Short Wave - What Makes Hawaii's Erupting Volcanoes Special

Episode Date: December 7, 2022

Just after Thanksgiving, for the first time in almost 40 years, Hawaii's Mauna Loa volcano erupted. It's one of several ongoing eruptions – including Kilauea, also on Hawaii, and Indonesia's Mount Semeru. At just over half the size of the big island of Hawaii, Mauna Loa is the world's biggest active volcano. Today, volcanologist Alison Graettinger talks to Scientist in Residence Regina G. Barber about what makes Mauna Loa's eruption different than Indonesia's and others around the Pacific, and what it reveals about planet Earth.Watch the U.S. Geological Survey's live video of the eruption here.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. For the first time in 38 years, Hawaii's Manoloa volcano has erupted. It's one of a few ongoing eruptions, including Kilauea, also on Hawaii, and Indonesia's Mount Samaru. Spectators have flocked to view monoloa over the last few days, as lava continues to erupt from one of the fissures in the rock, fissure number three. So far, no one's been injured in this eruption. The Hawaiian islands are situated in the middle of a huge Pacific tectonic plate. Monoloa covers just over half of the big island of Hawaii, and it's the world's largest active volcano.

We love to say the biggest, the longest, the largest, the whatever, but we always have to stop and define that. So for Manaloa, that's referring to its height. And so it comes from the bottom of the seafloor all the way to its summit. And so that makes it the largest on the planet that's active. That really isn't another. that can compete in the height category until you go to Mars, and then we can talk about Olympus Mons, which is like the size of Arizona. But that's not active.

Wow. So Monoloa still gets to be special. Alison Grettinger studies volcanoes at the University of Missouri, Kansas City. She says that even though the recent eruption at Maloas made headlines... The current eruption at Monoloa is a pretty typical one for what we'd expect for Hawaiian volcano. What is special is that Monolo is erupting at the same time as... as the smaller Kilauea volcano.

It's a dual eruption not seen since Montoloa's previous eruption in 1984. And for Allison, part of the excitement is seeing Earth-building in action. You can watch little blobs of red magma rising through the air, landing and building this cone. And so then it starts to look like a more circular feature.

You'll see sort of lines of little cones and lines where lava flows come out of, and it sees fissures. And all of these small eruptions are how this biggest active volcano on Earth built. I mean, it was lots of little eruptions again and again. That's our show today. The eruption of Hawaii's Long Mountain.

Why it's likely a once-in-a-lifetime event and what it reveals about how our planet works. I'm Regina Barber, and you're listening to Shortwave, the Daily Science Podcast from NPR. So, Alison, can you step back and give us, like, a primer on volcanoes? I want to take this in two parts. Like, first, another eruption that happened over the weekend in Indonesia. It's part of the ring of fire where a lot of volcanic activity happens.

But the volcanic activity in Hawaii, it's distinct from that, right? Like, what's going on here? So to get a volcano, you have to have a few things happen. And one is we have to have molten rock and not just really hot rock. So the mantle, which, you know, we live on the crest. That's the really thin part of the planet. Think of that like the skin of an apple in terms of scale, right? Like super thin relative to the hole.

And most of what you think of as the apple is the mantle. And it's really hot and it's under a lot of pressure. So as long as it's under pressure, it's content to be solid. So we have three mechanisms on the planet to make molten rock. One is to reduce that pressure. So think of Iceland is a great example, where the crust is pulling apart and it's decreasing the pressure. So that allows the melting. And you just get little blobs of melt and they rise to the surface again and again and again.

and you get a whole country, you get all of Iceland. The other option is what we think of at the Ring of Fire. So all of the Cascades, the Andes, Japan, Philippines, New Zealand, that's where we're taking rock and shoving it back into the planet. Because if you're going to crack it and spread the crust, you have to destroy that crust somewhere because the planet isn't getting bigger. So where you destroy the crust, you're shoving rock into the planet.

You're taking a little bit of water with it. So you're actually changing the chemistry. So we can change the pressure. We can change the chemistry. Or what we normally think of when we melt stuff is we make it hot, right? And that's what's happening in Hawaii. So there is hotter rock from deeper in the planet. We think it's coming from near the core mantle boundary.

So that's on the order of like 600 kilometers. It's pretty deep. Wow. And it is rising, not as a liquid, but is relative hotter rock. So buoyancy drive so much on this planet. Density differences make the ocean circulate. It makes the atmosphere circulate. It makes rock circulate.

Now this is slow, but that hot rock is rising and then it warms the rock above it, which melts it. And so you could almost think of Hawaii as like a torch. You know, it's sort of burning through the crust. There's this extra hot material is rising. It makes molten rock on the way. That turns into magma as we think of it. And it erupts at the surface and you get an island. And as long as the crest above it stays still, you can pile it up.

