 It's one o'clock on a Monday afternoon, so you must be watching Think Tech Hawaii Research in Manoa. I'm your host, Pete McGinnis-Mark, and every Monday we bring you some of the science updates from the University of Hawaii's Hawaii Institute of Geophysics and Planetology. And this week, we're dealing with the Planetology and Geophysics side because we're going to have Niels Grobe, who is a geophysicist, you're an assistant researcher, faculty member, newly minted at the university. So Niels, welcome to the show. You're a geophysicist who's just arrived in Hawaii. That's correct. To start off with, what does a geophysicist do? Well, first of all, thanks for having me here today, Pete. It's a great pleasure to talk a little bit more on geophysics and especially on Hawaii. A geophysicist basically tries to look in the subsurface of the earth. So underneath our feet, there's a whole world that we cannot look at. And what we're trying to do is to use physics techniques to make an image of the subsurface, similar to what happens in the hospital when people look at somebody's body, for example. So you're doing an MRI of the earth? Something like that, yeah, something like that, yeah. So and based on that, we can kind of like see what is where and where are the interesting features that we may be looking at. Cool. And a geophysicist is a different skill set from a geologist, correct? That's correct. So the geologists basically look at the rocks and the structural phenomena of the earth, like what is the earth composed of. A geophysicist tries to make an image because the geologist cannot look underneath the earth's surface. They can look what is out in the field, what you can see with your eye. But you cannot look what is below your feet. So did your physics tries to help and assist by making an image using these kind of... And for our viewers, Nils, can you say, is it literally below our feet, say the top five meters, or can you go deeper than that? It can go totally deep. So people have even learned that the earth consists of a core by using seismology waves, basically. So waves generated by an earthquake, sound waves traveling through the whole earth. And wherever there's a contrast, you get kind of like an echo. So as a child, we all scream down in a hole, for example. And listen until the sound comes back to our ear. That's the same kind of principle that they use there to see, like, where are the contrasts in the subsurface? And what can we learn about how it looks down there? And based on that, they even looked down in the earth and they discovered the earth as a core. Yeah, you can go as shallow as the first few meters down to the earth's core. Although, presumably, you don't get the same level of detail that the data you go. And in your particular application of geophysics, what depth range are you interested in? So I'm primarily interested in the earth's near surface, what we call. So that's the first few hundred meters up to, let's say, three kilometers. OK, so about two, two and a half miles down. Right, that's correct. And so you're here in Hawaii now. That would be sort of somewhere between if you're on the big island, it would be below sea level, but not down to the ocean floor, something like that. Yeah, so it depends in the near shore area. You obviously don't go that deep. So based on that, like the first two and a half miles, I would say, of the earth's crust. So really, where the earth is still consisting of the crust, the outer shell of the earth, basically, and we're not yet into the mantle or the core. And we should congratulate you, Niels. You're a newly minted faculty member at Manoa, right? That's correct, yeah. I'm sure the viewers can tell that I'm not from Hawaii. No, are you? Where have you just come from? So I'm originally from the Netherlands. So that's in Europe. And then I did near Amsterdam, I believe. Yeah, Rotterdam, Amsterdam, somewhere in between. Yeah, so that's where I did my studies, my undergrad and grad studies. Then I moved to Boston to MIT for a postdoc. And after that, I was lucky enough to come here and start as a faculty member at UH. And presumably the kind of geophysics you would do in the Netherlands or in Boston, is that the same as you're trying to do here? Or is it different? No, it's quite different. We don't have active volcanoes. Hopefully not in Boston. No, no, and also not in the Netherlands. So the Netherlands are typically quite a flat sedimentary zone. So we're at the stream mouths of some rivers. And that's what formed the Netherlands as a delta, basically. So it's totally different than a volcanic island chain like Hawaii is. But based in terms of geophysics techniques, actually, a lot of them are transferable because the technique itself is based on physics, the environment is different. And that can make a huge difference. Yeah, but I believe you had previously worked on volcanoes in the Atlantic. Yes, yes. So can you tell us a little bit about that? And maybe we can go to the first slide so you can show us the techniques. You can have the first slide up. We will see, I think, Niels actually doing some of his field work. Here we are. Yeah, that's me. So that's... So where are