Latest / PlanetGeo: The Geology Podcast / The Shape of Yellowstone - Dr. Mike Poland, Scientist-in-Charge, Yellowstone Volcano Observatory

Transcript

The Shape of Yellowstone - Dr. Mike Poland, Scientist-in-Charge, Yellowstone Volcano Observatory · PlanetGeo: The Geology Podcast

• 0:02
  SPEAKER_02: Welcome to Planet Geo, the podcast where we talk about our amazing planet, how it works, and why it matters to you.
• 0:13
  SPEAKER_02: Hey there.
• 0:14
  SPEAKER_02: Today we are really excited to release a short clip from an interview we did with a really, really, truly exceptional geoscientist, Dr.
• 0:22
  SPEAKER_02: Mike Poland, who is the scientist in charge of a really special place, both in geology, to Chris and myself, and really in U.S.
• 0:30
  SPEAKER_02: national history, which is the Yellowstone Volcano Observatory.
• 0:34
  SPEAKER_02: Our discussion with Mike covered a super wide range of topics, so we decided to cut out this little bit and release it this week.
• 0:40
  SPEAKER_02: Mike is an expert in geodesy, which, as he says, is studying the shape of the Earth, and it's a technique used to investigate a wide variety of processes on and in the earth.
• 0:50
  SPEAKER_02: So we focused this discussion on geodesy.
• 0:53
  SPEAKER_02: Before we get to the interview, just do one thing for us.
• 0:55
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• 1:01
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• 1:04
  SPEAKER_02: That really helps us spread the word about geoscience.
• 1:07
  SPEAKER_02: Enjoy this short clip and tune in next week for more from Dr.
• 1:10
  SPEAKER_02: Mike Poland.
• 1:16
  SPEAKER_02: So we've been talking about earthquakes quite a bit, and we've seen this stat where Yellowstone has hundreds, thousands, a few thousand uh earthquakes a year.
• 1:24
  SPEAKER_02: Can you talk about those?
• 1:26
  SPEAKER_02: And then we'd sort of like to get into sort of your expertise in geodesy.
• 1:30
  SPEAKER_02: But these earthquakes, they occur in kind of swarms, they're pretty small.
• 1:33
  SPEAKER_02: Uh do people feel them?
• 1:35
  SPEAKER_02: Are they often felt?
• 1:36
  SPEAKER_02: If like people who are visiting Yellowstone, can you kind of describe these for people?
• 1:41
  SPEAKER_01: Sure.
• 1:41
  SPEAKER_01: So Yellowstone is one of the more seismically active places in the country.
• 1:44
  SPEAKER_01: And this is one of the reasons that there is this broad public concern, I'd say, for Yellowstone as a volcanic.
• 1:53
  SPEAKER_02: And why is it one of the more seismically active in the country?
• 1:56
  SPEAKER_01: Well, there are faults everywhere.
• 1:59
  SPEAKER_01: So Yellowstone is sitting right on the edge of the basin and range extensional province.
• 2:05
  SPEAKER_01: So if you drive from, as I did many times as a kid, from say Central California to Salt Lake City, you go over these mountain ranges and then into a valley and then a mountain range and a valley.
• 2:17
  SPEAKER_01: Each one of these mountain ranges has a fault associated with it.
• 2:20
  SPEAKER_01: That topography exists because the entire West is being stretched.
• 2:23
  SPEAKER_01: So it's being stretched in an east-west way, and you get all these north-south mountain ranges.
• 2:27
  SPEAKER_01: Each one of these has a fault, and that's why you get these magnitude six earthquakes in the middle of Nevada or Utah or Idaho, all the way down to Sonora in Mexico.
• 2:39
  SPEAKER_01: So those faults exist in the Yellowstone area as well.
• 2:42
  SPEAKER_01: You can see them to the south, Grand Teton, you can see them in the north in Montana.
• 2:46
  SPEAKER_01: Hebgen Lake is one of these faults.
• 2:48
  SPEAKER_01: So there are faults anyway.
• 2:50
  SPEAKER_01: The area is weak because it's hot.
• 2:53
  SPEAKER_01: That is the magma chamber beneath Yellowstone.
• 2:55
  SPEAKER_01: And there is a lot of water moving around.
