How does a tsunami occur?

The Japanese world 'Tsunami' means 'Harbour wave' .it is a serious of water waves caused  by the displacement of a large volume of a body of water ,usually and ocean thought thought it can accused in large lakes.Tsunami are caused by undersea landslide or by 'seaquekes ' that is an earthquake whose epicentre lies below the ocean. If the seabed is displayed up to several meters,the water layer of several kilometres in thickness above it also moves with it. The wave caused by this movement has a lot of energy-much more than a wave of the same hight whipped up by the wind. This becomes apparent when the wave moves towards the coast.