you, Niels? So you see me in a beautiful landscape, which looks maybe a little bit like Hawaii, but it's not. This is on the Azores in Portugal, basically. So it's a volcanic island group, offshore Portugal, near the Mid-Atlantic Ridge, what we call. So that is where fresh ocean crust is and materials being formed. And at that spot, they have like active volcanic island chains similar to Hawaii. And this is where we did some field work. So this is me out in the field making some GPS measurements. But this looks as if it's fairly vegetated. So this island in the Azores might be equivalent either to Oahu or Kauai, perhaps. Yes, yes. So you have basaltic subsurface. So we're dealing with volcanic rocks and we're dealing with a lot of vegetation and meadows and everything on top of that. So there's not a lot of outcrops. All right. And I think your next slide will show us a little bit more of some of the techniques. So here you are again. You've got lots of little toys or gizmos with you. Going to the viewers, what they're looking at. Right. Yeah, so first of all, the thing that catches the eye most is the blue tent. So that was basically just to protect the equipment from the rain because as on the big islands, on the Azores, it can rain quite drastically and quite suddenly. So we protect our electric equipment that is underneath that tent. So you see this orange box, basically, which is the electrical resistivity meter. Next to it, you see a black battery which charges. It's just a car battery, but it charges the electrical resistivity. And you mentioned electrical resistivity. Right. What technique is that exactly? So what that does is you have in the field, you deploy some so-called electrodes. So those are just tiny rods that we stick into the ground. And based on that, this device, car battery powered, injects a little electric current in two of the rods and measures the potential difference with other two rods. So it basically describes how resistive is the earth. So how easy does the current flow through the earth, basically? So if it has a lot of water in it or salt water even, the current can go very easily through that. But if it's just a dry, basaltic rock, the resistivity of that rock may be much higher. So it basically gives you a map and an idea of which parts of the earth are more conductive, electrically speaking. And do you just measure the conductivity between two points on the ground or what kind of field techniques might you use? Right. So we deploy a typical array. So there's many of these electric rods, electrodes, we call them, over several hundred meters, or we can do whole transects basically through the landscape. And this device, it kind of just takes pairs of those electrodes where it injects and pairs where it measures. And then based on what we designed the acquisition to be like, it transfers along that transect and covers the whole area. So based on that, we get right underneath that line, we get an image of the electrical resistivity of the subsurface. And if we would deploy them on the whole surface, so in a 2D plane, you would get a 3D volume in the earth subsurface. And how does that tell you about that? I can understand that you might be able to measure conductivity between two points. Right. The depth part of the technique. Right, yeah. So based on the voltages what we measure, if the area is quite conductive, the currents will go through, but they will attend relatively quickly. So based on the different depths and the different variations that are there, the currents will go through these different depth sections. And by selecting different distances between electrodes, so I can take the two nearest ones, or I can take the two furthest ones, or anything in between, you can look deeper or shallower, depending on the distances. And all this is done with a car battery. That's all done with a car battery. Amazing, yeah. And I think the next slide will actually show a little bit more of this theoretical technique. We're talking about electrical techniques now. You're not gardening here. No, no. What is it you're doing here? So this is a similar technique, but it's a passive technique, so it's part of a magnetotelluric system. So in the previous example, I displayed an active electric current injected by the car battery. What we do here is we dig a little hole. You see, it's not very big. And what I have in my hand, that black little box, is another one of those electrodes, which we can bury in the subserver. So we put it there, we cover it up, and then we just listen and wait to the electromagnetic disturbances caused by the solar winds and the lightning in the atmosphere. And again, it looks fairly non-intrusive. That's good, yeah. You're in a field here, perhaps it's like a cow patty or something. It's not a major excavation. It's a cow patty, and we got permission by the landowners to do that for which we were very grateful because we don't leave a big footprint, basically, but it's crucial to make this little hole to get the best signal that we need, yeah. Now, Niels, you grew up in the Netherlands, you went to MIT, I've got to tell you that not all Hawaii volcanoes look like the one we have here on the screen. Right. I