Skip Navigation


Author(s): Deanne Erdmann, MS PhD and Nancy Moreno, PhD

Countries most affected by the tsunami, with the earthquake's epicenter. / Cantus

The word "tsunami" means "harbor wave" in Japanese. Even though tsunamis have little to do with tides, some people call them tidal waves. The term "tidal wave" was frequently used in older literature and popular accounts but is now considered incorrect. Tides occur in predictable twelve hour patterns based on the gravitational attraction of the sun and moon. Tsunamis, on the other hand, are usually caused by geological hazards, such as earthquakes, volcanic eruptions, undersea landslides, and—on rare occasions—meteor impacts. For example the tragic December 26, 2004 Indian Ocean tsunami resulted from a powerful earthquake (registering 9 on the Richter scale) southwest of Sumatra. This was the largest earthquake registered worldwide in 40 years.

Normal, wind-generated deep ocean waves and tsunami waves differ in the length of each individual wave and in the amount of time that passes between successive peaks (five minutes to an hour). The length of tsunami waves can sometimes exceed 100 miles and since a wave loses energy at a rate inversely related to its wavelength, a tsunami can travel for a long period of time without much loss of energy. Surprisingly, tsunami waves do not pose any real danger in the open ocean because they produce only a gradual rise and fall of the sea surface, sometimes just 12 inches in height. Tsunamis do move at extremely high speeds, often exceeding 500 mph. However, as a tsunami moves into shallow areas near a shoreline, it slows down and becomes compressed. This compression causes each wave to increase dramatically in height. If you drop a stone in the water and watch the series of concentric ripples radiate from the center, you will get an idea of what happens with a tsunami.

At best, the tsunami comes on shore as a quickly rising swell and gently floods low-lying coastal area. At worst, it takes lives, smashes buildings, and destroys vegetation and land formations. In addition, it is important to remember that the first waves are not usually the largest or most damaging. Areas at greatest risk are those less than 25 feet above sea level and within a mile of the shore.

Recovery from a natural disaster is multifaceted: emotional, social, economic, environmental, and political. Loss of police, fire, and medical facilities diminishes a community's ability to help those in need. Survivors of the recent tsunami face the loss of loved ones, homes, and possessions. Many jobs related to tourism and the national economy also have been lost. For example, it will be years before farmlands and rice paddies, now flooded with saltwater, are able to support crops again. Moreover, it appears that many hazardous chemicals, paints, and cleaners may have washed into surrounding coastal areas, with potentially detrimental affects on the fishing and tourist industries. In addition, trees, beaches, reefs, irrigation channels, and harbors also suffered damage, leading to significant changes in the habitats of native animal and plant species.

Because natural disasters cannot be avoided, it is important for communities to understand their vulnerability, and how to reduce future risks through alternative land use, site planning, and engineering. For example, communities can help to mitigate the effects of natural disasters by maintaining protective coastal vegetation (such as mangroves) and coral reefs; not positioning industrial facilities near fragile and populated regions; and resisting the urge to build in ravines, on steep slopes, or in flood plains. Many multinational scientists, agencies and governments are re-thinking strategies to help diminish the effects of future natural hazards. Possible strategies include increased public information and education, improved prediction methods and intensified collection of scientific data to better identify which areas of the world are most at risk.

Curriculum Idea

This is a topic with many cross-curriculum connections. Consider developing a small project with a social studies teacher (geography, culture, world organizations), a math teacher (causality calculation, estimations, statistics, graphs), or an English teacher (how information is presented).

Additional Resources

Please log in to rate this page.

View Comments

Related Content