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Diving Deeper: Episode 22 (April 21, 2010) —
What is a tsunami ?

HOST: Welcome to Diving Deeper where we interview National Ocean Service scientists on the ocean topics and information that are important to you! I’m your host Kate Nielsen.

Today’s question is….What is a tsunami?

A tsunami is a series of ocean waves caused by the displacement of a large volume of water.

To help us dive a little deeper into this question, we will talk by phone with Russell Jackson on tsunamis. Russell is a coastal hazards specialist with NOAA’s Coastal Services Center. Hi Russell, welcome to our show.

RUSSELL JACKSON: Hi Kate, thanks for inviting me here today to talk to your listeners about tsunamis.

HOST: Russell, so what causes tsunamis?

RUSSELL JACKSON: Well Kate, tsunamis are commonly generated by earthquakes in coastal and marine regions. And most tsunamis are produced by large, usually greater than a seven on the Richter scale, earthquakes that are associated with movement along the oceanic and continental plates. They frequently occur in the Pacific Ocean, Pacific Basin, where there’s dense oceanic plates that slide under the lighter continental plates. And when these plates fracture and move, the vertical movement of the plate actually transfers a lot of energy from the sea floor to the ocean and actually causes the wave to be created.

HOST: Is this how the catastrophic Indian Ocean Tsunami back in 2004 was generated?

RUSSELL JACKSON: Yes, it was a very powerful earthquake, a magnitude 9.0, and it was actually one of the largest earthquakes ever recorded, struck the coastal region of Indonesia. And the movement of the sea floor actually produced a tsunami in excess of 30 meters, or about 100 feet, along the adjacent coastline which actually killed over 240,000 people in Indonesia. And then, from this source, the tsunami radiated outward and within a few hours had claimed over 60,000 lives in Thailand, Sri Lanka, and India.

HOST: Such a tragic event. Are there other ways to generate tsunamis?

RUSSELL JACKSON: Yeah, there are a few other ways. One in particular that there’s been a lot of experiences happened in the past are from underwater landslides associated with smaller earthquakes, they’re also capable of generating destructive tsunamis. In Papua New Guinea in 1998, there was a tsunami that devastated that area. It was generated by an earthquake that registered about a 7.0, which usually would not generate a huge tsunami, but that earthquake apparently caused an underwater landslide that created waves over seven meters high that struck the coastline, devastated over three coastal villages, completely wiped it clean to where there was nothing but sand located on those islands, and killed over 2,200 people.

Other large-scale disturbances of the sea floor can also generate tsunamis such as explosive volcanoes and even potentially asteroids making impact. Fortunately we don’t have a whole lot of asteroids making impact here, but there was an eruption of a volcano in Indonesia called Krakatoa in 1883 that produced a 30-meter tsunami and it killed over 36,000 people.

HOST: Do tsunamis occur around the world?

RUSSELL JACKSON: Yeah, actually tsunamis have been recorded in all of the major oceans of the world. However, I do most of my tsunami-related work in Hawaii and the U.S. Pacific Island territories. And these areas are especially vulnerable to tsunamis because they’re in an area that’s been nicknamed the "ring of fire," and this area is the most geologically active area on the planet. In fact, 90 percent of the world’s earthquakes and 81 percent of the world’s largest earthquakes occur along the ring of fire. And tsunamis are actually Hawaii’s number-one natural disaster killer. And Hawaii, in particular, faces threats from these distant tsunamis created along the ring of fire as well as local tsunamis because there’s a lot of seismic activity in Hawaii related to volcanic activity there.

HOST: How long after a disruption, such as maybe an earthquake, occurs is a tsunami felt?

RUSSELL JACKSON: Well Kate, there’s kind of two different types of tsunamis. If a disturbance in the ocean floor is felt close to the coastline, this is called a local tsunami and the impact can be felt by local communities within minutes. However, a very large disturbance can not only cause local devastation, but also cause destruction thousands of miles away. Tsunamis that originate from a distant source are often referred to as a teletsunami, and this is kind of like the Indian Ocean Tsunami of 2004 that I mentioned earlier.

HOST: If a tsunami wave is relatively small out in the deep ocean, what creates these larger coastal waves that we often hear about?

RUSSELL JACKSON: Well, the height of the wave when generated, especially in the deep ocean, is very small, usually less than a few feet. And as these waves approach the coast, their speed starts to decrease and the amplitude, or height, increases. When the waves of a tsunami approach land, their appearance and behavior become dependent on several factors. Two of the most important factors are topography of the sea floor, or what we refer to as bathymetry, and the actual slope of the shoreline.

So as a tsunami encounters shallow waters surrounding the shoreline, its height can increase from less than a meter to rapidly over 15 meters. So depending on the depth of the water in which the tsunami is traveling, it can actually attain speeds of 500 miles an hour.
HOST: Thanks for the great background on tsunamis and helping to show us that there’s not only these local destructions from tsunamis, but even these teletsunamis. It’s amazing how far away these impacts can be felt. Back to the 2004 Indian Ocean Tsunami we talked about earlier, was this the largest tsunami on record?

