Ep. 443: Destroy and Rebuild Pt. 7: Tsunamis

Physics, Planetary Science, Planets | 0 comments

Surf’s up! Today we’re going to be talking about one of the most devastating natural disasters out there: tsunamis. We’re talking huge waves that wreck the seashore. But it turns out, there many ways you can get a tsunami, and one of those has to do with space.
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Pamela: Hey, everyone. This is Pamela. Once again, I am here to sing the awesome praises of BarkBox.com. We are so lucky, with Astronomy Cast, to have sponsors that we really believe in. And BarkBox is kind of one of my favorite things to get each month.
One of the reasons I really like it is the treats that come with the box. There’s a lot of dog treats that just smell really horrible. That’s not the ones that come from BarkBox. Back in October, I got Boo Berry treats as part of their Halloween theme. Last month, I got these Banana Safari Snacks, which went with their safari theme. And these are amazingly fruity, awesome-smelling treats that my dog goes gonzo for. So, when my dog, Eddie, decides he’s gonna sit right under my desk, chewing up his treat, I don’t mind – and I can go back on their website and order more.
I really love this chance to discover new things. They’re always finding new treats that are made in the USA or Canada and sending them out. And, in fact, Eddie’s coming in right now to beg for another Banana Safari Snack.
So, go online and do what Eddie’s glad that I do and get yourself a BarkBox. In fact, you’ll get an extra free month with your six- or twelve-month plan if you go to barkbox.com/astro. That’s an extra free month of BarkBox if you visit barkbox.com/astro and subscribe for a six- or twelve-month plan. I have the twelve-month plan. Thanks.
Fraser: Astronomy Cast Episode 443: Tsunamis
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know but how we know what we know.
My name is Fraser Cain. I’m the publisher of Universe Today and with me is Dr. Pamela Gay, the director of Technology and Citizen Science at the Astronomical Society of the Pacific and the director of CosmoQuest.
Hey, Pamela. How are you doin’?
Pamela: I’m doing well. And I have to congratulate you on getting my title completely right on the first try!
Fraser: You have a very impressive title – the longer the title, the sort of –
Pamela: More space it takes up on a grant application, irritating me later.
Fraser: Well, yeah – exactly. But no – I mean, you’ve earned every word of that title, Pamela.
Pamela: Thank you.
Fraser: Do you have anything to shamelessly self-promote this week or should we just get started?
Pamela: We are gearing up for Citizen Science Day in April. So, follow along at cosmoquest.org starting on Monday, as we begin our countdown to great new things that just might begin with the letter H or I, or both.
Fraser: I don’t know what it could be.
Pamela: Stay tuned on Monday.
Fraser: Alright.
One quick thing – I just did a collaboration video with Dr. Paul Matt Sutter; he’s one of the people from the Weekly Space Hangout and just, as you may know, Paul and I are going to be going to Iceland in February. Spaces are filling up pretty quick. I think there’s now, like, a pretty big list of people that are interested. You’ve got till August to put down your deposit and agree that you’re going to come with us. I think it’s going to be the trip of a lifetime, personally. I can’t wait to go. But, if this is a thing that you want to do, you should go to Astrotouring.com and you can find out more.
Alright, let’s get goin’.
Surf’s up! Today we’re going to be talking about one of the most devastating natural disasters out there: tsunamis. We’re talking huge waves that wreck the seashore. But it turns out, there are many ways you can get a tsunami, and one of those does have to do with space.
Alright, Pamela – what’s a tsunami?
Pamela: A tsunami is – well, directly translated from the Japanese – a “harbor wave”. It is a wave that is pretty much imperceptible out in the deep oceans but, as it approaches the shallows of a harbor, you suddenly end up with this giant wall of water that can be tens of meters high.
Fraser: Right. And, you know, it’s a Japanese word but these things happen all around the world. What is sort of the cause of a tsunami?
Pamela: The simplest way of putting it is: It’s a giant splash. It is a giant, seashore-destroying, horrendous splash.
Anytime you displace water, you create a wave. Drop a rock into the water, splash it with your hand, thump upwards the ground underneath the ocean or a pond or a lake; anything that compresses, moves, displaces the water is going to cause a wave and, if you do this just right, it causes a giant, destructive wave.
Fraser: But I think the thing that’s most fascinating about the tsunami is how far this wave can travel. Right? You can have an event on one continent and it generates tsunamis half a world away.
Pamela: So, we were almost late recording today because I went down a rabbit hole about exactly this.
