VIDEO DESCRIPTION:
When you talk to people about tsunamis or read about them or watch videos about them, you come across a lot of numbers referring to how high the tsunamis were. But what do those numbers really mean? Despite the large amount of actual tsunami video available online, do we cling to Hollywood images that aren’t true?
VIDEO TRANSCRIPT:
Good morning and welcome back to Planet Doug. And this morning I want to talk about tsunamis. And that’s a natural topic considering where I am right now. I’m in the city of Banda Aceh at the northern tip of Sumatra in Indonesia. And yesterday, December 26th, was the 21-year anniversary of the Boxing Day tsunami in the Indian Ocean that hit Banda Aceh and so many other places with such destructive force and loss of life. And to understand why that would happen, you need to know what a tsunami is. What makes it so destructive and so deadly? I had the question myself when I came here and I visited the tsunami museum. I visited the PLTD Apung 1 museum and I’ve watched countless videos on YouTube, documentaries about the tsunami, scientific videos explaining tsunamis, what drives them, how do they work? And I’ve got all this information rolling around in my head and I just wanted to share it with people out there this morning as I enjoy a good cup of coffee here at my favorite coffee shop. And I’ve come up with a bit of a thought experiment that anyone can do or a real experiment in real life if you have a bathtub. And imagine you’re in a bathtub. You’re immersed in the water. Take your hand and if you put it all the way down to the bottom of the tub and then raise it up quickly and then back down again. What happens when you do that is this wide column of water gets displaced, rises up above the surface, and then gravity pulls it back down and then a force spreads out to the sides of the tub. And that is kind of a rough analogy for a tsunami. Now, while you’re in the tub now, just sort of lower your head down until your mouth is level with the water and start blowing. Just blow across the surface of the water, and you’ll create all these little ripples that flow out over the water. And that is a rough analogy for a normal wave. A normal wave is created by wind and the wind blows along the surface of the water and disturbs just that top surface layer of water and creates these waves, little ripples that are just flowing out. That is a natural wind-driven wave. That’s what you see at the shore. You go down to the beach and you see waves coming in, they crash. Another wave is a few seconds behind it, comes in, crashes. Those are created by wind. The wave that you created in the bathtub by raising your hand from the bottom, that is more like a tsunami because tsunamis are driven by huge events deep in the ocean at the bottom of the ocean floor like an earthquake. And an earthquake raises the bottom of the ocean floor, just lifts it up. And a massive column of water from the very bottom of the ocean all the way to the surface is raised up. Again, gravity takes over at that point, pulls it back down, and then a phenomenally strong force flows out from that point, and that is a tsunami. So, I want you to keep that image in mind and I’m going to come back to it a little bit later and talk about why that difference is so significant in understanding what a tsunami is. And once you understand what a tsunami is, you can better prepare for it.
Now, let’s switch mental gears for a moment. Just think about your mental image of a tsunami and where did it come from? If you ask people this question, most people in their mind, they’re going to picture this huge wave, a towering wall of water heading towards the shore and destroying everything in its path. And that image, it’s kind of a common sense image in a way because we’ve all seen waves at the beach. And if somebody tells us that a tsunami is a big wave, well, we take that little wave and we just make it bigger. And that’s what we picture in our mind as a tsunami. And over decades and decades, Hollywood has reinforced that image with tsunamis. Think of any disaster movie you’ve ever seen that featured a tsunami. And there are a lot of them. The tsunami is always this massive wall of water, a giant wave towering as large as buildings and then hitting the shoreline. That is our mental image of a tsunami.
But now I want you to stop for a minute and think back over all of the real life footage you may have seen. There’s a lot of it available on YouTube. There was the tsunami in Japan in 2011 for example. There is probably hundreds of hours of footage, actual real life footage of that tsunami hitting so many parts of the coast of Japan. There isn’t as much video of the tsunami in 2004 here in Banda Aceh. There is enough that you can go on YouTube, look at tsunami documentaries, stories, scientific videos about the Boxing Day tsunami. There is enough footage from Banda Aceh and Sumatra in general where you can see an actual tsunami, what it looks like and what it does. So you see quite often you see the ocean water recede. Of course that’s a classic sign of a tsunami that everybody is aware of now, the ocean water receding, the ocean floor and reefs being uncovered and then the water comes back in and then the water is surging inland, reaches the shore. They quite often have tsunami barriers like in Japan where they’ve had a history of these. Many communities, harbor areas have built seawalls to prevent tsunamis from causing damage. And you see that water surging in. It reaches the wall and then the water just rises and rises and then it flows over the top of the wall and then flows into the city. There is some classic footage from Japan. I’ve watched all the video I can find from the 2011 tsunami in Japan. I was aware of it when it happened and I lost days if not weeks of my life at that time glued to the internet, glued to YouTube watching as much live footage of that event as I could. And there’s one very classic image I remember so clearly where a helicopter was filming the tsunami as it spread over this flat agricultural area of Japan. And you see its destructive power. It’s wiping out everything in its path. It’s some of the most astonishing video I’ve ever seen. So if you’ve seen all of that footage, you know what I’m talking about. If you haven’t, stop watching this video, pause it, go on to YouTube, just type in tsunami, watch one or two of the short science videos, watch some of the real footage from Banda Aceh, from Japan, from other places. Now, watch all of that video. What’s missing? Think about it. All that video that you’re watching, what don’t you see? What you don’t see is that Hollywood tsunami. In none of the footage do we ever see a massive towering wave higher than buildings 100 ft high going inland. You don’t actually see that in any of the real life footage of tsunamis.
