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Tsunamis a threat to Ja?
published: Wednesday | December 29, 2004
Rafi Ahmad, Contributor
SINCE THE evening of Christmas Day in Jamaica, we have been following the news of death and destruction caused by the Boxing Day tsunami in the Indian Ocean following a series of earthquakes that started in the plate boundary zone in Sumatra and then the seismic activity shifted North to the Andaman and Nicobar Island area.
News media reports suggest that there has been some 10 metres of movement along an approximately 1000 kilometres section of the tectonic zone that defines a part of the boundary between the Indian and Burmese tectonic plates.
FRESH IN OUR MEMORIES
Hurricane Ivan related storm surge along many sections of the south coast of Jamaica are fresh in our memories. Being an island nation with most of our population centres, infrastructure, and tourism related economics exposed to coastal flooding, we in Jamaica must learn from these happenings.
This is because of our geological and geophysical location, also in a plate boundary zone but of a different type than the subduction type boundary of the Indonesian archipelago. The present-day eastern Caribbean is similar to the Indonesian setting.
An important lesson from the Boxing Day Tsunami for the Caribbean is that earthquakes occurring thousands of kilometres away have the potential to generate a destructive tsunami as happened following an earthquake on November 1,1755 in Lisbon, Portugal.
HOW IT ORGINATES
What is a tsunami and how it originates?
A tsunami is not 'tidal wave for they have nothing to do with the tides that are due to gravitational forces of the moon and sun. They are sea waves caused by various processes as explained below.
Storm surges are an abnormal rise in sea water level associated with hurricanes and other storms at sea, for example, what has happened along the south coast of Jamaica following Hurricane Ivan in September 2004.
These processes result in the flooding of the coastline termed as 'coastal flooding'. The effects of coastal flooding caused by tsunamis are the same as those of storm surges. Flooding associated with the runoff in streams is 'riverine flooding'. In this article we are concerned with tsunami only.
TRAVELLING SEA WAVES
A gravity wave may propagate in seawater from a large disturbance of the sea floor started by an earthquake, eruption of a submarine volcano, or a massive landslide. Such a wave is called a tsunami, following a Japanese word meaning, 'harbour waves'.
In the English-language tsunami (soo-NAHM-ee) are termed seismic sea waves; in French, vagues sismique and raz de maree; and in Spanish, maremoto. Tsunamis are relatively more common in the area of the Pacific Ocean and especially along the Pacific Rim. There exists a tsunami warning network for the Pacific.
Tsunami is a collective name for a series of travelling sea waves of extremely long length and period caused by a number of physical processes, which may be genetically linked. Among the various types of faults that cause earthquakes, it is the dip-slip, thrust faults with predominant vertical movements that are generally tsunamigenic.
However, earthquakes may also trigger landslides both onshore and in the submarine environments that are responsible for many known destructive tsunami occurrences worldwide.
Submarine landslides, variety lateral spreads, are believed to be responsible for many of the localised tsunami in Jamaica.
The best example of this is the submarine landslide that took with it a part of Port Royal to the bottom of the Kingston Harbour on Tuesday, June 7, 1692 at about 11.40 a.m.
WAVE HEIGHT
Tsunamis may reach enormous dimensions and the energy associated with these waves enable them to travel across entire ocean basins. The velocity of a tsunami is equal to the square root of the product of the depth of water times acceleration due to gravity.
Upon entering shallow waters, the wave height increases dramatically, inundating low-lying coastal areas.
Harvey Blatt has estimated that a 4.8m high tsunami travelling at 643 km/hr (the speed of a jetliner) in the deep ocean water may hit a coastline at a speed of 48 km/hr with a wave about 30m high. In a real situation, the height of a wave will vary from place to place depending upon a number of factors including the offshore and near-shore coastal zone features.
TSUNAMI HAZARD ON JAMAICA
This author has reasons to believe that previous coastal flooding, including tsunami and storm surge events, may have played a significant role in shaping the present day coastline of Jamaica.
Jamaica has a history of tsunamis that have affected the coastline since 1688 causing loss of life and destruction of property.
The storm surge associated with a hurricane in 1912 caused comprehensive damage in Westmoreland. Jamaica's geologic setting makes the coastline particularly vulnerable to both tsunami and storm surge hazards.
The World Map of Natural Hazards prepared by Munich Re shows the entire coastline of Jamaica exposed to tsunami.
Since most of the urban population in Jamaica resides in coastal areas any future tsunami is likely to have a disastrous impact because of the development in the coastal areas.
It, therefore, makes sense to be aware of this hazard while determining the acceptable risks in the coastal settlements. Accounts of some of these events are not comprehensive and more research is needed to validate their practical and site specific use.
The Caribbean region is also vulnerable to teletsunami, which may have their origin outside of the region. It appears that it is the telestunami that has caused the loss of life along the rims of the Indian ocean, including Sri Lanka.
Closer to home, James Lander has reported that the tsunami generated by the November 1, 1755 Great Lisbon Earthquake, Portugal, sent waves into the Caribbean with amplitudes of 7m at Saba, 3.6m at Antigua and Dominica, 4.5m at St.Martin, leaving a sloop anchored in 4.6m of water laying broadside on the dry bottom, and 1.5-1.8m at Barbados.