• 2:58
  SPEAKER_01: Yellowstone is the highest part of the Rockies on average, buoyed up by all of that sheet from the magma system.
• 3:06
  SPEAKER_01: And so it gets a tremendous amount of snow and rain.
• 3:09
  SPEAKER_01: And so there's a lot of water moving around in the subsurface.
• 3:12
  SPEAKER_01: There's water that comes off the magmatic system as well.
• 3:14
  SPEAKER_01: Water releases magma.
• 3:15
  SPEAKER_01: Water is a component of gas and the volatile content.
• 3:19
  SPEAKER_01: These are these fluids that come out of magma.
• 3:21
  SPEAKER_01: So there's a lot of water moving around, hot, weak crust that's got a lot of faults in it.
• 3:26
  SPEAKER_01: That is a recipe for small earthquakes.
• 3:27
  SPEAKER_01: And there are typically 1,500 to 2,500 earthquakes a year.
• 3:32
  SPEAKER_01: 99% of them are magnitude two and less.
• 3:34
  SPEAKER_01: No one feels those.
• 3:35
  SPEAKER_01: But yeah, every every year we have a few that are felt.
• 3:38
  SPEAKER_01: There's typically, you know, a magnitude four every few years.
• 3:42
  SPEAKER_01: Those are always felt.
• 3:43
  SPEAKER_01: Every so often there's a magnitude five.
• 3:45
  SPEAKER_01: We had a magnitude six in 1975.
• 3:48
  SPEAKER_01: And then there was that magnitude seven just west of the park in 1959.
• 3:52
  SPEAKER_01: So yeah, but the common question is, well, isn't that magma moving?
• 3:56
  SPEAKER_01: And there's only one seismic swarm that we know of that had any characteristics that were even remotely reminiscent of magma moving around.
• 4:07
  SPEAKER_01: That occurred um in 2008, 2009 beneath Yellowstone Lake.
• 4:11
  SPEAKER_01: But even then it's it's sort of suspect.
• 4:12
  SPEAKER_01: We don't really know.
• 4:14
  SPEAKER_01: But everything else has these characteristics in water interacting with faults.
• 4:18
  SPEAKER_02: I think a lot of people listening to this might ask the question of how do you know?
• 4:21
  SPEAKER_02: How can you tell when a swarm is magma moving versus a fault reactivating or hydrothermal fluid circulating and expanding?
• 4:30
  SPEAKER_01: Well, there's there's something to the way the seismicity may propagate.
• 4:34
  SPEAKER_01: So if it's moving in a certain direction, like uh a magmatic intrusion, magma underneath the ground that's moving in in a direction, and then the question of whether or not there's deformation associated with that uh seismicity.
• 4:47
  SPEAKER_01: If it's just water infiltrating a fault and causing the fault to move because you're sort of ratcheting up the pore pressure or making the fault a little bit easier to slip, you're not necessarily going to see a lot of deformation associated with that because the faulting is really small.
• 5:01
  SPEAKER_01: But if you had an earthquake swarm that was associated with, for example, spreading, so you could see, say, from GPS sites on either side of the seismicity that the GPS sites were moving apart.
• 5:12
  SPEAKER_01: And that was a sign that volume was increasing.
• 5:14
  SPEAKER_01: You were pushing something in there.
• 5:16
  SPEAKER_01: That's not something we typically see with earthquakes that are associated with water and racking faults.
• 5:23
  SPEAKER_01: And there was a slight amount of deformation that occurred with that 0809 swarm beneath Yellowstone Lake.
• 5:29
  SPEAKER_01: Uh, it was really, really small, but it was detectable, and frankly, it's sort of a testament to the technology we have these days to be able to detect that kind of motion.
• 5:38
  SPEAKER_01: So that's still ambiguous, but that's the only one that's ever been recorded in Yellowstone that had deformation associated.
• 5:44
  SPEAKER_02: Okay, and this is a really great lead-in to the next sort of thing we're gonna touch on, is your your expertise here.
• 5:51
  SPEAKER_02: Uh, which is I uh there's a lot of hard words and there's a lot of fun words in geology, and geodesy is one of the ones that I find as like the most fun and the most mispronounced, perhaps.
