Note: This is a “classic” Interesting Thing of the Day article from over 10 years ago. It has not been edited recently, so it may contain broken links, outdated information, or other infelicities. We plan to eventually update or retire most classic articles, as time permits.

At the end of December 2004, I was among the millions watching the endless hours of TV coverage of the Indian Ocean tsunami. As I watched the huge death toll rise by the hour, I remember thinking, naïvely, “How could so many people not have known what was coming?” After a bit of reflection, I had a worse thought: “How could they possibly have known?”

Living in the U.S., I’ve become accustomed to having instant information about everything. When something newsworthy occurs anywhere in the country, television crews materialize out of nowhere and broadcast the story to a nation of information junkies. And if the TV or radio isn’t on, I’m never far from a cell phone or a Web browser. If I think I feel an earthquake—not an uncommon occurrence here in San Francisco—I can check a Web site that tells me its strength and epicenter within minutes. The notion that something cataclysmic could be occurring without my knowledge, whether in my neighborhood or across the continent, is almost unfathomable.

And yet, when I fantasize about a dream vacation, the picture in my mind is invariably that of a tiny, picturesque island out in the middle of the ocean somewhere. Maybe I’m even in a bungalow built on stilts over the water. I’ve left all my gadgetry behind, and have nothing to worry about but finishing the next chapter of my book and maybe taking a quick swim before dinner. I’m not thinking about staying connected to the rest of the world; that’s what makes it a vacation. And that, tragically, is exactly the situation many tourists found themselves in when the tsunami struck. Of course, even locals with phones and televisions were not warned, because the existence of the tsunami was largely unknown before it hit.

Since then, while the governments of every coastal nation in the world have talked about the urgent need for a global tsunami warning system, I’ve been wondering exactly how that could happen. On the one hand, I want to know why it isn’t trivially easy (Don’t we have satellites?), and on the other hand, why it isn’t immediately dismissed as impossible (What about all those people on the remote islands without communication equipment?). Although I knew that a lot of money was being spent on sensors and radios, I didn’t understand just how this proposed system would work. So I decided to look into it.

Little Things Mean a Lot

Tsunamis usually begin with strong earthquakes, and there is already a global network of sensors that can adequately detect and measure seismic activity. But not all strong earthquakes that occur in the ocean produce tsunamis, and even when they do, seismic data gives few clues as to the direction or speed of the waves. So although some regional tsunami warning systems are based on seismic data alone, such systems are notorious for false positives. The only way to know for sure if a tsunami is coming is to observe the waves as they move. But perhaps “observe” is not the right word; tsunami waves appear quite small at the surface when far out at sea, even near a quake’s epicenter. With a height of sometimes as little as a few centimeters, they look like ordinary waves from a boat or plane. Only as they approach land do they swell to dangerous sizes. This characteristic makes detection a tricky business—requiring high-tech equipment and computerized analysis.

The first method used to supplement seismic data was taking readings from tide gauges. Although some tide gauges are quite sophisticated, many are simple mechanical devices that measures the height of a float protected from waves by an enclosure called a stilling well. Because tide measurements require a fixed point of reference, tide gauges are normally installed on or near a coast. Thus the data they provide is more useful for landmasses farther out from the tsunami’s starting point.

A more direct way of detecting tsunamis is to measure changes in pressure on the ocean floor. The Deep-ocean Assessment and Reporting of Tsunamis (DART) program, already in use in the Pacific ocean, uses bottom-mounted sensors to detect changes in water pressure consistent with a tsunami. The sensors relay the information via sonar to a buoy floating on the ocean’s surface; the buoy, in turn, transmits the data to a satellite, which relays it to ground-based stations for processing. DART greatly increases both the speed and accuracy of tsunami warnings, but the sensors and buoys are prone to failure and must be serviced or replaced frequently. And there are at present far too few of them in place to monitor all the world’s oceans.

Although tsunamis out at sea are not visible to the naked eye, radar satellites, if they happen to be pointed in the right place at the right time, can detect them. The problem with satellites, apart from knowing where and when to look, is that the data they produce must be processed back on Earth; the time required—currently several hours—is generally too long to be of use for warnings. Future generations of satellites, however, may overcome these limitations.

The Challenge of the Last Mile

But even if and when the world’s oceans are populated with perfectly functioning tsunami sensors, the truly phenomenal challenge will be getting the information from the scientists who operate the equipment to the people living in the coastal areas where the tsunamis will hit. For one thing, tsunamis move incredibly fast—up to 1,000 km/h (about 600 mph). So land areas must be at least a few hundred kilometers away from a quake’s epicenter to have even a small chance of receiving a warning in time. Once the warning does come, the nation must have the infrastructure to relay it rapidly to coastal areas at any hour of the day or night. Although telephones, television, radio, and the internet can be used for such purposes, residents need something that can wake them in the middle of the night—such as a siren—to be assured of having maximum time to react. While such warning systems may be feasible in densely populated coastal towns, it’s inconceivable that every remote beach in the world is ever going to have a tsunami alarm.

Then, of course, there’s the little matter of preparedness. If someone told me right now that a tsunami was going to hit my house in 15 minutes, I wouldn’t know what to do—where to go, what to take with me, how to be as safe as possible. Every child attending school in California learns what to do in the event of an earthquake, but not, in general, how to cope with sudden giant waves. This is all the more true in many other parts of the world. No matter how great the technology is, there’s no substitute for education.

All that to say: if the world’s leaders keep their promises, spend enough money, and encounter no significant technological barriers, global tsunami detection could very well be a reality in a few years. Will we then—or ever—have the ability to effectively warn everyone of an impending wave? Absolutely not. But with diligent attention to education and civil preparedness, we can certainly hope to reduce the risks dramatically.

I learned long after the fact that some friends of mine had been very close to some of the tsunami zones when the waves hit, but all of them returned safely. This made the tragedy seem more personal, and the need for a warning system more urgent. Even knowing what I know now, I still long for that idyllic island getaway. I may, however, pack a cell phone on my dream vacation—just in case. —Joe Kissell

More Information

Soon after this article was posted, I received messages from two different readers pointing out that Robert Cringely has been talking about tsunami warning systems in his blog—see Wave of Change (December 30, 2004) and the second half of Help Me Help You (January 14, 2005). Cringely is an advocate of the Open Tsunami Alert System (OTAS), which seeks to automate the process of using seismic data to relay tsunami warnings to affected areas using the Internet, SMS text messages, and other means. OTAS will unquestionably be cheaper and more efficient to implement than the large-scale, government-funded projects I discussed above. On the other hand, it is (by its own admission) only a partial solution—the seismic data alone is notoriously unreliable, and the system does not address the needs of folks in areas without cell phones or Internet access (yes, there still are some!).

To learn more about tsunami warning systems, see:

News articles about tsunami warning systems:

Other pertinent sites include: