The picture of the 2004 tsunami at Ao Nang, Krabi Province, Thailand on 26 December 2004, photo by David Rydevik, Stockholm, Sweden.
The 2004 Indian Ocean earthquake, with a magnitude of between 9.1 and 9.3 the second largest earthquake ever recorded, was an undersea earthquake that occurred at 00:58:53 UTC on December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The resultant tsunami hit 14 countries inundating coastal communities with waves up to 30 meters (100 feet) high; one of the deadliest natural disasters in recorded history, Indonesia, Sri Lanka, India, and Thailand were the hardest hit.
Tsunamis are sea waves with long wavelength of long wave periods triggered by sudden movement of large volumes of water. In the open ocean the distance between two wave crests can be over 100 kilometers, and the wave periods can vary from five minutes to one hour. Such tsunamis can travel at speeds of 600 to 800 kilometers per hour, depending on the depth of water in the sea or ocean. Large tsunami waves, caused by an earthquake or a submarine (underwater) landslide, can overrun coastal areas on the path of tsunami in a matter of minutes. Tsunamis can also travel thousands of kilometers across the ocean and wreak destruction on far off shores hours after the earthquake that generated them.