The National Science Foundation calls tsunamis the Caribbean’s “forgotten hazard.” A tsunami (pronounced soo-nah-mee) is an ocean wave or series of ocean waves caused by an abrupt disturbance of the ocean floor that displaces a large mass of water. Earthquakes, landslides, volcanic eruptions, explosions and even the impact of asteroids, meteorites or comets can generate tsunamis.
The main sources for tsunami in the Caribbean are earthquakes (generated at the boundaries of the Caribbean Plate or within the Plate), submarine landslides, volcanoes, and large earthquakes which occur far away and generate a large tsunami which reaches the Caribbean. An example of the latter is the “Great Lisbon Earthquake” of 1755 which affected several islands. Waves as high as 7 meters were reported from Saba, and Barbados reported a rise in sea-level of about one meter followed by large waves.
Within the region there are numerous reports of tsunamis, some of which have caused fatalities. It is difficult to give a figure for fatalities from tsunamis in the Caribbean, because these are not usually differentiated from fatalities due to the earthquakes with which the tsunamis are often associated. However there are reports of 100 fatalities in the Dominican Republic from the 1946 Tsunami. Most recently, tsunami associated with volcano in Montserrat have been reported from neighboring islands.
The tsunami risk to the Caribbean, and by extension the Cayman Islands, is not very well defined. Work continues in this area. However the threat is real, and all residents of the region should know the warning signs and the basic precautions which are necessary.
Tsunamis can devastate coastlines, causing widespread property damage and loss of life. They strip beaches of sand, uproot trees and other coastal vegetation and cause large scale flooding. Most deaths from tsunamis are caused by drowning.
- Tsunamis are not tidal waves, as they are not caused by tides and are not related to tides.
- They are generally triggered by a major earthquake under the ocean.
- Once created, they may spread out from the point of creation very fast (up to 435 mph)
- In the ocean, these waves may only be 1.5 feet (0.5m) high, but 50-60 miles wide.
- They may be so low and broad that they may not be recognized by ships.
- The first hit on land is usually not the biggest. Other larger waves may follow in 15-minute to one-hour intervals.
- As the waves enter coastal waters, their speed decreases and height increases.
- Coastal water usually recedes before the first tsunami strikes.
- Damage is generally caused by the flow of water (the run-up and drawdown) on the coastal area.
- Normally encounters look more like a quickly rising high tide than a large breaking wave.
What to do in the event of a Tsunami
- If you are in school and you hear there is a tsunami warning, you should follow the advice of teachers and other school personnel.
- If you are at home and hear there is a tsunami warning, you should make sure you entire family is aware of the warning. Your family should evacuate your house if you live near to the coast. Move in an orderly, calm and safe manner inland or to a safe elevation in a high building. Follow the advice of Cayman Islands Government Authorities.
- If you are at the beach or near the ocean and you feel the earth shake, move immediately inland or to higher ground. DO NOT wait for a tsunami warning to be announced. A regional tsunami from a local earthquake could strike some areas before a tsunami warning could be announced.
- Tsunamis generated in distant locations will generally give people enough time to move to a safe location. For locally generated tsunamis, where you might feel the ground shake, you may only have a few minutes to move to safety.
- High, multi-story, reinforced concrete building and hotels are located in many low-lying coastal areas and in George Town. The upper floors of these buildings can provide a safe place to find refuge should there be a tsunami warning and you cannot move quickly inland. Homes and small buildings located in low lying coastal areas are not designed to withstand tsunami impacts. Do not stay in these structures should there be a tsunami warning.
- Offshore reefs and shallow areas may help break the force of tsunami waves, but large and dangerous waves can still be threat to coastal residents in these areas. Staying away from all low-lying coastal areas is the safest advice when there is a tsunami warning.
Before a Tsunami
- If you live in a low-lying area, familiarize yourself with the quickest way to retreat to a safer location. Make sure all family members know the evacuation plan.
- If you are close to the sea and notice that the water recedes by an abnormal amount, move to safer ground at once. Do not stay to see what happens.
- Listen to the radio for official updates and instructions.
- Gather emergency supplies.
- Develop a family emergency plan.
