How the Japan tsunami changed science: Catastrophic Science

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Welcome to Catastrophic Science, the new series that uncovers cutting-edge research that has resulted from catastrophes. The 2011 Japanese tsunami caused mass devastation and destruction. Surprisingly it also uncovered
some new science, which was alarming but has the potential to save thousands of lives in the future. And it all came down to this. So James, how has soil sampling turned traditional tsunami research on its head? Well look, let me explain. First of all here’s the coast and here’s the sea and the tsunami comes in, inundates the land like this and it brings a lot of sand with it. So traditionally we would look underneath the soil, dig some holes and we would say, OK, here’s the
sand deposited by the tsunami and it comes let’s say this far inland, and that’s great. The problem is that with the 2011 Japan tsunami, we realized that it didn’t just bring sand, it brings everything with it as well, so there’s the sand and there’s the mud and there’s the salt water as well. This is where the sand goes, about 60% of the way, and then we take the mud and the mud goes another huge
distance inland and then just saltwater here as well. So you’ve got literally all of this, about 2km of land where the people simply didn’t expect to be inundated. So what you’re saying is that we’ve drastically underestimated how far tsunamis travel inland. We have and it’s my science colleague and wife Catherine who’s done this by studying geo-chemistry. So Catherine, can you explain how the geochemistry works? Yeah sure, look at these 2 samples here that’s soil taken about 4.5km inland, looks about the same, taken 2 metres apart. This one here has 100 times more salt than this one and they actually match the extent of the tsunami. There’s a ditch in between, the tsunami just stopped there. And it’s what the witness accounts said. And when I went there 2 months after the event, there was just soil, no debris, but the geochemistry told me what it was. 2 metres difference but 100 times more salt. That’s right. So James, what do we have over here? Well this kind of puts what Catherine said in context a little bit. Here we have 4 cores, that go from the seaward end to the landward end and this is the 2011 tsunami deposit here. And as it goes further inland it gets much smaller, in fact here we are, a bit further inland, a little sand layer, and here we have mud and some re-worked soil and here we have some mud as well. Now you can’t see that, but we know it’s there because of Catherine’s geochemistry work. So, we look then back to the previous event and this is really important because that previous event was used to kind of gauge how big and how bad these tsunamis were going to be. And first of all you can see this big splodge here, that’s actually a volcanic ash that was put down a few years after the event. Here’s the event we’re talking about. This is the A.D. 869 Jogan Tsunami, and there’s a nice sand layer here, go further inland, that sand layer is a little thinner but it’s still there, you go further inland, it’s gone. Just like the 2011, it’s gone. But we know it is there because of Catherine’s geochemical work. And that’s really important because it means now we’ve gone beyond that sand layer that I talked about. But we can’t see this, so how are we measuring this? That’s where you use the ITRAX. Now before, we used to…by conventional techniques, you need to take a sample, you can take that one because you see it. The ITRAX is a high-resolution scanner, and then you get a signal, a chemical signature and you say here it is. People used to say “ what, salt, so what? We know there’s salt.” But they just looked at the sand and one thing I found is that by using the ITRAX I could discover layers that
were invisible. I made the invisible visible. The tsunami therefore is much bigger, we’ve traced it further inland beyond the sand, which is what I was talking about earlier, and that means that the thing that generated it, the actual earthquake that generated it, is bigger as well. What is this going to actually contribute to the field? It will save lives. This event in 2011, Japan was prepared for it, they are the best prepared country in the world and 18,500 people or so died as a result of that event. The reason why they died is this event was much bigger than they thought it was going to be because they didn’t understand how big the previous event was and what the geochemistry is essentially saying is “we knew it was bigger, we just didn’t actually look at it before the event happened.” We now know that these things were bigger and we can look back further in time and find out how big earlier events were and we get a much better understanding of the hazards that Japan is exposed to but equally any other country that is exposed to tsunamis around
the world. It’s pushing the envelope, getting people into things that they are not comfortable with. But that’s how science progresses,
you know we keep on moving and trying new things and this is really, really exciting.

8 COMMENTS

  1. Could you have Matt try to act a little less…awkward? Perhaps read his lines more naturally? His reading during the interviews just sounds blatantly scripted when it's so obviously trying to be more of a natural presentation. Maybe it's his acting, maybe it's just the dialogue he was given, but it lacks the kind of realistic back-and-forth an actual conversation would have. I realize that's a rather asinine comment considering Matt's a PhD student and I'm just some shmuck on the internet, but I know what what sounds good! 

    Other than that, this was fascinating! Thanks for publishing it.

  2. It'll be interesting to see what Aussie sample cores turn up. We've got a short written history to rely on, so it would be good to see what the science can show for coastal areas for a 1100+ year timespan. How prevalent are large tsunami's? How far inland have they gotten? Should I buy a unit on the Gold Coast? That sort of stuff.

  3. It may also be worthwhile correlating Australian core sample data with other known large tsunami events in the region. How many affected Australia as dangerous tsunamis, and how far inland did they actually get? Are there any exclusively Aussie tsunamis/earthquake events that don't show up in other region's core sample data? The gains in tsunami modelling and risk mitigation could be massive if a large enough data set from here and abroad could be studied.
    Other questions could be posed. Can AAustralian Aboriginal oral traditions of flooding or tsunamis be placed with any historical accuracy? Or even just a base prediction of the effects of certain tsunami events may have had on an area, that we have core data for, but no oral tradition relating to it.
    I'm sure councils and governments would love a 1100+ year tsunami effects map showing the proper effects of inland inundation from these disaster events, both here and overseas, and would be willing to fund it. Hopefully.

  4. As a simple starting point, could the effects of the explosion of Krakatoa on various regions and the actual tsunami inundation be determined with these scientific methods? Nice, historical, but affected large areas, some of which were very sparsely populated (in Australia especially), so little record of its maximum effect is known.

  5. Hey I really like your work and the videos you've been making, care to give me some pointers? Thanks! – Jordan

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