A tsunami is a series of large waves generated by an abrupt movement on the ocean floor that is usually caused by a powerful earthquake under the ocean floor, underwater landslide, a volcanic eruption, and very rarely large meteorite strike. (Zoltan, 2005).
It can also be described as a series of waves travelling across the ocean due to a sudden displacement of a large body of water. This displacement can be caused by events such as undersea earthquakes, undersea slides, and volcanic eruption, among others.
According to Stephen (2005), emphasized that over 80% of tsunami in the Pacific Ocean are been caused by an undersea earthquakes. These tsunamis can travel as fast as 950 kilometres per hour through deep water. They have extremely long wavelengths up to hundreds of kilometres, even as they reach shallow coastal water. As they approach coastline, they become bigger and dangerous.
Although not all earthquakes generate tsunamis, to generate tsunami, earthquakes must occur underneath or near the ocean. Be large and create movement in the sea. A tsunami can also be triggered by a volcanic eruption, landslide or other movement of the earth’s surface (Tsunami, The Great Wave, 2004).
Classification of Tsunamis
There are three main broad classes of tsunamis namely;
- Local tsunami
- Regional tsunami
- Distant tsunami
1. Local tsunami
This is a tsunami where its destructive effects are experienced on coasts with 100km from the sea source of the tsunami. In such cases, the travel time for the tsunami is generally less than one (1) hour. A local tsunami is usually generated by an earthquake, but can also be caused by a landslide or a pyroclastic flow from a volcanic eruption.
Locally generated tsunamis are very dangerous. This type of tsunami may reach a nearby shore in less than ten minutes. In such cases, there is no sufficient time for a tsunami warning centre or for local authorities to issue an official tsunami warning. Coastal residents and users should therefore take life saving action as indicated on the sign based on the shaking of the ground, which is a warning that tsunami may be imminent.
2. Regional tsunami
A regional tsunami is capable of destruction in a particular area which lies between 100 km – 1,000 km from the source of the tsunami occurrence. Regional tsunami can take between 1 – 3 hours to reach the affected shore-line. This gives individuals the opportunity to evacuate away from coastal area.
3. Distant tsunami
This can also be referred to as a Tele-tsunami or ocean wide tsunami. Distant tsunamis originate from a far away source (more than 1000km away) and generally take more than 3 hours to arrive at affected coasts. When a tsunami is formed, the waves generally radiate and move in opposite directions. A distant tsunami with sufficient energy to cause additional casualties and destruction on far away shores.
This type of tsunami allow more time for the warning centre to collect data and issue precise bulletins to communicate warning information and alert the vulnerable population (Bashir, Rasmusin & Jansan, 2004).
Types of Tsunami
There are three main types of tsunami namely;
1. Immediate waves:
These are generated locally by sudden lateral movements of walls. The water is pushed out of the way and initially has nowhere to go but upwards. This temporary hump then collapses outwards in both directions, forming an almost instant response to the ground movement. These waves may climb very high, although the volume involved is not very large.
2. Seismic seiches
These are generated by variations in the local vertical ground displacement. These waves are called seiche because the response of the water body is dependent on its resonance properties, and will take the form of wave recurring at time intervals determined by the various natural frequencies.
These waves are open sea waves resulting from the action of gravity following the initiating short duration disturbance with particular emphasis on the interaction between these waves and coast lines (Babeyko, Wachter & Kloth, 2005).
Causes of tsunami
An undersea earthquake
This is the most common form of tsunami formation; typically generating the most destructive tsunami (Grossman, 2005). The earth is constantly moving in large tectonic plates. When these tectonic plates move past each other, collide and/or slide under one another (subduction), an earthquake results.
Although not all earthquakes generate tsunamis, to generate tsunamis, earthquakes must occur underneath or near the ocean with displacement of sea bed causing a sudden rise of large volume of water (Tsunami, The Great Wave, 2004).
Landslides resulting in rockfalls, icefalls or underwater (submarine) which can also generates displacement of water to create tsunami. The most notable example of a landslide-induced tsunami can be traced to Southern France in the 1980s where the movement of a significant amount of earth for the construction of an airport triggered an underwater landslide, which resulted in destructive tsunami waves hitting the harbour of Thebes.
