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Science & Environment

The Science Behind The Indonesia Tsunami


We're going to spend a few minutes now trying to understand the natural disaster, a tsunami, that struck Indonesia overnight. It hit between Java and Sumatra, the two most-populous islands in the country. At least 200 people are reported dead, and hundreds more are missing or injured. According to Indonesian officials, the tsunami was triggered by underwater landslides caused by volcanic activity. Here to tell us and explain how this all unfolded is Stephen Johnston, head of the Earth and Atmospheric Science department at the University of Alberta. Professor Johnson, thanks so much for talking to us.

STEPHEN JOHNSTON: Very nice to be talking to you.

MARTIN: Now, I understand that this tsunami was triggered by volcanic activity on the island of Anak Krakatau. Could you just walk us through how this happened?

JOHNSTON: So that's the idea. We don't know for sure. But Anak Krakatau is the offspring of the famous Krakatoa volcano that erupted, I think, 1883. So this volcano has been building up steadily since then and cracked sea level a few decades ago and has continued to grow. And as you build up an edifice, just like you build up a sandcastle or anything like that, there's a chance that you'll end up with collapses. And oftentimes with volcanoes, as magma injects into them, the sides become over steepened. And they are prone to collapse.

MARTIN: So, you know, I think a lot of people will remember the massive 2004 tsunami that killed more than 200,000 people across Asia. I understand that that was triggered by an earthquake. And I think that tsunamis are usually triggered by earthquakes. How is this different?

JOHNSTON: Yeah. Well, this would have been the real shock for the people along the coastline that got inundated by this tsunami because there was no quake. And so suddenly, a wall of water appears out of nowhere with no warning at all. You probably had maybe a kilometer or two wide landslide beneath sea level that displaced a lot of water locally, but nothing like the scale of displacement that occurred in the 2004 earthquake.

MARTIN: Can we go back to something you mentioned earlier? And the news reports agree that people did not have any warning this time. Why is that?

JOHNSTON: Yeah. So the lack of the earthquake means that there's no natural warning trigger that there might be a tsunami. So that's No. 1. No. 2, we have, in the oceans, deployed buoys that are designed to sense tsunamis. So large tsunamis like the one that was spawned by the 2004 earthquake would have been sensed by these buoys. This one ended up being in such a small, restricted area and so close to shore where it happened that there was just, A, no time and no sensors in the way that would have detected it. So I think even if we had detected it, there would have been no chance for any significant warning to have got to these people.

MARTIN: And I think many people will remember that with earthquakes, there can be aftershocks. Is that a concern here as well?

JOHNSTON: It is a concern. So the earth obviously broke, and material moved down slope, giving rise to the tsunami. And they would be - and I believe they are - being very cognizant of the fact that the slope may still be unstable. And it still could give rise to other slips, and hence, other tsunamis.

MARTIN: And finally, climate change is very much on the minds of many people at the moment. A global conference on climate change just wrapped up. Could climate change and sea level rise affect the size and the destructive power of tsunamis? Is that a factor here?

JOHNSTON: Probably not a factor here. It seems like climate change is a factor in everything these days. But as sea level rises, and hence water attacks more and more of the coastline, I think that in the long run, the potential for more of these kinds of events is quite possible.

MARTIN: Geologist Stephen Johnston chairs the Earth and Atmospheric Science department at the University of Alberta. Professor Johnston, thank you so much for talking to us.

JOHNSTON: OK. Thank you, Michel. Transcript provided by NPR, Copyright NPR.