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Lava’s All You Need: Preview to Interview with Dr. Andrew Calvert (GeoShort) · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_01: Welcome to Planet Geo, the Planet, where we talk about our amazing planet, how it worked, and why it matters to you.
• 0:13
  SPEAKER_01: Today we are giving you a short preview to our interview with the scientist in charge of the California Volcano Observatory, Dr.
• 0:19
  SPEAKER_01: Andrew Calvert.
• 0:21
  SPEAKER_01: The full interview will come out next week where we cover everything from Mount Vesuvius to Mount Hood and everything in between.
• 0:26
  SPEAKER_01: But Chris and Andy both really share this deep passion for Mount Shasta in Northern California.
• 0:31
  SPEAKER_01: So here's an excerpt from that interview where they discuss how Mount Shasta was formed and some of the details of hiking around Mount Shasta.
• 0:38
  SPEAKER_01: Tune in next week to hear what volcano observatories do and their role in keeping people safe during times of unrest.
• 0:49
  SPEAKER_00: The best one of those.
• 0:55
  SPEAKER_01: So I have a few questions, okay, and like so first of all, Chris loves Mount Shasta, even more than he loves Mount St.
• 1:02
  SPEAKER_01: Helens.
• 1:03
  SPEAKER_01: So like I could see Chris was grinning ear to ear, you know, the whole time you're talking about your Mount St.
• 1:07
  SPEAKER_01: Helens story as a kid.
• 1:08
  SPEAKER_01: He was just jealous he wasn't in Idaho, you know, at when he was seven years old.
• 1:13
  SPEAKER_02: But well, I think though, because you know, we shared similar.
• 1:17
  SPEAKER_02: I mean, I didn't live in Idaho, I lived in Michigan, but when St.
• 1:20
  SPEAKER_02: Helens happened, I was I was I begged my mom to take me out there that following summer in 1981.
• 1:29
  SPEAKER_02: And I still have ash that I I wrote a lab for my high school students on the ash that I collected um when I was 10 years old.
• 1:38
  SPEAKER_01: Oh, Andy, I mean he gets it out every time in his lecture.
• 1:41
  SPEAKER_01: I mean, and I saw it in high school, I think.
• 1:43
  SPEAKER_01: This little vial of ice that Chris collected from I collected a lot.
• 1:48
  SPEAKER_00: Yes, I I have that was the first sample I ever collected.
• 1:52
  SPEAKER_00: I have a jar, it's like a mayonnaise jar with a green lid, and I if I were in my Metal Park office, I'd be showing it off right now.
• 2:01
  SPEAKER_00: In my seventh grade writing, it says Mount St.
• 2:03
  SPEAKER_00: Helens Ash, and it was collected from my front porch, and and I've got a huge bunch, and I'm gonna send you some.
• 2:10
  SPEAKER_00: Uh not Jesse.
• 2:11
  SPEAKER_00: Jesse, Jesse's not getting it.
• 2:12
  SPEAKER_00: Yeah, Jesse, he doesn't deserve it.
• 2:15
  SPEAKER_00: I definitely don't deserve it.
• 2:17
  SPEAKER_00: And I love it, definitely.
• 2:18
  SPEAKER_02: So, Andy, here's the question.
• 2:20
  SPEAKER_02: I love Mount Shasta because I think it's to me, Mount Shasta is the Mount Fuji.
• 2:26
  SPEAKER_02: It is so beautiful, and a lot of that has to do with Shastina, you know, this stratocone that comes off the side of of Mount Shasta.
• 2:33
  SPEAKER_02: So can you just tell us the overall story of Shasta and Shastina, please?
• 2:38
  SPEAKER_00: Yeah, so how much time do you have?
• 2:40
  SPEAKER_02: Because I give us the give us the the shortened version.
• 2:45
  SPEAKER_02: But uh, you know, like first of all, Andy, have you climbed Mount Shasta?
• 2:49
  SPEAKER_00: Yeah, I mean that's my big local project.
• 2:51
  SPEAKER_00: When I started at the USGS, I I started working primarily with Bob Christensen um on trying to get the eruptive history of Mount Shasta.
• 3:02
  SPEAKER_00: And he had made a geologic map of it starting in the 70s, he and Dan Miller, and um is a it's a beautiful map, but he had really little chronology.
• 3:12
  SPEAKER_00: Um, they they tried a few things and it was it was hard to date.
