A tsunami is usually caused by coastal earthquakes which force tectonic plates to shift and collide with one another, however, other causes have been noted such as: asteroids, iceberg calving and underwater volcanoes. In saying this, the majority of tsunamis are caused by coastal earthquakes such as Japan's 2011 Töhoku earthquake and tsunami (9.0 on the richter scale), and Indonesia's 2004 Boxing Day earthquake and tsunami (also 9.0 on the richter scale). Usually, the coastal quake has to be 6.0 or over on the richter scale to produce a massive tsunami.
The initial wave of a tsunami may only be less than a meter at the epicenter, however, as it picks up speed, it develops into a detrimental giant harbour wave (hence, its name) which destroys everything in its path. Countries near or on the edge of tectonic plates have high risks of being struck with a seismic destruction, although the build up may take centuries of years, it will strike and result with devastating sorrow. The disaster is preventable, but the loss of life can be reduced thanks to early notice from seismologists and tsunami warning centers like the 'Pacific Tsunami Watch Center'.
The initial wave of a tsunami may only be less than a meter at the epicenter, however, as it picks up speed, it develops into a detrimental giant harbour wave (hence, its name) which destroys everything in its path. Countries near or on the edge of tectonic plates have high risks of being struck with a seismic destruction, although the build up may take centuries of years, it will strike and result with devastating sorrow. The disaster is preventable, but the loss of life can be reduced thanks to early notice from seismologists and tsunami warning centers like the 'Pacific Tsunami Watch Center'.
The steps in the formation of a tsunami is as follows:
a sudden movement between tectonic plates sending powerful forces upward;
the water is thrown above sea level;
the water / waves move away from the epicenter at speeds of up to 950km/h (approximately 590 mi/h);
water reaches coast and friction reduces speeds to less than 50km/h.
As a side-note, because a tsunami moves so rapidly, it is recommended to stop what you are doing at the time of one and seek higher ground until it is deemed safe to return to land.
a sudden movement between tectonic plates sending powerful forces upward;
the water is thrown above sea level;
the water / waves move away from the epicenter at speeds of up to 950km/h (approximately 590 mi/h);
water reaches coast and friction reduces speeds to less than 50km/h.
As a side-note, because a tsunami moves so rapidly, it is recommended to stop what you are doing at the time of one and seek higher ground until it is deemed safe to return to land.