CDM - Tsunami

What is a Tsunami?

A tsunami (pronounced soo-NAHM-ee) is a series of ocean waves caused by a major disturbance of the ocean floor, such as a large underwater earthquake, landslide or volcanic eruption. The waves travel outwards away from the origin of the disturbance – much like the ripples you see when you throw a rock in a puddle. Tsunami waves can travel at hundreds of miles per hour and crash into shorelines with waves of over 30 metres. Tsunamis can last for several hours or only a few minutes. The word tsunami is Japanese and means “harbour wave”.

Tsunamis and the Caribbean

Right now, a tsunami is a potential hazard for the Caribbean, rather than a real major hazard. Although, that doesn’t mean you can go unprepared. There hasn’t been a deadly tsunami in the region for centuries but off the coast of Grenada, the submarine volcano, Kick `em Jenny, is evolving into a condition where it is more likely to generate a significant tsunami.

There is a 50% chance that Kick `em Jenny will generate a significant tsunami (amplitude more than ten meters at ten kilometers from source) within the next 50 years.

What a tsunami is not!

Tsunamis are sometimes called tidal waves, but this is wrong. A tsunami has nothing to with ocean tides. Tides are caused by gravitational influences of the moon, sun and planets while tsunamis are mainly caused by earthquakes, landslides and volcanic eruptions. In a Tsunami the sea first withdraws an unusual distance and then returns like a rapidly-rising tide flooding low-lying areas. This may be repeated several times.

Characteristics of a tsunami

  • Like all waves, tsunamis tend to be small – even unnoticeable while they move over open water, and do not “size up” until they approach a shoreline.
  • As a tsunami approaches shore, it slows down. Often, the sea begins to recede abnormally.
  • Tsunamis reach the coast with enormous amounts of energy because their height increases as they reach the part of the earth’s crust that slopes, or rises, from the ocean floor up to the land. Tsunamis may reach a maximum height onshore of 10, 20, and sometimes even 30 meters above sea level – in other words, they can be huge.
  • A tsunami is a series of waves and the first wave is not always the biggest.
  • Because tsunamis can travel very far without losing much energy they can affect places that are a great distance from their source.
  • Tsunamis that are the result of water displacement from above (e.g. landslides, meteor strikes) usually don’t last very long and have little impact on far away coastlines.


The most serious impact of a tsunami would be the flooding they cause. They are capable of flooding hundreds of meters inland. Water from the tsunami also moves fast and can crush homes and other coastal structures. Tsunamis can sweep boats onto shore and obviously, they can drown people and animals too. Drowning is the most common cause of death associated with a tsunami.

The deadliest tsunamis in recorded history were the Christmas tsunamis of 2004 in the Indian Ocean. On December 24, 2004, a massive 9.2 earthquake occurred off the island of Sumatra. It created a deadly series of tsunamis that swept Indonesia, India, Madagascar, and Ethiopia. The death toll was estimated to be in around 300,000 to 350,000.

Also, tsunamis can strip beaches of sand that may have taken years to accumulate and destroy trees and other coastal vegetation.

Areas are at greater risk for tsunamis if they are less than 25 feet above sea level and within a mile of the shoreline. Other hazards include contamination of drinking water, and fires from gas lines or ruptured tanks.


1. When?

    November 18,1867


    Virgin Islands


    A magnitude 7.5 earthquake-generated tsunami may have killed up to 20 people.
    The earthquake actually consisted of two shocks, separated by ten minutes. These
    shocks generated two tsunami waves that were recorded at several Island locations
    across the eastern Caribbean region, most notably on the Islands of St. Thomas and
    St. Croix. In the historical accounts there is some confusion between deaths caused
    by the tsunami and those caused by a hurricane a few days before.

    Eyewitness accounts describe the waves as being between 4.5 and 7.8 meters high.
    The waves destroyed many small boats anchored in the harbour, levelled the town's iron
    wharf, and either flooded out or destroyed all buildings located along the waterfront area.
    This tsunami was noticed as far south as Grenada but caused no damage or casualties
    anywhere else.

2. When?

    July 24, 1939


    Leeward Islands


    When Kick 'em Jenny erupted in 1939, it generated a tsunami with an amplitude of 1-2
    metres in the southern Grenadines and northern Grenada. Run up in Barbados was
    enough to flood roads on the west coast.

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