2013 Scientific Forum: understanding storm surges, tsunamis and sea-level rise


We’re going to be discussing some specific roles for nuclear science in management of the marine environment. The emphasis is going to be on how nuclear and isotopic techniques are improving global understanding of coastal processes. Thank you, and I’d like to thank the IAEA for giving me the opportunity to talk about the application of nuclear techniques to the study of storm surges, tsunami, and you can use it also for sea level rise. On 11 March 2011, a tsunami generated by the magnitude nine earthquake on the Japan Trench struck Japan. It’s called the Tohoku-Oki tsunami. It affected nearly 2000 kilometres of coast in Japan, and inundated up to five or six kilometres inland. The death toll was nearly 19,000 people – 16,000 dead and with 3,000 missing. The estimated cost was US$ 300 billion. In some areas like here on the Sendai Plain the land subsided or dropped down because of the earthquake. Up to about one metre, and so it made the tsunami worse because the water was much higher and it could go even further inland. If you look at the
tsunami coupled with land subsidence, it actually mimics the effect of very rapid sea level rise on the shoreline. This photo here is actually very relevant to my work, because it shows that’s where we worked. We worked along a transit from the shoreline, past the runway you see on the right-hand side you have the runway of the Sendai airport, and we went in over four kilometres inland. The tsunami deposited a deposit, and the deposit was not very thick. Actually, it ranged in thickness from about 30 centimetres near the coast, on the left, to about one or two millimetres
about five kilometres inland. The deposit was first just sand, then further inland it was sand-dominated with some mud and further inland it was just mud-dominated. The limit of the recognisable sand deposit, which is like five millimetres, was 2.8 kilometres inland. Now, because it’s very easy to see in a sedimentary record, it’s what geologists have been using to determine or estimate the magnitude of the tsunami and the generating earthquakes. Whereas you can see here, the sand stopped about 2.8 kilometres inland. The tsunami went another almost two kilometres. So using the extent of sand results in the magnitude of the tsunami and the earthquakes being underestimated. Now you’re going to tell me, how are you going
to recognise this mud deposited by the tsunami from the mud it’s deposited in, the terrestrial mud. There, you hardly have any marine microfossils, sometimes you find them but there there were none. Now you know a tsunami comes from the sea, and it left lots of salt behind. So I didn’t bring a salt shaker because you know what salt looks like, and all these white stains there, they’re just salt crusts over top of the mud, two months after the event, about three kilometres inland. And this graph here shows you the concentration
of chlorine, which is a component of salt, from the shore to about five kilometres inland,
and the darker area in the middle between about 1.5 and 3.5 kilometres inland is where
there were most of the salt was deposited. So you can use chemical fingerprinting to identify this mud that was deposited by the tsunami. Now, on the right-hand side, there, I’ll draw a line between two points, you can hardly see but one has a higher concentration than the other. That’s the site, here in May and towards you is the land and you go towards the sea in the background. See the land has been ploughed, there’s no debris, no evidence the tsunami has ever been there. Except for the chemical signature. There was more salt on the right than on the left, and there’s a little ditch in the middle. That’s as far as the tsunami went. And it fits the extent that had been mapped by the researchers that came just after the tsunami and went and mapped the extent of the tsunami using debris and watermarks. So here’s the limit of the tsunami. As you can see, the sand went 60%, the mud went about 95% of the inundation. You can use chemical fingerprinting to identify the true extent of the tsunami inundation, and you can also use it to redraw post tsunami inundation maps. It’s valid for Japan, it’s valid for anywhere else in the world. Now you’re going to tell me, why is it important? Why do we do that? We always ask the question, how big, how often? We know that Japan has been affected by a tsunami in the past. Here there’s a trench that was recently dug in Iwanuma, near Sendai. You can see a number of layers. Of course I show you here sand into salt, because if I showed you a photo of mud into mud it’s not very photogenic, it’s black and black and black. So I am showing you that example. And you see, sand layers between and salt in between. At the top you have the Tohoku-Oki tsunami, then here is probably the 1611 Keicho, here we have the here we have the 869 Jogan. And we have the Towada-a tephra here. That’s the late, late yellow layer. Now what we do, we can use nuclear technique like AMS who has a half life of 5,730 years to look at the timing of this event, these very old events. More recent events you can use lead 210, it has a half life of 22.3 years. I know lead 210 is better for up to 100, 150
years, it was just an example, here. In Japan, in the northern part, it’d be event in the
last hundred years, so you can use lead 210. Now in Japan it’s a very long historical record, so you can actually use this to test our nuclear techniques. Now, in Australia, where I live, the historical record is very short. Just 200 years. So we have to rely on these nuclear techniques to go back in time. In Australia, we’re also lucky, we don’t get affected by
that many tsunamis. There are some on the north-west side coast, they’re the tsunamis
generated by the Indian Ocean, and there’s a few others, but we don’t get affected by
many large tsunamis. What we get affected by are cyclones, and here is tropical cyclone Yasi in February 2011, this was a category five cyclone which is the highest category
for cyclones. Now the coast in north-east Queensland is not as densely populated, but it caused lots of damage and the estimated cost was US$3.6 billion. This photo here shows you gravel and sand that had been picked up by the storm surge at the time of the cyclone from the beach at the nearest shore, and dumped on the top of the beach ridge. So again the question arises, how big, how often? Now with climate change, events are likely to be, maybe not more intense but we are likely to have more So the more we know, better it is. So what we did, we dug a hole through that beach ridge because that’s what we do as geologists, we dig holes and you can see you’ve got sand layers, separated by salt layers. The top one here is Tropical Cyclone Yasi from 2011, and below we have Tropical Cyclone Larry 2006, and we’ve got eye-witness records of these
events, people told us they happened, they know how far they went. Below, we have Tropical Cyclone Winifred from 1986, below we have the Innisfail tropical cyclone of 1918. So
for these, we need to use nuclear techniques so we can go back in time, so we can understand better the timing and the frequency of these events and what the impact was on the shoreline,and how the shoreline or the coastline responded to these events. In a coastline which is sedimentary rich, you’ve got a formation of beach ridges and the record is preserved so you can study it, and here for example this beach ridge is probably the one in the middle, the five to eight. So you can study this event, you can go back in time, and this work is fairly urgent because we need it to be able to improve our management strategies. The government needs this information and so do the insurance industries. Thank you very much.

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