Short Wave - Thousands of earthquakes in Iceland may spell a volcanic eruption

Episode Date: November 15, 2023

Saturday, the entire coastal town of Grindavik, Iceland was evacuated. That's because over the weekend, the country experienced nearly 2,000 earthquakes within 48 hours. And they've kept coming since then – in swarms. Scientists think the quakes are indicative of magma moving closer to the surface in the country's southwestern peninsula and that a local volcano could erupt at any moment. Today on the show, host Regina G. Barber talks to volcanologist Diana Roman about the science behind these earthquakes. Got science to share? Email us at [e-mail] 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. This weekend in Iceland, there were nearly 2,000 earthquakes in 48 hours, and they've kept coming since then. Seismologists are watching to see if a volcanic eruption is coming next. I have spent a lot of time in the past few days, checking the news, checking Twitter. I've actually got a little iPad on the wall in our house, and we got it on the live stream video cameras that are pointed at potential eruption sites. I've been checking almost hourly to see if it has started erupting.

Diana Roman is a volcanologist at the Carnegie Institution for Science, and she says this area is seismically active. It's experiencing earthquakes pretty regularly. There have been about 20,000 in the region since late October. So it's been going for a few weeks now, but just this past Friday night, it picked up very strongly overnight. And so it's really changing just in terms of how intense it's getting over time. Most of them have been too small for people to feel,

but the biggest have reached a magnitude of 5.0, which Diana says is pretty big for the kinds of earthquake scientists usually see at volcanoes. And they've been accompanied by something called ground deformation. The ground is basically swelling, moving upwards in some places, and actually moving downward in other places. Most of the time when this happens, at a volcano, it's so subtle that you might not even be able to see it with your eye. So we're talking about, you know, centimeters or millimeters of deformation that can only be picked up by instruments. But in the past few days, it's actually been pretty intense up to a meter of the ground dropping in certain areas, tens of centimeters of the ground moving up in other areas.

You know, a lot of people don't think in meters, but like that's three feet of ground deformation. That's scary. And very quickly. And all of this has Diana and other volcanologists on pins and needles, because Diana says that these earthquakes are a result of magma forcing itself through solid rock, which often happens before a volcanic eruption. These earthquakes are telling us that something is pushing its way up through the crust. probably very quickly, probably a large volume, to be able to break so much rock so strongly. So it's really the combination of these earthquakes,

how the earthquakes are evolving through time, the fact that the ground is deforming and cracking, all of that together is really suggestive, clearly of magma causing this whole sequence of unrest. On Saturday, an entire town in southwestern Isis, was evacuated because seismic activity ruptured its main roads, which makes scientists think that magma is getting closer and closer to reaching the surface. And what it means is that an eruption is very likely to happen fairly soon.

We can't say when, whether it's the next hour, the next day, the next month. And there is a chance that magma may not erupt at all. But this is in a populated area, so there is a hazard associated. with it. So today on the show, the science behind the thousands of earthquakes and potential volcanic eruption in Iceland. I'm Regina Barber, and you're listening to Shortwave from NPR. Diana, we're talking to you at 6 p.m. Eastern Monday evening, and right now, there's a series of earthquakes still happening, right? But before we get into that, let's talk about plate tectonics. I've learned recently that Iceland was formed by divergent plates. What's a divergent plate?

So it's a divergent plate boundary. So basically there has a crust, a solid crust, and it's broken up into a dozen or so major plates, fragments. And a divergent plate boundary is where two of those plates are into contact, but they're moving away from each other. So the ground is kind of spreading around Iceland. It's creating more crust. And that's a situation that occurs commonly. in association with volcanism. So the East African Rift is probably the other obvious divergent plate boundary where there's a lot of volcanism. Iceland, though, is a little bit unique on Earth because not only is it a divergent plate boundary, but it's also got what's called a mantle plume or hot spot coming up beneath that place where the plates are moving apart. So yeah, so you're saying that magma is coming up between these plates. Tell me a little bit more about what a hot spot is? So a hot spot is a place where there's a plume of magma that's coming from somewhere within

the deeper parts of the earth, within the earth's mantle, and it's basically streaming upwards. And so these hotspots can form volcanoes even in the middle of a plate. So the Hawaiian hotspot is a very famous example. That's a very active volcanic system that's right in the... middle of a plate, not at one of the boundaries, but because there is this big plume of magma coming from the mantle, it's basically able to kind of create volcanoes through the crust as the crust moves over it. So you get these chains of islands that kind of go in the opposite direction

