Latest / PlanetGeo: The Geology Podcast / Caldera Chronicles - Unzipping the Mysteries of Long Valley With Dr. Andy Calvert

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Caldera Chronicles - Unzipping the Mysteries of Long Valley With Dr. Andy Calvert · PlanetGeo: The Geology Podcast

• 0:00
  SPEAKER_03: What I do want to say is that the um the area just north of Long Valley Caldera is uh a somewhat underappreciated, really active volcanic system.
• 0:12
  SPEAKER_00: So that's that's welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:26
  SPEAKER_00: We're live, Chris.
• 0:27
  SPEAKER_00: We're live, man.
• 0:29
  SPEAKER_00: Yes, straighten up.
• 0:30
  SPEAKER_00: Oh yeah.
• 0:33
  SPEAKER_00: Um Andy Calvert, what uh what a delight.
• 0:37
  SPEAKER_00: I love talking to him.
• 0:39
  SPEAKER_00: It's just so good.
• 0:40
  SPEAKER_00: And talking about Long Valley Caldera, that was a really it was a good way to maybe not wrap up, but to to kind of continue the conversation about Long Valley Caldera.
• 0:49
  SPEAKER_01: Yeah, absolutely.
• 0:50
  SPEAKER_01: I mean, he brought up some things that uh were maybe, I don't know if I would say new to us, but maybe framed in a different way that we hadn't thought about it that way before.
• 0:59
  SPEAKER_01: So I really appreciated this discussion about the card.
• 1:02
  SPEAKER_01: He's got a really good turn of phrase.
• 1:04
  SPEAKER_00: Yeah, the the uh this turn of phrase of like, oh, it's it unzippered the caldera all the way around and talking about geochronology and the I mean, really detailed, difficult geochronology they do to kind of work out the timing of not necessarily here in Long Valley, but in of other eruptive units.
• 1:20
  SPEAKER_00: It's um it's a rich place, the the geology of that of California.
• 1:24
  SPEAKER_01: Um and you did a good job, Jesse.
• 1:26
  SPEAKER_01: I'm gonna hats off to you for not getting all excited about geochronology in that discussion and and then just being all pushing Chris to the corner there and Andy and Jesse just sit and talk, you know.
• 1:38
  SPEAKER_01: So I appreciate that.
• 1:39
  SPEAKER_01: It was good.
• 1:41
  SPEAKER_00: He offered uh you know give us a tour of Long Valley, and I thought, oh, this would be dangerous.
• 1:45
  SPEAKER_00: It did I would just we'd just be sowing the weeds of geochronology the whole time, it'd be totally fun.
• 1:50
  SPEAKER_01: Uh but yeah, he I did tell you, I did say he's got to be careful what he asked for because last time he offered that, I flew out to California and we went out and had a a burger and a beer.
• 1:58
  SPEAKER_00: So that's right.
• 2:00
  SPEAKER_00: Oh man.
• 2:00
  SPEAKER_00: I mean, this would be great though.
• 2:02
  SPEAKER_00: I I uh it's a place that's just spectacular geology.
• 2:05
  SPEAKER_00: He describes it so well as like, why is it spectacular?
• 2:08
  SPEAKER_00: Why is it unique?
• 2:08
  SPEAKER_00: Why is it studied so much?
• 2:09
  SPEAKER_00: It's just got this really great record.
• 2:12
  SPEAKER_00: It's in a kind of a desert environment, it's old enough to have been cut through and in size, but young enough to still be really preserved really well.
• 2:19
  SPEAKER_00: So it's kind of this Goldilocks age.
• 2:21
  SPEAKER_00: He's got a really good turn of phrase for describing this and uh um some really interesting insights into comparisons of Long Valley with other you know volcanoes in uh in California and globally as well.
• 2:32
  SPEAKER_00: So the value of expertise is great.
• 2:35
  SPEAKER_01: And uh just uh for people that maybe aren't very familiar, uh Dr.
• 2:39
  SPEAKER_01: Andy Calvert used to be, he's the former scientist in charge of the Calvo observatory, and is now well, what he says is just back to geology.
• 2:51
  SPEAKER_01: He's back to geologic and relegated back to what he loves to do.
• 2:54
  SPEAKER_01: That's right.
• 2:54
  SPEAKER_01: That's right.
• 2:55
  SPEAKER_01: A U.S.
• 2:56
  SPEAKER_00: Geological Survey research geologist at the California Volcano Observatory.
• 2:59
  SPEAKER_00: Yeah, so I took the time, did an amazing job administering Calvo through the pandemic and dealing with a lot of issues, uh, and then and then you know, probably excited to get back looking at rocks and collecting data.
• 3:12
  SPEAKER_00: So good for him.
• 3:13
  SPEAKER_00: Well, hey, here's Andy Calvert.
• 3:15
  SPEAKER_00: Coming back.
• 3:18
  SPEAKER_00: Can I start, Jesse?
• 3:20
  SPEAKER_01: Yeah, go for it.
• 3:21
  SPEAKER_01: All right, all right.
• 3:22
  SPEAKER_01: All right.
• 3:23
  SPEAKER_01: Well, Andy, welcome back.
• 3:25
  SPEAKER_01: I I've been looking forward to this for a long time.
• 3:28
  SPEAKER_01: Um, as you know, we ask this question, and we asked you this, I don't know, was it two years ago, three years ago?
• 3:34
  SPEAKER_01: I can't, I can't remember.
• 3:35
  SPEAKER_01: It was a while ago.
• 3:37
  SPEAKER_01: Um, when we had you on the show.
• 3:38
  SPEAKER_01: This so this is Andy Calvert, part two.
• 3:41
  SPEAKER_01: But we always start with what got you into geoscience?
• 3:44
  SPEAKER_01: And so I I it's been a while, so I want to ask you that question again, and maybe your answers change.
• 3:49
  SPEAKER_01: I don't know if you remember what you gave us before, but uh what got you into.
• 3:52
  SPEAKER_00: Do you remember what he gave before?
• 3:54
  SPEAKER_01: I don't, but I do remember his best day as a geoscientist.
• 3:57
  SPEAKER_01: So I do remember that's pretty good.
• 3:58
  SPEAKER_01: Yeah, yeah, yeah.
• 3:59
  SPEAKER_00: All right, that's good.
• 4:00
  SPEAKER_01: And then also, Andy, if you could just follow along with that, with what are you up to now?
• 4:06
  SPEAKER_01: What have you been doing?
• 4:07
  SPEAKER_03: Yeah, well, it's delighted to be back on your show.
• 4:10
  SPEAKER_03: It's a fantastic show.
• 4:12
  SPEAKER_03: The thing that got me into geology mainly was just my family spending a lot of time out in the mountains and just the the whole natural system.
• 4:23
  SPEAKER_03: And and whether it was um on the west coast of Vancouver Island, up in the Canadian Rockies, or anything, that's what kind of started it.
• 4:32
  SPEAKER_03: The thing that really crystallized it was the eruption of Mount St.
• 4:35
  SPEAKER_03: Helens.
• 4:36
  SPEAKER_03: I grew up uh a couple hundred miles downwind of Mount St.
• 4:40
  SPEAKER_03: Helens in Moscow, Idaho, and we got a half an inch ash on May 18th.
• 4:45
  SPEAKER_03: And prior to that, we'd been just paying a lot of attention to the deformation on the volcano.
• 4:52
  SPEAKER_03: I'd seen the volcano a lot as I drove.
• 4:56
  SPEAKER_03: My family uh had a lot of family in the Willamette Valley in Oregon, and so we'd drive down the Columbia, and on a clear day you look north, and there was the beautiful platey modfuji-like mountains of mountains.
• 5:11
  SPEAKER_03: And to have it deforming and active was surprising as a seventh grader and interesting, and then to have it kind of blow up and land in my yard and get us out of three weeks of seventh grade May 18th.
• 5:32
  SPEAKER_00: Yeah, uh, that's so good.
• 5:34
  SPEAKER_00: How I I remember this story, and I remember I remember Chris, uh, you you guys uh are two of I think a huge generation of of people interested in volcanoes who really are passionate geologists about volcanoes who got into it in large part because of Mount St.
• 5:46
  SPEAKER_00: Helens.
• 5:47
  SPEAKER_00: I think Chris, you would share a similar story.
• 5:48
  SPEAKER_00: But Andy, how thick was the ash layer?
• 5:50
  SPEAKER_00: I think you mentioned this last time, but uh in front of your house.
• 5:53
  SPEAKER_03: About a centimeter.
• 5:55
  SPEAKER_03: Okay, okay, yeah.
• 5:56
  SPEAKER_03: Yeah, so some somewhere.
