To what extent are secondary effects the most hazardous aspects of tsunamis? Tsunami s are a series of giant sea waves created when a large volume of a body of water, such as an ocean, is rapidly displaced. Earthquakes, volcanic eruptions and other underwater explosions, landslides, asteroid impacts, and other mass movements above or below water all have the potential to generate a tsunami.
Due to the immense volumes of water and energy involved, the effects of tsunamis can be devastating. Their hazards can be split into primary and secondary effects.Primary effects are the immediate effects of a hazard impact whereas secondary effects are the after-effects that occur as a result of the hazard and can be present for a long time, as the problems do not stop when the hazard event is over. The primary effects of a tsunami involve a loss of life and the destruction of buildings and infrastructure. They are a direct result of the waves and can be split into three main types. Hydrostatic effects involve objects such as boats and vehicles, and structures such as wooden buildings, being lifted and carried inland by the wave.
The backwash or rundown, of the wave may have a similar effect, carrying objects offshore. Hydrodynamic effects involve the tearing of buildings apart, the washing away of soil and the undermining foundations of buildings, bridges and harbour structures. Finally shock effects involve objects be battered by debris carried in the wave. The human deaths therefore result from victims being drowned as they are lifted and battered, or hit by moving debris. The secondary effects of a tsunami involve both a loss of life and long-term economic problems.Tsunami waves can lead to long-term coastal flooding which in turn can lead to the spreading of water borne diseases such as cholera.
The drinking of contaminated fresh water supplies can therefore lead to widespread loss of life through dehydration caused by diarrhoea. The spread and severity of disease can further be intensified through the destruction of infrastructure and communications. With hospitals (and other infrastructure) often devastated by the tsunami, if local transport routes are destroyed or inundated, then aid, such as fresh water supplies, is not able to reach those who need it; leading to greater losses of life.There are often also major long term economic losses as a result of tsunamis. Tsunamis waves often can destroy commercial and service based businesses as well as leading to the salinisation of agricultural land through flooding. Tourism is also often a major sector in coastal regions. Tsunami waves often destroy offshore coral reefs which attract tourists for diving, they can pollute coastal waters due to the effects of the backwash, and can leave a long term stigmatism with the area as tourists are scared to return.
This can therefore cripple local economies that rely on such tourist activity to drive them. There are a number of variables which affect how hazardous the various effects of tsunamis are. One of these is the amount of, and type of disaster mitigation and preparedness schemes in place in an area. The most systematic measures to protect coastal areas against tsunamis have been taken in Japan, the country in which the largest number of people live in areas liable to tsunami attack.These measures have consisted of sea wall construction along low-lying coastal stretches, breakwater construction at the entrances to bays and harbours, and the planting of pine tree belts which rid the tsunami of some of its energy and act as a filter for any solid objects carried in the waves. The town of Yoshihima, Japan, which was completely destroyed by a tsunami in 1896, is now protected by a sea-wall some 800 metres long and 6 metres high. This proved effective against the Chilean tsunami of May 1960 which being of distant origin, produced waves of long period.
These schemes therefore have the ability to reduce both the primary and secondary hazardous effects of tsunamis, however some of the secondary effects, for example a loss of tourism due to tsunami risk, will still remain even if the waves physical impact is greatly reduced. The presence of such protection schemes might also lead to complacency in residents of coastal regions, which could intensify the loss of life due to primary effects, if the tsunami is of local origin, which the sea defences may not be able to withstand.These hard engineering schemes are also very expensive and therefore are only viable for developed countries like Japan; poorer countries like Indonesia have instead looked for less expensive schemes such as the one recommended below for eastern Java following the 1994 tsunami: The amount and type of preparedness schemes also affects whether secondary or primary effects are more hazardous.
In 1948, the Pacific Warning System for the 24 nations of the Pacific Basin was established with its centre near Honolulu, Hawaii.The 30 seismic and 70 tidal stations throughout the Pacific Basin detect all earthquakes in the area, and the events are interpreted to see if there is a risk of tsunamis. The aim is to alert all areas at risk of a tsunami within one hour, allowing them time to warn shipping and evacuate low lying coasts. On a regional level, systems are in place in many Pacific Basin countries also to help respond to locally generated tsunamis which pose a much greater threat due to short warning times (about 99% of tsunami deaths occur within 400km of the source area).
Such preparedness schemes therefore are able to reduce the primary loss of life from tsunamis from the destructive power of the waves through evacuations and warnings. However such schemes fail to protect against many of the secondary effects, with contamination of water, loss of communications and infrastructure, and long term economical damage e. g. from a loss of tourism still providing huge problems. There are some potential problems however with such preparedness schemes which could actually increase the loss of life due to the primary effects of tsunamis.
For example, the warning system in the Pacific Basin has to deal with the problem that not all earthquakes lead to tsunamis and false warnings result in high financial costs ($30 million for Hawaii alone. On a regional level, the warning systems put in place can also be flawed if the initial earthquake destroys communication or power systems which are needed to transmit the warning, or if the events are too quick to issue a warning. Over-reliance on such preparedness schemes means therefore if the system fails, the primary effects can be devastating.In response to this potential over-reliance, many LEDC countries in the Pacific Basin, which do not have the funds for such expensive preparedness schemes, have instead looked to utilise hazard and coastal mapping alongside public education schemes. Such schemes mean residents in coastal areas are better prepared to deal with both primary and secondary effects and do not have to rely heavily on potential flawed systems. Overall therefore the extent to which secondary effects are the most hazardous aspect of tsunamis depends greatly on the factors surrounding the event and there is no definitive answer.