Tsunami in a Tank
Air Date: Week of March 9, 2012
A crew of students puts gravel into a landslide simulation machine, which imitates how a landslide on a volcanic island creates a destructive tsunami that wraps around the island. (Photo: Lauren Sommer)
Massive tsunamis are rare, destructive, and nearly impossible to study in real time. At Oregon State University, researchers are learning from the next best thing: tsunamis they create in the lab. From the IEEE Spectrum special “Responding to Disasters: From Prediction to Recover,” Lauren Sommer reports.
GELLERMAN: It's Living on Earth. I'm Bruce Gellerman. Tsunamis can be triggered by earthquakes, undersea landslides, even meteorites striking the ocean. Thankfully, tsunamis are rare, but when they do strike they can be deadly. In 2004 giant tsunami waves smashed into Indonesia, Sri Lanka, India and Thailand, killing nearly a quarter of a million people.
U.S. scientists warn the Cascade fault line under the sea along the Pacific Northwest is overdue for a massive quake and fear that could trigger a tsunami along the U.S.-Canadian coastline. To prepare, the National Tsunami Hazard Mitigation Program provides evacuation maps, emergency training and educational materials. This is one of its videos:
[TSUNAMI VIDEO: "It can be many miles long from one to 100 feet high, traveling at 400 miles per hour. This ocean monster is known as a tsunami and it can wreak havoc on coastal populations and landscapes. Tsunamis can strike any coastline in the world and can affect locations thousands of miles away form where they’ve formed. They may be uncommon, but the devastation they cause makes them a deadly force in nature…”]
GELLERMAN: But forces within the federal budget may prove a match for the U.S. Tsunami Hazard Mitigation Program. President Obama proposes cutting nearly five million dollar in its funding next year.
Yet even in the best of times, studying tsunamis is difficult. Catching the rare waves at sea is tough, so researchers at Oregon State University are creating tsunamis in special swimming pools. From IEEE Spectrum’s program: “Responding to Disasters: From Prediction to Recovery,” Lauren Sommer reports.
[DOOR OPENING, BACKGROUND HUM]
SOMMER: Just off campus at Oregon State University, there’s a large warehouse that’s home to what looks like an Olympic-size swimming pool.
FRITZ: So this is the tsunami wave basin here. You know, it’s a hundred sixty feet long, a hundred feet wide…
SOMMER: Hermann Fritz is an associate professor of Civil and Environmental Engineering at the Georgia Institute of Technology. He’s here in Oregon with a team of students to do one thing: make tsunamis.
FRITZ: Right now there’s four feet of water in the basin.
SOMMER: Well, with four feet of water, they’re making miniature tsunamis. But that’s the whole idea. This wave basin simulates tsunamis, which, in the real world, are incredibly destructive.
FRITZ: You can see a conical island, which, ah, similar to an island in Hawaii or in the Caribbean.
SOMMER: Fritz and his team built the island in the center of the pool. They’re using it to simulate a very specific kind of tsunami, those generated by landslides.
FRITZ: So it’s a little bit like a volcano that’s collapsing and producing a tsunami wave.
SOMMER: When an eruption or earthquake occurs on the coast, it can send a massive amount of debris into the ocean, which creates a tsunami wave. These tsunamis are often much larger than normal. They’re mega-tsunamis and, as a result, much deadlier.
FRITZ: There’s of course, Krakatoa volcano in Indonesia. It’s a famous volcanic explosion and then engulfment collapse of an entire volcanic island.
SOMMER: That caused 36,000 fatalities in 1883. But landslide-generated tsunamis are relatively rare. Fritz is the first to simulate how they work.
[SOUND OF GRAVEL DUMPING]
SOMMER: The landslide in this experiment is simulated with 3,000 pounds of gravel. The team is loading it from an overhead crane into a sort of man-made landslide generator that’s sitting on the island. It’s basically a large bin that fires the gravel down the side of the island and into water when the time is right.
[SHOUTING: Coming down in 15 seconds!]
SOMMER: And that time is now.
[SOUND OF CRASHING GRAVEL]
SOMMER: The gravel shoots into the water, sending waves across the pool. The waves are being recorded by high-speed video cameras and by gauges that measure the height. Fritz and his students gather around computer monitors to watch the data come in.
FRTIZ6: There’s a little bit of noise at the beginning, you can see, kind of, nice waves over most of it but at the very beginning there is a little bit of a spark here …
SOMMER: On a good day, they’ll run this simulation up to eight times.
MCFALL: It’s pretty exciting to see the wave propagate around the cone and then collide on the backside.
SOMMER: Georgia Tech PhD student Brian McFall is talking about one of the stranger effects they’re studying. Say a tsunami is headed toward your island….
MCFALL: It seems like it’s so intuitive. ‘Oh the wave is coming from the north, let me get to the south side of the island.’ Not necessarily, it isn’t really the best idea, even though it seems like you want to be as far away from it as possible, you’re actually going to get hit a lot harder than if you’re on the sides.
SOMMER: That’s because once the tsunami hits the island, the waves wrap around both sides and collide at the back, combining their energy. That creates a larger wave, which runs up onto the land and makes the backside of the island one of the worst places to be.
Hermann Fritz says this kind of data can be used to update tsunami hazard maps, which, today, don’t include risk from landslide-generated tsunamis. That’s just one of the gaps tsunami researchers are trying to fill.