Back in 1700, there was a massive Cascadia earthquake. They have actually figured out, it was exactly in January of 1700. And the way they figured this out was because the tsunami tied to this Cascadia – so, like, your part of –
Fraser: Yeah, that sounds like a really scary place to live. Who’d want to live there?
Pamela: Right, exactly. That was kind of my reaction.
So, there was this amazing tsunami in January of 1700 that caused a tsunami that had long-perplexed Japanese historians because, about 12 hours later, it hit and destroyed a 600-mile-long swath of the Japanese coast.
Fraser: Ooh.
Pamela: Yeah.
Fraser: Yeah.
So, that is – You know, we made the earthquake and then it made it all the way across the Pacific Ocean and smashed into Japan and caused devastation there, thousands and thousands of kilometers away.
Pamela: And the kinds of displacements of land that we’re talking about is – there were areas of forest along the northwest coastline that suddenly plummeted in height so much that they ended up submerged below sea level. And this caused massive pockets of what are now called “ghost forests” – these places where we can tell there was a forest there and then – seawater kills trees. And thanks to dendrology, the ability to use tree rings to figure out when things happened, it was realized all of these trees died in the winter between 1699’s end of summer and the beginning of spring in 1700. This was step one.
Step two was looking at the Japanese records – and they had excellent written records in Japan because they had a written language there – and records of the orphan earthquake there; put the pieces together and this is part of how we learned that Cascadia is a very unstable place.
Fraser: Should I move, maybe?
Pamela: Yes.
Fraser: Okay. No, it’s not gonna happen. We’re not due.
Pamela: You’re good for a couple hundred years.
Fraser: We’re not due, right? As we –
Pamela: Not yet. No, this is one of those fault lines that appears to build up pressure for about 500 years or so and then fire – release all that built-up pressure – and we’re only about 317 years in. You’re good, you’re good.
Fraser: Okay. Alright, good.
So, this is one source of a tsunami – a gigantic earthquake.
Pamela: Yes.
Fraser: What are some other sources of a tsunami?
Pamela: So, you have this giant, momentary, everything shakes; everything plummets or rises, kind of earthquakes. We had this in Cascadia; similar things have been seen at the end of the Minoan culture, happening in Crete, happening along the Chilean coast.
But then there’s another kind of earthquake event that is completely terrifying because you have a slow earthquake. This is an earthquake where you don’t get this massive, suddenly everything is rocking and rolling; you, instead, get a slower, lower-magnitude earthquake that, because of the way it gives off its energy slowly, it can cause a disproportionately massive tsunami – so, still earthquake-related but slightly different.
And it’s important to know: You can get tsunamis from massive earthquakes – this had been well-known for thousands of years – but realizing you can also get massive tsunamis from wussy earthquakes was a lesson learned the hard way, unfortunately, in Japan, when they – on a holiday – had a minor earthquake during celebrations. And, because it was a minor earthquake, because it was during celebrations, no one sought cover and this actually led to a lot of standing stones being built to record: Do not live below this standing stone.
Fraser: Wow.
So, that’s one form, was the earthquake – the super-violent, huge earthquakes – and also the sort of slower ones, as long as you’re getting water displaced.
Possibly, the most devastating ones are landslides.
Pamela: Yes.
Now, luckily, these don’t seem to occur quite so often. There have been a few examples up along the Norwegian coast, for instance, sending tsunamis roiling across to head towards the British Isles and do bad things there in Scotland and Ireland. But luckily, the landslides are less common.
So, we get issues tied to volcanoes as well, where it’s this mix of the volcano and the landslide, and it’s hard to decouple which was which. But, again, it’s basically a giant splash. You throw a rock – in this case, an entire coastline – into the ocean and out goes the wave.
Fraser: And some of the biggest tsunamis have been from these landslides. And I know there was one in Hawaii that, I think, pushed seashells, like, a thousand – I’m trying to think – like, hundreds of meters up onto another island; that, every now and then, huge chunks of Hawaii just shear off and splash the nearby islands.
Pamela: And this has to do with a combination of, again, volcanoes and also, just the slopes; this is completely new land. And any of you who’ve ever built a sand castle know that, if you have that angle of incline on the side of the sand castle too steep, as you add dirt, it’s just going to start rolling down.
Well, volcanoes kind of can have the same problem now and then. They’re excreting lava – for lack of a better phrase – and, as that lava builds up, you get these steep angles – if you have just the wrong viscosity – and things shear off.
