A tsunami, also known as a seismic sea wave, is a massive ocean wave that is generated by large earthquakes that occur near or under the ocean, volcano eruptions, or landslides. Unlike average ocean waves, tsunamis are not produced by wind and storms. Consisting of multiple waves that roar onto the shore in a fast-rising and powerful manner, tsunamis can travel inland further than traditional waves and even the smallest kind can be dangerous. The speed with which a tsunami moves onshore is such that many have said if you can see it, it is too late to outrun it. If you hear a tsunami warning, feel strong shaking in coastal areas, or if the ocean is receding at a rapid pace, it is recommended that you quickly move to higher ground away from the coast until wave activity has normalized.
In 2004 a magnitude 9.1 earthquake shook Sumatra, Indonesia in the Indian Ocean. A tsunami was generated and an estimated 227,898 people were killed or listed as missing and presumed dead. 11 Indian Ocean countries were affected by the killer waves. This tsunami was also estimated to have traveled a 3,000 mile journey ending in Africa. Since this event, the Indian Ocean Tsunami Warning System (IOTWS), which uses surface buoys to gather data on wave height, has been deployed. This area has also improved awareness of tsunamis amongst the population and tourists. They have developed much more reliable warning systems to alert the public of impending tsunamis.
Sources:
www.usgs.gov
http://www.cnn.com/2013/08/23/world/tsunami-of-2004-fast-facts/
http://news.nationalgeographic.com/news/2004/12/1227_041226_tsunami.html