A Tsunami

 

A tsunami is a series of ocean waves that sends surges of water, sometimes reaching heights of over 100 feet (30.5 meters), onto land. These walls of water can cause widespread destruction when they crash ashore.

                  These awe-inspiring waves are typically caused by large, undersea earthquakes at tectonic plate boundaries. When the ocean floor at a plate boundary rises or falls suddenly it displaces the water above it and launches the rolling waves that will become a tsunami.

         Most tsunamis, about 80 percent, happen within the Pacific Ocean’s “Ring of Fire,” a geologically active area where tectonic shifts make volcanoes and earthquakes common.

Tsunamis may also be caused by underwater landslides or volcanic eruptions. They may even be launched, as they frequently were in Earth’s ancient past, by the impact of a large meteorite plunging into an ocean.

         Tsunamis race across the sea at up to 500 miles (805 kilometers) an hour—about as fast as a jet airplane. At that pace they can cross the entire expanse of the Pacific Ocean in less than a day. And their long wavelengths mean they lose very little energy along the way.

         Occur most frequently in the Pacific and East Indies. One of the largest tsunami:
In the Atlantic Ocean, the earthquake of November 1, 1755 that hit Lisbon
The wave reached a height of 7 feet from the normal level, affecting coastal areas including the Netherlands.

           
         According database NOOA (National Oceanic and Atmospheric Administration), there are:

     

              2400 tsunami sources:  -81% Pacific Ocean,

                                                  -9% Mediterranean Sea

                                                  -7% Atlantic Ocean

                                                  -2% Black Sea

                                                  -1% Indian Ocean

              7,000 locations where tsunamis can trigger:

                                                

                                                 -89% Pacific Ocean

                                                 -6% Atlantic Ocean

                                                 -3% Mediterranean Sea

                                                 -2% Indian Ocean

  

           Causes of tsunamis:

                     landslides - events: 64; 4,6%; total dead: 14661

                     earthquakes - events: 1171; 82,3%; total dead: 390929

                     volcanic eruptions - events: 65; 4,6%; total dead: 51643

                     unknown - events: 121; 8,5%; total dead: 5364

                TOTAL: events: 1422; 100%; total dead: 462597


           A tsunami can deliver: 
                  - destruction of life, damage of all sorts, spread of diseases, destruction of particular ecosystems.


           We can reduce the energy of a tsunami by - development of offshore breakwaters, that can produce preventive breaking of the waves, prevent invasion of water in urban areas.

 
            In deep ocean, tsunami waves may appear only a foot or so high. But as they approach shoreline and enter shallower water they slow down and begin to grow in energy and height. The tops of the waves move faster than their bottoms do, which causes them to rise precipitously.

                A tsunami’s trough, the low point beneath the wave’s crest, often reaches shore first. When it does, it produces a vacuum effect that sucks coastal water seaward and exposes harbor and sea floors. This retreating of sea water is an important warning sign of a tsunami, because the wave’s crest and its enormous volume of water typically hit shore five minutes or so later. Recognizing this phenomenon can save lives.

               A tsunami is usually composed of a series of waves, called a wave train, so its destructive force may be compounded as successive waves reach shore. People experiencing a tsunami should remember that the danger may not have passed with the first wave and should await official word that it is safe to return to vulnerable locations.

                Some tsunamis do not appear on shore as massive breaking waves but instead resemble a quickly surging tide that inundates coastal areas.

The best defense against any tsunami is early warning that allows people to seek higher ground. The Pacific Tsunami Warning System, a coalition of 26 nations headquartered in Hawaii, maintains a web of seismic equipment and water level gauges to identify tsunamis at sea. Similar systems are proposed to protect coastal areas worldwide.

         Video below shows a tsunami provoked by a testing submerged hydrogen bomb:

                    

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