Why tsunami occurs?what r its disadvantages?

Question

Why tsunami occurs?what r its disadvantages?

Answer 1

Tsunami usually are the results of sea quakes (earthquakes that occurs under the sea surface" or a underwater land slide.  When the ground moves, the energy of this movement will displace a volume of water.  This displaced volume of water becomes a fast moving energy wave.  As this energy moves across the ocean, the energy will mainly stay well under the surface of the water until it is forced upwards when it comes onshore to shallow waters.  

That is one major reason why a tsunami can be so deadly.  You will likely not be see this energy wave if you are above the water surface until it reaches the shallow area near the beach.  Once this energy reaches shallow waters, it will likely build into a  large or "monster" wave.  This wave energy then can be very destructive and deadly for those who are near the coast.  This I would consider as its significant disadvantage to people in the coastal communities.