• 5:57
  SPEAKER_03: I mean my recollection is an inch, and you know, and that is certainly off by a factor of two.
• 6:03
  SPEAKER_03: Yeah.
• 6:04
  SPEAKER_03: It was it was full of these stuff.
• 6:06
  SPEAKER_03: You look at the ice packs, it it was around a centimeter.
• 6:09
  SPEAKER_00: Okay.
• 6:10
  SPEAKER_00: But it's like those little, you know, when you're a little kid, everything's bigger, right?
• 6:12
  SPEAKER_00: You go walk back through your elementary school and all the lockers are actually really small when you thought they were huge back in the day.
• 6:18
  SPEAKER_03: Yeah, and it's you know, it was snow that didn't melt.
• 6:20
  SPEAKER_01: And yeah, so Andy Calvert did not graduate from the seventh grade then, and right?
• 6:28
  SPEAKER_01: I mean that's right.
• 6:30
  SPEAKER_03: I mean, it it's well for the rest of the year.
• 6:34
  SPEAKER_03: So it was the last three weeks of school.
• 6:36
  SPEAKER_03: We went back half a day, uh, sometime in June to turn in our books, and but there were notes in the lab.
• 6:42
  SPEAKER_03: Yeah, and it was a big hole in my academic record.
• 6:46
  SPEAKER_00: Yeah, yeah.
• 6:48
  SPEAKER_00: Yeah.
• 6:49
  SPEAKER_00: Well, you've patched it together since then, I guess.
• 6:51
  SPEAKER_00: You scrambled together some sort of academic career afterwards.
• 6:54
  SPEAKER_00: Yeah.
• 6:54
  SPEAKER_00: To frame this, the listener, many of the listeners will probably kind of know this, but this is the this is one of later episodes in our series about Long Valley Caldera.
• 7:02
  SPEAKER_00: What have you been up to now?
• 7:03
  SPEAKER_00: In and maybe if you could like zoom in on the your volcanology work recently.
• 7:08
  SPEAKER_00: Like, what have you been up to since we last spoke three years ago or something like that?
• 7:12
  SPEAKER_00: And actually, you two hung out since we last spoke too, right?
• 7:15
  SPEAKER_01: You guys met up in San Francisco.
• 7:17
  SPEAKER_00: San Francisco, let's go.
• 7:19
  SPEAKER_03: A delightful um burger is actually my first uh restaurant experience during the pandemic.
• 7:25
  SPEAKER_03: Um and we had a really nice dinner, and so it must have been 2020.
• 7:32
  SPEAKER_03: So I think it's been five years actually since we talked.
• 7:35
  SPEAKER_01: I think, unless it might have been, Andy, it might have been 2021.
• 7:40
  SPEAKER_01: Okay.
• 7:41
  SPEAKER_01: I I think it was, I think it was.
• 7:43
  SPEAKER_01: I think it was 2021.
• 7:44
  SPEAKER_03: Yeah, okay.
• 7:45
  SPEAKER_03: So at that time I was scientist in charge of Cal VO, which is about 35 scientists, and and and I was sort of guiding that group.
• 7:56
  SPEAKER_03: It's one of five observatories in the Volcano Science Center, so nominally in charge of um any eruptive activity or unrest in California or Nevada.
• 8:09
  SPEAKER_03: I stopped doing that last August and I'm back to being a dirty boots geologist.
• 8:15
  SPEAKER_03: So I'm back to being uh a research geologist instead of a supervisory geologist.
• 8:20
  SPEAKER_01: Which do you like better?
• 8:21
  SPEAKER_01: Can I ask?
• 8:22
  SPEAKER_03: I like being a geologist far more than it was a bit of a difficult tenure because the um I had the pandemic to deal with and then also had a move from where we'd been since 1952 in Menlo Park down to Moffat Field.
• 8:41
  SPEAKER_03: Uh, we built a new lab building, it's beautiful.
• 8:44
  SPEAKER_03: Then we re-renovated this place.
• 8:46
  SPEAKER_03: And so there were a lot of logistical challenges during that.
• 8:50
  SPEAKER_00: I mean, anybody in administration during COVID deserves, you know, all the um cudos and grace we can we can give them.
• 8:57
  SPEAKER_00: I I that's uh a lot of people I think got to that point a year or so ago.
• 9:02
  SPEAKER_00: It was like, okay, I'm done with this managerial thing.
• 9:04
  SPEAKER_00: I we survived through the pandemic.
• 9:06
  SPEAKER_00: I want to go back to doing my thing.
• 9:08
  SPEAKER_00: So what is your what is your research focus or or or multiple focus focuses?
• 9:13
  SPEAKER_03: Um there there are there are a few of them.
• 9:15
  SPEAKER_03: The the main focus is Mount Shasta.
• 9:18
  SPEAKER_03: So we this is a we started a project there.
• 9:22
  SPEAKER_03: Um, well, my predecessor started it about 50 years ago exactly in 1975, and and so making a geologic map and eruptive history of of Mount Shasta.
• 9:32
  SPEAKER_03: That's it in the background.
• 9:33
  SPEAKER_00: Um sorry, sorry, radio listeners.
• 9:36
  SPEAKER_00: But the he's got a beautiful painting of Mount Shasta behind him here.
• 9:41
  SPEAKER_03: That was a present from our um Duty Sur seismologist here when I stepped down from being uh scientist in Chinese.
• 9:49
  SPEAKER_03: Oh, it's great, it's a great gift.
• 9:51
  SPEAKER_03: So it's spectacular.
• 9:52
  SPEAKER_03: It is beautiful, and so it's it's finishing the map and writing up the eruptive history and writing a hazard assessment for Mount.
• 10:02
  SPEAKER_03: It is kind of number one priority on my list.
• 10:05
  SPEAKER_03: Uh, and then I've got a lot of other projects.
• 10:07
  SPEAKER_03: So I I'm a geochrinologist, so I I provide mainly argon geochrinology and now some cosmogenic isotope dating for kind of all the volcanoes in our purview in your eyes.
• 10:21
  SPEAKER_00: Andy, can I interrupt you a second?
• 10:22
  SPEAKER_00: Or in the USGS?
• 10:23
  SPEAKER_00: Sorry, Chris, in Calvo or in the USGS uh purview?
• 10:26
  SPEAKER_03: In all of the USGS, so so Alaska, Hawaii, Northwest.
• 10:31
  SPEAKER_03: Okay.
• 10:32
  SPEAKER_00: Um and so all the geochronology work gets gets funneled.
• 10:35
  SPEAKER_00: It's at Moffat Field, is the is where your lab is there?
• 10:37
  SPEAKER_03: Yes.
• 10:38
  SPEAKER_00: Yep.
• 10:38
  SPEAKER_00: Okay, wow.
• 10:39
  SPEAKER_00: Yeah.
• 10:39
  SPEAKER_00: Okay.
• 10:39
  SPEAKER_00: That's a serious amount of work going through there, then I'd imagine.
• 10:42
  SPEAKER_03: Yeah, we've we've got it, we've got a lot of so I'm a small part of a lot of projects, and then I have a couple of my own that I really spend spend large amounts of time on.
• 10:51
  SPEAKER_01: Um just can you explain to our listeners what exactly you're doing with geochronology then?
• 10:58
  SPEAKER_01: Can you kind of tease that out a little bit?
• 11:00
  SPEAKER_03: The best measure of what a volcano can do is what it's done in the past.
• 11:05
  SPEAKER_03: And and so we'll develop these eruptive histories for the volcano.
• 11:11
  SPEAKER_03: And it's essentially trying to figure out the the life story of the volcano.
• 11:16
  SPEAKER_03: We we look at the the composition of what comes out of the top of it.
• 11:21
  SPEAKER_03: Um, but my role is is often the timing, really, and trying to understand the last time it erupted or the episodes in which it erupted.
• 11:31
  SPEAKER_03: Typically, most of our volcanoes are very episodic.
• 11:34
  SPEAKER_03: So it'll be really busy erupting, erupting, erupting, and it'll sit for a thousand years or two thousand years.
• 11:40
  SPEAKER_03: So trying to understand those timescales of eruptive behavior.
• 11:45
  SPEAKER_03: And then that leads to understanding the plumbing system beneath it.
• 11:49
  SPEAKER_03: And so if we can understand what, you know, if a batch of magma stews up and then erupts like crazy and then it goes quiet, that can tell us about the process.
• 11:59
  SPEAKER_03: And so the the main products are things like hazard assessments for artners, and then a map, a geologic map that shows where the lava flows went, and then eruptive history papers on kind of the entire history of the volcano.
• 12:18
  SPEAKER_03: Uh, and then the petrology or the um the actual formative, you know, the the process that really got the the material to erupt at the surface.
