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Author: Conrad C. Lautenbacher Jr.
NOAA has been using technology to detect and warn of tsunamis for more than three decades.
When our planet flexes its natural muscles, it often creates hazards for the humans who live on its surface. The tsunami that struck Southeast Asia and parts of Africa in December was a shocking reminder of Earth’s power. Although we may not be able to control when Earth flexes her muscles, we can and should be able to provide people with the necessary resources and warnings to minimize losses of life and property from natural disasters.
Human curiosity leads us to try to make some sense of the world in which we live. But our understanding sometimes stalls in the face of the complexities of our planet. Undaunted, however, we continue the pursuit, knowing that the questions we ask today may not be answered until long after we are gone and that processes we put in place now may benefit future generations if not our own. In the meantime, we can use the information gained along the way in beneficial ways. Our reactions to tsunamis over the past half-century have followed this model.
In a television special about the December 26, 2004, tsunami, an individual interviewed said, “Before December 25, very few people knew what a tsunami was. After December 26, almost everyone does.” Even before this tragedy, however, much was known about tsunamis. We know what they are and what causes them, and when we detect one, we can make reasonable predictions of where and when it might strike.
Although infrequent, tsunamis are a significant natural hazard that can cause great destruction and loss of life within minutes on shores near their source. Approximately 85 percent of tsunamis occur in the Pacific region, but they are known to happen in every ocean and sea, except the Arctic. Some tsunamis can cause destruction within hours across an entire ocean basin, as was tragically demonstrated last December 26.
A tsunami wave can pass
under a ship without those
aboard the vessel noticing.
Tsunamis are series of very long waves generated by rapid, large-scale disturbances of the sea—the sudden displacement of a large volume of water, generally from the raising or lowering of the seafloor caused by undersea earthquakes; landslides above ground or under water; or even volcanic eruptions. Once a tsunami has been generated, its energy is distributed throughout the water column, regardless of the water depth, and the waves travel outward on the surface of the ocean in all directions away from the source, much like ripples caused by throwing a rock into a pond. The wavelength of the tsunami waves and their period depend on the generating mechanism and the dimensions of the source event.
In the deep ocean, the height of a tsunami from trough to crest can range from a few centimeters to a meter or more depending on the generating source. Tsunami waves in the deep ocean can travel at high speeds for long periods of time over distances of thousands of kilometers and lose very little energy in the process. The deeper the water, the greater the speed of tsunami waves. A tsunami wave can travel more than 800 kilometers per hour (km/h) in the deep ocean, but slows to 30 to 60 km/h in shallow water near land. At these high speeds, a tsunami generated in the Aleutian Islands in Alaska could reach Hawaii in less than four and a half hours, but, amazingly, pass under a ship in the ocean with those aboard the vessel hardly noticing.
Tsunamis arrive at a coastline as a series of successive crests (high water levels) and troughs (low water levels) usually 10 to 45 minutes apart. As they enter the shallow waters of coastlines, bays, or harbors, their speed decreases. For example, in 15 meters of water, the speed of a tsunami wave may be only 45 km/h. However, 100 or more kilometers away, another tsunami wave traveling in deep water toward the same shore is moving at a much greater speed, and behind it another wave is traveling at even greater speed. As the tsunami waves become compressed near the coast, their wavelengths are shortened, and the wave energy is directed upward—thus considerably increasing the height and force of the waves.
Tsunami waves may smash into the shore like a wall of water or move ashore as a fast moving flood or tide—carrying along everything in their path. The historic record shows that many tsunamis have struck with devastating force, sometimes reaching heights of 30 to 50 meters. It should be remembered that a tsunami run-up of more than 1 meter is dangerous and, because flooding by individual waves typically lasts from 10 to 30 minutes, the danger can last for hours.
Americans were introduced to the power of tsunamis on March 28, 1964, when the largest earthquake (magnitude 8.4) of the twentieth century in the Northern Hemisphere caused massive devastation in Alaska; some areas were raised as much as 15 meters and others subsided. The resulting Pacific-wide tsunami killed 120 people, destroyed Alaska’s port facilities, and affected the entire California coastline. Five of Alaska’s seven largest communities were devastated by the combination of earthquake and tsunami damage.
