Tsunamis and the Eastern Caribbean – Frequently asked questions

St. Augustine, Trinidad and Tobago – As a result of the tsunami that recently devastated several countries in Asia, scientists at the Seismic Research Unit have compiled a list of frequently asked questions to address concerns raised here in the region. The magnitude 9.0 earthquake, which occurred on December 26, last year off the west coast of northern Sumatra, was the fourth largest earthquake in the world since 1900 and is the largest since the 1964 Prince William Sound, Alaska earthquake. {{more}}The December 26th earthquake generated a tsunami which killed tens of thousands of people in at least 11 countries.

• QUESTION: Is it possible for a tsunami of similar amplitude and strength to the one that occurred in the Indian Ocean to occur here in the Caribbean?

• ANSWER: While it is possible for a similar event to occur in the region, scientists currently believe that there is a very low probability of this happening. As far as we know, the largest tsunami to affect the Caribbean in the past 500 years has been 8m in amplitude.

• QUESTION: Can an earthquake from outside of the region cause a tsunami?

• ANSWER: Yes, a tsunami may be generated from earthquakes occurring both within and outside of the region. However, there are three conditions necessary for the generation of a tsunami: the earthquake must occur beneath the ocean and be strong (at least of magnitude 6.5), the earthquake must occur at a shallow depth (less than 50km below the surface of the Earth), and the earthquake must be dip-slip in nature (which means there is a vertical component, which displaces a large volume of the sea).

• QUESTION: Are a tsunami and a tidal wave the same thing?

• ANSWER: No. Strictly speaking, a tidal wave is related to ocean tides while a tsunami is generated from tectonic earthquakes or volcanic events.

• QUESTION: How are tsunamis different from normal surf waves?

• ANSWER: Tsunami waves are long-period (200-2000 s) ocean waves having wavelengths of tens of kilometres. They are excited by large-scale displacements of water. Most tsunami waves do not break like normal surf waves at the beach that curl over as they approach shore. They come in much like very strong and very fast tides, i.e. a rapid, local rise in sea level. Those that do break often form vertical walls of turbulent water called bores.

• QUESTION: Is there a tsunami early warning system in the Caribbean?

• ANSWER: No, there is no tsunami early warning system in the Caribbean.

• QUESTION: Can an eruption from the Kick ’em Jenny submarine volcano cause a tsunami?

• ANSWER: Kick ’em Jenny is a submarine volcano located eight km north of Grenada. Currently, the threat of a tsunami from an eruption of the volcano is extremely low since a recent (2003) survey revealed that the summit of the volcano is quite deep. At the moment, Kick ’em Jenny poses a grave danger to shipping as the volcano is constantly emitting gases, which lower the buoyancy of the water and can cause vessels to sink. For this reason there is a 1.5km exclusion zone around the summit of the volcano.

• QUESTION: Is it true that there is a volcano in the Canary Islands that can cause a mega-tsunami in the Caribbean?

• ANSWER: The Cumbre Vieja Volcano is located on the island of La Palma in the Canary Islands (off the west coast of Africa). There is a school of thought which asserts that if the western flank of the volcano were to collapse and drop 150 to 500km3 of rock into the sea, massive tsunamis could be generated which could devastate islands in the Caribbean as well as coastal areas in North America. While this may be possible, this is in fact a worst case scenario and it is not the most likely scenario. Scientists at the Seismic Research Unit believe that the likelihood of this happening is remote and planning for such a rare event should not be a priority at this time; rather, attention should be placed on the dangers posed by immediate natural hazards in the region such as hurricanes, earthquakes and volcanic events.

• QUESTION: Why have we been having so many “big” earthquakes recently? Is something going wrong with the Earth? Are they all triggering each other?

• ANSWER: While all of these earthquakes have been caused by the same process, i.e. the movement of the Earth’s plates, one earthquake has not triggered another. Additionally, the succession of earthquakes does not necessarily imply that something is “wrong” with the Earth, rather the events are all part of the Earth’s natural processes.

• QUESTION: What can we do to prepare for a tsunami?

• ANSWER: If you live in a low-lying area make yourself familiar with the quickest way to retreat to high ground. Make sure all family members know the evacuation plan. If you are close to the sea and the water retreats by an abnormal amount, move to high ground at once. Do not stay to see what happens.