• 3:16
  SPEAKER_00: And so he invited me up and I started kind of picking away at it.
• 3:21
  SPEAKER_00: And so it's turned into my big California project that I've uh not only climbed it, I've collected a sample from every lava flow that I could get to.
• 3:31
  SPEAKER_00: And it's almost all of them.
• 3:33
  SPEAKER_00: How many times have you climbed it then?
• 3:35
  SPEAKER_00: Um I've been to the top probably five times.
• 3:39
  SPEAKER_02: Is that all via Avalanche Gulch?
• 3:42
  SPEAKER_00: No, I've been up Avalanche Gulch a couple of times, Clear Creek once, and then um uh the best though is from the north, uh the Holland Bowling route.
• 3:52
  SPEAKER_02: Okay, is that more technical?
• 3:53
  SPEAKER_02: I I've done Avalanche Gulch.
• 3:55
  SPEAKER_00: Yeah, it's a little bit more technical.
• 3:57
  SPEAKER_00: It's um it's it's on you're on snow a bit, and then there are a couple of spots you really don't want to fall.
• 4:02
  SPEAKER_00: But it's it's really more interesting, you know, because there are a lot of little spines you're walking through, and and then not many people do it either.
• 4:10
  SPEAKER_00: And and and yeah, come out, I'll take you up.
• 4:12
  SPEAKER_02: I'm coming out actually in June.
• 4:13
  SPEAKER_02: I'm going out with my family.
• 4:14
  SPEAKER_02: We're cool.
• 4:16
  SPEAKER_02: So yeah, we're flying to San Francisco and then we're going straight up to San Fran uh to St.
• 4:20
  SPEAKER_02: Helens, then we're gonna just work our way back down to Yosemite.
• 4:23
  SPEAKER_00: Oh, fantastic.
• 4:24
  SPEAKER_00: I'll I'll I'll give you some materials.
• 4:26
  SPEAKER_00: Um it's a very low snow year, so uh climbing Shasta is is is kind of miserable.
• 4:34
  SPEAKER_00: Shasta, it's it's my it is my big project, and it's by far my favorite volcano.
• 4:39
  SPEAKER_00: You know, St.
• 4:40
  SPEAKER_00: Helens is fine, but but so you can relate, right?
• 4:43
  SPEAKER_02: Like Shasta has a beauty to it that is just it's it's incredible.
• 4:49
  SPEAKER_00: And and and so I'm gonna I'm gonna race through a million years of of time.
• 4:54
  SPEAKER_00: So a million years ago, Mount Shasta wasn't there.
• 4:59
  SPEAKER_00: Off to the east, about 20 kilometers, you know, 12 miles, there was a Mount Shasta sized volcano called Rainbow Mountain, and similar composition, enormous, probably even larger than Shasta.
• 5:15
  SPEAKER_00: The reason we say that is because if you look at Mount Shasta and then look off to the east, like use Google Maps terrain view, and you'll see this valley that comes down.
• 5:26
  SPEAKER_00: It's a U-shaped uh glacial valley, and it dwarfs anything that's on Shasta.
• 5:31
  SPEAKER_00: It's enormous, and and that's uh that's an 800,000-year-old glacial valley.
• 5:37
  SPEAKER_00: It was a very deep glaciation, but it had to be coming off something that was at least as big as Mount Shasta.
• 5:42
  SPEAKER_00: It's huge because volcanoes are made out of kind of crappy rocks, right?
• 5:46
  SPEAKER_00: And they they just sort of fall apart.
• 5:48
  SPEAKER_00: And so it's down, but but that's the real Cascade Arc.
• 5:52
  SPEAKER_00: That's where the volcanoes mostly are.
• 5:54
  SPEAKER_00: That's where Ash Creek Butte is that I was telling about earlier.
• 5:57
  SPEAKER_00: Mount Shasta sits way out in the front, it's it's it's too far out toward the ocean for volcanoes, and and medicine lake volcano sits behind, and they they both seem like they started about the same time.
• 6:10
  SPEAKER_00: We don't know why.
• 6:11
  SPEAKER_00: That's a huge question up there.
• 6:13
  SPEAKER_00: Um they went from being on the arc to off the arc.
• 6:17
  SPEAKER_00: So that's a million years ago.
• 6:19
  SPEAKER_00: And fast forward now to 700,000 years, and that's when Mount Shasta really kicked it uh into gear.
