Tsunami Facts

Tsunami is a Japanese term meaning wave 'nami' in a harbor 'tsu'. Tsunamis are a series of long waves of extremely long length and period, usually generated by disturbances associated with earthquakes occurring below or near the ocean floor. Those tsunamis are also called seismic sea waves and incorrectly, tidal wave.

Volcanic eruptions, submarine landslides, and coastal rock falls can also generate tsunami, as can large meteorites impacting the ocean.

Tsunami waves can reach enormous dimensions and travel across entire ocean basins with little loss of energy. In the deep open water one will hardly recognize them. However tsunamis dramatically increase in height when approaching shallow waters. Tsunamis can inundate large areas and cause cataclysmic damage to life and property.

In the open ocean a tsunami wave travels as fast as a modern jet airliner - up to 800 km/h. It slows down when it reaches shallow water, building up to a towering wave and unstoppable surge of water.

Usually a tsunami is not just one but a series of waves. That's why it is important to wait for an 'all clear' before returning to lower areas.

Tsunami hazards exist in all oceans and basins, but occur most frequently in the Pacific Ocean.

Most tsunamis are triggered by underwater earthquakes which can't be predicted. However once an earthquake occurred modern science is able to estimate whether a tsunami was created with remarkable accuracy.

The time remaining from the initial earthquake until the arrival of the wave on the coast varies greatly and depends on the distance from the epicenter of the quake in the ocean to the coast.

In Indonesia where great subduction zones [collision zones of continental plates] are relatively close to shore early warning times vary between 10 and 25 minutes. In other areas like Sri Lanka it is likely that several hours lay between earthquake and arrival of the waves.

A selection of public early warning services can be found in the 'Resources' section of this website.

Because of the unstoppable and destructive force of tsunami, tsunami preparedness should become an integral part of everyday life on the coast.

Natural Early Warning Signs

Earthquake

If you feel a strong earthquake move away from the beach and to higher ground immediately as a precautionary measure.

Quickly receding waterline

If you observe the waterline quickly receding from the beach, chances are that a tsunami is imminent. Don't waste time and move away from the beach and as high up as possible. While a receding waterline is a relatively reliable natural early warning sign, it is not always occurring. You should under no circumstances move to the beach to observe the waterline in order to determine whether a tsunami has been generated or not. As a rule of thumb: If in doubt - get out!

Loud Roar

A loud roar coming from the sea - similar to an approaching jet airliner can be an indicator that a tsunami is travelling towards you.

The Asian Tsunami

The 2004 Indian Ocean earthquake is an undersea mega thrust earthquake that occurred at 00:58:53 UTC on Sunday, December 26, 2004, with an epicenter off the west coast of Sumatra, Indonesia. The quake itself is known by the scientific community as the Sumatra-Andaman earthquake. The resulting tsunami is given various names, including the 2004 Indian Ocean tsunami, Asian Tsunami, Indonesian Tsunami, and Boxing Day Tsunami.

The earthquake was caused by subduction and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing over 230,000 people in fourteen countries, and inundating coastal communities with waves up to 30 meters (100 feet) high. It was one of the deadliest natural disasters in recorded history. Indonesia was the hardest hit, followed by Sri Lanka, India, and Thailand.

With a magnitude of between 9.1 and 9.3, it is the third largest earthquake ever recorded on a seismograph. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm and triggered other earthquakes as far away as Alaska. Its hypocenter was between Simeulue and mainland Indonesia.

The plight of the many affected people and countries prompted a worldwide humanitarian response. In all, the worldwide community donated more than $14 billion USD in humanitarian aid.

The 'Tsunami Ready' initiative is a result of the lessons learned by the tourism industry from this terrible event.

Sources:
WIKIPEDIA - The Indian Ocean Tsunami
http://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami

UNESCO - IOC [2006]. Tsunami Glossary. IOC Information Document No. 1221. Paris

Tsunami Ready [2009]: The Tsunami Ready Toolbox for the Indonesian Hotel Industry. Jakarta