ODPEM Government of Jamaica
Office of Disaster Preparedness and Emergency Management
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Disasters Do Happen
Learn More About Tsunamis

What Are Tsunamis?

Tsunamis are often incorrectly referred to as tidal waves, but a tsunami is actually a series of waves that can travel at speeds averaging 450 - 600 miles per hour in the open ocean. As the waves approach the coast, their speed decreases and their amplitude increases. Unusual wave heights have been known to be over 100 feet high. However, waves that are 10 to 20 feet high can be very destructive and cause many deaths or injuries.

From an initial tsunami generating source area, waves travel outward in all directions, much like the ripples caused by throwing a rock into a pond. As these waves approach coastal areas, the time between successive wave crests varies from 5 to 90 minutes. The first wave is usually not the largest in the series of waves, nor is it the most significant.   Furthermore, one coastal community may experience no damaging waves while another, not that far away, may experience destructive deadly waves. Depending on a number of factors, some low-lying areas could experience severe inland inundation of water and debris of more than 1,000 feet.

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What Causes Tsunamis?

Earthquake-induced movements of the ocean floor most often generate tsunamis. Landslides, volcanic eruptions and even meteorites can also generate a tsunami. If a major earthquake is felt, a tsunami could reach the beach in a few minutes, even before a warning is issued. Areas at greatest risk are less than 25 feet above sea level and within one mile of the shoreline. Most deaths caused by a tsunami are because of drowning.   Associated risks include flooding, contamination of drinking water, fires from ruptured tanks or gas lines, and loss of vital community infrastructure (police, fire and medical facilities).

The 2004 Indian Ocean tsunami could rank as the most devastating on record. More than 200,000 people lost their lives, many of them washed out to sea. The most damaging tsunami on record before 2004 was the one that killed an estimated 40,000 people in 1782 following an earthquake in the South China Sea.

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Tsunamis in the Caribbean

In the past 500 years there have been ten confirmed earthquake-generated tsunamis in the Caribbean Basin, with four causing fatalities. An estimated 350 people in the Caribbean were killed by these events.

All known sources capable of causing tsunamis occur within striking distance of the Eastern Caribbean, and there are also distant sources across the Atlantic. Since the islands lie in an area of relatively high earthquake activity for the Caribbean, the most likely tsunamis to affect the region are those which can be triggered by shallow earthquakes (<50km depth), in the region, greater than magnitude 6.5. The recurrence rate for tsunamis in the Caribbean is approximately one destructive tsunami per century for local earthquakes and one destructive tsunami per 200 years for distant earthquakes.

Currently, there is no tsunami warning system for the Caribbean, however, an interim arrangement exists with the Pacific Tsunami Warning Centre. Scientists at the Seismic Research Unit at the University of the West Indies St. Augustine campus in Trinidad and Tobago, together with other regional agencies such as the Caribbean Disaster Emergency Response Agency (CDERA), are in the process of developing a warning system but it may be several years before this is complete.

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Related Resources:

Empowering Coastal Communities to Prepare for and Respond to Tsunamis and Coastal Hazards (CDERA Project)


Related Websites:

Seismic Research Centre, St. Augustine, Trinidad & Tobago

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