Violent Volcanic eruptions represent also impulse disturbances, which can displace a volume of water and generate extremely destructive tsunami waves in the immediate source area (BBC Report, 2005).
Stages of tsunami
Tsunamis are of three major stages viz;
1.Generation stage/initiation of a tsunami
A tsunami often thought to be one large and very destructive wave that crashes into a coastal region, but it is really more like a series of waves. Whereas most waves are caused by the wind, tsunamis are usually formed by geological phenomenon such as an earthquake or volcanic eruption. A tsunami caused by such events is uplifted by tectonic plate activity. The incredibly potential energy of the water column is transferred into kinetic energy, which creates the series of waves known as a tsunami.
2.Tsunami split stage
After the initiation of a tsunami, the first wave that is formed by the displaced column of water splits into two waves. One wave is called a distant tsunami and is sent into the deeper ocean. The other wave is called the local tsunami. This is the one that moves towards shallower water and coastal regions that if often decimates. The speed at which both tsunamis travel is determined by water depth, distant tsunami that moves over deeper water than local tsunamis.
As the tsunami travels into shallower water over the continental slope, its wavelength decreases dramatically as its amplification increases. In layman’s terms, this means that the waves becomes shorter but more numerous.
Inundation is essential when a tsunami reaches the coast. This stage is often referred to as “run-up” because of the way the water level above sea level. A tsunami causes the ocean to overflow onto the land, which can be incredibly devastating to land not far above sea level. Since tsunami can travel much farther inland than wind-swell waves, they can devastate places relatively far away from a coast. It is important to note, however, that it is not the water itself that causes so much damage as much as it is the energy moving through it (Kaseny, 2007).
Effects of tsunami
The following are some of the effects of tsunami;
Effects on land
The effects of a tsunami on a coastline can range from unnoticeable to devastating. The effects of a tsunami depend on the characteristics of what generated it. Other factors that determines a tsunami effect on land depends on the distance from its point of origin, and the size of the tsunami.
Some tsunamis often too far away from land or they are too small to have any effect when they hit the shore. When a small tsunami comes to the shoreline, it is often seen as a strong and fast-moving tide.
Tsunamis have long periods and can overcome obstacles such as gulfs, bays and island.
Generally, tsunami arrives, not as giant breaking waves, but as a forceful rapid increase in water levels that results in violent flooding causing displacement of individuals, homes, landed properties, building collapsing, electrocution, explosions from gas, loss of life, farmland etc. Tsunamis have been known to rise to over 100 feet high (Earthquake & Tsunami, 2011).
Effects on hydrosphere
Combined with the issue of waste is that of hazardous materials and toxic substances that can be inadvertently mixed up with ordinary debris. Contamination of water is the second key environmental impacts of a tsunami. Salination of water bodies such as rivers, wells, inland lakes and groundwater aquifers can occur in most cases. Due to salination and contamination which affect hydrospheric environment of the sea results to the death of aquatic life and contamination of water supply.
Effect on man
Tsunami may have consequences as they hit less developed countries. The building infrastructures in these poorer nations are not well built and cannot withstand the impact of the tsunami. Whole areas and towns are a picture of destruction as the tsunami leaves at trail devastation and misery behind it.
One of the biggest and worst effects of a tsunami on man is the cost of human life because a healthy nation is a wealthy nation. Unfortunately, escaping a tsunami is nearly impossible. Hundreds and thousands of people are killed by tsunamis.
Since 1850 alone, tsunamis have been responsible for the loss of more than 430,000 lives. There is very little warning before a tsunami hits land. As the water rushes towards land, it leaves very little time to map an escape plan.
The violent force of the tsunami results in instant death; most commonly by drowning, building collapsing, electrocution and explosions from gas, damaged tanks and floating debris are another cause of death.
The tsunami of December 2004 that struck South East Asia and East Africa killed over 31,000 people in Sri Lanka only leaving 23,000 injured. (Brooke et al., 2005)
Tsunamis not only destroy human life, but have a devastating effect on insects, animals, plants and natural resources. A tsunami changes the landscape. It uproots trees, plants and destroys animal habitats such as nesting sites for birds.
Land animals are killed by drowning and sea animals are killed by pollution if dangerous chemicals are washed away into the sea body; thus poisoning the marine life.
