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.