Tsunami is a Japanese word that translates as "harbor wave." It is a name given to very long waves in the ocean that are generated by an earthquake or any other event that displaces a large volume of water. Tsunamis differ from normal wave events in that a tsunamis main source of energy is a water displacement event rather than a normal wind driven wave.
The long wavelength of a tsunami travels at a very fast speed. There have been many tsunamis throughout history that have devastated coastal areas. The 1960 tsunami which occurred off of the coast of Chile reached the Hawaiian coast in 15 hours and the Japanese coast in 22 hours. The most recent tsunami occurred in 2011 off of the coast of Japan. The Tohoku earthquake of 2011 was a magnitude 9.0 earthquake. It triggered a tsunami with waves that reached heights of 133 feet. The tsunami disrupted nuclear facilities and caused over 15,000 deaths. The 2004 Indian Ocean tsunami was one of the deadliest natural disasters in human history. During the destruction of that tsunami, over 230,000 people in fourteen countries lost their lives. All of these earthquakes were caused by subduction under the ocean.
Subduction is the process of one geological plate moving underneath another plate. This causes a huge disruption in the stability of the ground and an earthquake usually occurs. When these earthquakes occur in the middle of the ocean, they send a huge force of energy through the water which causes gigantic waves. These waves can be hundreds of feet tall depending on where the earthquake occurs. Tsunamis are some of the more dangerous natural disasters because human beings do not have as much time to prepare for a tsunami. Once an earthquake occurs in the ocean, it gives people very short notice to find safety or evacuate.