Tsunami means 'harbour wave' in Japanese and is the term used to describe the huge, powerful waves which occur in large bodies of water. Tsunamis are caused by several natural events, all catastrophic in proportion and all causing energies to be released which are trapped in the water body mass and travel through it, causing damage when they reach land when the energy comes to a natural barrier.
One cause of tsunamis is earthquakes. Where continental shelves either converge or are moving away from each other, energy is stored because one shelf is pushed under the other. When this energy is released by the plate moving, an earthquake occurs and this can cause a tsunami.
Tsunamis can also be casued by underwater volcanoes. At the convergent edges of continental plates or over hot spots in the Earth's crust like those of the Pacific 'Ring of Fire' volcanic activity unleashes vast amounts of energy from beneath the Earth's surface, along with volcanic material. These, if they occur on land, cause massive damage but if they occur underwater the damage to land is minimal but the energy unleashed can result in a tsunami.
Another cause of tsunamis can be underwater mud slides or land sliding into the sea. Either of these can cause the immense waves we know as tsunamis.
Tsunamis can cause a huge amount of damage and often the damage is caused hundreds of miles away because the waves travel away from the epicentre of a catastrphoic event, the wave only being interrupted where it makes land fall and here the energy stored in the wave is unleashed causing immense damage, with the wave often travelling several miles inland.
Tsunamis, though devastating, are a rare event and many natural activites occur on a much smaller scale. There are earth tremors, small volcanic eruptions, landslides and other events which occur regularly as the Earth's plates move, converge and move apart. The Earth's crust sits over a liquid lithosphere, which means there will always be activity and movement, resulting in potential tsunami causing events but the majority of these do not result in tsunamis, the energy dissipating in much lesser waves.
Some parts of the Earth are far more likely to see tsunamis than others and these include the Pacific islands, some of which were formed after volcanic events, the coast of Sothern America and other places where continental plates run next to each other, the type of movement resulting in a ridge or crest. Crests are far more likely to have tsunami causing events occur than ridges as the movement of the plates is quicker.
Sadly it is some of the most beautiful places on Earth which are most susceptible to tsunamis as well as some of the poorest and, while they are rare, their possibility should never be ignored.