Fraser: Folks in the chat are talking about the Canary Islands as well, as another situation where you’ve got this gigantic landslide that is inevitably going to shear off and just send a huge splash into the water nearby.
Okay. And then, let’s talk about the space source.
Pamela: Oh, yeah.
So, this is one of those things that we don’t actually have any written historic records of happening but, oh my goodness, we have amazing computer models. And a lot of these amazing computer models were inspired, you might say, by the asteroid, Apophis, which looked like it just might – but we now know, it’s probably not – looked like it just might make an impact into the Pacific Ocean.
And, when we ran these computer models, it turns out that when you impact the ocean, it’s sort of like throwing a giant rock into your swimming pool; but you take all the water in the column that’s the diameter of the rock, you remove it, push it sideways – all the way down to the bottom of the pool – except you’re doing that where our pool is the Pacific Ocean.
Fraser: Yeah.
Pamela: And then, not only do you have the displacement factor, but you also have the heat energy, the kinetic energy – all of this – that’s also getting added into the system. So, you have multiple causes for the water to get displaced, and displaced water has to go somewhere – some of it will crash back in but you know a whole lot of it will do things like – well, in the models we had for Apophis hitting – remove everything west of the Rockies.
Fraser: Right – a tsunami that would scour everything to the Rockies.
Pamela: Yes.
Fraser: Ooh!
Pamela: It’s glorious.
Fraser: You monster!
So, then – okay. So, let’s talk a bit about, then, you know – In our imagination, a tsunami is like this, you know – you look off to the horizon and you see this gigantic wave – like a big, breaking wave – and then it hits and surf’s up.
But that’s not what people who are on the ground experience when they have that. When the tsunami hits your area, what happens?
Pamela: It’s really terrifying, especially in fishing communities, because there is record after record after record of the Japanese fishing villages, the Indonesian fishing villages, the Mediterranean fishing villages – you have the fishermen/women going out to sea in their boats and nothing’s amiss. And they’re out, just out of sight of the shore, and they come back and there’s massive destruction. And a few people may be left up on high land, who describe one of two things: Either the wave comes absolutely out of nowhere, or there’s this amazing pulling back –
Fraser: Yeah, yeah.
Pamela: – of the water. And the horrifying thing I didn’t know, until I prepped for the show, is you don’t always get that pulling back of the water. And this is because when the tsunami is crated on one side of – it’s often a subduction zone earthquake. On one side of the subduction zone earthquake, you have the water going on the upside of the wave; and on the other side, you have the trough – the downside of the wave. And if that trough hits first, that’s when you get the pulling back of the water from the shore first; if you get hit from the crest side, you don’t see that.
And during the Indonesian earthquake that caused so much destruction back in 2004, we all remember the stories of – in Indonesia, where the water went away. And there was actually a whole lot of people that were saved by a little British girl, who had just learned about this in school and credits her geology teacher, where she saw what was happening and told her mom and dad and they told everyone around them – and everyone ran and they survived.
But, on the African coast, where they got hit by the crest side first, there was no withdrawing from the land and –
Fraser: Yeah.
Pamela: They just got the tsunami.
Fraser: And, once again, right – sort of in our mind and imagination – it’s the big cresting wave. But it is, you know, much more like someone just kind of took the ocean, tilted the whole thing sideways and then just – the ocean just sloshes into the land; like, the water level just comes up and up and up and up and up and up, and it just pushes through the city, knocks over trees. It’s not what you would expect but it is as devastating as you can imagine.
Pamela: And it’s this combination of – you have a massive wave length that can be kilometers wide. And, as it approaches shore, it gets compressed and everything in that wave, as it gets compressed, the amplitude goes up and up and up. And so, what appears to be just maybe a meter increase – but then spread out, over a vast distance – we don’t notice that at sea. If you go up a meter or so, for a long period of time, who’s going to notice that – except with GPS sensors.
But you take all of that water and you compress it. And it’s that “taking that one meter higher” out at sea and “taking one meter higher spread over a vast distance” out at sea and making it – all of that one-meter higher – becoming, instead, 100 meters higher over a shorter distance – not really 100 meters. We don’t really see that but we do see 20 meters, 30 meters higher.
Fraser: Right. But the point being that you don’t see that big, breaking, cresting wave; it’s that just the water comes in and it just goes higher and higher and higher – and fishing boats are plopped inland and –
The best example of this is after the Japanese earthquake – the one that –
Pamela: 2011 Japanese earthquake.