The impact of a tsunami on the environment relates not only to the landscape and animal life, but also to the man-made aspects of the environment. Solid waste and disaster debris are most critical environmental problem caused by a tsunami (Tsunami Environmental Impact, 2004).
Victims of tsunami events often suffer psychological problems which can last for days, months, years or an entire life. Survivors of the Sri Lanka tsunami of December 2004 were found to have PTSD (Post Traumatic Stress Disorder) when examined by the World Health Organisation (WHO); 14% to 39% of these were children, 40% of adolescents and 20% of mothers of these adolescents were found to have PTSD 4 months after the tsunami.
The people were suffering from grief and depression as their homes, businesses and loved ones were taken away from them. Many still had PTSD in Periliya village counts 2,000 dead and 400 families becomes homeless. These people were found to still have psychological problems two (2) years after the tsunami (WHO Report on Sri Lanka Tsunami, 2004).
Effects on socio-economics
Massive costs hit communities and nations when a tsunami happens. Victims and survivors of the tsunami need immediate help from rescue teams. Government around the world may help with the cost of bringing aids to devastated areas. National institutions, the United Nations, other international organisations, community groups and variety of other entities come together to provide different kinds of aids and services.
Reconstruction and clean up after a tsunami is a huge cost problem. Infrastructure must be replaced, unsafe buildings demolished and rubbish cleared. Loss of income in the local economy and future losses from the destruction of infrastructure will be a problem for some time to come.
The total financial cost of the tsunami could be millions or even billions of dollars of damage to coastal structures and habitats. It is difficult to put an exact figure on the monetary cost but the cost may represent an important share of a nation’s GDP (Clif, 2011).
Safety measures to combat the effects
Although there are no preventive measures for tsunami, but definitely the bad effects of tsunami have a lot of preventive actions viz;
- Respect warning issued by both local and international bodies.
- Grow lots of dense mangrove instead of degrading and deforestation which is now a happening phenomenon.
- Ensure that the coastal regulation and zone regulations are not violated.
- When there is an abnormal water level variations, try and get away from sea front. It could be a warning sign.
- Do not try to be too adventurous or try to explore (fish in troubled waters).
- Rise in protest against systematic abuse of nature in the name of development.
- Learn about the potential for danger and prepare in advance both evacuation plan and safety pack.
- Heed to natural warnings such as occurrence of earthquake or landslide near coastal area. Do not ignore them.
- Take action; react immediately evacuation plan and move inland.
- If been caught up in the water, grab onto something that floats.
- Keep away until the clear signal is broadcast.
- Try to get reliable information, listen to radio for updates.
- Realize that fear is the exact opposite of faith.
Dibiagio and Kjekstad also emphasized on the following as mitigation measures
- Land use plans
- Enforcement of building and good construction practice to avoid collapsing.
- Early warning systems.
- Construction of physical projection barriers.
- Network of escape route plan.
- Emergency plan.
- Lastly, community preparedness and awareness.
Things you will need when tsunami struck
- Food (Emergency food and water)
- Clean water
- First aid kit – per family or group
- Dry, warm clothing and a waterproof coat if possible.
- Medicines needed by any person on a regular basis. E.g. heart medication.
- Flashlight and batteries per family or group.
- Battery radio per family or group.
- Mobile phone/ cell phone.
- Utility knife (Army knife) etc.
Natural disasters frequently cause major problems which affect a population’s socio-economic development. However, Government and national institutions around the world should help with the cost of bringing both financial and non financial aid to devastated areas.
Also policymakers should convert their ability and contribution in the reconstruction, rehabilitation and development of affected areas. Measures should also be in place for functional necessity to prevent, prepare and to the disaster. Disaster medical handbook and further study should be given on the scale of environmental displacement disaster such as tsunami.
Quick response to emergency situations saves life and reduces mortality rates of victims. It is important therefore that appropriate authorities especially healthcare professionals should vigorously prepare themselves, understanding the situation, identify areas pertaining to them and take life saving actions. Healthcare professionals such as the environmental health officers have significant role to play in all stages of tsunami management.
There should be challenge desire for policymakers such as WHO, UNDP and other world organisations to convert their ability and contribution to home country in reconstruction, rehabilitation and development of affected areas by tsunami.
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