• 12:29
  SPEAKER_03: So say at Mount Shasta, you know, that involves ultimately subduction and then dewatering of the subducting slab and mantle and crustal processes, and then the stuff comes out of the top.
• 12:44
  SPEAKER_01: And then what do you mean by cosmogenic dating?
• 12:47
  SPEAKER_01: I think like uh I don't think a lot of people are really all that familiar with that.
• 12:52
  SPEAKER_01: What's that process look like and and what are you doing?
• 12:55
  SPEAKER_03: Right.
• 12:55
  SPEAKER_03: And so so that my main tool is argon geochronology, where we have a radioactive isotope, in this case potassium for you, that decays to argon-40.
• 13:04
  SPEAKER_03: And so that's potassium that's in crystals in the rock that um decays to argon, and the kind of the clock starts when it crystallizes and then accumulates over time.
• 13:17
  SPEAKER_03: There are a lot of samples that we can't date on volcanoes because they're they're not the potassium isn't housed in the right material to to hang on to that.
• 13:28
  SPEAKER_03: And so we kind of use other techniques.
• 13:31
  SPEAKER_03: One is carbon-14, right?
• 13:33
  SPEAKER_03: And so if if this volcano, if this lava flow flowed over a tree and killed that tree, we can we can date that and and carbon age.
• 13:44
  SPEAKER_03: And then there's a technique that's often used for uh understanding ages of glaciation or really understanding surfaces and trying to understand how long something's been at the surface, and that's cosmogenic surface exposure dating.
• 13:59
  SPEAKER_03: And it's uh it's complicated.
• 14:01
  SPEAKER_03: You have cosmic energy coming in from supernovas and interacting with gas in the upper atmosphere and and creating other radiation, but there's essentially there's radiation coming down and and hitting us and hitting the rocks, and that causes reactions within the rocks and commonly will produce radioactive isotopes that decay.
• 14:26
  SPEAKER_03: Carbon-14 is actually a cosmogenic isotope, so cosmic rays will come in and interact with gases and produce carbon-14 in the upper atmosphere.
• 14:37
  SPEAKER_03: That's slightly different than what we're doing with surface exposure dating, the reactions happening within the rock, but it we generally use um chlorine-36 that has a half-life of 300,000 years, or beryllium-10 that has a longer half-life, or aluminum-26.
• 14:56
  SPEAKER_03: There are a couple of stable isotopes too that are produced, neon-21 and helium-3 by these processes.
• 15:03
  SPEAKER_03: And so depending on what target minerals there are, we can date how long.
• 15:09
  SPEAKER_03: It's like a kind of like getting a sunburn, uh, like what sunburn the rock has gotten from being on the surface for for some length of time.
• 15:18
  SPEAKER_03: So when we have a lava flow, we've got to make sure that we're seeing the very tippy top of that lava flow, and then we've got to get the right sample rock and then and then run it.
• 15:28
  SPEAKER_03: So it's it's complicated, but it's it's a way that we can date things that we can't date with argon.
• 15:34
  SPEAKER_00: So why I I don't actually know this.
• 15:36
  SPEAKER_00: Why what um prevents a lava flow from being useful for potassium argon?
• 15:42
  SPEAKER_00: Is it that you don't have any micas or feldspars crystallizing in it's just glassy or you need something with potassium that'll hang on to the argon.
• 15:51
  SPEAKER_03: And so that could be a crystal-like sanidine, is very good for, and so out of a very glassy volcanic rock that has a mineral fanidine, which is a potassium aluminum silicate, that will produce argon.
• 16:05
  SPEAKER_03: It'll hang on to it until you bring it into the lab and measure it.
• 16:09
  SPEAKER_03: In most of the rocks I work on, there isn't sanitine.
• 16:12
  SPEAKER_03: There actually isn't a mineral phase that has a lot of potassium in it.
• 16:16
  SPEAKER_03: The potassium is all in the glass.
• 16:18
  SPEAKER_03: So Mount Shasta uh is notorious for this.
• 16:22
  SPEAKER_03: The there really aren't any minerals that have potassium that I can date.
• 16:28
  SPEAKER_03: There aren't phenocrysts anyway.
• 16:30
  SPEAKER_03: So the place that does preserve the argon that the potassium produces is in the slowly cooled middle of the lava flow.
• 16:41
  SPEAKER_03: So the lava flow comes to rest and the top and bottom quench immediately.
• 16:46
  SPEAKER_03: They're very glass.
• 16:48
  SPEAKER_03: The melt doesn't have time to make crystals, it just it just ends up as a glass.
• 16:53
  SPEAKER_03: And the trouble with glass is it doesn't really hang on to its orgo reliably.
• 16:59
  SPEAKER_03: But the middle of the lava flow flu cools slowly enough that you'll get these ground mass crystals.
• 17:06
  SPEAKER_03: They're they're sanidine or an orthoclase, but they're tiny.
• 17:10
  SPEAKER_03: They're they're on the order of 10 or 15 or 20 micrometers across.
• 17:14
  SPEAKER_03: But if it cools slowly enough, you'll get these feldspars.
• 17:18
  SPEAKER_03: They're in there with pyroxines and and oxides.
• 17:21
  SPEAKER_03: You can get um good crystals that'll hold on to their argon.
• 17:26
  SPEAKER_03: So if you can get to a a lava flow that's been glaciated or eroded enough, you can actually get material that you can date very well using from the center of the flow, kind of as it's exposed.
• 17:38
  SPEAKER_00: Okay.
• 17:38
  SPEAKER_03: Yeah, using potassium argon or argon 43.
• 17:41
  SPEAKER_03: So that's sort of my bread and butter is finding those, those sorts of rocks that we can date.
• 17:46
  SPEAKER_03: And it's challenging.
• 17:48
  SPEAKER_03: It involves a lot of kind of walking around and trying to find the right stuff and and iterative work.
• 17:53
  SPEAKER_00: And uh, okay, so then one last question on this, and then we can move on to long care long valley.
• 17:57
  SPEAKER_00: But what is the uh there's a lot of misconceptions about the potassium argon system, especially for dating young stuff.
• 18:03
  SPEAKER_00: When does your sensitivity be um become detrimental to the system?
• 18:08
  SPEAKER_00: What is the youngest rock you could reasonably expect to date with potassium argon system?
• 18:14
  SPEAKER_03: Yeah, so with the crystals, and we've dated historic things.
• 18:17
  SPEAKER_03: We we dated the AD 79 eruption of Vesylvius, and we got the right number.
• 18:23
  SPEAKER_03: Pliny was there, he you know, it was mid-auditor.
• 18:26
  SPEAKER_00: Plus or minus what?
• 18:27
  SPEAKER_00: What what was the minus your age?
• 18:29
  SPEAKER_03: Plus or minus 90 years one thing.
• 18:32
  SPEAKER_03: Wow.
• 18:32
  SPEAKER_03: And it took us a month.
• 18:34
  SPEAKER_03: We had to date like 20 different incremental heating experiments, and and we ended up we had individual experiments for kind of plus or minus 250 years or so.
• 18:44
  SPEAKER_03: And as you average them, you know, we stopped when we got the right number.
• 18:49
  SPEAKER_00: But yeah, but you stopped yeah, plus or minus some significant amount of things.
• 18:53
  SPEAKER_03: That's interesting.
• 18:53
  SPEAKER_03: Plus or minus 90 years, and and and so that's gratifying, right?
• 18:58
  SPEAKER_03: That there's a historic sample that that we actually got a got uh got an age on the time itself.
• 19:05
  SPEAKER_03: On on rocks, um, we've certainly dated things that young, but we don't have the confidence that it came out on a particular day, 79 in in 79 AD.
• 19:15
  SPEAKER_03: Typically on the best stuff that's that's under about 20,000 years, we can get plus or minus between 500 years and 3,000 years.
• 19:24
  SPEAKER_03: And so on really good stuff, we can get we can get something plus or minus 500 years.
• 19:29
  SPEAKER_03: Some of these cosmogenic isotopic systems, we can do far better than that.
• 19:33
  SPEAKER_03: We can get plus or minus 50 or 100 years.
• 19:37
  SPEAKER_00: On a 20,000-year-old flow?
• 19:39
  SPEAKER_03: Wow.
• 19:40
  SPEAKER_03: Yeah, or or even like a yeah, so on a on something that's that's less than 20,000 years, but even things that are two or three thousand years old.
• 19:47
  SPEAKER_03: So we can get things that are quite precise and we have to show that they're accurate by dating the stratigraphy or by using multiple systems.
• 19:59
  SPEAKER_03: Typically in the last 10,000 years, I try to use two different systems and get them to agree before we really hang our hat on it being correct.