of the way the plate is moving. So it's kind of stationary and builds a certain type of volcano. So this is the other element of what's going on in Iceland in terms of its tectonics. Okay. So how do all these elements interact to make earthquakes and like eruptions relatively common in the region? Well, first you have a big supply from the mantle plume of magma. And then you have plates that are moving apart, which makes it easier for magma to get out to the surface. You know, you're basically creating a pathway passively for that magma to come up through the crust. So that's why Iceland is basically a country that is entirely volcanic. And the earthquakes in Iceland are a combination of that plate movement, and then this magma, which still does have to push its way through the crust and move it aside as it goes through,

and that's what produces earthquakes that are more localized, focused in certain areas and that we see before and during eruptions. Yeah, I heard from our producer that you have a really good metaphor for this that involves silly putty. Yeah. So one way to think about an earthquake is if you think about a ball of silly putty, and if you stretch that silly putty really slowly, it'll just kind of stretch out and you'll get a thin string.

And so that might be a way to think about deformation. You're kind of just bending things. But if you pull that silly putty really quickly, it'll snap. And so that's an earthquake. And so if you've got something that's basically pushing on the crust very strongly, very quickly, then you'll snap the crust and you'll get an earthquake. Or if your silly putty is kind of dried out, it'll be more brittle, and you won't have to pull it as quickly to get it to snap rather than just kind of ooze as you deform it.

Oh, wow. Okay. Yeah. That's a good visual. I like it. Okay. I understand that as of this recording, the seismic activity in Iceland is actually slowing down. There's fewer, I guess, of these snaps. Is that a good thing? Well, so what we occasionally see before eruptions and actually what was observed before the eruptions in Iceland that started in 2021 is that you get this strong swarm, but then it kind of calms. down a little bit before the eruption. Oh, wow. And the thinking there is that as the magma kind of gets closer to the crust, it's, it's, you know, not, it's not dealing with as much rock. So it doesn't have to break as much or as strongly.

So you can think about it like if you're under a pile of heavy blankets versus under just a thin bed sheet, you don't have to work as hard to move that bed sheet as you do the big pile of blankets. And so the fact that it's kind of gotten seismically quiet is consistent with that magma being a little closer to the surface where the crust is a little bit weaker. And like I said, you know, this is something that was observed before the past eruptions at Fagas Fjall, which is nearby. That things got quiet as the system got closer to the eruption after the initial big swarm of earthquakes. Right. And to that point, to get a little technical here, the third. thousands of earthquakes that have happened so far, they're a swarm of earthquakes, not aftershocks. And I think there might be some people out there when you say a series of earthquakes, they might think aftershocks. So could you give us just a quick definition of like a swarm of

earthquakes versus an aftershock of an earthquake? Right. And this is actually an important distinction that we make, especially about volcanic seismicity. So the simple difference is that in a swarm of earthquakes, the largest magnitude event is not the first one. It happens somewhere in the middle of the sequence. Whereas a main shock after shock, you get the big one, and then every earthquake that follows it is lower in magnitude. So that's not a swarm. So it's a bit of a subtle distinction, but it actually is one of the things that we observe in volcanic systems that they don't follow that you know, tectonic process of big one followed by smaller ones, which are aftershocks. Right. Okay. And so my last question is, are there any open questions for you as you continue

to monitor the situation in Iceland? Well, I think one of the big open questions right now is about the hazards if this system does erupt. And so Iceland is a hot spot, which is typically more like effusive lava flows, not big explosive Mount St. Helen-style eruptions. But this sequence of earthquakes actually runs out into the ocean south of Grindivik. And so one possibility is that if this eruption starts underwater, lava erupting through seawater has more of a potential to be explosive. So I think there's some question about, you know, what kind of hazards to expect, which really depends on if the system starts erupting exactly where that eruption going to be. You know, this whole sequence of events was 15 kilometers long. So the sense right now

is that it's likely to erupt just a bit north of Green DeVic, but there is a possibility that it could erupt at the southern end of this swarm, which would be underwater and would be a very different type of situation. And different precautions would need to be taken. Exactly. And I think that's one of the open questions that's a challenge right now. Diana, thank you for taking the time to talk to us today. Thank you so much for having me.

If you enjoyed listening to this episode, hearing the science behind natural events in the world, follow us on your podcast app. That way you'll get notified every time a new shortwave episode drops. And if you have a science question you've been itching for us to cover, email us at shortwave at npr.org. This episode was produced by Rachel Carlson. It was edited by our showrunner, Rebecca Ramirez, and Britt Hansen, Check the Facts. Maggie Luther was the audio engineer.

Betzunovan is our senior director and Anya Grunman is our senior vice president of programming. I'm Regina Barber. Thank you for listening to Shorewave from NPR. You got these names down. Good for you. I get coached by my Icelandic colleagues. Oh, good, good. They, like, sit you down and look you in the eye and they're like, say it again.

Say it again. And then they give up.