As a direct result of the 1964 earthquake, the West Coast Tsunami Warning Center was built in Palmer, Alaska, in 1967. This center was subsequently combined with a similar center built in 1949 in Hawaii to protect everyone living along the U.S. Pacific coast. With knowledge comes power, and these two centers have combined observations and monitoring with research into the mechanics of tsunamis to offer some warning when a tsunami might strike. The center in Hawaii has since become a partner of the U.N. Intergovernmental Oceanographic Commission International Coordination Group to provide timely tsunami warnings to other Pacific nations.
These warning centers are connected to seismic monitors around the globe and sea-level monitors in the deep ocean and in harbors around the Pacific Ocean. When an earthquake occurs, scientists are alerted, triggering a rapid earthquake analysis. If the earthquake exceeds a magnitude of 7.5 and is near a coastline, a tsunami warning is issued immediately for the area surrounding the earthquake. The warning center then monitors sea-level instruments to determine if a tsunami has actually been generated. If the sea-level instruments do not detect a tsunami or if they detect a small tsunami, the warning is cancelled. If the instruments detect a large tsunami, the warning is expanded to all coastlines of the Pacific.
The Deep-Ocean Assessment and Reporting of Tsunamis (DART) System
Although much of the world has focused on tsunamis relatively recently, the National Oceanic and Atmospheric Administration (NOAA) has been conducting research on the causes and consequences of tsunamis and using technology to help detect and warn of their presence for more than three decades. The first deep-ocean assessment and reporting of tsunamis (DART) buoy, or “tsunameter,” was created in the engineering laboratory of NOAA’s Pacific Marine Environmental Laboratory (PMEL) in Seattle, Washington. DART systems use bottom-pressure recorders (BPRs) capable of detecting and measuring a tsunami with an amplitude as small as 1 centimeter in 6,000 meters of water. Data are then relayed by acoustic modem to a surface buoy, which transmits the information to a ground station via satellite. The data are displayed in real time at http://www.ndbc.noaa.gov/dart.shtml.
PMEL began development of the DART system in 1987, and a prototype system was deployed for two months off the Washington-Oregon coast in the summer of 1995. The surface buoy performed well, but data losses of approximately 5 percent were noted. In March 1997, a redesigned system was deployed in deep water off Oahu, Hawaii. This newer system was designed to reduce data loss by quantifying the acoustic-beam pattern, signal-to-noise levels, acoustic-modem baffle performance, and mooring and hardware design parameters. The deep-water test was successful, and two demonstration systems were subsequently fabricated and tested.
The standard DART surface buoy has a current design life of one year, and the seafloor BPR package has a life of two years. The system has proven to be robust and reliable with a cumulative data return of 96 percent since 1998. The DART, or tsunameter, which costs about $250,000 for each station, has demonstrated its value many times over for the state of Hawaii.
DART is one of NOAA’s many research-to-operations success stories. The transition period for the newest system began in 2001 and ended in October 2003. On November 17, 2003, DART detected a small tsunami generated by an earthquake near Adak, Alaska, but based on data collected from DART buoys, no warning was issued for this event, which saved Hawaii an estimated $68 million. This event showed that sometimes the greatest benefit of a warning system is knowing when not to evacuate. This becomes clear when we look back to an event of similar magnitude in 1986 in the same region that resulted in the evacuation of Hawaii’s coastal areas. At the time, predictions of the amplitude of tsunamis were difficult to make, and the tsunami that eventually struck the coastline was less than a foot in height. Thankfully, it caused no damage, but the Hawaii Department of Business, Economic Development and Tourism estimated that the evacuation cost the state $40 million in lost productivity and business.
The Next-Generation Systems
NOAA is working on the next generation of tsunameters, learning from the lessons of the first generation of buoys, and using new technology to increase their usefulness. NOAA has also incorporated numerical modeling technology to forecast tsunamis in real time. Tsunameter data, sent from the DART system in real time, is assimilated into a set of nested numerical models that produce a forecast for a specific coastal town or city. The new generation of tsunameters will be the sentinels in the sea for the expanded tsunami network. The first generation of tsunami forecast models will convert data from these sentinels into tsunami forecasts in time for coastal populations to take evasive action, if necessary.
The tsunami forecast models were first used to create inundation maps for tsunami-susceptible areas. These models simulated tsunami events and indicated areas of possible flooding. In Hawaii, similar inundation maps are printed in the front of telephone directories so residents will know where to seek shelter.