After a Tsunami
- Avoid floodwaters. The water may be contaminated by oil, gasoline or raw sewerage. The water may also be electrically charged from downed power lines.
- Avoid moving water. Moving waters only six inches deep can sweep you off your feet.
- Stay away from downed power lines and report them to CUC.
- Stay away from designated disaster areas unless authorities ask for volunteers.
- Return home only when authorities indicate it is safe. Stay out of buildi ngs surrounded by floodwater. Use extreme caution when entering buildings. There may be hidden damage, particularly in foundations.
- Consider your family’s health and safety needs:
- Wash hands frequently with soap and clean water if you come in contact with floodwaters.
- Throw away food that has come in contact with floodwaters.
- Listen for news reports to learn whether the water supply is safe to drink.
- Listen to news reports for information about where to get assistance for housing, clothing and food.
- Seek necessary medical care at the nearest medical facility.
- Service damaged septic tanks, cesspools, pits and leaching systems as soon as possible. Damaged sewerage systems are a serious health hazard.
- Drain and clean cisterns as they may also be contaminated
TCI TSUNAMI RISK PROFILE
Although tsunami events in the Caribbean region have been rare, this is not an indication that there is no threat for the area. Located within a seismically active zone, historical records indicate that, the Caribbean and adjacent regions has experienced in excess of 75 tsunamis over the last 500 years (von Hillebrandt-Andrade, 2013). Examples of significant tsunami events in the region include:
- 1692 tsunami, Port Royal, Jamaica – the result of an 8.1 magnitude earthquake; with over 2000 deaths (USGS, 2014).
- 1842 tsunami, Haiti – the result of an 8.1 earthquake. The event killed 300 persons (NOAA, 2015a). Pusey, J.H (1897) indicated in his book, The Handbook of the Turks and Caicos Islands, that the TCI also felt impacts from this earthquake.
- 1964 tsunami, Dominican Republic – the result of an 8.0 earthquake. 100 deaths and approximately 20,000 left homeless (USGS, 2012).
Given the geographical location and topography of the Turks and Caicos Islands, there is a low to moderate risk for seismic activity (CCRIF, 2013). The primary source of high seismic activity and tsunami hazard in the area is the Septentrional Fault system. This fault system marks the major North American-Caribbean plate-boundary fault in Hispaniola (Prentice et al., 1993); running several hundred kilometers south of the Turks and Caicos Islands (CCRIF, 2013). Any earthquake/tsunami generated along the North American-Caribbean plate margin therefore represents a potentially significant hazard/threat. Additionally, the TCI is also vulnerable to seismic activity generated along the Puerto Rican Trench (Smith Warner International, 2006).
Existence of this degree of risk therefore requires the Department of Disaster Management and Emergencies (DDME) to have an Emergency Response Plan (ERP) in place to coordinate response to such an identified threat. Granted that a tsunami cannot be prevented, tsunami impacts can be mitigated through community preparedness, timely warnings dissemination and effective and timely response.
Tsunami Susceptibility Mapping.
It essential that tsunami susceptibility maps for all major islands/cays in the TCI are produced to help guide decision making and response activities. However, it is important to note that the tsunami susceptibility maps are a work in progress and will be updated whenever new safe routes and locations are established.
Areas most at risk and thus requiring evacuation was determined utilizing these maps and through field inspection of all coastal areas throughout the islands to identify any natural or manmade conditions that could specifically impact local tsunami inundation e.g. – roads, structures, vegetation or trees. General consensus is that areas most vulnerable to tsunami inundation are those which are not protected; either by coastal engineering hard structures, wide beaches, dunes, coral reefs, or other barriers.
Note that these susceptibility maps are practical tools in hazard mitigation planning, urban planning, natural resource management, and disaster response management. Susceptibility maps by nature do not provide detailed information of the magnitude or the extent of water levels. They cannot provide specific locations of hazardous areas. Rather they identify the likely regions to be affected within the island. They are based on general land and topographic characteristics over the island but at this scale, they cannot incorporate detailed hydraulic properties of drainage facilities in the regions. Additionally, it is important to note that historic or current tsunami prediction data were not utilized in the production of these maps.