A tsunami is a very large seismic sea wave, generated by an earthquake shock on the ocean floor.
Tsunamis travel for considerable distances across the sea as long waves (the wavelength may be over 100 km, the wave height as little as 1 m, and the forward velocity as much as 600 km per hr).
As the tsunami approaches the shore, the wave height increases markedly and sometimes exceeds 15 m; it is thus capable of causing immense destruction to coastal settlement and severe loss of life.
For example, the great Krakatoa eruption of 1883, associated with seismic disturbances, caused tsunamis that drowned 36,000 people in coastal villages of Java and Sumatra.
Effects of the tsunami are:
- Flooding in coastal areas
- Death of people, for example the 2004 Indian Ocean tsunami caused the death of quarter million people
- Destruction of houses, hotel industries, and other properties. For example, in the 2004 Indian Ocean tsunami, two million people lost their homes and a lot of properties were destroyed
- The decline of economic activities such as tourism and industries
- The high cost of rebuilding the economy after the occurrence of the tsunami
- Psychological effects: Tsunami victims suffer psychologically in the days and weeks after destruction. This could continue for years, often their entire lifetime. The study by WHO on the survivors of the tsunami in Sri Lanka in December 2004 found that three to four weeks after the tsunami between 14 and 39 percent of the children had post-traumatic stress disorder (PTSD).