• 20:08
  SPEAKER_00: Okay.
• 20:09
  SPEAKER_00: I mean, that's really interesting, and that that kind of I think Chris transitions nicely to Long Valley because we talked a lot about the the uh the ages of the Long Valley system, the magmas and the well, excuse me, the lavas in the area.
• 20:20
  SPEAKER_00: Um, and I think that that kind of frames the time scales pretty well between you know four million years all the way up till sort of the big eruption and modern stuff too.
• 20:30
  SPEAKER_00: So I uh that was a really nice description.
• 20:32
  SPEAKER_00: Thanks for that, Andy.
• 20:33
  SPEAKER_03: Yeah, and and argon geochronology, potassium argon works all the way back to the age of the earth.
• 20:38
  SPEAKER_03: You know, so we dated the moon rocks using it.
• 20:41
  SPEAKER_03: What our specialty in our laboratory is is really pushing it to the young end and and trying to characterize these active systems.
• 20:50
  SPEAKER_01: Is there a limit, Andy, to the young end?
• 20:52
  SPEAKER_01: Like how how young can it be before you you diminishing returns?
• 20:56
  SPEAKER_03: Yeah, I think we've we've kind of hit it um at you know at the the historic um that that sort of a couple thousand years plus or minus a hundred or so, but we might not it's the the problem is that potassium 40 has a half-life of one and a quarter billion years, right?
• 21:16
  SPEAKER_03: So it's a long time, so it's a very and then the other problem is that we're breathing one percent argon, and that's that's of the same isotope argon 40, the radiogenic argon.
• 21:28
  SPEAKER_03: Um so we've got to deal with the stuff that's in the room and in all materials, you know, and in your eyeglasses, if you if you melt this stuff, you get a bunch of argon out, and and rocks have have argon in it.
• 21:41
  SPEAKER_03: And so it's that's the challenge is is really separating out the radiogenic argon from the atmospheric argon and then time.
• 21:50
  SPEAKER_03: And and so you know, sometimes when we say when you when you can't date something because it's too young, you say, Well, we're gonna leave it in the field a little bit longer.
• 22:01
  SPEAKER_03: Let it hang it.
• 22:02
  SPEAKER_03: Let it let it cook for a little bit longer.
• 22:04
  SPEAKER_03: Two years, it'll be fine.
• 22:06
  SPEAKER_00: Yeah, that's great.
• 22:08
  SPEAKER_00: I like that one.
• 22:10
  SPEAKER_00: All right, Chris, how how how should we start picking up the colour?
• 22:14
  SPEAKER_00: I got an idea.
• 22:14
  SPEAKER_00: You got an idea?
• 22:15
  SPEAKER_00: Okay.
• 22:15
  SPEAKER_00: I got an idea.
• 22:16
  SPEAKER_00: Take it away.
• 22:16
  SPEAKER_01: Okay.
• 22:17
  SPEAKER_01: So Andy, when when Jesse and I had this like brilliant idea to to do a c a couple episodes on Long Valley Caldera, I think it caught both of us off guard with how complicated this is.
• 22:31
  SPEAKER_01: And it was really kind of hard to this was a monumental task, actually.
• 22:35
  SPEAKER_01: It took a lot of time.
• 22:36
  SPEAKER_01: Why do you think the geology of Long Valley is so complicated and so difficult?
• 22:43
  SPEAKER_03: Well, it it really is one of the best places to go.
• 22:49
  SPEAKER_03: Look at a volcanic system.
• 22:51
  SPEAKER_03: Everything's complicated.
• 22:52
  SPEAKER_03: The world's complicated, but often you can't see the complications.
• 22:56
  SPEAKER_03: What you have at Long Valley is the ability to see the wall rocks of the Pluton, the stratigraphy that was above the Pluton, just a fantastic exposure of the Bishop Tuff.
• 23:11
  SPEAKER_03: What came before it, what came after it.
• 23:14
  SPEAKER_03: It's a remarkable place to visit.
• 23:17
  SPEAKER_03: And you can have a really great one-day field trip.
• 23:22
  SPEAKER_03: You can have a week-long field trip, you can have a month-long field trip, and you can work out there for years and still be drilling down and figuring out new stuff.
• 23:32
  SPEAKER_03: And it's it it is a remarkable place.
• 23:35
  SPEAKER_00: And and so can I can hold on, Andy?
• 23:37
  SPEAKER_00: Can I can I ask you just a sub-question to this?
• 23:40
  SPEAKER_00: Are you inferring that it's not more complicated than other places, that this is actually just normal amounts of complication?
• 23:46
  SPEAKER_00: I I'm I'm honestly asking.
• 23:51
  SPEAKER_00: That makes sense to me.
• 23:52
  SPEAKER_00: Um, I just never thought of it that way.
• 23:54
  SPEAKER_03: Yeah, I think I you know it certainly is an extremely complicated place.
• 23:59
  SPEAKER_03: But I think a lot of geology, you know, the challenge is, you know, we're looking at a puzzle that has 90% of the pieces missing.
• 24:10
  SPEAKER_03: And we're trying to sort through that and figure out what happens.
• 24:13
  SPEAKER_03: I mean, especially you looking at at these multi-billion-year-old systems, you don't get to see so much of the data, right?
• 24:24
  SPEAKER_03: And so this is a place where the complexity really hits you in the face.
• 24:29
  SPEAKER_03: And um, you know, there is simplicity to see there.
• 24:32
  SPEAKER_03: And and there's, you know, it's it's lovely, and you can you can see the caldera, and you can see the outflow sheet, and you can see the fall units, and you can see the um resurgent dome afterwards.
• 24:45
  SPEAKER_03: So you can see all those pieces of a caldera system.
• 24:48
  SPEAKER_03: You can see the framework before.
• 24:50
  SPEAKER_03: And and yeah, I think that places are they're always more complicated than we portray in journal articles or we portray on podcasts, right?
• 25:02
  SPEAKER_03: And and we're the challenge is simplifying it down.
• 25:05
  SPEAKER_03: And it's a place where you can, there is a lot of value in spending time at Long Valley because you can you can see these these processes.
• 25:14
  SPEAKER_03: And if you if you go back to the Paleozoic, there's a good thick Paleozoic section of sediments that sits on top of what is now Long Valley, and you can see those in the wall of Convict Lake just west of the caldera.
• 25:31
  SPEAKER_03: There are the granitoid plutons that are there in the Sierra Nevada that crystallized between you know 250 and 90 million years ago that are on the edge of it and and really well exposed.
• 25:48
  SPEAKER_03: There's Glass Mountain off to the east, that's the 2 million-year-old rhyolite intrusions that that are similar in volume to what comes out of Long Valley.
• 26:02
  SPEAKER_03: And you can see those.
• 26:03
  SPEAKER_03: And that's that's the neat thing about the place.
• 26:06
  SPEAKER_03: And and that's why it's worth doing multiple podcasts on it, is because there is so much exposed there.
• 26:13
  SPEAKER_03: There are so many parts, and and people, you know, generations of geologists have have worked on this and and figured out different portions of it and and made it pretty accessible for yeah, for people to read about it.
• 26:28
  SPEAKER_03: Okay.
• 26:29
  SPEAKER_03: Well, that's I like that framing.
• 26:30
  SPEAKER_01: I do too.
• 26:31
  SPEAKER_01: Uh Andy, I think that um, you know, for for Jesse and I, it was it was difficult to take this complicated system and and like you said, simplify it down for for doing you know a couple of episodes, a couple you know, podcast episodes.
• 26:45
  SPEAKER_01: But you know, one of the one of those difficulties is well, a couple of them actually are are what generated the magma?
• 26:52
  SPEAKER_01: Where did the magma come from?
• 26:53
  SPEAKER_01: And then it is very evolved.
• 26:56
  SPEAKER_01: So can you talk a little bit about those, those aspects of Long Valley?
• 27:01
  SPEAKER_01: Why here, right?
• 27:02
  SPEAKER_01: Why is Long Valley where it is, and then you know how the magma kind of changed from beginning almost four million years ago to where we are today?
• 27:12
  SPEAKER_03: Yeah, so um it's there because of basin range extension, really.
• 27:18
  SPEAKER_03: You know, so you have the whole basin range.
• 27:21
  SPEAKER_03: If you go from the Sierra Nevada to the Wasetch front, the distance between those two has doubled in the last 20 million years.
• 27:28
  SPEAKER_03: So we've thinned the crust there, and and we've gotten as you thin the crust, you get hot rocks closer to the surface, and that causes melting and ultimately volcanoes, right?