FRITZ: So the main problem is in tsunami research there are very few benchmark cases out there that you have with data.
SOMMER: Historically, researchers have had little data about tsunamis in action.
FRITZ: Up ‘til 2004 there were almost no even videos or photos of tsunamis. So, tsunami was kind of this almost unseen hazard that can destroy entire coastlines.
SOMMER: Fritz says their miniature tsunami experiments tell them about the basic dynamics of tsunami waves. That data can be used in sophisticated computer models, which can forecast where tsunamis might happen and what their impact will be.
Of course, tsunami researchers still try to observe real events. Fritz is often part of a research team that rushes to sites where tsunamis have hit.
FRITZ: We try to get the ephemeral information, the perishable data, the things that go away. When we go right after the event, we try to get watermarks, just to see how high the water was.
SOMMER: The data they collect helps tsunami researchers model future tsunamis more accurately. And recently, he’s been busy.
FRITZ: Well, I've been to the Indian Ocean tsunami in 2004, that's a very large event. And then to several smaller events in Indonesia, Java, 2006, South Pacific, Solomon Islands, 2007 and Somoa, 2009…
SOMMER: While most of these tsunamis didn’t make the headlines, the devastating 2004 Indian Ocean earthquake and tsunami certainly did. Combined, the events caused more than 200,000 deaths.
FRITZ: Banda Aceh is a huge city and was essentially wiped out. And so it's a very large area of total destruction. The human scale kind of gets lost when once you have a field of destruction that's so big.
SOMMER: For the first time, the world witnessed the devastating power of a major tsunami in action through videos and photos that were shot as the wave advanced. What those images showed was a relentless wall of water. Tsunami waves are astonishingly long. And when they hit land, Fritz says it’s like car hitting a wall.
FRITZ: So the front slows down while the back is still pushing. And the wavelength is getting shorter and shorter and the wave height gets higher and higher.
SOMMER: Against that kind of power, coastal communities have two main defenses: warning and evacuation.
FRITZ: Warning systems are primarily designed for far field events, for events where for example, they have an earthquake in Alaska, and then you have four hours until the tsunami waves reaches Hawaii.
SOMMER: But for coastal communities close to an earthquake’s epicenter, a warning may not provide enough time.
FRITZ: There's very little time between when the earthquake happens and when the wave arrives. And that can be, it's typically on the order of 15-30 minutes in most places. But in some cases it can even be as short as five minutes in extreme scenarios. And then there's really no time.
SOMMER: Fritz says that’s where public education comes in. And the rule is pretty simple.
FRITZ: For local residents, the rule is typically if you feel the earthquake and it goes on for more than 30 seconds, or if you see the water surface withdraw, then you should evacuate.
SOMMER: Public education proved to be critical during the recent earthquake and tsunami in Japan.
YEH: So we turn on the TV about five til ten and it's something going on.
SOMMER: Harry Yeh is a professor of coastal and ocean engineering at Oregon State University. On the evening of March 11, he was settling in to watch a cooking show with his wife.
YEH: I am half Japanese and I grew up in Japan, and my wife is Japanese, so we have Japanese TV.
SOMMER: As soon as Yeh saw the size of the earthquake, he braced himself for the worst.
YEH: There's no doubt. There's tsunami is coming. Significant tsunami's coming, but we do not know how big.
SOMMER: Yeh says Japan is no stranger to tsunamis and the evacuation following the quake certainly saved lives. Still, around 20,000 people died.
YEH: In the coastal community, because they are wealthy society, they build the buildings with reinforced concrete. So in Japan, people told if tsunami happen, if the higher ground is not nearby, get into this concrete buildings, climb up to the fourth stories. And that's why lots of people saved their lives, but not all.
SOMMER: That’s because in some cases, the tsunami went above the fourth floor.
YEH: That was a sad story. But that’s some lesson we should learn.
SOMMER: Japan’s past history of tsunamis has helped the country prepare for disasters, but it can also get in the way.
YEH: They built sea walls to protect the small coastal communities. But those are based upon the experience, experience of the 1933 tsunami and the 1896 tsunamis.
SOMMER: Yeh was part of a team that surveyed the damage after the tsunami. He says it’s given them an unprecedented look at how modern buildings survive in a disaster of that scale. It’s also made him rethink building codes that he’s contributed to, like the ones for tsunami evacuation centers for people who can’t reach higher ground.
YEH: I said that well if this building was built by reinforced concrete, you know, it's probably 95 percent safe. Case closed.
SOMMER: But in Japan, Yeh saw entire concrete buildings toppled over, completely on their side. He believes the earthquake could have liquefied the soil under the buildings, making their foundations fail. Also, the tsunami may have trapped air inside the buildings, making them more buoyant.
YEH: Reinforced concrete structure is always standing if you go to the site. That was not the case.
SOMMER: Yeh believes that studies in Japan will be especially relevant in Oregon and Washington, where the tsunami risk is among the highest in the country. What researchers learn will improve building codes and tsunami risk maps and, ultimately, save lives. I’m Lauren Sommer.
GELLERMAN: Our tsunami story is part of the IEEE Spectrum, National Science Foundation program “Responding to Disasters: From Prediction to Recovery.”
For more information, go to our website LOE dot org.
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