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Tsunami Behaviours
How Do Tsunamis Behave?
A tsunami in the open ocean is small and less than a few tens of centimetres (1 foot) high. It can go unnoticed by ships at sea and cannot be seen from the air. A tsunami begins to ‘size up’ as it approaches shallow water nearer to the coast. It is here that it begins to slow while increasing in height. Often at this point, the shoreline begins to recede; drastically exposing the seafloor – reefs, rocks and stranded fish may be seen on the sand.

Tsunami waves arrive at a coastline as a series of successive crests (high water levels) and troughs (low water levels), usually 10 to 45 minutes apart. Flooding by each wave lasts from 10 minutes to half-an-hour, so the danger period for successive waves can last for hours. This is why it is important to stay out of danger areas until the “all clear” is issued by a recognized authority.
 
The historic record shows that there have been many tsunamis that have struck shores with devastating force, sometimes reaching heights of more than 30 meters.

 

For more information:

Tsunami Science Poster (1.79 MB)

 


Characteristics and Wave Size

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