyser. So Chris, let's dive into that. And we gotta start with like the regional [00:13:00] Geology or just a little bit of the background here, like what are the rocks around this geyser? And then we can talk about the morphology of the geyser itself.

Chris Bolhuis: Okay. Yeah, we're in a basin, most of the geysers are in this sunken down area, but if you look around, you see all these hills that kind of surround this whole upper geyser basin. These are the lava flows that we've alluded to in earlier chapters. This this 631,000 year old eruption - the last of the cataclysmic eruptions of Yellowstone. After it, it oozed these very [00:13:30] thick and viscous lava. I mean, this was really, really sticky stuff that, you know, we've talked a lot about that in prior chapters. We also have a lot of evidence of glacial activity. And this is important to note because this kind of glacial kitty litter, you know, this kind of stuff that just covers the Rhyolite lava flows, is really porous and it's really permeable, which means that water can flow through it easily. It provides then really nice way - It's kind of like a water tower effect. It [00:14:00] stores the groundwater that supplies the hot springs and geysers.

Dr. Jesse Reimink: Yeah, Chris, let me just double click on that a little bit and describe what you mean by this kind of kitty litter thing. When a glacier retreats if ice is over a region, the glacier is eroding. It's like a conveyor belt that's always bringing ice from up high or up to the north down and flowing across any eroding. When a glacier retreats, it starts to melt in that conveyor belt. The end of the conveyor belt moves back and all the stuff that's being brought down is dumped off, and glaciers are one - [00:14:30] probably the only type of feature that creates unsorted sediment. So glacial, what we call till the sediment, is a loose assemblage of everything from clay size particles to sand size particles to big boulders. We talked about erratics in a previous chapter, and so this stuff is really loose. It's unconsolidated. That means water can flow through it, and we're sitting here looking at a hydrothermal feature. We need water. We need to get water down into the earth. And that's a great way to do it through this till. So that's, I wanted to, double click on that a little bit and explain that [00:15:00] in a little more detail. So do we move into the morphology of the of the thing now? Are we talking about, this is so cool. Let's look at image number five real quick and we're gonna talk about this. This is one of the reasons we understand this guys are so well, is we've sent probes and cameras down this beast. It's so cool that this has happened. Chris, I, I,

Chris Bolhuis: Can I paint a picture of this? Like, I mean, imagine Old Faithful erupts and team of scientists is standing by waiting for this eruption to end, okay? And when it ends, you get a few [00:15:30] spurts that kind of come out and they're like, okay, I think it's done now. And they quick run out to the geyser and they have time between 50 and 90 minutes now to put a probe down into this thing. And that's what you're looking at in this image number five, that's the probe. And they shove this thing down. They gotta do their stuff. They gotta learn what they can learn and then get that thing out of there before the next eruption starts. So we're talking about

Dr. Jesse Reimink: super cool.

Chris Bolhuis: not a lot of time involved here. Right.

Dr. Jesse Reimink: a bunch of scientists sprinting [00:16:00] out there, chucking it down, reeling it back up, and then running away and looking at the images. All very excited, right? Uh, it

Chris Bolhuis: That's right.

Dr. Jesse Reimink: It’s great.

Chris Bolhuis: Here's what we've learned. We know that the plumbing network of Old Faithful is not a tube. You know, the water looks like it's coming out tubular. It's not. It's more like a narrow slot. It's about four to five feet long at the surface, and it's about one foot wide at the surface. And you can see that. with the probe.

Dr. Jesse Reimink: You can see that in image number 4. You know, [00:16:30] it's clearly this sort of gash, right? It is a slot in the earth And this is a really common thing in, in Geology more generally. It's pretty rare that we have perfectly tubular features in Geology. They're often. Linear in some way, and that's what's going on here. And I think, Chris, let's, before we move into the next phase here, point to image number 6, which shows a schematic of this. And we're gonna get into the internal structure of this geyser, which is why it's so faithful, is partially due to the internal structure here. So what happens, what's the key [00:17:00] point here that we've discovered with these probes?

