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A tsunami hitting a coastline. This article lists notable tsunamis, which are sorted by the date and location that they occurred. Because of seismic and volcanic activity associated with tectonic plate boundaries along the Pacific Ring of Fire, tsunamis occur most frequently in the Pacific Ocean, but are a worldwide natural phenomenon.
A tsunami is a series of enormous waves – of up to 30 metres or more – created by disturbances near or below the ocean. Shutterstock. Alex Izeman. Summary. Possible causes. What are the risks? Types of tsunami. Common misconceptions. What to do? Possible causes. Such disturbances include: Earthquakes.
Oct 16, 2006 · What is a Tsunami? A tsunami is a massive, fast-moving wave created by an underwater earthquake or landslide. The large volume of water displaced by a sudden movement of the seafloor creates a pulse in the ocean that races out from its source at speeds of up to 500 miles per hour and extends thousands of feet below the surface. In deep water, a ...
- Overview
- As Fast as a Commercial Jet
- Warning Signs
- Advice for Sailors
National Geographic News looks at how the killer waves are caused, what the warning signs are, and how to respond when a tsunami threatens.
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•Where the ocean is deep, tsunamis can travel unnoticed on the surface at speeds up to 500 miles an hour (800 kilometers an hour), crossing an ocean in a day or less. Scientists are able to calculate arrival times of tsunamis in different parts of the world based on their knowledge of water depths, distances, and when the event that generated them occurred.
•A tsunami may be less than a foot (30 centimeters) in height on the surface of the open ocean, which is why they are not noticed by sailors. But the powerful shock wave of energy travels rapidly through the ocean as fast as a commercial jet. Once a tsunami reaches shallow water near the coast, it is slowed down. The top of the wave moves faster than the bottom, causing the sea to rise dramatically.
•Geological features such as reefs, bays, river entrances, and undersea formations may dissipate the energy of a tsunami. In some places a tsunami may cause the sea to rise vertically only a few inches or feet. In other places tsunamis have been known to surge vertically as high as 100 feet (30 meters). Most tsunamis cause the sea to rise no more than 10 feet (3 meters).
•Where the ocean is deep, tsunamis can travel unnoticed on the surface at speeds up to 500 miles an hour (800 kilometers an hour), crossing an ocean in a day or less. Scientists are able to calculate arrival times of tsunamis in different parts of the world based on their knowledge of water depths, distances, and when the event that generated them occurred.
•A tsunami may be less than a foot (30 centimeters) in height on the surface of the open ocean, which is why they are not noticed by sailors. But the powerful shock wave of energy travels rapidly through the ocean as fast as a commercial jet. Once a tsunami reaches shallow water near the coast, it is slowed down. The top of the wave moves faster than the bottom, causing the sea to rise dramatically.
•Geological features such as reefs, bays, river entrances, and undersea formations may dissipate the energy of a tsunami. In some places a tsunami may cause the sea to rise vertically only a few inches or feet. In other places tsunamis have been known to surge vertically as high as 100 feet (30 meters).
•An earthquake is a natural tsunami warning. If you feel a strong quake do not stay in a place where you are exposed to a tsunami. If you hear of an earthquake be aware of the possibility of a tsunami and listen to the radio or television for additional information. Remember that an earthquake can trigger killer waves thousands of miles across the ocean many hours after the event generated a tsunami.
•Witnesses have reported that an approaching tsunami is sometimes preceded by a noticeable fall or rise in the water level. If you see the ocean receding unusually rapidly or far it's a good sign that a big wave is on its way. Go to high ground immediately.
•Many people were killed by the Indian Ocean tsunami because they went down to the beach to view the retreating ocean exposing the seafloor. Experts believe that a receding ocean may give people as much as five minutes' warning to evacuate the area.
•Remember that a tsunami is a series of waves and that the first wave may not be the most dangerous. The danger from a tsunami can last for several hours after the arrival of the first wave. A tsunami wave train may come as a series of surges that are five minutes to an hour apart. The cycle may be marked by a repeated retreat and advance of the ocean.
•Stay out of danger until you hear it is safe. Survivors of the Indian Ocean tsunami reported that the sea surged out as fast and as powerfully as it came ashore. Many people were seen being swept out to sea when the ocean retreated.
•A tsunami surge may be small at one point of the shore and large at another point a short distance away. Do not assume that because there is minimal sign of a tsunami in one place it will be like that everywhere else.
•NOAA advises that since tsunami wave activity is imperceptible in the open ocean, vessels should not return to port if they are at sea and a tsunami warning has been issued for the area. Tsunamis can cause rapid changes in water level and unpredictable, dangerous currents in harbors and ports. Boat owners may want to take their vessels out to sea if there is time and if the sailors are allowed to do so by port authorities. People should not stay on their boats moored in harbors. Tsunamis often destroy boats and leave them wrecked above the normal waterline.
•Heightened awareness of the potential for a tsunami to inundate the U.S. western coastline has caused NOAA, the U.S. Geological Survey, and the Federal Emergency Management Administration to initiate a program to predict tsunamis more accurately. As a tsunami traverses the ocean, a network of sensitive recorders on the sea floor measures pressure changes in the overhead water, sending the information to sensors on buoys, which in turn relay the data to satellites for immediate transmission to warning centers.
•The Tsunami Warning System (TWS) in the Pacific, composed of 26 member countries, monitors seismological and tidal stations throughout the Pacific region. The system evaluates potentially tsunami-causing earthquakes and issues tsunami warnings. An international warning system for tsunamis in the Indian Ocean was launched in June 2006.
•Use your common sense. If you feel or hear of a strong earthquake do not wait for an official tsunami warning. Tell your family and friends to join you in leaving for high ground.
May 4, 2024 · On December 26, 2004, at 7:59 am local time, an undersea earthquake with a magnitude of 9.1 struck off the coast of the Indonesian island of Sumatra. Over the next seven hours, a tsunami —a series of immense ocean waves—triggered by the quake reached out across the Indian Ocean, devastating coastal areas as far away as East Africa.
- The Editors of Encyclopaedia Britannica
May 6, 2024 · Tsunami is a Japanese word that means "harbor wave." It is a large wave caused by movements in Earth's outer layer, or crust, which move ocean water. For example, an earthquake or a volcano in the ocean could cause a tsunami. Earth's crust is made up of pieces called tectonic plates.
What is a tsunami? A tsunami is a series of waves caused by earthquakes or undersea volcanic eruptions. On September 29, 2009, a tsunami caused substantial damage and loss of life in American Samoa, Samoa, and Tonga. The tsunami was generated by a large earthquake in the Southern Pacific Ocean.
