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What is a tsunami? -

A tsunami is a seismic sea wave, caused by an earthquake. The name originates from the Japanese language's words for harbor, tsu, and wave, nami.

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What is a tsunami? -

A large and sudden displacement occurs in the ocean, which triggers a tsunami, i.e. a series of extremely long waves.

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A destructive force -

Tsunamis are some of the most powerful and destructive forces of nature. From their point of origin, they radiate outward in all directions.

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A destructive force -

Some tsunamis are so strong that they move entire ocean basins. As they reach coastal areas, they can cause flooding as well as dangerous currents that last for days afterwards.

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Not a tidal wave -

Sometimes people get confused between tidal waves and tsunamis, but a tsunami's formation is not related to tidal activity; it's related to seismic activity.

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Unpredictable -

In the same way that earthquakes are an unpredictable phenomenon, so too are the tsunamis that are caused by them.

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Unpredictable -

However, warning centers know if an earthquake is likely to cause a tsunami, based on the defining factors of that earthquake, i.e. Richter scale magnitude, the location of the earthquake, and the depth at which it's occurred.

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Seismic networks and stations -

To give accurate and timely tsunami warnings, scientists depend on information from water-level and seismic networks around the world.

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Seismic networks and stations -

Seismic stations send information gathered about their detection, measurement, and recording of earthquakes to tsunami warning centers in real time, through satellites and other methods.

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Seismic waves -

Seismic waves travel around 100 times faster than a tsunami. In other words, usually information about an earthquake is received prior to a tsunami being generated.

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Initial messages -

In the US and Canada, initial warning messages can be generated within five minutes of an earthquake. These messages issue alert levels (warning, advisory, watch, information statement) for a tsunami.

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Initial messages -

Multiple different channels are used to send warning messages to emergency managers, other officials, news media, and the public.

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Suspected tsunami -

These messages may also include wave arrival times, recommended actions, and potential impacts, if a tsunami is suspected. They are regularly updated as more information becomes available.

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Detected tsunami -

If a tsunami is detected, the warning centers use tsunami forecast models to predict wave height and arrival times, location, and amount of flooding, as well as how long the tsunami will last.

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Not enough time for a warning -

Unfortunately, in some cases, for example if the source of a tsunami is close to a coast, there may not be time for the warning centers to issue a detailed forecast for all at-risk coastal areas.

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It's important to recognize the signs -

There are natural warning signs of a tsunami that could save your life, so it's important to recognize exactly what they are.

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Natural warning: long, strong earthquake -

A very long, strong earthquake might be the first, and perhaps only warning, that a tsunami is on the way, depending on where you live.

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Natural warning: ocean roar -

A roar from the ocean that sounds like an airplane or train can indicate a tsunami is en route. Likewise, unusual ocean behavior is also a sign.

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Natural warning: unusual ocean behavior -

This unusual behavior could take the form of a fast-rising flood or a wall of water (bore) developing. Equally, if you see the ocean receding suddenly, to the point where you can see the ocean floor, reefs, and fish like an extremely low tide, a tsunami could be on the way.

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Know all the warning signs -

You might get both an official warning and a natural warning, or you might only get one of these warnings. It's important to know both and to take the risk seriously, as both are equally important to know if you need to evacuate.

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Evacuation -

How you respond to a tsunami warning depends on the kind of warning you receive. If you are in a tsunami hazard zone and receive an official warning to evacuate, follow evacuation signs to safety or go as high or as far inland (away from the water) as possible (at least 100 feet above sea level or a mile inland).

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Evacuation -

If you're in a hazard zone and receive a natural warning, a tsunami could occur within minutes. Take action as soon as you safely can, after the earthquake occurs. Be mindful of earthquake damage when evacuating, i.e. avoiding fallen power lines and cracks in the ground. Try to get at least 100 feet (30 m) above sea level or one mile (1.6 km) inland.

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Don't stay in your car in a traffic jam -

If you're in a car stuck in a traffic jam during a tsunami warning, once it's safe to do so, park it, get out, and evacuate on foot. If a car becomes swamped in a tsunami, it's difficult to open the windows due to the pressure from the water.

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Avoid bodies of water -

In the event of an official tsunami warning, stay out of the water and away from beaches and bodies of water. Keep up to date with official news updates via radio, mobile devices, etc.

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High-rise buildings -

Many high-rise buildings are not constructed to withstand tsunami impacts. However, the upper floors of buildings made from strong materials, e.g. reinforced concrete, could provide protection when there are no other options.

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High-rise buildings -

If you're concerned, contact your local emergency management officials who can advise about cases where vertical evacuation is appropriate.

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In a boat -

If you're in a boat in harbor or at sea when a warning comes, it's generally recommended (in the US) to either leave your boat in the harbor and go to high ground or as far inland as you can. Or if you're at sea, to move to a safe depth.

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Extremely fast moving -

The deeper the water, the faster a tsunami can travel. In the deep ocean, tsunamis can move as fast as a jet plane, over 500 mph (805 kph), slowing to the speed of a car (approximately 20 or 30 mph/30-48 kph) as they reach the shallow water near land.

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There's no way to know how long you have to escape -

As the length of time to escape from a tsunami will depend on the magnitude, location, and depth of the earthquake that causes it (which there is no way to predict), unfortunately there's also no way of knowing how long you have to escape from a tsunami. But knowing the warning signs will allow you to come up with an emergency plan.

Sources: (U.S. Tsunami Warning Centers) (Japan Lifesaving Association)

See also: In pictures: Japan's devastating earthquake

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