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Please note this is a "Scientific Report" not an essay please bare this in mind. Introduction The word Tsunami is a Japanese term meaning wave in the harbour. It is the most apt description for the hazard as tidal wave or seismic wave lead to incorrect connotations and misunderstandings. The dictionary definition of the word Tsunami itself means a very large ocean wave caused by an underwater earthquake or volcanic eruption, this is only half accurate, which I will attempt to illustrate in this report. Although 85 percent of Tsunamis occur in the Pacific Ocean (PTWC, web), it is possible for them to occur in any body of water on any part of the Earth.
They are not restricted to large oceans and there is the possibility of a tsunami threat in any enclosed body of water. Tsunamis occur infrequently and often with little or no warning especially in regional areas. They can cause unprecedented loss of human life and billions of dollars worth of damage to property and infrastructure. Geologic Cause A tsunami may be generated by any disturbance that displaces a large body of water from its equilibrium position. Most commonly tsunamis are caused by seismic activity on the ocean floor (Hays, 1981). Less commonly they are caused by sub and super marine landslides, sub and super marine volcanic eruptions and very rarely by meteor impacts in the ocean.
Tsunamis travel outwards in all directions from where they are generated and can travel huge distances from their point of origination (USGS, web). Earthquakes in subduction zones at convergent plate boundaries where there is enormous stress between the plates generate most tsunamis (USGS, web). When there is a rupture the sudden movement causes energy to be released into the overlying water column. Deep ocean troughs are another area that tsunamis may originate this is from the slumping of sediments on the sea floor and from direct surface rupture on a fault trace (Shane, lecture 16).
Collapses of volcanic edifices can also upheave the overlying water as sediment and rock slump downwards and are redistributed across the sea floor. Similarly, a powerful submarine volcanic eruption can create an abrupt force that elevates the water column and generates a tsunami (Hays, 1981). Contrarily, super marine landslides or debris avalanches and meteor impacts displace the water from above, as momentum from falling debris is transferred to the water in which it falls. Tsunamis travel across the open ocean at tremendous speeds 500 to 1000 Km per hour depending on the depth and geomorphology (PTWC, web). Their height at sea may only be up to one metre high; most are undetectable by boat or aeroplane. When they reach shallower water they begin to slow down and build up a crest 5 to 40 metres high.
Tsunamis are generally not one single crest but many and there can be as much as 500 to 650 Km between them and between 10 and 45 minutes in wave arrival time. Regional Tsunamis are by far the most common travelling a short distance from their origination (geology. com, web). Impact on Society Tsunamis can cause devastation to any coastal and low-lying areas. There has been evidence of Tsunamis causing devastation as far back as 1480 BC (Paras-Carayannis, 1986). It is believed that the Minoan Civilisation was wiped out by colossal waves (Paras-Carayannis, 1982).
With more and more human development taking place in coastal areas due to population pressures it is evident that warning systems are needed to protect life and property. In 1992 and 1993 over 2, 000 people were killed by tsunamis occurring in Nicaragua, Indonesia and Japan. Damage to property was about one billion dollars. In 1960 an earthquake in Chile spawned a Pacific-wide tsunami that caused widespread death and damage in Chile, Hawaii, Japan as well as other areas in the Pacific (PTWC, web). In 101 years the Tsunami Laboratory in Novosibirsk recorded 796 tsunamis in the Pacific Ocean (PTWC, web). 117 of these caused death and destruction mostly near their point of origin.
Nine of these tsunamis caused large-scale destruction across the Pacific. There was no year in the period between 1900 to 2001 where there were no Tsunamis recorded in the Pacific Ocean (NOAA, web). The Sumatran tsunami that occurred on December 26 th, 2004 was the biggest ever-recorded in respect to loss of human life as well as billions of dollars worth of damage to property and infrastructure. Approximately 300, 000 people lost their lives and it will take many years for the areas surrounding the Indian Ocean to recover (National Geographic, web).
Mitigation The only warning for Tsunamis triggered locally is ground shaking or a quickly receding tide. This is caused by a trough approaching in front of a crest likewise if sea level rises abruptly people should be educated to move quickly to higher ground. The reason so many people died in Sri Lanka from the Boxing Day Tsunami is that they were not educated about what it means if the tide recedes very quickly (BBC, web), thousands of people went down to the beach to see the phenomenon of exposed fish flapping on the beach and were cut down by the large approaching crest. Education is paramount in developed and undeveloped countries alike (NOAA, web). The first element of mitigation is monitoring seismic activity and sea level changes.
The Novosibirsk Tsunami Laboratory of the Russian Academy of Sciences has a database holding information on historic tsunamis in the Pacific (PTWC, web). New information is cross-referenced with this database and conclusions can be made about the likeliness of a tsunami from the forthcoming evidence. Finally a communications network needs to exist between the monitoring stations, the warning centre and the at risk coastal settlements. The National Oceanic and Atmospheric Administration of America have set up the Pacific Tsunami Warning Centre in Hilo, Hawaii. This centre has a network comprised of 26 international member states (PTWC, web) and has the capability of monitoring the entirety of the Pacific Basin. Potentially tsunami genic earthquakes are evaluated and warnings are put in place for areas that are likely to be impacted.
It was popular theory that a large-scale devastating tsunami could only happen in the Pacific region but since the December 26 th 2004 tragedy this has been proven otherwise (NOAA, web). It clearly demonstrates that a warning system is needed in all vulnerable regions with low lying coastal settlements and the Indian Ocean, Atlantic Ocean, Mediterranean, Caribbean and Black Seas all need systems in place also. Efforts have been made to set up a warning centre in the Indian Ocean and there have been several conferences in Perth, Western Australia (BBC, web). The US plan to set up a system there costing 16. 6 million dollars and it should be completed in two years. Scientists believe that it is necessary to have a global tsunami warning system and efforts are in place. U.
N. Secretary-General Kofi Annan is working to make this a possibility (UNESCO, web). Thousands of people would have been spared in the Boxing Day Tsunami had warnings been issued. This is a phenomenal task as it would be very expensive and many areas lack communications networks to receive a warning and react in a timely fashion.
However it is theorized that the global cyclone warning system could be adapted to warn of tsunamis also. References Hays, W. W. , ed. , 1981, Facing Geologic and Hydrologic Hazards Earth Science Considerations: U. S.
Geological Survey Professional Paper 124 OB, 108 p. G. Paras-Carayannis from Violent Forces in nature, Ch. 11, Lamond Publications, 1986, p. 157 - 169 G. Paras-Carayannis from Impact of Science on Society, Vol. 32, No. 1, 1982, p 71 - 78 BBC New website web Geology. com website web National Geographic Website web National Oceanic and Atmospheric Administration of America Website web Pacific Tsunami Warning Centre Website web United States Geological Survey Website web United Nations Educational Scientific and Cultural Organization website web
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