• 6:27
  SPEAKER_00: The oldest rocks we've dated on on the older part of Mount Shasta proper are 700,000 years old.
• 6:32
  SPEAKER_00: It made a big old volcano.
• 6:34
  SPEAKER_00: And then somewhere about 300 to 350,000 years ago, it fell apart, kind of like Mount St.
• 6:41
  SPEAKER_00: Helens did.
• 6:42
  SPEAKER_00: And a huge chunk of it, a huge fraction of it, ended up in Shasta Valley.
• 6:48
  SPEAKER_00: So when you're driving up I-5, you drive past all these little weird-shaped hills, it's this hummocky topography.
• 6:57
  SPEAKER_00: Geologists didn't know what that landform was at the time, prior to 1980.
• 7:03
  SPEAKER_00: It was really weird.
• 7:04
  SPEAKER_00: There were great geologists that just couldn't figure that place out.
• 7:08
  SPEAKER_00: And it wasn't until Mount St.
• 7:10
  SPEAKER_00: Helens did what it did.
• 7:11
  SPEAKER_00: So Mount St.
• 7:12
  SPEAKER_00: Helens, there was an intrusion to form the north side of the volcano, it oversteepened it, and an earthquake caused the largest landslide that we've actually seen as humans off to the north and uncorked this big eruption.
• 7:28
  SPEAKER_00: So it was a huge landslide, and it you saw this hummocky topography.
• 7:34
  SPEAKER_00: And geologists actually came up from Menlo Park, drove up to St.
• 7:37
  SPEAKER_00: Helens, as they were driving past Mount Shasta.
• 7:40
  SPEAKER_00: They said, Wow, that's how that formed.
• 7:43
  SPEAKER_00: That that's what it was.
• 7:44
  SPEAKER_00: That's good.
• 7:45
  SPEAKER_00: People just couldn't think big enough uh to understand that it was it was this big debris apple.
• 7:51
  SPEAKER_01: That's awesome.
• 7:52
  SPEAKER_01: What a great story.
• 7:53
  SPEAKER_01: So so former Mount Shasta just collapsing on itself and and being kind of just pushed aside.
• 7:59
  SPEAKER_00: That's right.
• 8:00
  SPEAKER_00: That's early Mount Shasta, the 700,000 to 400,000-year-old volcano collapsed and ended up out in Shasta Valley.
• 8:07
  SPEAKER_02: Jesse, this is the stuff you and I climbed around when we had that day uh on Mount St.
• 8:14
  SPEAKER_02: Helens.
• 8:14
  SPEAKER_02: The one exactly what we were in.
• 8:16
  SPEAKER_00: So cool.
• 8:17
  SPEAKER_00: Yeah, and and all that's left of that on the mountain is it's called Sand Flat.
• 8:22
  SPEAKER_00: It's um you can drive up a paved road, um, and it's it's got beautiful red firs on it, and it all all forested.
• 8:29
  SPEAKER_00: That's the old part of the volcano.
• 8:31
  SPEAKER_00: And then the next part of Shasta, we call it Sargent's Ridge, and it was uh it's a little south of the current summit, and it made a nice straddle cone.
• 8:40
  SPEAKER_00: And then that's since been eroded away, and that was from about 300,000 years down to 125,000.
• 8:48
  SPEAKER_00: If you crawl down in the bottom of Mud Creek, you get to the oldest stuff in that part of the history, it's about 290,000 years old, and then there's this part that sticks up that Chris, you walk past called the thumb.
• 9:02
  SPEAKER_00: Do you remember the thumb?
• 9:03
  SPEAKER_00: So you're walking up Avalanche Gulch and the thumb sticks up.
• 9:07
  SPEAKER_00: The thumb, I've dated that at 125,000 years, and that those two bracket sergeant's ridge.
• 9:14
  SPEAKER_00: It's been since it rudded out, and the vent after that was up to the north, about another half mile north.
• 9:22
  SPEAKER_00: And that part of the history is we call it Misery Hill.
• 9:26
  SPEAKER_00: It made the Casibal Ridge, so that really there's a very rugged ridge north of Avalanche Gulch.
• 9:32
  SPEAKER_00: It sent lavas down both sides, some east and some west.
• 9:37
  SPEAKER_00: That part of the history was very episodic.
• 9:41
  SPEAKER_00: We we had eruptions at about 60,000 years and 40,000 years.
