A tsunami is an ocean wave or series of waves caused by a large-scale disturbance of the ocean floor or surface that abruptly displaces a large mass of water. Tsunamis may be caused by earthquakes, volcanic events, landslides into the sea or impact of stellar objects such as asteroids, comets and meteorites. This article focuses primarily on tsunamis generated by earthquakes and volcanic events. While it is possible for the region to be hit by a tsunami such as the one recently experienced in Asia, scientists currently believe that there is a very low probability of this phenomenon occurring in the Caribbean.
In the past 500 years there have been at least ten earthquake-generated tsunamis in the entire Caribbean which have been reported and verified. Four of these have led to deaths. In total about 350 people in the Caribbean have been killed by these events.These tsunamis occurred as a result of earthquakes in:
- May 1842, Haiti – An intense local tsunami was believed to have killed up to 200 people in the town of Port-de-Paix.This figure is highly uncertain since total casualties caused by the earthquake were more than 7,000.
- November 1867, Virgin Islands – Death toll about 20, all in the Virgin Islands
- October 1918 Puerto Rico – Death toll about 29 in Puerto Rico
- August 1946 , Dominican Republic – An intense local tsunami which mainly affected the town of Matanzas where up to 100 people were killed
Additional earthquake-generated tsunamis of note also occurred in 1843 affecting Guadeloupe and Antigua and in 1690 in St. Kitts Nevis.The number of casualties related to these tsunamis, if any, is uncertain. In July 2003, a major dome collapse from the Soufriere Hills Volcano in Montserrat caused a tsunami that was experienced in Guadeloupe at about 1m high and in some parts of Montserrat at 4m in amplitude.
Potentially, there are two groups of earthquakes which may generate tsunamis in the Caribbean. These are (1) Earthquakes occurring within the region which may generate local tsunamis (by local we mean that only nearby islands are affected).In the past 500 years there have been approximately 50 potentially tsunamigenic local earthquakes but only 10-20% of these earthquakes actually generated tsunamis that caused significant inundation.(2) Distant earthquakes occurring outside of the region may generate tele-tsunamis.
In November 1755, a major earthquake in the Azores fracture zone near Portugal resulted in a tele-tsunami which crossed the Atlantic and was noticed throughout the eastern Caribbean from Barbados to Antigua and as far west as Cuba.This earthquake is commonly referred to as the Great Lisbon Earthquake. The amplitude of the tsunami in all islands was about 2-3 metres and waves continued to arrive for many hours. No damage or casualties were reported.European sources also reported that the Azores fracture zone generated a second tele-tsunami in March 1761 but no local confirmed observations were made in the Caribbean.
While recent events in Asia have caused much concern over the Caribbean’s vulnerability to tsunamis, it is important to note that all oceans can experience tsunamis but there are more large, destructive tsunamis in the Pacific Ocean because of the many major earthquakes along the margins of the Pacific Ocean and also because dip-slip earthquakes (which involve vertical rather than lateral ground motion) are more common in the Pacific than elsewhere. As a result of the immediacy of the tsunami hazard to countries in the Pacific, there is currently a tsunami early warning system in that region.
There is no tsunami warning system in the Caribbean where the recurrence rate is approximately: 1 destructive tsunami per century for local earthquakes and 1 destructive tsunami per 200 years for distant earthquakes.It should be noted that these recurrence rates are small but not negligible. For comparison, earthquake engineers design buildings to withstand earthquakes with a recurrence period of once in 475 years.
The first sign of an approaching tsunami is usually a significant retreat of the sea. As a result, the trailing waves pile on top of the waves in front of them, thereby significantly increasing the height of the wave before hitting the shore.Although a tsunami advances much slower as it approaches land, its momentum is powerful enough to cause severe destruction.If you are close to the sea and the water retreats by an abnormal amount, move to high ground at once.
While it is possible that the region could be affected by earthquake-generated tsunamis, scientists currently believe that the more immediate threats posed by earthquake hazards such as collapsing buildings, falling electricity lines, ruptured gas lines, rock slides and/or landslides on mountains and hillsides (as recently witnessed in Dominica, Trinidad, the British Virgin Islands and the Cayman Islands) are more of a present danger to the region. Greater focus should, therefore, be placed on ensuring that effective public education programmes are undertaken to sensitize the public to these hazards and serious consideration should be given to constructing sound earthquake-resistant buildings.
For updates on these and other geologic events occurring in the region please visit the Seismic Research Unit’s website at www.uwiseismic.com. Based at the University of the West Indies in St. Augustine Trinidad, the Seismic Research Unit is the agency responsible for monitoring earthquakes and volcanoes throughout the English-speaking Eastern Caribbean.