What is a tsunami?
A tsunami (soo-NAH-mee) is an ocean wave or series of waves caused by a sudden disturbance of the ocean floor that displaces a large amount of water. Tsunamis are caused generally by earthquakes, less commonly by submarine landslides, infrequently by submarine volcanic eruptions and very rarely by large meteorite impacts in the ocean.
Why is it called a tsunami?
The word tsunami is taken from two Japanese words which mean harbour (tsu) wave (nami). Tsunamis are quite common in Japan.
Do all earthquakes cause tsunamis?
No, all earthquakes do not cause tsunamis. There are four conditions necessary for an earthquake to cause a tsunami:
- The earthquake must occur beneath the ocean or cause material to slide in the ocean.
- The earthquake must be strong, at least magnitude 6.5.
- The earthquake must rupture the Earth’s surface and it must occur at shallow depth – less than 70km below the surface of the Earth.
- The earthquake must cause vertical movement of the sea floor (up to several metres).
How do volcanic eruptions cause tsunamis?
Although relatively infrequent, violent volcanic eruptions can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area. According to this mechanism, waves may be generated by the sudden displacement of water caused by a volcanic explosion, by a volcano’s slope failure, or more likely by a phreatomagmatic explosion and collapse/engulfment of the volcanic magmatic chambers. One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36, 417 people. It is also believed that the destruction of the Minoan civilization in Greece was caused in 1490 B.C. by the explosion/collapse of the volcano of Santorin in the Aegean Sea. (Courtesy: UNESCO IOC – International Tsunami Information Center)
Are a tsunami and a tidal wave the same thing?
No. Strictly speaking, a tidal wave is related to ocean tides while a tsunami is triggered by earthquakes, landslides or volcanic events.
How are tsunamis different from normal ocean waves?
- Ocean waves are related to changes in the atmosphere while tsunamis are related to changes within the Earth.
- Tsunami waves are distinguished from ordinary ocean waves by their long wavelengths (distance between two crests or highest point of the wave), often exceeding 100 kilometers in the deep ocean and by the long amount of time between the arrivals of these crests, ranging from five minutes to an hour.
- Most tsunami waves do not break like normal surf waves at the beach that curl over as they approach shore rather they come in much like a very strong and very fast wall of water. Those that do break often form vertical walls of turbulent water called bores.
Click here for more information on how tsunamis differ from normal ocean waves.
Can a tsunami occur anywhere in the world?
Yes, all oceanic regions of the world can experience tsunamis, but in the Pacific Ocean large, destructive tsunamis occur much more frequently because of the many large earthquakes occurring in the margins of the Pacific Ocean.
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?
The magnitude 9.0 earthquake which occurred on 26th December, 2004 off the west coast of northern Sumatra, was the fourth largest earthquake in the world since 1900. The tsunami triggered by that earthquake killed over 250,000 people in at least eleven countries. While it is possible for a similar tsunami to occur in the Caribbean, scientists currently believe that there is a very small chance of this happening. As far as we know, the largest tsunami to affect the Caribbean in the past 500 years was 8m in height.
Can an eruption from the Kick-’em-Jenny submarine volcano cause a tsunami?
Kick ‘em Jenny is a submarine (underwater) volcano located 9 km north of Grenada. Currently, scientists believe that there is a very small chance that an eruption of the volcano would trigger a tsunami. Measurements of the volcano were taken in 2003 and the results showed that the summit (highest point) of the volcano is quite deep below the surface of the sea, too deep for an eruption of the kind normally seen to trigger a tsunami.
Is it true that there is a volcano in the Canary Islands that can cause a mega-tsunami in the Caribbean?
The Cumbre Vieja Volcano is on the Island of La Palma in the Canary Islands (off the west coast of Africa). The institution in charge of the monitoring (INVOLCAN) does not recognise the volcano-edifice stability as a potential tsunami risk. Pyroclastic density currents that can cause tsunamis are unlikely to occur at these volcanoes. Even though they can occur, evidence shows that tsunamis produced, as a result of instability of the volcano-edifice, are generally localised. Trans-oceanic tsunami generated by eruptions are unlikely and as such the statement above cannot be considered true.