“Tsunami” is a Japanese word in which “tsu” means harbor and “nami” means wave. Thus the word means “harbor wave”. Tsunami is a series of waves that can travel at speeds averaging 450 (and up to 600) miles per hour in the open ocean. Most of tsunamis are caused by earthquake even though landslides, volcanic eruptions, and even meteorites can also generate a tsunami. From an initial tsunami generating source area, waves travel outward in all directions much like the ripples caused by throwing a rock into a pond. As these waves approach coastal areas, the time between successive wave crests varies from 5 to 90 minutes. The first wave is usually not the largest in the series of waves, nor is it the most significant. As the tsunami enters shallow water near coastlines in its path, the velocity of its waves decreases and its wave height increases. It is in these shallow waters that tsunamis become a threat to life and property for they can crest to heights of more than 10 m (30 feet), strikes with devastating force, and flood low-lying coastal areas[1].
Source: tsunamis.com
Characteristics
Tsunami is characterized as shallow-water waves which are different from the wind generated waves. Wind-generated waves usually have a period (the time between two successive waves) of five to twenty seconds and a wavelength (the distance between two successive waves) of about 330 to 660 feet (100 to 200 meters). Tsunami in deep water can have a wavelenght than 300 miles and a period of an hour. The ratio between water depth and wavelength is very small. These shallow-water waves move at a speed equal to the square root of the product of the acceleration of gravity (9.8m/s/s) and the water depth. The deeper the water, the faster and shorter the wave is. For example, when the ocean is 20,000 feet deep, a tsunami travels at 550 miles per hour. At this speed, the wave can compete with a jet airplane, travelling across the ocean in less than a day. Because a wave loses energy at a rate inversely related to its wavelength, tsunamis can travel at high speeds for a long period of time and lose very little energy in the process[2].
Learn also about tsunami characteristics based on scientific measurement by University of California.
Impacts
The most obvious fact about tsunami impact is death. An example from tsunami 2004, 159.687 people was killed by tsunami and thousands of missing person. There are a lot of more impacts caused by tsunami, infrastructure and house destruction, environment impacts, social impacts, etc. Another figure of the impact on the tsunami 2004, it was estimated that the total damages in Maldives about $460 million. It was a sharp drop of tourism in Maldives. Most of people in Maldives whom strike by tsunami were homeless, have no food, water, etc[3]. Here are only several examples the impacts of tsunami.
- Economic Impact. Tsunami will affect many aspects of life, especially economy, fisherman loss their boats, farmers loss their farmland, lots of fallen building (offices, trade centres, market, etc), the collapse of tourism, etc. One witness is the devastation in southern Asian area[4].
- Biodiversity Impact. Direct mortality of animals is one obvious fact; damage to forests; damage to conservation infrastructure; and damage to wetlands[5].
Learn also the impacts of previous tsunami in Asia and also the impact of tsunami on fishing, aquaculture and coastal communities in Malaysia.
Emergency Action
If a tsunami Warning is issued, NEVER go down to the beach to watch the wave comes in because you will not live to tell the story! Remember that a tsunami is a series of waves and the first wave is not necessarily the biggest. Stay out of danger until an "all-clear" is issued by the competent authority[6]. Here are also several steps to do in an emergency situation[7]:
- Keep listening to current information, radio for instance, to know what the current situation is.
- Move to inland and stay there until the situation is save enough to go back to down land.
- Stay away from the beach if there is warn of tsunami.
- If there is noticeable recession in water away from the shoreline this is nature's tsunami warning and it should be heeded. You should move away immediately.
Learn also an emergency preparedness and response in CDC and initiative community emergency response on tsunami.
Mitigation
Tsunami mitigation plan is important if we are looking back the impacts of the latest tsunami in Asia on 2004. Several things should be done regarding to mitigation plan[8]:
- Provide hazard and disaster information where and when it is needed. This step is the way to provide necessary data and information about tsunami, the hazards, risks assessment.
- Provide appropriate research on better understanding the protective role coastal marshes, coral reefs, barrier islands and other coastal features during tsunami.
- Develop hazard mitigation strategies and technologies. It is necessary to develop structural and non structural mitigation. Structural such as develop appropriate technology on coastal zone like sea walls. Non structural such as land use planning on coastal zone.
- Reduce the vulnerability of infrastructure. Develop assessment models to inform the location of lifelines, hospitals, schools, power plants and utilities, fire and police stations, and equipments away from the risk area.
- Assess disaster resilience. Develop improved and standardized assessments of societal, economic, and environmental vulnerability to, impacts of, and a more robust response and recovery capacity related to tsunami.
- Promote risk-wise behaviour. This is the step to educate citizens and community to be more aware to tsunami risks, what to do before, during, and after tsunami. But the other hand, this step is also an important part to include risk reduction into policy action by government/state.
Learn also the US national tsunami hazard mitigation program.
Further Information
Several actions related to tsunami disaster management:
1. The benefit of using GIS on emergency management in Indian Ocean earthquake/tsunami. (click here)
2. Tsunami risk reduction as a framework for action in US. (click here)
3. State tsunami emergency management plan in Australia. (click here)