• 27:43
  SPEAKER_03: So there's there's kind of high heat flow in general when you go from Ray to Reno to Salt Lake City.
• 27:49
  SPEAKER_03: But there aren't volcanoes everywhere, and so that's a that's a head scratcher, right?
• 27:54
  SPEAKER_03: So why are there some out in the middle, where there's some near the Wasatch, where there's some on the the west side?
• 28:02
  SPEAKER_03: That whole basin and range is a fantastic laboratory for seeing things because we're you can see down into the crust differently in different places, but some places, like um uh especially on the edges of the basin and range right now, seem to be the the areas that have a bit more volcanism and uh a bit more perhaps seismic activity.
• 28:26
  SPEAKER_03: Long Valley itself, you're right that it starts out so that that heat, when you're down in the the mantle, um, and if you melt mantle rocks, what you get is basalt, right?
• 28:39
  SPEAKER_03: And so that's that's a mafic rock.
• 28:41
  SPEAKER_03: And that's the ultimate source of the heat and and the material.
• 28:47
  SPEAKER_03: And so as you're thinning the crust, it's that basalt that's getting a little bit closer to the surface.
• 28:52
  SPEAKER_03: And as you decompress it, it allows partial melting, right?
• 28:57
  SPEAKER_03: And it causes some melting and you generate basalt.
• 29:02
  SPEAKER_03: And then as that basalt sits around and stews, say in the middle crust, it crystallizes little bits of olivine and and and that stuff rains out.
• 29:14
  SPEAKER_03: And what's left is a little bit more evolved, right?
• 29:19
  SPEAKER_03: A little bit higher silica, and and you rain out more crystals and it becomes more and more higher silica, more evolved.
• 29:28
  SPEAKER_03: And that's what we call fractional crystallization, right?
• 29:31
  SPEAKER_03: And and and so if you have a magma system that sits around and crystallizes long enough, then you'll get to rhyolite, right?
• 29:45
  SPEAKER_03: And and rhyolite is um lower temperature, higher silica, stickier magma.
• 29:53
  SPEAKER_03: If you if you erupt basalt, it comes up and it tends to flow across the the surface.
• 29:59
  SPEAKER_03: It's low viscosity, it's very hot.
• 30:02
  SPEAKER_03: If you erupt rhyolite, it doesn't flow across the surface, and it's more explosive because it's um it's stickier, it's cooler, it's it's a higher viscosity material.
• 30:16
  SPEAKER_00: Okay, a couple, well, I don't know, a couple things that came to mind there.
• 30:19
  SPEAKER_00: You so you're describing the this basin range extension, which you know, uh you know, thinning the crust by a factor of two, mantle up wells to replace that, and we do this melting thing.
• 30:30
  SPEAKER_00: The volcanism on the edges, though.
• 30:33
  SPEAKER_00: So in that juxtaposition between the Sierra Nevada and the basin and range extension, we'd often seen this described as a transpressional, you know, regime in here, or transtentional regime, really.
• 30:44
  SPEAKER_00: That's that's kind of that's adding i in the in the in this area here.
• 30:48
  SPEAKER_00: Is that is that one of the reasons?
• 30:49
  SPEAKER_00: Like, you know, basin range, I'm kind of thinking of it like it's just extending, sort of pierce your ship, you know, just or um just flattening out sideways, but on the margins you've got these big stable blocks, so you kind of get weird interactions.
• 31:01
  SPEAKER_00: Is that is that why you're getting more volcanoes on the edges of the basin and range rather than kind of you know homogeneously throughout it?
• 31:10
  SPEAKER_00: Or is it just randomness?
• 31:12
  SPEAKER_00: Like the crust has all these inherited features to it, and like it doesn't break evenly, so when you stretch it, like old fault zones get reactivated, and that's where you know lava can come out or something.
• 31:23
  SPEAKER_00: Like, is there a rhyme or reason to this, I suppose, in your mind, in this where the volcanoes are situated with relation to the basin and range extension?
• 31:32
  SPEAKER_00: Yeah, I'd I know that's a really tough like long winding question, but no kidding.
• 31:37
  SPEAKER_00: I'm trying to understand this because really, Jesse.
• 31:39
  SPEAKER_00: Was that was that a long-winded question, Jess?
• 31:41
  SPEAKER_00: Huh?
• 31:41
  SPEAKER_00: You want me to to to summarize it here?
• 31:44
  SPEAKER_00: Uh why are they all at the edges and is it random?
• 31:47
  SPEAKER_00: There we go.
• 31:48
  SPEAKER_01: There we go.
• 31:49
  SPEAKER_00: There's the question.
• 31:50
  SPEAKER_00: Okay, all right, perfect.
• 31:51
  SPEAKER_03: The answer is I don't know.
• 31:53
  SPEAKER_03: And but I don't think it's random.
• 31:54
  SPEAKER_03: You know, I don't think it's random.
• 31:57
  SPEAKER_03: I think that there's there's something about the the the process of of spreading that um, well, they haven't always been at the edges.
• 32:08
  SPEAKER_03: There are large caldera systems that go up the kind of northern Nevada Rift, the Caetano calderal.
• 32:15
  SPEAKER_03: So certainly back in the in the Miocene and Oligocene, there was a lot of eruptive activity in what's now the middle basin.
• 32:24
  SPEAKER_03: But now, um, for whatever reason, the it seems that the extension is localized at the edges a little bit more and there's more more volcanism.
• 32:34
  SPEAKER_03: But I I don't have a very good answer.
• 32:37
  SPEAKER_03: I think probably West Hildreth Wood and and some other might.
• 32:43
  SPEAKER_03: Um let's talk for a second about the tectonics.
• 32:46
  SPEAKER_03: So so yeah, things are extensional across the basin range.
• 32:51
  SPEAKER_03: On the west side of the basin range, so the California side, there are some things going on that there is a lot of transtension.
• 32:59
  SPEAKER_03: And one of the things that's happening is so the Pacific Plate is moving northwestward relative to North America, and it's trying to pull a bit of California, actually, all of California along with it.
• 33:15
  SPEAKER_03: And about 20% of the strain, the difference in motion between the Pacific Plate and North America is taken up along a fault on the east side of the Sierra, a series of faults.
• 33:28
  SPEAKER_00: And see, this this was news to me diving into this Long Valley Color.
• 33:32
  SPEAKER_00: I'd never heard of this.
• 33:33
  SPEAKER_00: Is the Walker Lane belt?
• 33:34
  SPEAKER_00: Is that what you're referring to?
• 33:35
  SPEAKER_00: Kind of here.
• 33:36
  SPEAKER_00: I never knew this, and this struck me as just like such a great teaching example of it's complicated.
• 33:42
  SPEAKER_00: Like we teach this really simple thing, like okay, the San Andreas fault, you know, here's what it's doing, you know, it's moving in this direction.
• 33:49
  SPEAKER_00: Look at it.
• 33:50
  SPEAKER_00: Strike slip.
• 33:51
  SPEAKER_00: And actually, like, no, it's way more complicated.
• 33:53
  SPEAKER_00: You got this big block that's in the middle that's probably getting rotated.
• 33:56
  SPEAKER_00: That's I I just that was a really cool uh realization for me.
• 34:01
  SPEAKER_00: Uh Chris, I don't know if you feel similarly about this, but when we dove into Long Valley Caldera.
• 34:05
  SPEAKER_00: So sorry, Andy, continue.
• 34:06
  SPEAKER_00: This was I just wanted to highlight.
• 34:08
  SPEAKER_00: Yes, sir.
• 34:08
  SPEAKER_03: I want to point a good thing to do is to look at California and look at the San Andreas Fault.
• 34:13
  SPEAKER_03: And it starts off in the in the um kind of Salton Sea, and then it goes up toward LA and it takes a big bend off to the west, and then another bend to come back in.
• 34:24
  SPEAKER_03: And so the it's a right lateral strike slip system.
• 34:28
  SPEAKER_03: And so you can imagine those those mountains that are around LA or these big knuckles that are coming up because there's a big bend in the fault.
• 34:36
  SPEAKER_03: So, what's happening at the eastern side of the Sierra is kind of trying to solve that problem.
• 34:40
  SPEAKER_03: Instead of having that big compressional problem, it's trying to reroute the plate boundary, really, to the east side of the Sierra.
• 34:50
  SPEAKER_03: And it's been doing that.
• 34:51
  SPEAKER_03: Walker Lane's been gone for about 10 million years, and it's it's a series of faults on the on the east side that essentially start at Long Valley.
• 35:01
  SPEAKER_03: Walker Lake is just north of Long Valley, and that's where that that Walker Lane starts.
• 35:07
  SPEAKER_03: To the south of Long Valley, it's a more discrete fault.
