● How are tsunamis generated?

        A tsunami can be generated by any disturbance that displaces a bulk amount of water from its equilibrium position. Such disturbances may be caused by submarine earthquakes, landslides, collapses of volcanic edifices or eruptions of submarine volcanoes, or, even meteorite impacts.

         •By submarine earthquakes

        Tsunamis can be generated when the sea floor abruptly deforms due to tectonic earthquakes. Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crust deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. Waves are formed as the displaced water mass attempts to regain its equilibrium under the influence of gravity. When large areas of the sea floor elevate or subside, a tsunami can be created.

(left figure shows continental crust is slowly bent due to the subducting of oceanic plate; right figure shows that continental crust suddenly unbends when the bending beyond the threshold of tolerance  and displaces large amount of water mass, becoming the source of a tsunami, figures from Nature online)

        Large seafloor displacements of the earth's crust can occur at plate boundaries. Plates interact along these boundaries called faults. Around the margins of the Pacific Ocean, for example, denser oceanic plates slip under continental plates in a process known as subduction. Subduction earthquakes are particularly effective in generating tsunamis. The earthquake generating 2004 Giant Tsunami occurred where Indian ocean plate subducting Sumatra plate.

        •By submarine landslides, volcanic or meteorite impacts

        Submarine landslides, which often accompany large earthquakes, as well as collapses of  volcanic edifices, can also disturb the overlying water column as sediment and rock slump downslope and are redistributed across the sea floor. Similarly, a violent submarine volcanic eruption can create an impulsive force that uplifts the water column and generates a tsunami. Conversely, supermarine landslides and cosmic-body impacts disturb the water from above, as momentum from falling debris is transferred to the water being displaced. Generally speaking, tsunamis generated from these mechanisms, unlike the tsunamis caused by some earthquakes, dissipate quickly and rarely affect coastlines distant from the source area.