Tsunami

The tsunami is a series of ocean waves of very great length and period generated by impulsive disturbances of the earth's crust. Large earthquakes with epicenters under or near the ocean and with a net vertical displacement of the ocean floor are the cause of the most catastrophic tsunami. Volcanic eruptions and submarine landslides are also responsible for tsunami generation but their effects are usually localized. Although infrequent, tsunami are among the most terrifying and complex physical phenomena and have been responsible for great loss of life and extensive destruction to property. Because of their destructiveness, tsunami have important impact on the human, social and economic sectors of our societies. Historical records show that enormous destruction of coastal communities throughout the world has taken place and that the socioeconomic impact of tsunami in the past has been enormous. In the Pacific Ocean where the majority of these waves have been generated, the historical record shows tremendous destruction with extensive loss of life and property. In Japan, which has one of the most populated coastal regions in the world and a long history of earthquake activity, tsunami have destroyed entire coastal populations. There is also a history of tsunami destruction in Alaska, in the Hawaiian Islands, and in South America, although records for these areas are not extensive. The last major Pacific-wide tsunami occurred in 1960. Others have also occurred but their effects were localized.

We have witnessed in the last twenty years rapid growth and development of the coastal areas in most of the developing or developed Pacific nations. This is the result of a population explosion and of technological and economic developments that have made the use of the coastal zone more necessary than before. Fortunately, tsunami are not frequent events and therefore their effects have not been felt recently in all developing areas of the Pacific. History, however, has proved that although infrequent, destructive tsunami indeed do occur. A major Pacific-wide tsunami is likely to occur in the near future. Among the countries bordering on the Pacific, a number are not prepared for such an event while others have let their guard down. The social and economic impact of future tsunami, therefore, cannot be overlooked. The purpose of this paper is to provide an overview of the social and economic impact of past, recent and future tsunami, to examine tsunami hazard management, and to indicate the need for future planning, at least for the Pacific Ocean where tsunami frequency is high.

Historical record of destructive tsunami

The impact of tsunami on human society can be traced back in written history to 1480 B.C., in the eastern Mediterranean, when the Minoan civilization was wiped out by such waves. (photo of ancient city of Knossos, the capital of the Minoan civilization).

Japanese records documenting such catastrophes extend back to A.D. 684.(1) North and South American records have dated such events back to 1788 for Alaska and 1562 for Chile. Records of Hawaiian tsunami go back to 1821.

While most of the destructive tsunami have occurred in the Pacific Ocean, devastating tsunami have also occurred in the Atlantic and Indian Oceans, as well as the Mediterranean Sea. A large tsunami accompanied the earthquakes of Lisbon in 1755, that of the Mona Passage off Puerto Rico in 1918, and at the Grand Banks of Canada in 1929.

Most of the people in the Pacific countries live on or quite near the coast since the interior is often mountainous and most of the good flatland is in the form of coastal plains. Many of these countries have populations with a natural maritime orientation. For many of these countries, foreign trade is a necessity and some maintain large fleets of ships and have major port facilities. Many of the Pacific island countries and those with extensive continental coastlines depend also on transport by small coastal ships necessitating many small ports to facilitate inter-island and coastal trade as well. Countries like Japan, for example, maintain many ports and have extensive shipbuilding facilities, electric plants, refineries and other important structures.

Similarly, many of the other developing and developed countries of the Pacific have harbors as bases for their large fishing industries. Peru, for example, at the port of Callao near Lima, maintains a large fleet for anchovy fishing. Callao is located near a strong seismic and potentially tsunamigenic region. Finally, when we also note that a number of coastal sites throughout the Pacific have begun aqua cultural industries and canneries, we can only conclude that this combination of factors makes these developed and developing Pacific islands and continental Pacific nations socially and economically vulnerable to the threat of tsunami. The extensive coastal boundaries, the number of islands, the long coastlines of Pacific countries containing a number of vulnerable engineering structures, the numerous large ports, the productive fishing and aqua cultural industries and the great density of population in coastal areas can only place these countries in a very vulnerable position.

Planning for the tsunami hazard

There is very little that can be done to prevent the occurrence of natural hazards. Floods, droughts, earthquakes, hurricanes, volcanic eruptions and tsunami cannot be prevented. But humankind, being as adaptable as it is, has learned to live with all these hazards. In the past, we have taken a passive approach to hazards, justifying them as acts of God or nature about which we could do very little.

But while these natural disasters cannot be prevented, their results, such as loss of life and property, can be reduced by proper planning. To plan for the tsunami hazard, however, we must have a good understanding not only of the physical nature of the phenomenon and its manifestation in each geographical locality, but also of that area's combined physical, social and cultural factors. Some of these areas are more vulnerable to tsunami than others. Because tsunami frequency in the Pacific Ocean is high, most efforts in hazard management have concentrated in this area of the world. No matter how remote, the likelihood of a tsunami should be considered in developing coastal zone management and land use. While some degree of risk is acceptable, government agencies should promote new development and population growth in areas of greater safety and less potential risk. These agencies should formulate land-use regulations for a given coastal area with the tsunami risk potential in mind, particularly if such an area is known to have sustained damage in the past.