Chris Bolhuis: Yeah, I think the key to this whole thing is that at 22 feet below the surface, below the vent, there is a narrow constriction in this slot where it goes from, you know, like roughly a foot wide, it's constricted to four and one eighth inches. It's six and a half feet long. So it's really this narrow slot at this point, and that's the key to the whole thing because all of that water - all of that gas, that steam has to be squeezed through that narrow [00:17:30] constriction. And so it's like bottleneck right there at 22 feet below the surface during the peak eruption. Water is coming up through that at about 157 miles per hour. That's just,

Dr. Jesse Reimink: it's great. And so Chris, I think you know, one thing to note here, In a previous chapter, we have talked about how geysers kind of work, and this is the throat. That four inch slot is the throat that you kind of cough through that makes a geyser possible, [00:18:00] right? And that's also the thing that could give way. That four inch slot could break at some point, and then Old Faithful will have a very different eruption dynamic to it, because the slot has changed shape. Or you could get some more sinter forming and that slot narrows over time. And that will change how the geyser actually functions, right? So this is another point about how these things actually change. So if we look at image number six, we're kind of working through how an eruption happens, and this is really cyclical, hence the term Old Faithful. So if we [00:18:30] look at this image number six, the the schematic of Old faithful, the Interior. We also see as we move past this choke point or this constriction, the slot opens back up to about two feet wide and there's this kind of cool waterfall that's spilling down in. It's very cool to see on the probe. We don't have this in the gif, but if you go to you know, a website, you can just find this video. It's on the National Park Service website, and you can watch the entire video. It's like 20 minutes of this probe down in the geyser, right? Which we can't upload, but, it's really quite cool. And there's a little waterfall, and then there's a [00:19:00] couple ledges, and then you make it down into a larger chamber.

Chris Bolhuis: probes get stuck on those ledges. It’s kind of a pain in the butt for those scientists.

Dr. Jesse Reimink: Yeah, it's su super funny to, super funny to, uh, watch that happen, but around 35 feet down it opens up into a large cavity and this is quite big the size of, you know, a large vehicle. And this is kind of where the activity starts to happen during an eruption. This is kind of the beginning of the process of an eruption.

Chris Bolhuis: Okay, so Jesse, let's stay on image number six here a second. Or this gifified image you just talked about. This cavity [00:19:30] the size of an automobile. First of all, I wanna say that they had a lot of difficulty in here because it is so turbulent. described it almost like tornado. It was very, very active in there. In fact, they couldn't get the probe, They couldn't get it through that. So they couldn't see deeper down than that. Now, we were able to get the temperature and, uh, pressure probes deeper, but not the camera itself. So let's take a look at this eruption cycle here with this gif. First of all, a couple things that I wanna [00:20:00] note - at about 20 feet. We never see water. While it's not erupting, that fills the plumbing network above that point. So you have to go down 20 feet just to get to where you got standing water. Otherwise it's just kind of spilling in and, and trickling from the sides and so on. So what happens then is as this system fills up, it heats up, but you have this bottleneck at about 22 feet. And so everything is kind of constricted there. And so happens then is [00:20:30] the water deeper down in the plumbing network gets super heated. It's above what the boiling point of that water would be. Right. But it's under pressure. So it's like a pressure cooker.

Dr. Jesse Reimink: And it's under pressure just to remind us, it's under pressure because of the weight of the water above it. That's what's causing the pressure. If you go back a couple chapters and remember, Chris, you have this beautiful analogy where you're boiling a pot of water and you got this big, long, stem coming off of it. The analogy that you do on the boardwalk, you set up this experiment on the boardwalk when you're teaching [00:21:00] students there. This is what's going on, right? The weight of the water above it. Is holding that superheated water in the liquid state and preventing it from becoming a gas.

Chris Bolhuis: And so when the Old Faithful is getting ready, it's primed to erupt. It'll shoot out a couple spurts at the top, and that's usually enough then it loses enough water, which lowers the pressure, down below, and it causes the water to flash into steam. That rises up rapidly and it gets through that constriction and it kind, all those [00:21:30] bubbles then kind of pile up and then they just squirt through that and they push in water with it as it goes. And that's when the eruption then hits full steam.