Fraser: Yeah, the one that we just had. There were a lot of cameras that were watching it and so we got a chance to really see, from sort of a bird’s-eye view and various views from on the ground, just how the water level just kept coming up and up and up. Like, it was like – how do I? Like someone had poured water over the top of a bathtub, you know? And then the water was just coming in and coming in.
So, for those of us who, perhaps, live in parts of the world which are at risk for tsunami, what should we be aware of? What should we do? How in-terror-for-our-very-mortality should we be?
Pamela: Well, first of all, it’s important to realize it’s not just an ocean problem. And this is, again, something new I got to learn, prepping for the show – which is part of why I love doing the shows: I learn new things.
There are actually weather-caused tsunamis that can happen with the Great Lakes, with Lake Geneva and other large bodies of water. This is where we have the atmospheric pressure will compress a large area of the water and it’s sort of like taking a big basin and just pushing down; it displaces the water and can cause its own kind of tsunamis. So, if you are near any fairly significant body of water, you, too, may experience a tsunami. And what you should know is: What is your fastest route to get to higher land?
Now you, unfortunately, are on an island and, if the Cascadia fault goes – there is, in the historic record, like, everyone on the island died. So, have a helicopter handy?
Fraser: Okay. I can go to higher ground. I got lots of higher ground all around me – no problem.
Pamela: So, knowing to go to higher ground is important.
And one interesting thing to know about earthquakes is the longer they last, the higher the overall magnitude. If you have an earthquake that’s over four minutes long – which is what they had in Japan, back in 2011 – you’re looking at a Magnitude 9. Magnitude 9 is “everyone dies now” – at least in the tsunami zone, where it’s going to hit.
So, if you have a subduction zone near you – so, we’re looking off the coast of Chile, off the coast of the American Northwest; there’s one, clearly, off the coast of Japan, down in Indonesia area – if you’re near a subduction zone, these are the ones that are most at risk of causing tsunamis because of how the fault lines slip. It’s basically like taking a sheet, raising the edge and just creating a wave – which many of us have done to smooth our sheets – except you’re doing it with the ocean. And this kind of sudden displacement, up and outwards, that can occur with this kind of a fault slip, tends to cause tsunamis more than the San Andreas fault, for instance – which is slip fault, side/side.
Fraser: Right.
Pamela: So, know your kind of fault line; pay attention to the weather; pay attention to rocks falling out of the sky; make sure you don’t have anything that’s going to have a massive landslide near you – we’re looking at you, Scandinavia, you’re the cause – know your geology. And those of us living in the great flat fly-over states can rejoice. We’re some of the only ones that aren’t going to be affected by this.
Fraser: Oh, wait. Wait – what’s that sound? Is that your tornado alarm going off again?
Pamela: Yeah, I know – we get tornados instead. It’s a tradeoff.
Fraser: Yeah.
Pamela: It’s a tradeoff.
Fraser: But so, you know, as a person who does live in a tsunami zone, you are made aware of it; that, you know – we drive out on the west coast of Vancouver Island and there are tsunami regions where it’s very low-lying, it’s right on the Pacific Ocean and the sign says when you are going in to the region and the sign tells you when you’re coming back out again. And just – And part of your brain is this thought, like, “Okay, when I hear the tsunami” – and there are alarms on the beach in the whole area and their only job is to sound off when the tsunami happens. And then you, in theory, hop in your car and head for high ground.
And we get a warning – tsunami warnings. I would say we get them every five years or so. That we get a warning, you know – and it’s always like, “There’s one in Chile.” You know, we got a tsunami warning during the Boxing Day one that happened over in Indonesia, right – and the Japanese one too. So – because those waves can cross.
Now, they’re not going to be as devastating as they are right next to it but, even halfway across the planet, you have to be careful. And there was one in Alaska that caused a tsunami to come right up one of the fiords on Vancouver Island and took out the city of Port Alberni back in the 1950s – super-devastating. Because it sort of concentrated the waves that came up this channel and just wiped this city off the map on Vancouver Island. So, we’re made well-aware of it.
And the same thing, if you ever have driven down the west coast of the United States; there’s these low-lying areas in California and Oregon, where – there’s the sign and then you’re – It’s very unnerving to be driving in this region where you know that, should the tsunami happen, you’ve got to quickly book it to higher ground. It’s a very interesting experience. So, just for anyone who doesn’t live in that, you are made aware.