• 35:11
  SPEAKER_03: The Owens Valley fault, it looks like when you're standing there, it looks like it should be a pure normal fault because you've you're down in Bishop at at 5,000 feet, and then you see 14,000 foot Mount Whitney off to the west, and it's currently also a uh a strike-slip fault, so that there's a lot of transtention there.
• 35:32
  SPEAKER_03: So that's sort of enough about tectonics.
• 35:34
  SPEAKER_03: When you look at the at the magma system, or or kind of why is Long Valley there, one of the things that seems to have have happened, there's a lot of mafic volcanism around Long Valley that's older, that's between three million years and three and a half million years or so.
• 35:56
  SPEAKER_03: Actually, a big swath that goes all the way from the San Joaquin drainage well into Nevada.
• 36:03
  SPEAKER_03: And and this is a this is a fairly new discovery.
• 36:07
  SPEAKER_03: It we've written it up, it's not quite published yet, but the there's a big swath of Mafic volcanism with Long Valley about in the middle of it.
• 36:16
  SPEAKER_03: Why that's there, so so one, it's it's an odd swath because it's it's essentially kind of east-west and where everything else flows San Andreas Fault goes north-south and and all the structures go north-south.
• 36:31
  SPEAKER_03: This is something that across them.
• 36:33
  SPEAKER_03: One possibility is that there was a a Mafic route to the Sierra Nevada that actually delaminated and and and let go three and a half to three million years ago.
• 36:46
  SPEAKER_03: And the the basalt that comes out on the surface is reflecting that.
• 36:51
  SPEAKER_03: And that that heat that of so you have the the root of the Sierra Nevada gives way, heat comes in, heats everything up, and kind of starts the beginning of the stewing that ultimately ends up as Long Valley caldera.
• 37:07
  SPEAKER_03: That's hypothetical.
• 37:09
  SPEAKER_03: We don't know that that is what happened, but there was a tremendous amount of pliocene of this 3.5 million to 3 million year old volcanism in the same spot where you see Long Valley now, sort of preheating the crust and kind of helping to situate the Long Valley caldera in there.
• 37:29
  SPEAKER_00: So there's maybe there's multiple factors that could go into creating more decompression melt, uh more mantle melting in this particular area, whether it's transtension, basin range, extension, and root delamination, perhaps, to kind of start this this uh this heat source, this you know, power source for driving Long Valley Caldera eventually, you know, the big eruptions.
• 37:50
  SPEAKER_00: Yeah.
• 37:50
  SPEAKER_00: Is that would that be fair to say that there's many ways to do it here?
• 37:54
  SPEAKER_03: Yeah, and it was it was the contribution of of probably several different mechanisms that caused it to be localized there.
• 38:02
  SPEAKER_03: Because there there is other Pliocene volcanism down at Coso, you know, kind of the Coso Center, 100 miles south of there, and and other scattered Pliocene volcanism, but none of it's as big as what sits under Long Valley.
• 38:18
  SPEAKER_03: Go ahead, Chris.
• 38:19
  SPEAKER_00: You look like you're ready for a question here.
• 38:21
  SPEAKER_01: Well, I mean, so Andy, you've talked a lot about um you've brought up some basic geologic concepts in reference to Long Valley, you know, fractional crystallization.
• 38:33
  SPEAKER_01: You talked about um decompression melting, uh based in range extension and and so on in its relation to generating magma.
• 38:40
  SPEAKER_01: And that's what one thing that came through to us as we were as we were diving into the geology of Long Valley was that you know, there's this is a a really good way to teach just regular, kind of like basic concepts that are important in geoscience.
• 38:56
  SPEAKER_01: Are there others that you can think of that are involved in Long Valley that can be used as like a this case study to teach concepts in geology?
• 39:06
  SPEAKER_03: Yeah, so let's see.
• 39:08
  SPEAKER_03: The um it's a really good place to go see physical volcanology.
• 39:13
  SPEAKER_03: So to look at how say you have this very large super eruption, right?
• 39:18
  SPEAKER_03: Uh where hundreds of cubic kilometers of material are are coming out.
• 39:23
  SPEAKER_03: How does it start?
• 39:24
  SPEAKER_03: And and so one of the things they've worked out very well is where the uh, and this is work by Wes Hildreth and Colin Wilson and and Judy Feirstein, where did the eruption actually start?
• 39:39
  SPEAKER_03: And so the first stuff out, the deposits are the the Bishop Tuff deposits um include fall deposits, so pumice falls that are very thick close to the volcano, but then head all the way out to Kansas.
• 39:54
  SPEAKER_03: And then um, probably Michigan too.
• 39:57
  SPEAKER_00: And and don't leave Michigan, don't mention Kansas without bringing in Michigan.
• 40:00
  SPEAKER_03: I mean, why why would you throw a Kansas in there?
• 40:03
  SPEAKER_01: Seriously, who cares about Kansas?
• 40:07
  SPEAKER_03: And then and then you have pyroclastic flows where you'll have this Plinian column that comes up and collapses, and you'll generate these glowing avalanches of pyroclastic flows.
• 40:20
  SPEAKER_03: And it's a great place to go and see all those to see how they vary around around the uh around the caldera.
• 40:28
  SPEAKER_03: But the one of the things they spent a lot of time with um looking at the fall deposit, um, the geology around Long Valley varies tremendously.
• 40:37
  SPEAKER_03: So on the east side, there's Glass Mountain, there are all these kind of high silica rhyolites.
• 40:43
  SPEAKER_03: On the west side, there are Sierra Nevada granites and metamorphic rocks and sedimentary rocks.
• 40:53
  SPEAKER_03: And so by looking at the lithics, by looking at the the accidental rocks, the the things that just got blasted out that were older, that were in this um in this this pumice fall, you can kind of figure out where the the eruption started.
• 41:10
  SPEAKER_03: So down at the base, if if I Oh wait, hold on.
• 41:13
  SPEAKER_00: That's really interesting.
• 41:14
  SPEAKER_00: So the rocks that are caught up in the early phase of the eruption give you a window into where in the caldera it started because the the geolog the initial like the starting point pre-eruption geology of the caldera was different enough across the caldera that you can kind of pinpoint what's getting dragged up first.
• 41:33
  SPEAKER_00: Exactly.
• 41:34
  SPEAKER_00: So if you know really interesting.
• 41:36
  SPEAKER_03: If you know the geology around it, and we do very well, you can look at the lithics and you can figure out where the eruption started.
• 41:44
  SPEAKER_03: And so essentially how the how the whole culture is amazing.
• 41:49
  SPEAKER_00: I uh that uh that's a that's a really cool approach.
• 41:53
  SPEAKER_00: And this is in the ash fall, so they're like little or you said they have to fall above.
• 41:57
  SPEAKER_03: It's in the pumice fall, yeah.
• 41:58
  SPEAKER_03: In the in the fall units, and so in the lit in with all the little juvenile pumuses or these accidentals, right?
• 42:06
  SPEAKER_03: These these lithic pieces of the wall rock.
• 42:09
  SPEAKER_03: And so you can say, well, it started started over here and unzipped around clockwise.
• 42:15
  SPEAKER_03: Um kidding.
• 42:17
  SPEAKER_03: All the way around to the other side.
• 42:18
  SPEAKER_00: Yeah, were there surprises that it hold on, Chris?
• 42:21
  SPEAKER_00: Is that the conclusion?
• 42:22
  SPEAKER_00: It like zippered around in like a no kidding.
• 42:26
  SPEAKER_03: And this has also been shown um in New Zealand, so in at uh Taupo volcanic zone.
• 42:33
  SPEAKER_00: Oh, is that right?
• 42:33
  SPEAKER_00: Taupo, that's another you know, famous big eruptive center.
• 42:36
  SPEAKER_00: Yeah, yeah.
• 42:37
  SPEAKER_03: And so looking at the Orinui, which is the 26.5 million or thousand-year-old eruption, or the more recent eruption too, by by looking at the accidentals in the in that pumice ball, you can figure out the wall rocks of what it's of what's being broken.
• 42:54
  SPEAKER_00: How reliable do if you go to multiple places, multiple fault deposits, do they record the same kind of trajectory from the base to the top?
• 43:01
  SPEAKER_00: Like it's it's definitely zippering in one spot.
• 43:05
  SPEAKER_00: Or it's erupting from one spot.
• 43:08
  SPEAKER_00: Because I can imagine multiple centers popping off during this eruption, like either side of the caldera erupting at the same time, sending ash in kind of different directions.
• 43:16
  SPEAKER_00: Or maybe that's maybe that part's not accurate, but it it's one eruptive center that's kind of that that's pretty clear.