Dr. Jesse Reimink: Absolutely. And so if we move on to what else we understand about this geyser? I think there's some really cool things that we can talk about during this eruption cycle cuz it is a cycle. It's a very regular thing. And so one thing is to look at the pressure and temperature and image seven and eight. We're gonna talk about those really quick, but these are. pressure and temperature probes we've sent [00:22:00] down into

Old Faithful and monitored over the course of eruption cycles. And the pressure is kind of an obvious one, like the pressure increases until the eruption's over. That makes sense, right? The pressure is increasing at the base, and then when the eruption flashes to steam, all of a sudden the pressure is decreased. Then that water is no longer boiling down at depth. You get colder water influxes in it builds up and builds up, and builds up and builds up until it goes again. It builds up pressure as well. And so that's image seven is [00:22:30] the pressure so we're looking at one eruption cycle from start to end of a single eruption cycle. What about the temperature?

Chris Bolhuis: Like you said, Jesse, I think this is very intuitive that the temperatures and pressures are gonna kind of increase until the eruption happens, and then they drop off. But the cool thing about this though, is we're looking at real data. These are pressure numbers and actual temperatures because we've sent probes down in 'em. So when you look at image number eight, you can see that [00:23:00] the, you know, the temperature, it gradually rises just a little bit until right before the eruption happens. And so what that means to me is, right before the eruption, the temperature shoots up. Or right during the eruption, the temperature shoots up. That's because that water is coming from way down in the guts of Old Faithful. Does that make sense though? The temperature probe is in the upper part of the plumbing system, it's not way deep down. We can't get it down that [00:23:30] far. So when we have this temperature probe sitting there, that temperature - it remains relatively stable, and then all of a sudden it shoots up because that water during the eruption is coming from very, very deep and it's super, super heated.

Dr. Jesse Reimink: Yeah, I think a couple things to note on this, Chris. It, it is intuitively, you might think that the temperature of the water would gradually increase, like the pressure does, right? But it, it doesn't. It fluctuates and it kind of maybe gradually increases or it starts cooler and then gets a little bit warmer. Also, note the temperature. We are [00:24:00] above the boiling point of water at sea level, and so this is hot water. This is already kind of superheated down there, so it is under pressure a little bit, but then it becomes superheated, exactly as you said during the eruption, even hotter stuff. Comes up and this gets really hot, gets up into the 250 degrees Fahrenheit or 125 degrees centigrade. This stuff gets super, super hot during this eruption cycle, and then it kind of resets and, and starts back over.

Chris Bolhuis: Hey, that's a great segue, Jesse, to talk about like, Old Faithful follows a [00:24:30] script. So let's just to, to kind of round this out, let's go through this script. What are you gonna see as you watch this? Right?

Dr. Jesse Reimink: Yeah, Let’s do it.

Chris Bolhuis: So it begins with the plumbing system filling up, heating up, which of course, we can't see, but we know that that's what's going on.

Dr. Jesse Reimink: totally. And then you just mentioned it, we have these little spurts of water. That's the beginning stage, right? That's the little bit of the releasing of pressure.

Chris Bolhuis: And then these spurts will kind of grow in size that releases the pressure. Escaping [00:25:00] water allows the water at depth to flash into steam, and then that really is, when we start to really rock and roll.

Dr. Jesse Reimink: And that's the main event, the full eruption is throwing water when you're looking at it between a hundred and 185 feet in the air. So this is. Pretty sizable eruption, right? This is pretty violent. You would not want to be there. The scientists with the probes don't want to be put in a probe into into Old Faithful's throat during this time. This is pretty violent, and so it's throwing water up and that water's splashing around near the vent. You can see this. This is like what we [00:25:30] get to watch, right?

Chris Bolhuis: And then you'll see as the eruption kind of nears the end of its cycle, the height of the plume will kind of lower and lower and you'll see a few last spurts then kind of come out and there we go. That eruption cycle is done.

Dr. Jesse Reimink: And I think it's worth noting that Old Faithful is famous because of the length of duration between the eruption cycles. The eruption cycles themselves last between 1.5 and five minutes. And we'll come back to why that's important a little bit. But the amount of water that this thing erupts is [00:26:00] quite impressive depending on the length of the eruption. We're talking about 3,700 to 8,400 gallons of water. That's between 3,700 and 8,400 gallons of water that are erupted. And so if you filled up a pool with that water, it'd be 10 foot wide, 22 feet long, and five feet deep. That's a, a fairly substantial backyard pool.