But the crest is moving ever so slowly. So that's why we get a chain because there's this. blow torch of hot magma coming through the crust and as the crust moves you you make a volcano and then if it gets too far away you got to make a new one wow so you talked about how these volcanoes it's kind of like you said a torch so they are actually not on this ring of fire they're kind of surrounded by it in a way so they're like in the middle yeah like in the middle of the largest tectonic plate we have so the crust of the planet is broken up into bits and the pacific plate is like one of the largest chunks. And all around it is old cold crust. It's been around for a long time. And that

enables it to dive underneath the continents. And so basically you have these subduction zones where we're destroying crust and creating volcanoes all the way around the Pacific Plate. And so that's, it's not a perfect ring because, you know, spheres and geometries make everything complicated. But that's why we have this sort of pattern of numerous volcanoes around the Pacific. but then Hawaii in the middle of it is a hotspot. And there are other hotspots on the planet. So there's tens of them, and you can find them in different ocean basins. So the Galapagos are also a hotspot, but they're sort of closer to the edge.

And with monoloz eruption, there's something called a RIF zone. Can you talk about what that is geologically? Yeah. So the RIF zone, you can think of as a product of the weight of this massive accumulmonary. lava at the surface, and it sort of spreads out a bit under its own weight. And this, this cracks the surface. So it's areas that are full of fractures that become pathways for magma. Magma's lazy. It's coming to the surface because it's hotter than what's around it, and it's got gas in it. So buoyancy drives it to the surface, but it's going to take the easiest path.

And that's one of the reasons that there's these lines and fissures is because the easiest path is to flow as a sheet rather than to be a blob or a balloon like we sometimes have drawn in the past in kids' books. So if you want the line about me saying that people are wrong, it's frequently the way we draw the plumbing system of volcanoes. We frequently are too simple. But the RIF zone allows Magma to travel out away from the summit. So as magma comes up sort of through a plumbing system near the center, it's not a nice straw, but then it can spread out into the RIF zones.

And that's really common for both Manaloa and Kilauea that we have, we can have activity at the summit, but it'd rather come out in these rift zones. And it tends to be there for more of the eruptions that we watch with lava flows and fire fountains and stuff like that. So how good is the monitoring to be able to warn people when an eruption might threaten an area that people live in? Right. There's different aspects of an eruption that we monitor. So with the case of Monoloa, we watched for signals before the eruption started. Well, I say the USGS and then anybody else who was looking at a seismometer near the islands was watching. But they were able to see evidence of magma moving towards the surface.

And so they even had like town hall meetings with the residents of the island of Hawaii before the eruption started. But then we also have to monitor once it starts, where are these things going? And for this eruption, we're watching where the lava flows are going, where maybe future fissures might open, and gas hazards. And so there's teams who are devoted to each one of these. And we have numerical models and numerical simulations that we use to estimate using topography and our understanding of lava flow physics to see how far a flow might go. that gives us sort of an idea of the paths it might take. And then knowing how fast these lava flows have been going and the composition information they've gotten from the existing lava flows,

they can make estimates about how long it might take to get somewhere. But those forecasts are guidance, right? They're not like super, like we know it's going to be just here yet. And then the gas monitoring, they're very much relying on meteorologists. So there's lots of partnerships between different scientists. fields because once the gas goes in the air, that's all about the atmosphere. And so they're providing forecasts about where they expect the volcanic gas to go. They call it Vogue or volcanic fog. And thankfully, because this eruptions at higher elevations, it's been higher than most of the

community. So they have to worry about it going downwind. But the effects have been less severe because just the eruption site is so much higher than where people live. So what does this all tell us about how the planet functions? Volcanoes are a great way of studying the inside of the planet. It's one of our few ways to see what's inside because the volcano brought it to us. So magma and lava that we see at the surface has come from the mantle, and it gets to tell us about that composition. So we have direct samples of minerals and the chemistry of the interior of the planet.

And then even bigger picture, the fact that we have monoloa and Kilauea both erupting there, And we have evidence from chemistry and from geophysics. So it's looking at the density and the way the rocks respond to earthquakes and everything like that, that those are two different sources. So that there's two different systems. They're not connected. And so that tells us something about how the planet works. But there's still a lot to learn. So whenever we're studying the deep parts of the planet, we have cool techniques and amazing insights.

But we're still new to this of studying at depth. We've only been doing that since the mid-20th century. And so it's like one of those biggest places. If you want to learn something new and have an amazing discovery, like hotspots, there's still much we could learn there. Why there's so many of them, why they are exactly where they are, how long they're going to last. We got big open questions that I would encourage anyone who wants to study the planet to come join us. That's awesome. I want to thank you for giving us time.

I really had a great time talking about volcanoes. It's like a childhood dream. Good. I'm glad to help. You can follow the ongoing eruptions in Hawaii at the live stream set up by the United States Geological Survey. We'll link to the video in our episode notes. This episode was edited and fact-checked by our senior supervising editor, Giselle Grayson, and produced by Rebecca Ramirez. Brendan Crump is our podcast coordinator. Beth Donovan is our senior director of programming, and Anya Grunman is our senior vice president of programming.

I'm Regina Barber. Thanks for listening to Shortwave, the Daily Science Podcast from NPR. See you tomorrow.