There are no reports for their effects in other islands in the Caribbean, but with waves of these sizes, they probably affected most of the islands.
"We do not have data on the return time of this event," Lander has further stated that, "Such tsunami will have about eight hours of lead time before they arrive from the source of the Lisbon tsunami, and have long periods of up to an hour. The danger period may last for up to 12 hours".
Kick'Em Jenny is a submarine volcano, located between Grenada and Carriacou in the Lesser Antilles volcanic arc. It has erupted from time to time in the past and has a potential to generate a tsunami. A tsunami travel time chart prepared by Lander shows that a tsunami generated by this volcano would take about 150 minutes to reach Kingston, Jamaica.
LIVING WITH A TSUNAMI
This writer would like to know how many tide gauges are operating in Jamaica at the present time and who is responsible for their operation.
Is it not prudent for us in Jamaica to become a part of the worldwide tsunami warning groups?
Should it not be a responsibility of the citizens to learn about the hazards and protect their lives and property?
A person living in a coastal area should be interested in the following:
* Is information on tsunami hazard available? How reliable it is?
* If a tsunami were to affect my town how bad it would be?
* What is my acceptable risk?
* Is it worthwhile to distribute potential losses by taking an insurance policy?
* Is there a tsunami warning system? Is there any guidance available on construction of houses?
* How do I protect myself?
* What are the escape routes?
* Do I need to have a personal hazard protection plan for the family?
SOME TSUNAMI SAFETY RULES
The following rules are adapted from the Tsunami Glossary (UNESCO, 1991)
* All earthquakes do not cause tsunami, but many do. When you hear that an earthquake has occurred, stand by for a tsunami emergency.
* An earthquake in your area is a natural tsunami warning. Do not stay in low-lying coastal areas after a local earthquake.
* A tsunami is not a single wave, but a series of waves. Stay out of danger areas until local authorities issue an 'all clear'.
*A noticeable rise or fall (withdrawal) of coastal water sometimes heralds approaching tsunami. This is nature's warning and should be heeded.
* A small tsunami at one beach can be a giant a few miles away. Don't let the modest size of one make you lose respect for all.
* All tsunami like hurricanes are potentially dangerous, even though they may not damage every coastline they strike.
* Never go down to the beach to watch for a tsunami. When you see the wave you are too close to escape it.
* Stay tuned to the radio or television during a tsunami emergency-bulletin issued by local authorities (ODPEM) can help save your life.
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published: Wednesday | December 29, 2004
Rafi Ahmad, Contributor
SINCE THE evening of Christmas Day in Jamaica, we have been following the news of death and destruction caused by the Boxing Day tsunami in the Indian Ocean following a series of earthquakes that started in the plate boundary zone in Sumatra and then the seismic activity shifted North to the Andaman and Nicobar Island area.
News media reports suggest that there has been some 10 metres of movement along an approximately 1000 kilometres section of the tectonic zone that defines a part of the boundary between the Indian and Burmese tectonic plates.
FRESH IN OUR MEMORIES
Hurricane Ivan related storm surge along many sections of the south coast of Jamaica are fresh in our memories. Being an island nation with most of our population centres, infrastructure, and tourism related economics exposed to coastal flooding, we in Jamaica must learn from these happenings.
This is because of our geological and geophysical location, also in a plate boundary zone but of a different type than the subduction type boundary of the Indonesian archipelago. The present-day eastern Caribbean is similar to the Indonesian setting.
An important lesson from the Boxing Day Tsunami for the Caribbean is that earthquakes occurring thousands of kilometres away have the potential to generate a destructive tsunami as happened following an earthquake on November 1,1755 in Lisbon, Portugal.
HOW IT ORGINATES
What is a tsunami and how it originates?
A tsunami is not 'tidal wave for they have nothing to do with the tides that are due to gravitational forces of the moon and sun. They are sea waves caused by various processes as explained below.
Storm surges are an abnormal rise in sea water level associated with hurricanes and other storms at sea, for example, what has happened along the south coast of Jamaica following Hurricane Ivan in September 2004.
These processes result in the flooding of the coastline termed as 'coastal flooding'. The effects of coastal flooding caused by tsunamis are the same as those of storm surges. Flooding associated with the runoff in streams is 'riverine flooding'. In this article we are concerned with tsunami only.
TRAVELLING SEA WAVES
A gravity wave may propagate in seawater from a large disturbance of the sea floor started by an earthquake, eruption of a submarine volcano, or a massive landslide. Such a wave is called a tsunami, following a Japanese word meaning, 'harbour waves'.
In the English-language tsunami (soo-NAHM-ee) are termed seismic sea waves; in French, vagues sismique and raz de maree; and in Spanish, maremoto. Tsunamis are relatively more common in the area of the Pacific Ocean and especially along the Pacific Rim. There exists a tsunami warning network for the Pacific.