understand you off to the big island soon. What are your expectations of actually applying some of these techniques on an active volcano, even? Yeah, that's fascinating. I'm very excited to go to the big island to see what it actually looks like, how is the volcano being built up, how it's being formed, and also, what are we dealing with? Because it's kind of crucial, like you say, if you have access to the field area, if you can walk there, if you can carry your equipment, and then also how hard is the rock? Can we actually make a little hole in the rock or is it totally rough hard rock surface? I wish there was a way that you could put down your thoughts before you go to the big island because obviously an active lava flow or even some of the thick, historic lava flows, the landscape is really different from what we're seeing here. That's what I've seen on the topography and the pictures and the journal articles and everything. So this is my first time going there and I'm very excited to see what it is really like. Now, you talked about electrical technique, but what kind of skill sets does a geophysicist need? As you were coming through high school or college, are you a computer geek? Do you build equipment? What's your background? Yeah, so for me, it was kind of interesting because I liked all the science courses, basically, so math, physics and chemistry. Those were the ones that I liked. And I was looking for a job that could encompass all of those. And at the same time, I had a profound interest in nature and I loved being outdoors. So I started looking at all those ingredients and see how best that come together in what kind of studies. And geophysics is exactly doing that. So you need some mathematics to understand the physics and to develop your models. You need obviously the physics. It's even in the name of geophysics. Some geochemistry also plays a role in general in earth sciences and geology and the structures that you're after. And then you mentioned the computer aspect of things. So the coding and the programming, many of our geophysics techniques and models are being converted to a numerical model to do forward predictions using a computer. But also once we have acquired the data, you basically, so we acquire the data, but that gives us hidden in that what kind of structure is beneath it, but it doesn't directly give us the image. So in order to make the image, we would have to do something which is called an inversion or imaging. And we basically take the data that we got, which has the effect of the subservers where all that technique and these currents went through, and we're trying to find the best model that explains what we have measured. So that's where all the computation has come in. Computer scientist, physicist, geologist, and someone who knows how to use a lot of equipment. Exactly, yeah. Great. Well, Niels, we're getting close to the middle of the show, so we're gonna have to take a break now. When we come back, hopefully you can tell us a little bit of your expectations for doing geophysics in Hawaii. So let me just remind all the viewers you are watching Think Tech Hawaii Research in Manoa. I'm your host, Pete McGinnis-Mark, and our guest today is Dr. Niels Grobe, who is an assistant researcher at the University of Hawaii's Institute of Geophysics and Planetology. And we'll be back in about a minute. See you then. I'm going to the game and it's gonna be great. I usually drink, but won't be drinking today because I'm the designated driver and that's okay. It's nice to be the guy that keeps his friends in line, keeps them from drinking too much so we can have a great time. A little responsibility can go a long way because it's all about having fun on game day. I'm the guy you wanna be. I'm the guy, say goodnight. I'm the guy with the H-2-O. And I'm the guy that says, let's go. Hello, my name is Howard Wigg. I am the proud host of Code Green, a program on Think Tech Hawaii we show at 3 o'clock in the afternoon every other Monday. My guests are specialists from here and the mainland on energy efficiency, which means you do more for less electricity and you're generally safer and more comfortable while you're keeping dollars in your pocket. And welcome back to Think Tech Hawaii Research in Manoa. I'm your host, Pete McGinnis-Mark, and I guess today is Dr. Niels Grobe, who is an assistant researcher at the Hawaii Institute of Geophysics and Planetology, and we're learning all about geophysics. Now, Niels, the university was really successful. We stole your way from MIT, presumably, to do something here in Hawaii, right? That's correct, yeah. So what is the potential for doing research in your line of work in Hawaii? Oh, it's fascinating here. That's one of the things that attracted me so much because this is really where new Earth's crust, new Earth materials being formed. This is where active volcanoes are. This is where the earlier mentioned earthquakes can occur. So in terms of having a real-life laboratory out there and being able to do your geophysics in a live laboratory on the scale of the Earth is fantastic. So it's really great to be able to test your methods here. And I understand it's a fairly new