Chris Bolhuis: Pretty crazy. That's but pretty awesome too. All right, Jesse. Let's transition into just some other things that [00:26:30] factor into Old Faithful, just some things that maybe are little known facts, right? First of all, we see a difference between spring and summer and like fall and winter in terms of the interval between eruptions, right? And let's think about that a second. Why would spring and summer have a longer interval between eruptions? If you just think about that a second, right? What's the difference between spring and summer in Yellowstone versus fall and winter? Well, the amount of water. Is the [00:27:00] main factor, right? Spring and summer, it's wet. We got snow melt. It's so you have a lot of groundwater, so it takes more time for this cycle to go cuz we have to superheat the water, right? Fall and winter. Less water, less time needed then to heat it. And so a a shorter interval between eruptions.

Dr. Jesse Reimink: And I think that's the really important point here, Chris, is that it's temperature. I mean it's really all about the, the interplay between temperature and pressure. And so temperature is a key component into how Old Faithful erupts, when it erupts, how [00:27:30] frequently it erupts. And the water in this geyser is old water, quote unquote - old water, meaning it took a while to work its way through that pathway that we showed in image number three. where it works its way down into the depths and then it gets heated up and it kind of migrates through and it starts to dissolve some of the silica and the rocks around it, and then it makes its way into the plumbing system of old, faithful, proper. And because of dissolving all that silica, the plumbing system is lined with sinter. We talked about sinter in a previous [00:28:00] chapter where we talked about basically how these things form and why there's so many geysers in Yellowstone. So many geyser's actually in the upper basin that we're talking about specifically is all of the sinter. And that is a really important thing when we think about the lifespan of geysers. And we kind of touched on this, Chris, but I think it's worth driving home again. Like we gotta hammer this point. I think. So why is sinter important?

Chris Bolhuis: It's very resistant. It's really tough stuff, first of all, and it precipitates on the throat, on the lining on the inside of that, [00:28:30] which you saw the camera probe going down into precipitates in there. And over time then that increased precipitation can cause the plumbing system to literally close up. I mean, think about it, 22 feet down. Old faithful is only four and one eighth inches wide. If that closes up. Then that water has to find a new path to the surface. And we can actually see this with Old Faithful. There are two other mounds that are near the current Old Faithful vent. And we think that these are the old [00:29:00] vents for Old Faithful that have closed up and then new ones have subsequently opened up, which I think is a pretty cool thing. Uh, just like look for those when you're there. Look for those other two old vents for Old Faithful.

Dr. Jesse Reimink: And the last thing here to note about Old Faithful and just more generally large geysers, I think, is that sometimes, maybe not when it's peak season, and there's a lot of people in the park and milling around and talking. But sometimes you can feel a thudding popping sound beneath your feet if you're really [00:29:30] quiet, like around the time of the eruption that's going on. What this is, is it's actually little tiny sonic booms, and the water is expanding so rapidly, this expansion, this transition from the liquid phase to the gas phase, and then this explosion out is exceeding the speed of sound. So these are little tiny sonic booms that kind of propagate through the ground. I, I think it's just, Chris, this is one thing to think about - when we're standing there watching Old Faithful, it's such a spectacular thing. [00:30:00] It's obviously an awe-inspiring event to watch this geyser throwing hot superheated water up hundreds of feet into the air. It's an amazing event, but it's also really cool. We're seeing only the last bit. We're seeing one minute to five minutes of the story, and the story's a lot bigger than that, and so I think it's always kind of really interesting to, to think about that while you're watching this eruption.

Chris Bolhuis: So I want to talk a little bit about this, and this is gonna be very quick because we don't want to intrude on your experience in your - what you want to [00:30:30] explore. But there are some other things that the Upper Geyser Basin that I think are really important. There are four other geysers that Rangers can predict, in the upper basin. There's Riverside, Castle Geyser, Daisy and Grand Geyser. And image number nine in your stack actually shows a video of Grand Geyser erupting, which is pretty cool.

Dr. Jesse Reimink: a really cool one, and Grand Geyser is the tallest geyser on the planet. It shoots water between 150 and 200 feet in the air. [00:31:00] Eruptions happen fairly frequently, every four to eight hours and are kind of more or less predictable and they last up to 10 minutes, 10 to 12 minutes long. These are long, big eruptions. It's building up a lot of pressure down at depth and throwing this superheated water really high into the air. What's another one, Chris? What's another go-to for you in the upper geyser basin?

