The facts about tsunamis
Here is everything you need to know about tsunamis: causes, impacts and early warnings systems.
March 03, 2010
What is it? (1/10)
sunami is a wave or series of waves with extremely long wave length. They are caused by underwater earthquakes, landslides, or volcanic eruptions. Tsunamis travel extremely fast and can flood coastal communities within minutes.
Tsunami is a Japanese word: The Japanese characters “tsu” and “nami” mean “harbor” and “wave”. Tsunamis have also been called “tidal waves”, but this is a misnomer because they are not caused by tides in any way.
Huge Tsunami in Japan (2/10)
Cars and airplanes swept up by a tsunami are pictured among debris at Sendai Airport, northeastern Japan, March 11, 2011.
A massive 8.9 magnitude quake hit northeast Japan causing many injuries, fires and a ten-meter (33 feet) tsunami along parts of the country's coastline.
Speed & Size (3/10)
Waves break on the beach at Lhok Nga in Indonesia. The area was severely hit by the Indian Ocean Tsunami in December 2004. Tsunamis occur suddenly, often without warning, and are extremely dangerous to coastal communities.
A tsunami can travel at over 900 km/h (560mph) in the open ocean. A regular wave travels at only about 90km/h (56mph). As it approaches the coast, the tsunami slows down, but rises as high as 30 meters (about 100 feet).
An expert of the National Oceanic and Atmospheric Administration (NOAA) looks at computer graphs that show the travel time of a tsunami. The wave stemmed from a huge sub-sea earthquake that hit American Samoa in September 2009.
About 80 percent of all tsunamis occur in the Pacific Ocean, affecting countries along the edges of the ocean the most. Although tsunamis are rare, they can occur at any time of the day or night all year round.
The 2004 Indian Ocean Tsunami (5/10)
People launch floating paper lanterns in remembrance of the 2004 Indian Ocean tsunami victims, in Khao Lak, Thailand. On December 26, 2004, a 9.15 magnitude earthquake triggered a series of tsunamis in the Indian Ocean, killing 230,000 people in fourteen nations.
Kenya, Indonesia, Sri Lanka, India, and Thailand were hit hardest.
Humanitarian Impacts (6/10)
The shoreline of Banda Aceh, Indonesia, in June 2004 and in December 2004, shortly after the Indian Ocean tsunami struck. According to the NOAA, tsunamis have claimed more than 420,000 lives since 1850 and caused billions of dollars of damage to coastal structures and habitats.
This doesn't include wider humanitarian impacts, such as water and food shortages and disease epidemics due to the collapse of infrastructure.
A fisherman in Calang, Indonesia. In the 2004 Indian Ocean tsunami, countless fishermen lost their income because the tsunami damaged their boats and fishing gear.
The Indian Ocean tsunami had severe impacts on local economies. Farmers suffered as their fields were swamped with salty water, killing crops. Hotels and resorts–often the first ones to be hit by a tsunami–were affected twice. First by the tsunami then by cancellations. Reconstruction costs amounted to billions of dollars.
An Acehnese worker carries mangrove tree saplings. After the 2004 tsunami, farmers had to clear surface drains to remove salt water and wait until the salt concentration of the soil was reduced. They used chemical and physical means to make their soil fertile again.
Tsunamis also damage coral reefs and coastal forests. They spread waste and chemicals and pollute freshwater supplies and fields with salt water. The destruction of sewage facilities can impact affected regions for years.
Prevention and Prediction (9/10)
Elementary school students in Banda Aceh listen to a tsunami training exercise provided by Indonesia's Red Cross. A tsunami cannot be prevented, and it is impossible to predict when and where a tsunami will strike.
But once it is triggered, modeling and measurement technologies can forecast where and when it will hit. Timely warnings can then alleviate its impacts. Some warning signs are visible for everyone. Before a tsunami arrives, the water along the shore recedes dramatically, sometimes hundreds of meters. This is known as a drawback.
Early Warning (10/10)
Indonesian engineers unload a tsunami early warning buoy into the sea in Banten province, Indonesia. When an earthquake generates a tsunami, a sensor on the ocean floor measures the water pressure and sends the data to the buoy on the surface.
The buoy then sends it to a satellite, which in turn sends it to early-warning stations. Such data allows to determine the path and the strength of a tsunami.