field in terms of doing this kind of work here in Hawaii. I know the US Geological Survey have done a little bit of work in the past, but there's a lot to learn, correct? Right, yeah. So another aspect of what attracted me so much is the water-related aspect of it. So part of the projects that we're working on here is trying to make a characterization of the Earth's subsurface and see where does the water go, where is it sitting, where is it flowing, how is it connected? All right, so back up. We were talking about internal structure of volcanoes. Right. And now you're mentioning water. Right. Make the connection for the viewers. Right, so what it is is that a lot of groundwater is being used as a freshwater source, which comes out of our faucets, which we use for showering and so forth. So Hawaii gets its water naturally from the islands, where it rains somewhere in the mountains and somehow it flows down to the ocean. But a lot of the water infiltrates and flows underneath the ground, and that is the domain where I come in. So that's basically where we're trying to characterize, all right, what are the structures that control where the water flows? How do we know where we can drill a well to actually produce the water that we use? And to understand that in such a complex environment as the Hawaiian volcanic islands is a real challenge and it's very important. Right, so the inside of the volcanoes we have in Hawaii control where the, eventually the rainwater falls on the, some of the volcanoes that eventually flows down towards the coast. Exactly, yeah. You're hoping to be able to tell us what pathways that water is following. Precisely, yeah. So where is it going? How does it control how much water we can actually use? Are different aquifer systems as we call it connected? So this must be very important for our community. This is crucial, yeah, this is crucial, especially since Hawaii is self-sustaining in terms of the water, like you can't ship in all the water from anywhere else. So the fresh water that we're talking about, not the ocean water, but really the fresh water that we use, that really has to come from the groundwater and from where it rains in the mountains, down to the ocean, somewhere in that path, we have to capture it and use it sustainably. The way to drill a new well, for example, or how much a particular catchment area is influenced by surrounding mountains. Yeah, yeah, so that controls all the management issues that we're dealing with in terms of using the water optimally, sustainably. You sound like an important person to have here. Thanks. Let's take a look at the next slide, because I think we're going to go into a few examples. All right, and here I believe we've got a stylized view of Oahu. Explain for the viewers what we're looking at here. So here we see kind of like a schematic of the hydrological cycle or hydrological flow paths on Hawaii. So at the right side of the picture, you see the ocean, you see Honolulu and you see something yellow, which is called sediments, so that is the sedimentary zone. On the left side, you see the mountains and you see some vertical red lines, which are the dike intrusions, so the volcanic intrusions of rock. The underground structure. Right, so that is all underground structure. So you see the diagonal line, which depicts like the air separated from the earth's subsurface, basically, the underground. And then the idea is that somewhere on the slopes of the mountain, rainfall will fall. It will infiltrate somehow in this subsurface structure, and it will try to move down slope, basically, towards the ocean. But as you can see in the underground, there's a lot happening. So you see something called salt water, you see a brackish water zone, and you see some fresh water. So the fresh water typically floats on top of the salt water, but it interacts with all the subsurface structures that you're seeing. So when you look at the dike complex, you see that there's also a lot of water in between those red lines. So your geophysics could tell us something about where the dikes are located? Exactly. Or how deep might we be able to go with the electrical techniques you described in the first half? Can we get down to the brackish water, for example? Right, so that depends a little bit on the method. So the magnetotelurics, the passive method where I had to dig the hole, it basically can go down very deep. So we can kind of reach those zones, but you will lose the resolution of that picture. So we see less detail with that method. The electrical resistivity can give us a higher resolution image, but for the first, like let's say kilometer up here. And of course, all of the Hawaiian islands are a little bit different in terms of not only their age, but the detailed structure of where the rift zones are located or whether they had what are called these post-erosional volcanics like diamond head or punch bolt or Hanama Bay, that sort of thing. So your technique can actually tell us. Well, we have to separate the challenge and not study this yet. Right. So we have to separate the different geology, the controlling structures. You mentioned the dikes, for example. Those are very important because they