• 9:46
  SPEAKER_00: This is all leading up to the really big, exciting Shastian eruption.
• 9:50
  SPEAKER_01: So so we had the So I can I interrupt here a minute, and I you just described this as like, oh, we went through 200,000 years of a volcano growing, but that's a really cool thing.
• 9:59
  SPEAKER_01: And I guess I didn't notice how episodic that was.
• 10:02
  SPEAKER_01: I mean, every 20,000 years there's an eruption and it adds another layer onto Mount Shasta, and then it kind of puts a little puts a pin prick out somewhere and erupts off one side, and then it erupts from the other side, and it kind of gradually builds up this beautiful stratovolcano.
• 10:20
  SPEAKER_00: Yeah, yeah.
• 10:21
  SPEAKER_00: That's what a stratovolcano really is, is is just all these different eruptions building themselves and eroding themselves, making making a big, a big cone.
• 10:32
  SPEAKER_00: And and but Mount Shasta in particular is really episodic.
• 10:37
  SPEAKER_00: It it tends to just go nuts and then just sit there for thousands of years.
• 10:44
  SPEAKER_02: So, Andy, 20,000 years though, that's pretty long an interval for Cascadia volcanoes, right?
• 10:52
  SPEAKER_00: Yeah, yeah.
• 10:53
  SPEAKER_00: Generally, you look at say Mount Rainier or St.
• 10:56
  SPEAKER_00: Helens or Hood, they're erupting many times in 20,000 years, typically.
• 11:01
  SPEAKER_00: For sure.
• 11:02
  SPEAKER_00: And and and Shasta, not so much.
• 11:05
  SPEAKER_00: We seem to have these times, at least coming out of the tippy top, where it sits there for a long period of time.
• 11:12
  SPEAKER_00: Now we don't know that because something might have been erupted and then gotten eroded off entirely, and the perfect crime.
• 11:19
  SPEAKER_02: So if it's this episodic, is it extremely violent in nature then?
• 11:26
  SPEAKER_00: You know, Shasta is not as violent as even Mount St.
• 11:30
  SPEAKER_00: Helens is or some others.
• 11:32
  SPEAKER_00: It tends to produce these domes.
• 11:35
  SPEAKER_00: You don't want to be really close, but typically the deposits don't make it very far off the flank.
• 11:43
  SPEAKER_00: There's really only one eruption that made a what we call a Plinian eruption, one of these big mushroom clouds uh that uh headed off to the east.
• 11:52
  SPEAKER_00: And and that eruption was was next.
• 11:55
  SPEAKER_00: It's the it's the one I'm going to tell you about that was 11,000 years ago.
• 11:59
  SPEAKER_00: So so we had the we had that sand flat, and then we had the avalanche, and then we built uh another cone, and then it's eroded off.
• 12:07
  SPEAKER_00: We built another cone and eroded off.
• 12:09
  SPEAKER_00: And then and then we get to this period between 11,000 and 10,000 years, which is crazy.
• 12:17
  SPEAKER_00: There's so much happen.
• 12:18
  SPEAKER_00: It's it's so neat.
• 12:20
  SPEAKER_00: The first thing that happened was there was a uh explosive eruption.
• 12:25
  SPEAKER_00: We call it red banks, and and the red banks is is what you climb over, Chris, when you get to the top of Avalanche Gulch.
• 12:31
  SPEAKER_02: It's this kind of it's really the only dangerous part of the climb.
• 12:35
  SPEAKER_00: Yeah, it's this you don't want to fall there, right?
• 12:38
  SPEAKER_00: It's this tack welded um scoria kind of near vent deposit.
• 12:42
  SPEAKER_00: And the pumice from that eruption went all the way to Medicine Lake, and that was really the the biggest, the most explosive eruption that we can find anywhere in that 700,000-year-old history.
• 12:54
  SPEAKER_00: That's a long ways, yeah.
• 12:56
  SPEAKER_00: It's a pretty long ways, but not very long compared to Mount St.
• 12:58
  SPEAKER_00: Helens or Crater Lake or Andy.
• 13:01
  SPEAKER_00: It's it's a pretty self-contained volcano.
• 13:04
  SPEAKER_02: And Andy, why is that?
• 13:05
  SPEAKER_02: Is it is it the silica content of the magma?
• 13:08
  SPEAKER_02: Is it just not as viscous as St.
• 13:10
  SPEAKER_02: Helens and Rainier?