Interestingly, even the tsunami here in Banda Aceh has been affected by this Hollywood image. In fact, there are two classic numbers that you will hear over and over again whenever anybody is talking about the tsunami that hit Sumatra back in 2004. The first number is 30 m. Again, you can go look for yourself. Go online, look for newspaper articles, magazine articles, watch videos, documentaries, scientific. Almost every one of those videos will open with a statement about how powerful, how destructive the tsunami was here in Banda Aceh. And they will say the wave, the tsunami was 30 meters high when it hit the shore. At the shore, it was 30 meters high. That’s 100 ft high. Again, picture that mentally. We’re talking about the equivalent of a 10-story building. A 10-story building wall of water coming to shore. And these videos and documentaries will also mention that tsunamis are unbelievably fast. They’ll say that these tsunamis move at the speed of a jetliner from 500 to 800 km an hour. Most of the videos open with those two facts that the tsunami is moving through the ocean at the speed of a jetliner going 500 km an hour and then a 30-meter 100 ft wave hits the shore. That is what people say happened and that’s what everybody pictures in their mind. But I’ve been around destructive water. I’ve seen it for myself. I’ve talked about it a lot in my other videos that I was in Tacloban in the Philippines when a storm surge, that storm surge was very similar to a tsunami in most respects. I’ve seen what that amount of water, I’ve seen how destructive water can be and you don’t even need to have that personal experience. I think common sense will tell you that if there is a 100 ft a 30-meter-tall wall of water and especially moving at 500 km an hour if that hit Banda Aceh we’re talking about a very different situation. There would be no buildings left standing. You couldn’t talk about what buildings survived and what didn’t. Everything would be gone. You couldn’t talk about who survived, who died, how many victims there were, how many survivors there were. There would be no survivors. A wave 100 ft high hitting Banda Aceh at any speed would wipe out the entire city, kill everyone. It would scour the earth down to bedrock. It would be that powerful. So my own experience and common sense tells you that the wave, the tsunami that hit Banda Aceh could not have been 30 meters high at the shore.
But if that’s true, where did this number come from? And that for me is the most fascinating thing about this story and what I’ve learned about tsunamis. That number that everyone associates with the tsunami in Banda Aceh, 30 m, it is a real number. It’s not wrong. It’s an accurate actual number used to describe this tsunami. The problem is it got mismatched. It doesn’t mean what everybody thinks it means. So, not to get too technical or get too lost in the science or vocabulary of tsunamis, but that 30-meter figure is not how high the wave was. It doesn’t refer to how deep the water is. What that means is 30 meters is the highest point on land above sea level that the water reached. So imagine what we already saw in the videos. We saw in the Japan videos, the Banda Aceh videos, we see this surge of water moving across the land. And in the videos, it’s clearly not 30 meters high. But we can see how destructive even 2 meters of water is moving across the land. But it definitely isn’t 30 meters high. You can see that for yourself in the videos. And what’s going on here? We can go back to our thought experiment in the bathtub where you lifted your hand up to simulate the ocean floor lifting during an earthquake, raising this massive column of water and then gravity pulls it back down and then the tsunami is a force going out from that point heading towards shore. And what you have to realize there is that we are talking about the entire depth of the ocean. The regular wave created by the wind blowing across the surface. It’s only affecting that little bit of water at the top. But a tsunami moving through the ocean is the entire depth of the ocean from the bottom all the way to the surface. And it’s extremely wide. That is another key difference. When you blew across the water, you created all these little ripples and they’re all very very close together. So here’s the trough of one wave and then the trough of another and another and another. You can think of that as the wavelength and it’s very very short. When you go down to the beach, a wave crashes, another one is right behind it. 10 seconds later another wave crashes. It’s got a very short wavelength. A tsunami created by this massive column of water can be 100 km wide. It can have a wavelength of 200 km. So that force is moving through the ocean at 500 km an hour up to 800 km an hour. But when it reaches shore, it slows down dramatically as the depth of the ocean decreases. So out in the open ocean, it’s the entire depth of the ocean that’s being affected by the tsunami. When it gets close to shore, and as I said, that tsunami can be 100 kilometers wide. And then it moves towards shore. The front of the tsunami starts to slow down as the ocean becomes more and more shallow as you approach the shore. And then as the front of the tsunami slows down, the water starts to pile up. Meanwhile, you’ve got 100 km of tsunami behind it