Tsunami

 

Tsunami is a Japanese word meaning “harbour wave”. A tsunami is a wave or series of waves generated in the ocean by such phenomena as earthquakes, undersea land-slides, volcanic eruptions and meteor impacts. It should not be confused with ocean swell waves, which are generated by the action of wind on the surface of the sea, or tides, which are produced by gravitational effects of the Sun and Moon.

 

 

When an earthquake occurs near or under the ocean, a tsunami can be generated, and the characteristics of this type of wave are markedly different to the “normal” waves we are used to seeing down at the beach. The normal beach waves may break on the shore say every 10 or 12 seconds (called the “wave period”), and have a distance of around 100 to 120 metres between wave crests (called the “wavelength”). But tsunamis may have a period of up to an hour and a wavelength of around 100km, with the second and third waves still maintaining massive power.

 

 

When a Tsunami wave approaches a shoreline and the water becomes shallower, the wave begins to slow as a result of friction with the ocean bed. But the overall energy of the wave stays much the same, so to compensate for the slower speed, the height of the wave ramps up. This means that a tsunami, whilst barely noticeable at sea, quickly grows in height and cases of waves reaching heights of 30 metres are known. An entire tsunami event may consist of several waves, called a wave train, each of which can carry a major destructive punch.

 

 

Undersea earthquakes are common around the so called Pacific Ring of Fire, a geologically unstable region that extends from New Zealand, across the Tongan region, Papua New Guinea, Indonesia and then northwards to Japan. It then travels east across the northern Pacific and moves down the west coast of both North and South America. This zone is largely generated by the movement of the Pacific tectonic plates against other adjacent plates.