A tsunami is a series of water waves caused by the displacement of a large volume of water, often from earthquakes, volcanic eruptions, landslides or other disturbances below or above water. Tsunami waves have a very long wavelength and can cause enormous destruction in coastal areas, with wave heights over tens of metres. The 2004 Indian Ocean tsunami was one of the deadliest natural disasters, killing over 290,000 people across 14 countries.