Everyone remembers in vivid detail the horrific events of a tsunami that devastated parts of Indonesia and Sri Lanka in December, 2004. Ever since that date, the word "tsunami" strikes fear in the hearts of those living in the area where it is predicted to occur.Throughout history there have been incidences of these gigantic waves destroying everything in their path in many different parts of the world. Approximately 30,000 people lost their lives when a tsunami struck the coast of Japan in 1896. The memories of those that lived through this type of natural occurrence on the Burin Peninsula of Newfoundland and Labrador in 1929 is recorded in the book, Tsunami, written by Maura Hanrahan. In 1946, the city of Hilo on the island of Hawaii was partially destroyed due to a tsunami.
In every recorded occurrence, the scientific explanation for a tsunami is an earthquake that takes place far out into the ocean. This causes a huge underwater ocean wave, and even though they are called tidal waves, tsunamis do not have any connection to the rise and fall of the tides.
The vertical movements of the Earth's floor under the ocean are the cause of tsunamis. These movements are so strong that they cause earthquakes to occur. They do not have to take place in areas of deep water because the most common depth of water has been found to be about 30 meters. It has been compared to the effect you receive when you drop a large object into a bucket of water or a small pool. The force of the drop when the object hits the water results in a series of concentric waves that move out from the area where the object hit the water.
There is a tremendous amount of energy in a tsunami. Some are only small depending on the size of the earthquake. The energy comes from the great volume of water that is affected by the movement beneath the surface. On the open ocean, the waves may not reach to any great height, but the distance between the crests may be as much as 100 miles. These waves travel very rapidly, often reaching speeds in excess of 500 miles an hour. When the waves come in contact with the shallow water off low lying areas of land a huge wave results and this floods over the land.
Coastlines that are some distance away from the source of the earthquake may not even feel the effects of a tsunami. This is because the waves will wear down before they reach land. There is no advance warning of an impending tsunami, but the presence of high waves near a shoreline that is normally calm could be an indication that such an event is likely to occur.