Chris Bolhuis: Yeah, I. I'm just gonna throw the names out and I'm really just gonna leave it at that, Jesse, because I, again, I think this is something that is kind of personal, you know, that people just need to do their own thing. But Beehive, [00:31:30] Geyser, Splendid Geyser, splendid is really kind of cool because thunderstorms can trigger eruptions with this. You know, it's that that sudden drop in air pressure when a thunderstorm rolls in and the thunderstorms in Yellowstone can be so impressive. That's just so cool to me that that little thing can trigger eruptions. So I say we leave it at that

Dr. Jesse Reimink: Okay. I agree. No more stuff to look at, but I just want to talk about this thunderstorm thing a minute, because it is such an amazing,[00:32:00] realization that drops in air pressure can trigger this, and I think it, it's representative of a larger phenomenon in Geology. That a lot of the stuff we're talking about, we've been talking about volcanoes with the Yellowstone super volcano. We've talked about earthquakes and faults. A lot of the stuff in Geology is hanging right on the edge. And geysers represent this really well. That super heated water is hanging right on the edge of eruption or not eruption. And any little thing can kind of push it over the edge. And an earthquake is the same exact way. A [00:32:30] volcanic eruption behaves almost the exact same way as a geyser. You know, this magma is super heated, got a lot of gas, and the triggering event of getting a volcanic eruption to go can often be a very, very small thing. And I, I think it's really cool representation. This thing about splendid geyser and thunderstorms triggering it, is meaningful in the broader scheme of processes in Geology.

Chris Bolhuis: One thing that I do wanna say that I think is extremely important is, As you make your way through these areas, please do not [00:33:00] throw anything into the geysers. These are not wishing wells. It's happened, you know, this is, and you, you will see signs of this, of people pitching pennies and coins into like, Morning Glory Hotsprings and so on. And also, this is your national park. Don't allow anybody else to do this either. Have the gumption to say something, or at the very least, report it. If you see something going on like this.

Dr. Jesse Reimink: That's a great point, Chris. I mean we, yeah, we definitely can't be doing that stuff. Okay, Chris, a couple of FAQs which allow [00:33:30] us to again, dive a little bit deeper into Old Faithful. So Old Faithful as the name implies, is quite faithful. Uh, One of the commonly asked questions, and I'm sure your students have this when you're talking about it, is, is it always faithful? We talked about how there's variation spring, fall, winter, there's variation in the eruption cycle. And I think one question is, what's the source of that variation? Why does it vary so much, and how has it changed over time?

Chris Bolhuis: I'll take this one first. I guess in terms of Old Faithful is faithful. It's as [00:34:00] faithful as it's ever been, but the length of time between eruptions has increased. It's about 50% over the last 50 years, but those haven't been gradual changes. Now, Old Faithful averages about 92 minutes between eruptions, but even within that, the interval between eruptions is really based upon the length of the previous eruption. So if there's a shorter eruption, there will be a shorter interval then between the next one. And a longer [00:34:30] eruption means a longer interval. So the Rangers then, when they do these predictions, they're basing that prediction over what happened during the last eruptive cycle. So that's pretty cool stuff. Bottom line is, yeah, Old Faithful, still pretty faithful.

Dr. Jesse Reimink: That's right. And I think I just want to touch on why that is, right. The reason that the duration. Between eruptions is dependent upon the length of the last eruption is because this is emptying the chamber gotta refill the chamber. How much hot water did you lose? How much hot water do you need to refill [00:35:00] before the eruption can go again? So there's actually some pretty, I think, understandable physics going on here. You just have to refill that basin with the correct temperature of water and then you can predict how this thing works. So that's why there's this relationship here. And it's not to say that Old Faithful will always be this way. Many things can affect this. And there have been earthquakes, like you said, that have affected this before. And so we could see the timing of Old Faithful change or even the reliability of Old Faithful change with geological [00:35:30] events.

Chris Bolhuis: That is such a good point, that I think is worth putting a pin in that let you know, all of these features that we've talked about, they can change at any time. And so if you're getting information from older books or pamphlets and things like that, that very well may have changed from then and now because these are dynamic systems that change all the time,

Dr. Jesse Reimink: Absolutely.

Chris Bolhuis: something that's important. So

Dr. Jesse Reimink: Absolutely. Hey Chris, I think that's a wrap for Old Faithful coming up next. is [00:36:00] Mammoth Hot Springs

Chris Bolhuis: There you go. Cheers.

Dr. Jesse Reimink: Peace.