RUSSELL JACKSON:Well Kate, there’s kind of different ways of defining the “largest” tsunami. In terms of devastation and loss of life, the Indian Ocean Tsunami in 2004 was definitely the worst tsunami. And just for background, the worst tsunami to actually strike the United States actually occurred in 1946, the 1946 Alaska tsunami that killed 165 people, almost all of those deaths were in Alaska and Hawaii.

HOST: What is the greatest impact of tsunamis?

RUSSELL JACKSON: The greatest impact has to be the potential for loss of life. Since tsunamis are fairly rare events and can occur at any time of day, many of the folks that live and visit coastal areas are for the most part unaware of the risks of tsunamis and therefore, don’t really know what to do if one’s threatening the area.

Sure tsunamis can also have a huge impact on our infrastructure, and our built environment, our natural resources, and our economies, but most of that can always be replaced or there are ways to actually mitigate or lessen the impacts on those. But loss of life is something that would be the most devastating impact from tsunamis.

HOST: Besides obviously the traumatic loss of life that you just mentioned, do we have enough data to assess the impact of tsunamis to our economy?

RUSSELL JACKSON: In some areas we do, but some areas we are still lacking data. Back in 1995, the U.S. government created a program called the National Tsunami Hazard Mitigation Program to help us lessen the impacts from tsunamis. The program’s led by NOAA, and includes partners from other federal agencies like the U.S. Geological Survey and the Federal Emergency Management Agency and it also includes each of the coastal states and territories.

And during the initial stages of this program, most of the efforts really focused on modeling and mapping efforts to help communities create evacuation plans – with the main goal of lessening the loss of life. And more recently though, efforts have expanded to look at mitigating, or lessening, the impacts of tsunamis on our community as a whole, so also looking at how do we lessen the impacts to infrastructure, housing, business, economies.

HOST: Russell, can we predict a tsunami before it reaches the land?

RUSSELL JACKSON: Well Kate, predicting when and where the next tsunami will strike is currently impossible. But, once an earthquake has occurred and a tsunami is generated, we can forecast the tsunami arrival time and roughly what we think the impact will be through modeling and measurement technologies, but only a small window of time say 10 to 30 minutes can really be given to communities for local tsunamis. We have better capability for these long-distance teletsunamis to provide good information.

There are a few warning signs though that you may experience if you’re in an area just prior to a tsunami that can help you if you’re not aware of the warnings coming from government or through the radio or something. These things to keep in mind are if you see the water receding from the shoreline or if you see or hear approaching water, many tsunami survivors that I’ve talked to described the sound as a tsunami’s approaching similar to a freight train approaching, very loud, also if you feel a strong earthquake. These are all good indicators that there could be a tsunami coming so you should right away just move to high ground.

HOST: That is so frightening to think of that sound you just mentioned, the freight train before a tsunami. I’m sure we’ll all remember this if we’re ever in an area before a tsunami occurs. Can you talk a little more about how we forecast tsunamis?

RUSSELL JACKSON: As I mentioned, we can’t really forecast when a tsunami will be generated, but once it has been generated and we have some methods out there to detect whether or not a tsunami’s been generated, we do have the capability to forecast approximately when the tsunami will arrive.

NOAA has several Tsunami Warning Centers – there’s one in Alaska and one in Hawaii – that have been working with the research arm of NOAA to create models that can take inputs from our detection devises (so some of these devices for example we have devices that detect the earthquake itself like seismometers, we have tsunami detection devices, these  Deep Ocean Tsunami Detection Buoys that we kind of refer to them as DART buoys, and we also have water level gages), all this information we can take and feed into the models that will help us forecast where and how fast the tsunami is traveling.

And the forecast system is still in development, but we hope for it to be fully operational in the near future. There’s a few areas where it is operational, but we’re still working on expanding it for the entire U.S.

HOST: Russell, what is the role of the National Ocean Service in preparing for and then assessing the aftermath of tsunamis?

RUSSELL JACKSON: Well Kate, there’s really a wealth of expertise across all of NOAA, not just the National Ocean Service, involved in tsunami preparedness, education, and hazard assessment. These NOAA offices all work together to provide reliable tsunami forecasts and warnings and to promote community resilience. As I mentioned earlier, NOAA leads the National Tsunami Hazard Mitigation Program. As part of that program, the National Ocean Service works with the U.S. Geological Survey and the U.S. Army Corps of Engineers and others to provide data on ocean bathymetry, shoreline, and elevation or topography data, which better helps scientists understand how and where a tsunami wave will come ashore. The National Ocean Service also operates our National Water Level Network. The gages in this network help us detect tsunamis and the info from them can be used after an event to help identify the actual heights of the tsunamis, we use this information to validate models afterwards.