pushing forward. So what you end up with is a tidal wave. And that’s the key thing about tsunamis. It’s not how high they are. That’s not the destructive factor. It’s the fact that they move inland at speed wiping out everything in front of them. And this massive wavelength of a tsunami 100 or 200 km wide is pushing and pushing and pushing. And that tidal wave, the tsunami just keeps going inland, inland, inland. And that was particularly destructive here in Banda Aceh because most people don’t realize this until you come here. You don’t see it. Banda Aceh is flat. It sits on a flat flood plain. So if this is Banda Aceh and then the tsunami is moving moving moving inland for kilometers 1 kilometer 2 kilometers and the huge tsunami out in the ocean is still coming in still pushing it inland inland inland and it might be 2 meters deep as it’s flowing across the land then it reaches a hillside right so pay attention here this is the key point the water that’s 2 meters deep hits this slope. It starts to go up the slope being pushed from behind and it reaches 30 meters above sea level. That’s where the number comes from. The water flows up the hillside until it reaches 30 meters above sea level. Then it stops at that point and begins to recede. The important thing is the wave at the shore, it wasn’t 30 meters high. The water at this point isn’t 30 meters deep. At no point in the land is the water ever 30 meters deep. What they’re saying is the water reached a maximum altitude of 30 meters above sea level. And at the point where you reach 30 m, the water there could be half a meter deep. It could be 1 meter deep. It could be just ankle deep. That’s irrelevant because run-up is altitude above sea level. And there are places along the coast like not in Banda Aceh itself where because of the geography where you might have like the hills are closer to the shore and there’s a valley and then the power of the tsunami gets funneled into the valley and it gets concentrated and there on the coast you get a run-up of up to 50 m. So that is where those numbers are coming from. It’s the maximum point that the water reached expressed as a height above sea level. It’s not wave depth, not wave height. It’s not water depth. Those have other scientific terms applied to them that I’m not going to talk about. So this 30-meters figure is the tsunami run-up. So that number is real. It’s accurate. It refers to something real in tsunami science. But then that number came off all the scientific papers, all of the studies, all of the public statements coming from tsunami experts. They talked about 30 meters as the run-up and then that number just went out into the world and people started saying that a 30-meter tsunami hit Banda Aceh. You see that in one article, somebody quotes that article, someone writes another article. And when you’re doing your research, every single article, every movie, every documentary, every scientific video will say the same thing that the tsunami that hit Banda Aceh was 30 meters high. It’s just been repeated over and over and over again so many times that nobody questions it anymore. But as I said, that 30-meters figure is the tsunami run-up. It’s got nothing to do with the height of the wave and it’s got nothing to do with the depth of the water. It’s just a point a highest high point where the water reached above sea level. So, I hope that was a little bit clear. I guess the key takeaway that I want people to have from this video is that if you watch a tsunami video, think about the numbers critically. Even if you go to the museums here in Banda Aceh because you want to learn about the tsunami and you start seeing that number everywhere, 30 m, 30 m, 30 m. It’s important to understand what that number really means and where it came from and how over time it’s become dramatically misunderstood.
I want to close this video with one important point. It’s that by talking about this, understanding the true nature of a tsunami and that 30 meters figure in particular and how it’s misunderstood. By coming to grips with that information, you’re not minimizing the disaster in any way and you are not minimizing the power of a tsunami. You’re just expressing it in the correct terms. And the key point here is if you think a tsunami is 30 meters high and you are preparing people for that, educating them how to deal with that, you’re preparing them for the wrong thing. So if you’re educating people about tsunamis, about how to prepare for one, how to survive them, how to get your own family ready in case of another tsunami. You don’t want to prepare them for the wrong thing. Don’t prepare them for the Hollywood tsunami. Prepare them for the real tsunami as it is in real life. That force of water, that tidal wave surging across the land. And the danger comes from not how high it is, but how unstoppable it is, how far it goes inland. And as I said, I’ve had some personal experience with this and I know how destructive water can be. And a tidal surge flowing across land 2 meters deep, 3 meters deep, that is going to wipe out almost everything in its path. That is dangerous enough. And that’s what you have to prepare for. That’s what you have to understand. Don’t prepare for the Hollywood tsunami because they don’t really exist. Prepare for the real tsunami as it exists in real life.