• 43:23
  SPEAKER_03: It's it's been a while since I read that paper, but um but yes, that that it um it's it's multiple deposits from around around Long Valley, you look at, and there's a consistent story of how it unzips.
• 43:39
  SPEAKER_01: Can you put a timestamp on that?
• 43:41
  SPEAKER_01: How long did it take to do this?
• 43:43
  SPEAKER_03: Yeah, they've they've tried.
• 43:44
  SPEAKER_03: This is something that Colin's really good at is um is trying to figure out whether it's hours, days, weeks.
• 43:53
  SPEAKER_03: And again, details escape me, but my recollection is they think that it was.
• 44:00
  SPEAKER_03: you know, a week or two of of eruption that that produced this.
• 44:05
  SPEAKER_03: And you have to make a lot of assumptions about, you know, how how quickly things are being deposited and whether things are being eroded and and trying to trying to find time layers.
• 44:18
  SPEAKER_03: But it's a it's a game that we try to play at at all of these large eruptions is did this happen in hours, days, weeks?
• 44:27
  SPEAKER_03: And were there were there long breaks?
• 44:29
  SPEAKER_03: Was there a break of a year or two?
• 44:32
  SPEAKER_00: Yeah.
• 44:32
  SPEAKER_03: Okay.
• 44:32
  SPEAKER_03: Yeah.
• 44:34
  SPEAKER_03: That is really interesting.
• 44:34
  SPEAKER_03: My recollection for Long Valley is that it was a fairly continuous probably a couple of weeks.
• 44:40
  SPEAKER_00: Yeah I think I think for uh Chris I think it's six days is what we pulled from from you know some USGS literature.
• 44:48
  SPEAKER_01: So I want an animation.
• 44:49
  SPEAKER_01: I want to I want to I want to see this I know we want a video yeah I know right that's so good.
• 44:53
  SPEAKER_03: The zipper so I um I just spent a couple of months in in New Zealand after kind of getting some projects finished that I'd started down there and and starting a couple of new ones colleagues down there one of them Colin Wilson and another Graham Leonard made an incredible video of the Oranui eruption.
• 45:15
  SPEAKER_03: It's at the National Museum Te Papa and then they have a fantastic display but they sat down with uh professional um kind of cinematographers and and and some computer animation and and made an incredible video.
• 45:31
  SPEAKER_03: I'm sure it's on YouTube and it shows and it's actually geologically accurate they they sat there and argued about and and and made a very very nice video.
• 45:43
  SPEAKER_00: Oh that is totally cool.
• 45:45
  SPEAKER_00: I okay so this this we're kind of getting to the eruption part in the bishop tough so it's some I I didn't we did this calculation when we were talking made this episode about the bishop tough but I looked up the number I just like went on Scopus or whatever and typed in Bishop tough as a keyword looked at the number of papers and it's like four times as many papers written on the Bishop Tough as there are on Acosta the Acosta Nice complex which is like you know one of the more famous individual rocks in the world which kind of blew my mind how many papers I mean I've always heard of the Bishop Tough as anybody who's developing some new oxybarometer or magmatic geochemical tool goes to the Bishop tuff to try it right because it it's kind of become and I described it I want to know if you're if you agree with this we kind of described it as the geological fruit fly like it's valuable because it's been studied so much and there's a feedback loop on that.
• 46:34
  SPEAKER_00: So is that accurate and and what is your view of the the value or the importance of Bishop tuff to petrology really like geology generally but petrology and geochronology more specifically maybe yeah no it is it's it's it's and part of it is that it's very well exposed and and there are things that are very systematic.
• 46:55
  SPEAKER_03: So if you if you look at the eruptive deposits they start off being you know higher silica more evolved and and they become more mafic as you go up and and it's because you know you're emptying this magma chamber that that is zoned where the the highest silica kind of most explosive stuff's on top and it gets more mafic as you go downward.
• 47:19
  SPEAKER_03: And so as it erupts you know you're kind of seeing the whole thing upside down.
• 47:23
  SPEAKER_03: It's quite systematic and and Wes Hildreth for his thesis long ago uh worked on the temperatures and developing the magmatic temperatures the ways to measure magmatic temperatures using oxide compositions.
• 47:39
  SPEAKER_03: There are some systematic changes within that system and some completeness of the volcanic record such that it's a good place to do these it's it's it's a very good type locality because you you know it's oh that's a good word type locality yeah I like that type locality for what what what type locality for if you want to study X go to Long Valley or Bishop Tuff what is that X to you uh yeah so it's it's a good example of the of eruption and emptying of the zoned magnet okay all right I like that that's yeah would be one thing um but also a bit I think you know just that unzipping of the caldera is systematic and interesting and progressive and then sort of uh what's come after the sort of resurgent system what what how uh how a caldera system behaves after eruption too is is uh very commonly in these in these large caldera systems you'll you'll have these what they call a resurgent dome what that often has kind of degasted magmas not as explosive they'll fill up parts of the caldera and they might be domed up it has all of the hallmarks of other caldera systems like Vias caldera or Yellowstone caldera but it's exposed in a desert environment and it's young enough that you can see most things it's old enough incised a little bit so you can see through parts of it.
• 49:17
  SPEAKER_03: It's so accessible it's it's really you know it's close to major airports and and good highway you can see a lot of great things by going to the Puna in you know in Bolivia and and Peru but um but it's it's a lot harder to get to and it's maybe not as incised and and so it's it's there's there's been beauty to just having something that's accessible.
• 49:44
  SPEAKER_00: Yeah okay that's I have a I have a question something we don't think about the desert environment the the the Goldilocks age and stuff like that.
• 49:50
  SPEAKER_00: Sorry Chris go ahead.
• 49:51
  SPEAKER_01: No I have a question for both of you actually um and I don't know if you'll know the answer to this but does Yellowstone show this same kind of zoned magma chamber in in its tough deposits?
• 50:08
  SPEAKER_03: I haven't worked as much on Yellowstone but there's um it's not as zoned as Bishop Tuff to my knowledge.
• 50:15
  SPEAKER_01: Do we have an idea why that would be well I think there's a lot more sticky rhyolite at Yellowstone than just didn't wasn't able to tap down as deep into the magma chamber you think than or like um there there certainly is basalt at depth providing the heat but the to my knowledge the eruptive deposits aren't as zoned as Long Valley and and um Wes may well chide me and and say that that's not correct.
• 50:50
  SPEAKER_00: That's all right it wouldn't be the first time you know was somebody on Planet Geo has been chided uh not who it is.
• 50:58
  SPEAKER_01: Jesse usually gets chided more than you know every once in a while um but uh I I I would agree with that.
• 51:05
  SPEAKER_00: I mean I'm I I haven't again I'm not an expert on this at all but uh the stuff I have seen that looks at zoning in the eruptions in Yellowstone has mostly seen like looked at zircons and seen oxyndized populations that are very very different speaking to chemical composition of different magma chambers so kind of disaggregated batches of magma that are coalescing into eruption and from what I remember there's two clear seismic seismically imaged sort of mush zones in Yellowstone an upper one and then the bigger lower one and so there's probably like quite different magma dynamics in that in a system like that as opposed to this sort of single zone thing that's being coming out all at once maybe or something like that.
• 51:44
  SPEAKER_01: Anyway I um I don't know one more example of uh of a basic concept that applies to Long Valley Caldera again from uh you know intro level geoscience perspective so yeah absolutely cool very cool all right Andy we're running short on time here so I want to make sure I get to this question what's next for Long Valley Caldera?
• 52:06
  SPEAKER_03: Yeah well I think one um one of the things that we're having difficulty agreeing on is whether there is kind of a big evolving magma system at death whether whether there are more eruptions to come or whether it is you know kind of done and and so there've been a lot of geophysical studies that are in conflict actually in trying to trying to figure out whether we had just a week after Mount St.
• 52:37
  SPEAKER_03: Helens erupted in 1980 there were several large magnitude six earthquakes in Long Valley and intense um inflation of the caldera and people were really scared especially you know Mount St.
• 52:54
  SPEAKER_03: Helens had just erupted and now now look there's all this deformation and these earthquakes at in Long Valley.
• 53:00
  SPEAKER_03: And so there was a bit of an overreaction maybe maybe not and um people were very concerned and and um but there have been myriad geophysical studies that have tried to figure out how you know what what is the potential of another large large eruption there.
• 53:21
  SPEAKER_03: And so I think trying to reconcile what we see at the surface which it looks like it's kind of done at the surface and that there's not likely to be another clover forming eruption there or we aren't poised to to have another large explosive eruption there.
• 53:38
  SPEAKER_03: And so kind of reconciling what we think we see at the surface with what um geophysical what's happening at depth.