• 13:11
  SPEAKER_02: Yeah.
• 13:13
  SPEAKER_00: Yeah, the thing that really controls explosivity is viscosity.
• 13:18
  SPEAKER_00: It's it's how sticky a magma is, right?
• 13:21
  SPEAKER_00: So if you have all magma has gases in it, and as those gases get up to the surface, they want to get away.
• 13:29
  SPEAKER_00: They don't want to be stuck in the rock, right?
• 13:31
  SPEAKER_00: So if you have a if you're in Hawaii and there's a basalt, there's lots of gas coming out of it, but it's about the viscosity of water.
• 13:40
  SPEAKER_00: And and so the gas can just bubble freely through and it doesn't typically explode.
• 13:47
  SPEAKER_00: But then as you go to slightly cooler or slightly different compositions, like higher silica compositions, like andesite and dacyte and rhyolite, the viscosity is more like toothpaste.
• 14:03
  SPEAKER_00: And the gas, instead of being able to bubble freely out, it causes the rock to fragment.
• 14:09
  SPEAKER_00: It explodes.
• 14:10
  SPEAKER_00: Because when something goes from being a solid or from a liquid to a gas, there's an incredible expansion.
• 14:18
  SPEAKER_00: That's what drives the explosive part.
• 14:21
  SPEAKER_00: So Shasta is is kind of in a in that sweet spot of not too non-viscous to be able to for the gas to be able to bubble out, but not too viscous to really explode.
• 14:37
  SPEAKER_00: The domes that are created and the flows that are created still flow.
• 14:41
  SPEAKER_00: There are small explosions, but not really big explosions.
• 14:45
  SPEAKER_02: Why is that, Andy?
• 14:47
  SPEAKER_02: Like this is for my own curiosity.
• 14:50
  SPEAKER_02: Why is the silica content different for Shasta than the rest of or further north?
• 14:57
  SPEAKER_00: Well, most magmatism on Earth is fundamentally basaltic, right?
• 15:03
  SPEAKER_00: That's what you get when you when you have the uh the mantle and you you melt the mantle.
• 15:10
  SPEAKER_00: You you start with basalt.
• 15:12
  SPEAKER_00: And then uh for an arc stratovolcano like Mount Shasta, above that you have some sort of plumbing system.
• 15:19
  SPEAKER_00: As the magma is is moving from its source, where it starts off probably as a basalt or maybe as a primitive magnesium andesite or something, it starts forming crystals, and those crystals will rain out and they'll be separated from the liquid.
• 15:36
  SPEAKER_00: And those crystals that form early on tend to be uh low silica and high in magnesium, and so what's left is higher in silica and lower in magnesium.
• 15:53
  SPEAKER_00: So the composition of the magma is changing as it's moving upward, as it's fractionating and differentiating.
• 16:02
  SPEAKER_00: And so if you have a if you have a long path and enough time for these crystals to rain out, you can create a really high silica magma.
• 16:15
  SPEAKER_02: But the part that I struggle with is that these are infrequent eruptions, which would allow for more crystallization to happen, which would make it more silica rich, which would make it more viscous.
• 16:26
  SPEAKER_02: It doesn't seem to be assimilating crustal rocks a lot.
• 16:31
  SPEAKER_00: Yeah, and it's the it's it's a very complicated plumbing system.
• 16:35
  SPEAKER_00: You know, we don't actually know whether there's a constant source of basalt from below.
• 16:42
  SPEAKER_02: There might be a so it's not getting injected with fresh heat.
• 16:45
  SPEAKER_00: There might be a batch that comes in every 10 or 15 or 20,000 years, and other batches might end up going off a little bit and freezing down there.
• 16:56
  SPEAKER_00: We there's a lot that we don't know about the the guts of these volcanoes, and it's very hard to measure because seismic energy doesn't go through that very well, and and volcanoes are fluffy and don't really transmit seismic energy very well.
• 17:15
  SPEAKER_00: So, anyway, that's that's the thorny part.
• 17:17
  SPEAKER_00: That's that's what we spend 80% of our time on, really, is trying to understand the plumbing system.
• 17:24
  SPEAKER_02: What a fascinating field.
• 17:26
  SPEAKER_02: I uh I love that.
• 17:27
  SPEAKER_02: It just uh gets me going.
• 17:29
  SPEAKER_01: So thanks for listening.
• 17:30
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• 17:41
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• 17:43
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• 17:47
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