kind of form a barrier for the groundwater. So it kind of traps the water or diverts the water around it. So it is really important to know where are those and how is this all interacting with the geology. So if you have different ages of geological sediments, they all may play a different role in how the water flows. So yeah, like you mentioned, there's a lot of different rocks here and it's very complicated. And you're doing this from this sort of imaging technique, which I think is shown in the next slide. What we've got here, it is a model of groundwater flow on the big island, right? And so this is Kona coast. We see on the left-hand side, Huala Lai volcano, right? What are the little diagram on the right-hand side? Do you know? What is that? So we see here, indeed, the big island and the red line on the left picture is basically describing the modeling domain that you see on the right. So this is hydrological modeling. So it basically tries to identify the flow paths on where the water falls from the rainfall, where it goes in the subsurface and how it may have moved down to the coast. And you see all those black dots and those are wells, so those are actual measurements where the groundwater people have basically seen where is the water and what is the height of the water. That's the control. So that is the ground truth. Yeah. So that is what is there, but where there are no wells, we kind of have no idea where the water is going. So that's where the geophysics would come in to also answer that question mark, like where is it really going? Like there's all these errors being drawn. But where is it actually? Yeah, I see, for example, in the right hand diagram that the red arrow model flow crosses with zone as a geologist, presumably that's not a very plausible. Right, right. Like I said, that those dike complexes will hopefully or predominantly form a barrier for the water. So the fact that the water goes straight through that dike is very unlikely in the sense it would rather go elsewhere than through a zone where the water is basically being blocked. So even though the groundwater model seems to show it goes through, the question is, does it really go through or does it go elsewhere? Affailability of water on the big island, particularly the Kona coast is a present day issue, right? It is crucial. And I would imagine that you need to know whether or not in Kona you're getting water from monolow or you're getting it from monocale or whether it's just localized around Hualile. Right, yeah. It all plays a major role in how much water is there available, where does it actually come from and all those sources of where the water can fall, monolow, monocale or Hualile, all contribute to how much water is there available in total and what can we do? But if you go out to a place like Makapu on Oahu and you see the cliff just by the lighthouse, for example, it looks incredibly complicated. It is, yeah, yeah. Won't it be even more complicated when it's a young? It must be extremely complicated. So that's why it's also a very challenging project. And as you may have heard, or the viewers may have heard, there's this Ikewai project of the University of Hawaii, where different disciplines, geology, geochemistry, hydrology, geophysics and social economics are all working together to try and address this challenging issue. So this was a project Nicole Laozi was on the show six months ago. So it's the same project. It's the same project. It's a massive project. But the challenges are also massive. So we have to do something. And I would imagine, Hualile is an active volcano erupted in 1801. If you're looking at Kilauea, it's active today. There must be a lot of differences between the Big Island and Oahu because the Oahu has been extinct for two million years. Yeah, so there are various study areas that we can look at. And depending on where we are, the complexity may vary and also the flow patterns what we observe. But we have the impression that there may be some similarities also between the islands. Well, this is fascinating, Niels, because you're just at the start of your professional career in Hawaii. You're enthusiastic. You haven't been out into the field. Can I suggest that when you've actually made some of these measurements and you've got some results, can you come back on the show? Oh, I would love to. Yeah, yeah, I think that is very nice to show the audience. Like, to see what do we actually see underneath our feet in real life on the Big Island or on Oahu? And how can it help the local population, the water supplies, as well as I'm a sort of a geologist myself, just learning much more about the inside of an active volcano would be fascinating. So please come back. Unfortunately, we've got to the end of the show. It goes really quickly. I know. Let me just remind our viewers you are watching Think Tech Hawaii Research in Manoa. I've been your host, Pete McGinnis-Mark, and my guest today has been Dr. Niels Grobe, who is an assistant researcher at the Hawaii Institute of Geophysics and Planetology. So thanks for watching and join us again next Monday at 1 o'clock for another episode of Think Tech Hawaii Research in Manoa. Goodbye for now.