• 53:46
  SPEAKER_03: And so I think we we we need to get a lot smarter on that.
• 53:50
  SPEAKER_00: So I I won't ask you to to weigh in on what you think the future necessarily to make a suggestion about the future but I I'll ask you the idea about the a concept what do you make of the argument that a lot of this um activity is due to second boiling we we spent some time talking about second boiling in one in you know one of our episodes in in this what do you make of that theory I guess and without saying here is what the future of Long Valley is going to be is that something and maybe is it something that we've seen similar geophysical evidence for in other large volcanic eruptions or or large any any magma chambers basically like seismically see second boiling because that struck me as interesting as an idea that we could that the geophysical data could point to second boiling.
• 54:34
  SPEAKER_03: Yeah so that's what the geology favors that interpretation certain and and so so as you have a you know there's residual magma depth it's cooling and crystallizing and as it crystallizes you concentrate more volatiles and and that's that's second boiling and that can lead to inflation it can lead to gas we've got both those things and that's the you know I think the geologist most of the geology points that direction but a lot of the geophysical measurements point a different direction where they think they see um large amounts of melt down there and and fresh melt um and so that's the crux of the argument is is can the can second boiling explain all the phenomena we see we we do get we get tons of earthquakes there.
• 55:29
  SPEAKER_03: We've got um a lot of you know hot water and alteration and and and things that you know there's there's a a lot of geothermal activity there.
• 55:41
  SPEAKER_03: But yeah so so my bias is that it's it is a waning system second boiling explains most things but there's significant scientific you know controversy about that interpretation.
• 55:56
  SPEAKER_03: Is it controversy between geologists and geophysicists is that is it a disciplinary kind of um uh tension or or is it really yeah okay that's interesting I always find it really interesting when those yeah uh different disciplines kind of subdisciplines kind of collide together with an idea it's always very interesting it leads to interesting results and in interesting conversations I would say yeah and you know I think it's it's it's always the struggle and it's it's a great place to do this because there are so many constraints.
• 56:24
  SPEAKER_03: We we have we have so many things aren't well exposed.
• 56:28
  SPEAKER_03: We know the history quite well so it is kind of a perfect place to do the laboratory experiment of trying to sort out what what could happen.
• 56:38
  SPEAKER_00: What a cool place.
• 56:39
  SPEAKER_00: It is a cool so interesting so many very cool stories to uh that that come out of this Long Valley Coldera geological story.
• 56:47
  SPEAKER_03: Yeah um okay well we're over time Chris what do you think should we uh should we close it out here yeah before we do and before Jesse you can go ahead and ask the last question but Andy is there anything else that you want to say about Long Valley that maybe we missed that we didn't ask that you were prepared for or um I wasn't I didn't prepare very much for this that's the way we like it what I do want to say is that the um the area just north of Long Valley Caldera is uh a somewhat underappreciated really active volcanic system so that's that's mono lake and the mono craters and and in yo domes so that that whole system is young is capable and and is worth study and scrutiny it's a fascinating place.
• 57:40
  SPEAKER_03: The last eruptions there were around 600 years ago possibly that was in that was in mono right yeah yeah so that um well there there were mono craters eruptions in there and then um probably some uplift of the what's now what are now islands in the middle of mono lake but in in the last thousand years there's been a there's been a lot of volcanism in there and and studying that and and understanding that in a lot of ways you know you you look in Long Valley Caldera and and it's worrisome because it's so big and so crazy but that turn around and and you look at something could erupt tomorrow um or no okay well that it could erupt in the next hundred years.
• 58:24
  SPEAKER_03: Interesting it's really fascinating and it's a nice place to look at the relationship between magmatism and strain is there are you know it's kind of the beginning of Walker Lane and and um it's a it's a pretty fantastic place.
• 58:39
  SPEAKER_03: And so I I think there there are the likelihood of activity out of something north of Long Valley, whether it's Silicic and out of mono craters or Mafic and out of near Mammoth Mountains there is a lot of potential there.
• 58:56
  SPEAKER_03: Unlikely to have any caldera forming you know or or anything really out of the caldera proper but it's a it's a very active artery active that's uh that's a good one.
• 59:10
  SPEAKER_00: That's a good thing to think on and I don't know who knows maybe we need to do Chris no more episodes on on this area then lots to learn yeah that's right um all right Andy we've we've taken up too much of your time uh we always close with your best days a geoscientist but we've heard that one from you before so what's been the best day since we last spoke in the last th four years let's say as a geoscientist the best day the last probably um uh yeah so I I I just got back from New Zealand and I spent a week with six folks on on a on an island that called Mare Island.
• 59:47
  SPEAKER_03: It's the the local Maori name for it that is favored now is Tahua.
• 59:52
  SPEAKER_03: It's uh pantellaritic lavas that erupt in kind of the back arc behind uh the the subduction system and it is beautiful and spectacular and very young.
• 1:00:05
  SPEAKER_03: So it's a kind of an island of obsidian.
• 1:00:08
  SPEAKER_03: And so I was working there with a there's a student who's working on her PhD theme thesis um at Victoria University and and helping her sample and helping her collect the right stuff so we can get good dates on this pentellaritic um what is pentellaritic you mean you we have to it's a um yeah high silica high iron of a strange composition of um kind of like a rhyolite really but okay but a th sort of a tholitic rylite type great alkalic um okay yeah just okay well perfect that's great i mean it's not i've heard i've heard great things about the geology and the scenery and the fishing yeah um in uh new zealand so yeah and and and actually and one of the students um who came along brought her spear gun and so we had fresh fish three nights in a row or three man it's that was it was spectacular life is rough andy life is hard it was really pleasant but but really good scientific discussions over that fish and and um collecting good rocks and it's a it's a neat new zealand in general is really fantastic because it's a it's a really active place and a and it's it's a testbed for a lot of the things we do where we're trying to understand rates of volcanism and and it's it's got more rhyolite there than anywhere else in the world and so the the rates of seismicity and rates of volcanism are higher than anything in California.
• 1:01:41
  SPEAKER_03: It's good to go to a place like this to to work on something that's kind of hyperactive and and teaches us how to do our job better uh in the Western US.
• 1:01:52
  SPEAKER_01: Any takeaways from your trip like from a knowledge standpoint to like you know did you learn anything that you didn't expect or or is that to come later maybe yeah I think a lot of it's coming later.
• 1:02:06
  SPEAKER_03: Let's see I think um the the complicated tectonics of of New Zealand were interesting to me where you're um the South Island you're right on the plate margin both on the South Island and on the North Island but you're on the kind of opposite side so it's the the edge of the Pacific plate and then the the Australian plate.
• 1:02:30
  SPEAKER_03: And the way strain gets partitioned along that boundary is very, very different when it done on the South Island than it is on the North Island.
• 1:02:39
  SPEAKER_03: And and so it was what was fascinating to me is how just how differently in that really active place strain gets partitioned.
• 1:02:49
  SPEAKER_03: And what I'd like to explore with geochronology is how that's developed with time and both on the kind of faults and tectonics side and then on the volcanic side and really trying to trying to work out the the long-term timing of um tectonics on both the South and North Islands.
• 1:03:10
  SPEAKER_00: So very cool.
• 1:03:11
  SPEAKER_00: Well it sounds like we're gonna have to have a an another discussion about New Zealand geology at some point here uh you know once you guys work out some of this gear chronology stuff.
• 1:03:20
  SPEAKER_00: Uh Andy thank you so much for your time that I it's really been uh great to to talk to you again uh hear where you're up to and and help um thank you very much for helping us kind of continue the conversation about Long Valley Caldera it's a super interesting place and and you framed it really well for us.
• 1:03:33
  SPEAKER_03: Yeah thank you both thank you both for doing what you're doing because I think that uh you know kind of getting the word out about how cool geology is is it's it's a tremendous service.
• 1:03:43
  SPEAKER_00: Yeah well well we'll keep at it I I have to put up with Chris to do it but whatever.
• 1:03:48
  SPEAKER_00: We'll do it at all whatever.
• 1:03:50
  SPEAKER_00: All right thanks very much Andy appreciate it.
• 1:03:53
  SPEAKER_00: Yeah absolutely thank you Andy thank you too very much Andy appreciate it hey that's wrap you can follow us on all the social media at Planet GeoCast.
• 1:04:01
  SPEAKER_00: Shoot us an email there's there's a contact us link on our website Planetgeocast.com you can download our Camp Geo mobile app there you can get visual podcast series including this episode as one of the later episodes in our Long Belly Caldera audiobook is available there.
• 1:04:13
  SPEAKER_00: First link in your show notes uh and uh please leave us a comment a like and a subscribe uh channel you're missing cheers