• 6:01
  SPEAKER_02: So this is like geodesi, is what it looked like.
• 6:04
  SPEAKER_00: How do you geodesi?
• 6:05
  SPEAKER_00: Is that what you've heard of?
• 6:07
  SPEAKER_02: Geodesi, geodesi, geo geoda, yeah.
• 6:10
  SPEAKER_02: So they're all sorts of different pronunciations.
• 6:12
  SPEAKER_02: But can you, Mike, just what is this word?
• 6:15
  SPEAKER_02: What is your expertise at a really broad level?
• 6:18
  SPEAKER_02: And then I think this is probably a place where we're going to go into the weeds.
• 6:21
  SPEAKER_02: Great place for it.
• 6:22
  SPEAKER_01: Um, geodesy.
• 6:23
  SPEAKER_01: Let's study the shape of the earth, basically.
• 6:25
  SPEAKER_01: The shape and the gravitational field of the earth.
• 6:28
  SPEAKER_01: And so a geodicist would be uh someone that studies the shape that changes the gravity field, those kinds of parameters.
• 6:37
  SPEAKER_01: And my specific area of interest in volcano geodesy is how volcanoes change shape and how they change their gravity field.
• 6:45
  SPEAKER_02: It's a cool party trick, you know.
• 6:46
  SPEAKER_02: So I'm a geodicist and oh, I study the shape of the earth.
• 6:49
  SPEAKER_02: You know, that's a pretty cool party trick, I'd say.
• 6:52
  SPEAKER_02: So, how do you go about doing this?
• 6:54
  SPEAKER_02: What are the techniques you referred to?
• 6:55
  SPEAKER_02: The the technological advances, which are incredible.
• 6:58
  SPEAKER_02: I don't know a lot about them, but I they're amazing and always blow my mind.
• 7:02
  SPEAKER_01: Oh, I could go on like I could go on about this for a long time, but I'll spare the gory details.
• 7:06
  SPEAKER_01: And the key technologies today, I'd say, are effectively GPS.
• 7:12
  SPEAKER_01: GPS is the US system for navigation and positioning.
• 7:17
  SPEAKER_01: The kind of global method and that name for it is GNSS, global navigation satellite systems, because different countries have different systems.
• 7:25
  SPEAKER_01: So we can use those and record positions with receivers, basically the same thing that's in your phone or in your car, but we record a different kind of the part of the signal.
• 7:34
  SPEAKER_01: And that allows us to get millimeter level precision with positioning.
• 7:38
  SPEAKER_01: And then you repeat that measurement on a daily basis, and you can see how your antenna, which is cemented to the ground, how it's moving around with time, which is how the ground is moving around with time.
• 7:49
  SPEAKER_00: Mike, so wait a minute.
• 7:50
  SPEAKER_00: You're saying that you do this geodesy at the ground level?
• 7:54
  SPEAKER_00: Yes.
• 7:55
  SPEAKER_00: Some of it.
• 7:56
  SPEAKER_00: So you how well, okay.
• 7:58
  SPEAKER_00: How often do you use satellites versus like walk in the contact?
• 8:02
  SPEAKER_00: I mean, uh, how's that work?
• 8:03
  SPEAKER_01: So for uh GPS, we would generally take a an antenna, GPS antenna that receives the signals, and we would install it in such a way that it is very well coupled to the ground.
• 8:16
  SPEAKER_01: You would usually you know drill a hole into the ground, put a monument there so that it's very well coupled, and then you just sort of screw the antenna onto the top of the monument.
• 8:24
  SPEAKER_01: And now when the ground moves, the antenna moves.
• 8:26
  SPEAKER_02: Would you only anchor that in bedrock or put it in soil too, or either or?
• 8:31
  SPEAKER_01: Bedrock is easy, right?
• 8:32
  SPEAKER_01: Because you don't have to you know dig a giant hole or drill a giant hole.
• 8:37
  SPEAKER_01: If you want to put it in some place that's not bedrock, you can do it.
• 8:41
  SPEAKER_01: You can basically uh drive a survey rod down into sediment, and you keep sort of attaching rods, you know, and driving it into the ground attached, and you go until it won't go any further.
• 8:54
  SPEAKER_01: And that's sort of is anchoring it.
