The term "tsunami" is a borrowing from the Japanese tsunami津波, meaning "harbour wave". For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in the Japanese. Some English speakers alter the word's initial /ts/ to an /s/ by dropping the "t", since English does not natively permit /ts/ at the beginning of words, though the original Japanese pronunciation is /ts/.
What Are the Effects of a Tsunami?
The effects of a tsunami are devastating. They are one of the world's worst natural disasters that can hit a country.
Tsunami damage is first caused by the immense force of the tidal wave hitting the shoreline. Tsunami flooding then continues to cause damage for several more weeks.
The effects of the tsunami on the country during this period range from destruction and damage, death, injury, millions of dollars in financial loss, and long lasting psychological problems for the inhabitants of the region.
The initial impact of the tsunami is often publicised across the world through the news media. However, the actual effects continue for many years after the natural disaster strikes.
For many of the people affected, they will never forget the terrifying ordeal of being caught in a tsunami. The scars that are inflicted on the land can be present for decades to come, and this only serves as a reminder to people living in the area of the terrible losses caused by the tsunami, and the lingering danger that yet another killer tidal wave could strike at any moment with very little warning.
Tsunami: Tidal wave hits the shore
Tsunami Damage and Destruction
A tsunami's tidal waves batter the shoreline and can destroy anything in their path.
This includes boats, buildings, houses, hotels, cars, trees, telephone lines - and just about anything else in their way.
Once the waves have knocked down infrastructure on the shore the waves continue inland for many more miles - obliterating yet more buildings and homes. As the water rushes across the land it can sweep away yet more trees, gardens, garages, cars and other man made equipment.
Boats have often been hurled into the sky and iron parking metres have been bent to the ground, demonstrating the sheer power of the water.
Tsunamis often hit poorer and less-developed countries around South Asia that are close to the ''ring of fire'' in the pacific ocean - a area with high seismic activity.
Because these countries are poor their buildings are not built strongly to withstand natural disasters such as Tsunamis.
This means that when the water hits the buildings they are easily washed away.
The water leaves a trail of destruction that looks like an enormous bomb has exploded in the area. Entire towns and villages are often destroyed in minutes.
To get an idea of just how powerful a tsunami can be, take a look at the pictures below of the Thai navy boat 813. The vessel was moored one nautical mile off the coast of Khao Lak, Phang Nga province in Thailand when the tsunami struck on December 26, 2004. The large metal boat - strongly built - was flung around like a toy. The water carried the boat 2km inland through buildings and tress, before dropping it down on a patch of land. Some 4,500 people were killed in Khao Lak, a small area in the south of Thailand on the east coast. The Navy boat was left in its resting place and a memorial has been built around it.
The Thai Navy boat 813 in its final resting place after being flung 2km inland by the Indian Ocean tsunami in 2004
Death
There is very little warning before Tsunamis hit. This means that people living in towns and villages on the coast do not have time to escape.
Unfortunately one of the biggests and worst effects of a Tsunami is the cost to human life. Hundreds and thousands of people are killed by Tsunamis.
The force of the tsunami wave may kill people instantly or they may drown as water rushes on the land.
People may also be killed if a building is knocked down by the tsunami and it hits them. They can also be electrocuted if wires fall down into the water or they may be killed by fires or explosions.
The tsunami that struck South Asia and East African on Decmber 24 2004 killed a staggering 31,187 people in Sri Lanka. There were 4,280 missing people and a further 23,189 were injured.
Destruction: Homes are destroyed by the tsunami
Chaos: Palm trees on the coast are battered by the water
Disease
Tsunamis flood the areas closest to the coast. This can cause disease to spread in the stagnant water.
Illnesses such as malaria form when water is stagnant and contaminated. This can cause more deeath and sickness.
Disease can also spread from the dead bodies that begin to rot on the ground once the water has subsided. This was the case in Indonesia in 2004. In fact, one BBC security guard actually burned the corpse of a baby because it had become infested with maggots and the risk of disease spreading caused a risk to the television crew.
Often the infastructure such as sewage and fresh water supplies for drinking are damaged from the tsunami. This makes it more difficult for people to stay healthy and for diseases to be treated. In these conditions for diseases are likely to spread.
Desperate: A child hit by the tsunami in India is carried away
Cost
There is immediately a massive cost when tsunamis happen. Rescue teams come in to the area and victims of the tsunami need to be treated.
Governments around the world may help with the cost of bringing aid to a tsunami-hit area. There might also be appeals and donations from people who have seen pictures of the area in the media.
After the initial cost of rescue operations there is the clean up cost. Debris from the destruction caused by the tsunami needs to be cleaned away. Damaged buildings that are no longer structurally safe may need to be knocked down.
There is also the cost that comes from loss of earnings in the local economy and also future losses as the area will be damaged for some time.
The total financial cost of the tsunami could be millions or even billions of dollars. It is difficult to put an excat figure on the monetary cost but is a lot.
Help: Rescue teams carry away a man injured by a tsunami
Sretcher: A woman who was caught in the wave is carried to safety
Psychological Effects
Tsunami victims suffer psychology problems in the days and weeks after the destruction. This could even continue for years - often their entire lifetime.
A study by the World Health Organisation on survivors of the tsunami in Sri Lanka on December 24 2004 found that three to four weeks after the tsunami between 14 and 39 per cent of the children had post traumatic stress disorder (PTSD).
In another study, 41 per cent of adolescents and approximately 20 per cent of those adolescents' mothers had PTSD four months after the event.
Many people from the Peraliya area of Sri Lanka where 2,000 people died and 450 families became homeless had problems up to two years after the tsunami.
They were anxious and stressed because they felt like their life was in danger from another tsunami. They were also suffering from grief because they knew somebody who had died.
There were also people who were depressed because they had lost their home, their money or their business in the tsunami. Many still have PTSD.
Causes
The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea. This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests. The waves formed in this way are then sustained by gravity.
Seismicity
Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal (extensional) faults can also cause displacement of the seabed, but only the largest of such events (typically related to flexure in the outer trench swell) cause enough displacement to give rise to a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events.
Overriding plate bulges under strain, causing tectonic uplift.
Plate slips, causing subsidence and releasing energy into water.
The energy released produces tsunami waves.
Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.
Drawback
An illustration of the rhythmic "drawback" of surface water associated with a wave. It follows that a very large drawback may herald the arrival of a very large wave.
All waves have a positive and negative peak; that is, a ridge and a trough. In the case of a propagating wave like a tsunami, either may be the first to arrive. If the first part to arrive at the shore is the ridge, a massive breaking wave or sudden flooding will be the first effect noticed on land. However, if the first part to arrive is a trough, a drawback will occur as the shoreline recedes dramatically, exposing normally submerged areas. The drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.
A typical wave period for a damaging tsunami is about twelve minutes. Thus, the sea recedes in the drawback phase, with areas well below sea level exposed after three minutes. For the next six minutes, the wave trough builds into a ridge which may flood the coast, and destruction ensues. During the next six minutes, the wave changes from a ridge to a trough, and the flood waters recede in a second drawback. Victims and debris may be swept into the ocean. The process repeats with succeeding waves.
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