|
| Devastion caused by a tsunami |
The phenomenon called 'tsunami' is a system (or series) of ocean gravity waves formed as a result of a large-scale disturbance of the sea that occurs in a relatively short duration of time. Most tsunamis are caused by earthquakes or by: volcanic eruptions next to or underneath the ocean, displacements of submarine sediments, coastal landslides that enter the sea, or large-scale explosions in the ocean caused by man-made detonations or meteor impacts.
From their source or origin, tsunamis travel in the deep ocean at speeds of 500 to 1,000 kilometers per hour. There they may measure only a meter in height and have periods of from just a few minutes to as much as an hour. Near the shore a tsunami's speed slows down to a few dozen kilometers per hour and its height can grow up to dozens of meters at the shoreline. Tsunami wave energy extends to the ocean bottom and is concentrated. Depending on several variables - size and period of waves, near-shore bathymetry and shape of the coastline, state of the tide and other factors - a tsunami might induce only minor flooding or it can come ashore as a bore (vertical wall of turbulent water). Destruction from tsunamis is the direct result of three factors: inundation, wave impact on structures and erosion. Though no major destructive Pacific-wide tsunamis have occurred since 1960 - when the combined tsunami and earthquake toll included 2,000 fatalities, 3,000 injured, 2,000,000 homeless and US$550 million in damages - local tsunamis in the 90s have claimed more than 4,500 lives and caused hundreds of millions of dollars in property damage.
The
Tsunami Warning System in the PacificThis system was established in 1965 to provide, on an international basis, timely tsunami warnings, alerting the system's participants as to the approach of a potentially destructive tsunami wave and informing them of the time of the wave's arrival at various locations. Twenty-five Member States of the Pacific region pool their resources in this international co-operative effort. The system's operational headquarters, known as the Pacific Tsunami Warning Center (PTWC), are located in Honolulu, Hawaii, USA. PTWC's main responsibility is to issue timely warnings on any tsunami-genic earthquake in the Pacific basin to all participants having designated an appropriate emergency management organization to receive the message.
In 1965, IOC also established the International Co-ordination Group for the Tsunami Warning System in the Pacific (ICG/ITSU), which meets every two years to review progress and co-ordinate activities for the improvement of the service.
Outside the Pacific, no tsunami warning systems or centres exist, although the tsunami hazard exists on both sides of the Atlantic Ocean, in the eastern Indian Ocean, and in the Mediterranean, Caribbean and Black Seas. In some of these regions, efforts have already been launched for the establishment of warning systems in these areas. ICG/ITSU provides information and guidance, and shares knowledge and experience with the IOC Member States of these regions.
Information
CenterIOC also maintains, with support from the USA, the International Tsunami Information
Center (ITIC) which is also located in Honolulu and works closely with PTWC
and ICG/ITSU. ITIC's mandate includes: (I) bringing, to Members and non-Members
of the System, information about activities of the warning system, ITIC and
ITSU; (ii) gathering and distributing knowledge on tsunamis and fostering tsunami
research and its application; (iii) assisting Members in capacity-building and
tsunami-preparedness efforts by organizing training courses; (iv) monitoring
the warning system and recommending improvements, etc. For more information,
consult:
References:
TWSP Master Plan, Second Edition, April 1999, IOC/INF-1124, UNESCO (available
in English, French, Russian and Spanish);
Summary Report of the Seventeenth Session of the ICG/ITSU, October 1999, Seoul,
Republic of Korea (available in English, French, Russian and Spanish).
Note:
The above references are available in electronic form in the IOC's e-library
and in hard copy from the IOC Documentation Centre. (p.boned@unesco.org)