• 8:56
  SPEAKER_01: And and sometimes you're going down like hundreds of feet.
• 8:59
  SPEAKER_01: It's like it takes you days.
• 9:00
  SPEAKER_01: Oh my gosh.
• 9:01
  SPEAKER_01: Um wow, but that that is really not preferred because the sediment can expand and contract as water gets in and freezes and thaws, and and so you could get all kinds of spurious signals.
• 9:11
  SPEAKER_01: Those are not really stable places.
• 9:13
  SPEAKER_01: So I would not choose to put something in an environment like that unless there was a really compelling reason.
• 9:20
  SPEAKER_01: And there have been a couple places where we've where we've done that, but usually you look for bedrock.
• 9:24
  SPEAKER_02: So, how many GPS antennas are there in Yellowstone right now for people?
• 9:28
  SPEAKER_01: In terms of continuous sites, there are about 15 in the park, and there are about another 15 that surround the park.
• 9:35
  SPEAKER_01: We supplement that during the summer months with something we call semi-permanent GPS.
• 9:40
  SPEAKER_01: The continuous ones are connected via radio links.
• 9:43
  SPEAKER_01: So we get the data in a continuous stream.
• 9:45
  SPEAKER_01: But there are some places where radio communications are hard.
• 9:49
  SPEAKER_01: And of course, you're not going to just go and put, you know, radio towers up all over the place in Yellowstone.
• 9:54
  SPEAKER_01: It's mar the landscape and be really expensive.
• 9:57
  SPEAKER_01: Yeah, it's a bad idea.
• 9:58
  SPEAKER_01: So we will put temporary sites uh and we'll put them out for the summer months.
• 10:03
  SPEAKER_01: They're pretty low to the ground, they run off solar panels, they don't have radio links.
• 10:07
  SPEAKER_01: So you let them run for the summer, and then you come at the end of the summer, you pick them up, you download the data, and you have sort of five, six months of data for this subset of sites.
• 10:16
  SPEAKER_00: There's about another 15 of those in the park.
• 10:18
  SPEAKER_00: You don't have a ton of bedrock inside the caldera to put these, do you?
• 10:24
  SPEAKER_00: There's enough.
• 10:25
  SPEAKER_01: Um lava flows.
• 10:27
  SPEAKER_01: There's a lot of lava flows in the caldera uh you can get to.
• 10:30
  SPEAKER_01: And there are outcroppings, even in you know, Hayden Valley, which is mostly like lake sediment and glacial sediment, where you can find little outcroppings of rock and and drop a put a put a monument there.
• 10:41
  SPEAKER_01: The key is finding the sort of environment that will get you the data you want.
• 10:44
  SPEAKER_01: You need it to be in the right place.
• 10:46
  SPEAKER_01: You don't want them to have all 15 of these in the same place, right?
• 10:48
  SPEAKER_01: They need to be spread out.
• 10:50
  SPEAKER_01: You don't want them in areas that are going to be affected by processes you're not interested in.
• 10:54
  SPEAKER_01: So we have actually avoided to this point putting GPS stations in hydrothermal areas because those deform like crazy because water's moving all over the place.
• 11:05
  SPEAKER_01: And if you're interested in whether or not the whole volcanic system is going up or down, you don't want to have your GPS station next to a geyser, which is, you know, going crazy.
• 11:14
  SPEAKER_01: Um and that's a whole nother can of worms there because okay, now we've we've got the volcano system monitored pretty well, but shouldn't we also be monitoring these geyser systems?
• 11:23
  SPEAKER_01: Because we talked earlier, like they explode from time to time.
• 11:26
  SPEAKER_01: So we need to get into that as well at some point and saw GPSs in the places we've avoided.
• 11:31
  SPEAKER_01: But yeah, there's enough bedrock, but you got to be careful about where you put them.
• 11:35
  SPEAKER_01: It's not uh it's not a willy-nilly kind of thing.
• 11:39
  SPEAKER_02: Hey, thanks for listening, and tune in next week for much more from our interview with Dr.
• 11:44
  SPEAKER_02: Mike Pollen, scientist in charge of the Yellowstone Volcano Observatory.
• 11:48
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• 12:00
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• 12:11
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• 12:18
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