Tsunami is a collective name for a series of travelling sea waves of extremely long length and period caused by a number of physical processes, which may be genetically linked. Among the various types of faults that cause earthquakes, it is the dip-slip, thrust faults with predominant vertical movements that are generally tsunamigenic.
However, earthquakes may also trigger landslides both onshore and in the submarine environments that are responsible for many known destructive tsunami occurrences worldwide.
Submarine landslides, variety lateral spreads, are believed to be responsible for many of the localised tsunami in Jamaica.
The best example of this is the submarine landslide that took with it a part of Port Royal to the bottom of the Kingston Harbour on Tuesday, June 7, 1692 at about 11.40 a.m.
WAVE HEIGHT
Tsunamis may reach enormous dimensions and the energy associated with these waves enable them to travel across entire ocean basins. The velocity of a tsunami is equal to the square root of the product of the depth of water times acceleration due to gravity.
Upon entering shallow waters, the wave height increases dramatically, inundating low-lying coastal areas.
Harvey Blatt has estimated that a 4.8m high tsunami travelling at 643 km/hr (the speed of a jetliner) in the deep ocean water may hit a coastline at a speed of 48 km/hr with a wave about 30m high. In a real situation, the height of a wave will vary from place to place depending upon a number of factors including the offshore and near-shore coastal zone features.
TSUNAMI HAZARD ON JAMAICA
This author has reasons to believe that previous coastal flooding, including tsunami and storm surge events, may have played a significant role in shaping the present day coastline of Jamaica.
Jamaica has a history of tsunamis that have affected the coastline since 1688 causing loss of life and destruction of property.
The storm surge associated with a hurricane in 1912 caused comprehensive damage in Westmoreland. Jamaica's geologic setting makes the coastline particularly vulnerable to both tsunami and storm surge hazards.
The World Map of Natural Hazards prepared by Munich Re shows the entire coastline of Jamaica exposed to tsunami.
Since most of the urban population in Jamaica resides in coastal areas any future tsunami is likely to have a disastrous impact because of the development in the coastal areas.
It, therefore, makes sense to be aware of this hazard while determining the acceptable risks in the coastal settlements. Accounts of some of these events are not comprehensive and more research is needed to validate their practical and site specific use.
The Caribbean region is also vulnerable to teletsunami, which may have their origin outside of the region. It appears that it is the telestunami that has caused the loss of life along the rims of the Indian ocean, including Sri Lanka.
Closer to home, James Lander has reported that the tsunami generated by the November 1, 1755 Great Lisbon Earthquake, Portugal, sent waves into the Caribbean with amplitudes of 7m at Saba, 3.6m at Antigua and Dominica, 4.5m at St.Martin, leaving a sloop anchored in 4.6m of water laying broadside on the dry bottom, and 1.5-1.8m at Barbados.
There are no reports for their effects in other islands in the Caribbean, but with waves of these sizes, they probably affected most of the islands.
"We do not have data on the return time of this event," Lander has further stated that, "Such tsunami will have about eight hours of lead time before they arrive from the source of the Lisbon tsunami, and have long periods of up to an hour. The danger period may last for up to 12 hours".
Kick'Em Jenny is a submarine volcano, located between Grenada and Carriacou in the Lesser Antilles volcanic arc. It has erupted from time to time in the past and has a potential to generate a tsunami. A tsunami travel time chart prepared by Lander shows that a tsunami generated by this volcano would take about 150 minutes to reach Kingston, Jamaica.
LIVING WITH A TSUNAMI
This writer would like to know how many tide gauges are operating in Jamaica at the present time and who is responsible for their operation.
Is it not prudent for us in Jamaica to become a part of the worldwide tsunami warning groups?
Should it not be a responsibility of the citizens to learn about the hazards and protect their lives and property?
A person living in a coastal area should be interested in the following:
* Is information on tsunami hazard available? How reliable it is?
* If a tsunami were to affect my town how bad it would be?
* What is my acceptable risk?
* Is it worthwhile to distribute potential losses by taking an insurance policy?
* Is there a tsunami warning system? Is there any guidance available on construction of houses?
* How do I protect myself?
* What are the escape routes?
* Do I need to have a personal hazard protection plan for the family?
SOME TSUNAMI SAFETY RULES
The following rules are adapted from the Tsunami Glossary (UNESCO, 1991)
* All earthquakes do not cause tsunami, but many do. When you hear that an earthquake has occurred, stand by for a tsunami emergency.
* An earthquake in your area is a natural tsunami warning. Do not stay in low-lying coastal areas after a local earthquake.
* A tsunami is not a single wave, but a series of waves. Stay out of danger areas until local authorities issue an 'all clear'.
*A noticeable rise or fall (withdrawal) of coastal water sometimes heralds approaching tsunami. This is nature's warning and should be heeded.
* A small tsunami at one beach can be a giant a few miles away. Don't let the modest size of one make you lose respect for all.
* All tsunami like hurricanes are potentially dangerous, even though they may not damage every coastline they strike.
* Never go down to the beach to watch for a tsunami. When you see the wave you are too close to escape it.
* Stay tuned to the radio or television during a tsunami emergency-bulletin issued by local authorities (ODPEM) can help save your life.
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