And I guess where I want to take this conversation next was just about warning systems; about how this is one of those natural disasters that, now, we have identified and we do learn and we’re able to kind of prepare a bit when one of these happens.
Pamela: So, it used to be that the Japanese, for instance, carved rocks to leave warnings because it was recognized that, within about three generations, memories of these devastating events would start to fade. Parents would tell their children; parents would become grandparents – tell their grandchildren. And then the memories would be lost and people would start building things where they shouldn’t.
So, you see in Japan, these literal standing stones, where there is one that says, “Do not build below this point.” And there are many that are commemorating the places that survived and the places that didn’t. There are villages that have names that translate to things like “Octopus Place” because that’s where the octopuses were after the tsunami brought the octopuses into land.
Fraser: Right.
Pamela: So, knowing the history and realizing that these things happen in this every-several-generations kind of iterative pattern is important. Knowing, where I am now, do I need to worry? Knowing, is there a set of buoys that is going to be measuring between me and the other places that have these problems?
After the 2004 Indonesian earthquake, it was fully recognized that our tsunami preparedness, globally, was not what it needed to be. There was not a sufficient set of buoys deployed in the ocean that allow us to monitor – thanks to the Global Positioning System – the subtle rises and sinking, the crests and the troughs, that indicate there is displacement of the water; there is something we need to be aware of and prepare people to evacuate.
There is an amazing Pacific tsunami warning system – they have a great website you can monitor what all of the buoys are doing. But the question is: Is it enough? Do we have enough of these buoys? Do we have enough sirens? Do we have a way to let people know?
Japan has, perhaps, the most advanced system in the world because they are an island nation that has an entire history of dealing with this. And they’ve reached the point where they can give amazing warnings because information travels at the speed of light and earthquakes don’t.
Fraser: Right.
Pamela: So, once the earthquake starts to be detected in one place, they lock down the public transportation systems, they set off sirens to get people to hide under their desks and doorways, evacuate buildings that need to be evacuated; they send out helicopters to follow what’s happening in the oceans.
Fraser: Yeah.
Pamela: The rest of the globe isn’t so ready and we never know. We’re a world of subduction zones, earthquakes and landslides waiting to happen.
Fraser: I mean, with the modern age with mobile phones – I mean, I don’t know about you. Does your mobile phone freak out when there’s twisters in the area?
Pamela: Oh, yes.
Fraser: Yeah.
Pamela: Oh, yes.
Fraser: Yeah. And, you know, I’ve been traveling in the states for – Like, I was in Las Vegas and there was a flood warning and my phone bee-booped at me. So, I think that the level of communication now, in theory, if there was a tsunami coming our way – that all of our phones would all go off and everybody would be seeking higher ground. And anyone who didn’t have a phone would have enough people around them with phones that they would be able to –
But, as you said, it’s the people who are in places where maybe they don’t have the detection system, they don’t have the monitoring to know that there’s a tsunami inbound. So, the more –
Pamela: And we have to be careful of how vulnerable is our infrastructure.
Several years ago, as you may remember, my husband and I accidentally drove through a tornado. I don’t recommend this. We didn’t mean to. It came out of the sky, directly in front of our Jeep. We had nowhere to go.
But the reason we were out driving in tornados is because the first thing the tornados destroyed was the building with the emergency alert system in it.
Fraser: Right.
Pamela: So, instead of getting the text message –
Fraser: They’re drawn to them, yeah.
Pamela: Yeah! So, I didn’t get the text message warning I would normally have received. And thus, stupidity occurred.
Fraser: That’s amazing.
Alright. Well, thanks Pamela. I don’t know if our series will continue. I got a bunch more topic ideas I want to pitch at you, so –
Pamela: And we will be during fractals for Episode 444 next week.
Fraser: Well, there ya go, then. I think destruction and rebuilding is at an end.
Pamela: It’s been a pleasure.
Fraser: And then we’ll start again on why Pluto isn’t a planet again.
Pamela: Okay, that sounds great.
Fraser: Alright. Thanks, Pamela.
Pamela: Okay. Bye-bye.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
We record the show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern or 2030 GMT. If you missed the live event, you can always catch up over at cosmoquest.org or our YouTube page. To subscribe to the show, point your podcatching software at astronomycast.com/podcast.xml, or subscribe directly from iTunes. Our music is provided by Travis Serl and the show was edited by Chad Weber.
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[End of Audio]
Duration: 31 minutes

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