NOAA Research then also develops models that forecast tsunamis and these same models are used to create inundation maps that help emergency responders both issue warnings to communities at risk as well as responding to the actual disasters. The National Weather Service provides tsunami warnings and they actually don’t do this just for the U.S., they actually provide warning capability for the Indian Ocean region that’s sort of an agreement after the Indian Ocean Tsunami. One of the things that could have saved a lot of lives there would have been having a warning system in place and now the Pacific Tsunami Warning System serves that role for the Indian Ocean region.

Specifically at my office, the NOAA Coastal Services Center, we work with states, territories, and local communities to enhance their resilience to tsunamis. We do this by providing better access to tsunami information such as maps, awareness materials, and even videos of survivor interviews, so they can know what people actually experienced first hand and learn from their experiences. We also provide guidance and assistance when conducting tsunami risk and vulnerability assessments, create decision support tools, assist with modeling for U.S. Pacific Island Territories, and provide assistance with developing tsunami hazard mitigation plans.

HOST: Russell, we spoke to Sandy Eslinger from your office, the NOAA Coastal Services Center, back in June 2009 on resilience. Can you remind everyone what resilience is?

RUSSELL JACKSON: Sure. Resilience is the ability of a community to absorb the shock and bounce back after a hazardous event like a tsunami or a hurricane. The more informed and prepared that a community is, the more quickly they can rebound from this type of event. They can even reduce negative impacts to the environment and most importantly, they can reduce the loss of lives.

HOST: Can you expand more on how we can all prepare for tsunamis? Are there any tools we can use to help us get started?

RUSSELL JACKSON: Well Kate, there’s a growing wealth of information out there to help your audience learn more and become prepared – much of this information is available from NOAA on the NOAA Tsunami Web site. There’s other resources such as the Pacific Tsunami Museum that has gathered a lot of information throughout time of how people have responded to tsunamis. Actually a good friend of mine, a colleague in Hawaii, she was actually a survivor from the 1960 event that impacted Hilo. And she, as a result, created the Pacific Tsunami Museum to help educate others and to try to lessen the loss of life.

But one tool in particular I’d like to highlight is called the Hawaii Tsunami Hazard Awareness tool. This tool has been developed so far for Hawaii and then expanded to Oregon. And what it does is allow you to enter your address and then the tool will return an interactive map that allows you to see whether or not that address is in a tsunami zone or not. Hawaii uses this to educate people about tsunami risk. The tool has, besides these interactive evacuation maps, they also have important information that helps you understand what to do if you’re under a warning and you hear the siren go off.

HOST: Russell, that is great and sounds like such simple tool to use and it also gives really critical information to help prepare. Are you planning to expand this tool to other areas besides Hawaii and Oregon?

RUSSELL JACKSON: We’re looking at ways right now and we’re looking to expand it to Guam, we’ve been doing a lot of work there and as soon as they create their evacuation zones based on our more recent modeling that we’ve just finished, we’re hoping to expand it there. We’ve been in talks with the state of Washington to expand it there.

But, we’re also looking to expand the tool in other locations not just for tsunamis. The same tool can be used for hurricane evacuation zones and other things, flood zones, so we’ve been looking to expand throughout the U.S. for other hazards as well. 

HOST: What impacts, if any, do non-coastal residents feel from tsunamis?

RUSSELL JACKSON: Well, there’s definitely the impact from tourism and recreation, people that don’t necessarily live in coastal areas may actually be on vacation at the time when there is a tsunami impact or threat. Tsunamis can be such a devastating event, it can impact an entire national economy. In a lot of cases, the Indian Ocean Tsunami had such a huge effect on the economies of those countries impacted the most.

Everything from impacting the ability to continue shipping, importing and exporting goods into a country based on damages to ports, it could also have a devastating impact on your natural resources that can then impact other parts of your economy like fisheries, or in some cases it could even lead to rising insurance rates.

HOST: Russell, do you have any final words for our listeners today?

RUSSELL JACKSON: Yeah, thanks for allowing me to give this talk today. One thing I definitely want to remind people is that we cannot prevent a tsunami, but we can be prepared for one. So hopefully you can reference a lot of the resources from the Web site here and learn more about tsunamis.

And one thing I would also like to mention is that April is Tsunami Awareness Month in Hawaii. And this event is held each year to commemorate the loss of 159 lives from the April 1, 1946 tsunami that was the most devastating, destructive tsunami in Hawaii’s history. So you can go to a lot of resources in Hawaii right now, a lot of their local newspapers and the Pacific Tsunami Warning Center and the Pacific Tsunami Museum Web sites and learn a lot about tsunamis this month. But you don’t really have to wait until a tsunami awareness month to learn about it, so hopefully you will listen to this podcast and go find out more about tsunamis on your own.

HOST: Thanks Russell for joining us on Diving Deeper and talking more about tsunamis and the importance of community preparation to help minimize these disasters. To learn more, please visit   

That’s all for today’s show. Please join us for our next episode on NOAA’s navigation response teams on May 19.