On January 14, 2005, the United States announced plans to expand its U.S. tsunami detection and warning capabilities and committed $37.5 million over two years to do so. That investment will enable NOAA to deploy 32 new buoys, thus expanding existing coverage to all countries on the Atlantic and Pacific oceans, including almost 100 percent coverage in the United States, where half the population lives in coastal areas. The new tsunami-monitoring system is truly a multinational effort that will have multinational benefits, a good example of integrated observations that can make people safer.
The new tsunami-monitoring
system is a multinational
effort that will have
Looking to the Future
Unfortunately, the capabilities of technology are limited. Despite the extensive technology and procedures in place to detect tsunamis in the Pacific, no similar systems are in place in the Indian Ocean, which greatly increased the devastation caused by the December tsunami. With no buoys or tide gauges in the Indian Ocean, it was impossible to determine if a tsunami was generated by the December 26, 2004, earthquake, and specific warnings could not be issued. As I noted in my remarks to the Earth Observation Summit this February in Brussels, “Tragic as the tsunami was, it also served to illustrate the power of a networked system. By linking our observational capabilities in a more comprehensive way, we will be able to keep the citizens of every nation more safely out of harm’s way.”
Although there are thousands of moored and free-floating data buoys and thousands of land-based environmental stations around the world and more than 50 environmental satellites orbiting the globe, all providing millions of data sets, most of these cannot yet “talk” to each other. Until they do—and until all of the individual technologies are integrated into a comprehensive system of systems—there will continue to be blind spots and scientific uncertainty. Linking observational capabilities is precisely the goal of an international effort now under way to develop what is being called the Global Earth Observation System of Systems (GEOSS for short). With benefits that will reach the entire planet, this U.S.-led initiative promises to make people and economies around the globe healthier, safer, and better equipped to manage basic daily needs.
The U.S. tsunami warning system will be an integral part of this larger Earth-observing system. Combined with efforts under way in the Indian Ocean, we will be casting a safety net across the world to prevent the kind of devastation we saw last December. The goal is to make twenty-first century technology as interrelated as the planet it observes and protects and to provide a scientific basis for making sound policy decisions. With an integrated system, we will truly be able to take the pulse of the planet.
Technology, however, is only as good as our ability to use the information it provides. An effective communication system for issuing warnings and all-clear messages, coupled with well marked evacuation routes and public education, must complete the picture. Children in Hawaii and many U.S. West-Coast communities, especially communities that have been designed TsunamiReady by NOAA’s National Weather Service, conduct evacuation drills to ensure that citizens know what to do if an alarm is sounded.
In some parts of the country, the first week of April has been designated Tsunami Preparedness Week. Bright blue and white “tsunami hazard zone” signs mark evacuation routes, although, sadly, some communities have reported that the signs have attracted souvenir hunters. In addition, a variety of items, including mugs, magnets, and bookmarks, carry instructions about how to get out of harm’s way, and posters and other printed materials can be found on many websites.
The National Tsunami Hazard Mitigation Program, working with the International Tsunami Information Center, creates educational materials and provides information for all age levels and encourages their use. Even when technological means are not available, education alone can save lives. This was demonstrated after the 1998 Papua New Guinea tsunami, when more than 2,000 lives were lost along the north coast of the country’s main island. Subsequently, an educational video created by the United Nations Education, Science, and Cultural Organization (UNESCO) was distributed to some tsunami-prone areas. One such area was a village on Pentecost Island, one of 83 islands in the southwest Pacific that compose the nation of Vanuatu. When a tsunami struck that village in 1999, only five of the 500 inhabitants (1 percent) died. The majority of villagers said they had learned from the video that they should move inland or flee to higher ground when they felt the ground shaking. Thus, it is important to educate everyone who lives near a coast about what to do when an earthquake hits and the ground begins to shake.
When fundamental research is transferred into operational technology, science gains real value for citizens of the world. When operational technology is combined with a coordinated educational campaign, it becomes fully integrated into the fabric of society and creates a legacy of understanding for generations to come. The recent tsunami was a tragedy of epic proportions, but just as tragic would be for us not to do everything in our power to give people the tools they need to protect themselves from these natural disasters in the future.