Although there is no calculated volume of water that constitutes a standardized quantity that will generate a tsunami, the amount displaced must be significant enough to create waves underwater in the vast ocean. Waves are formed as the displaced water mass moves under the influence of gravity to regain its equilibrium and radiates across the ocean like ripples on a pond. The larger the displacement, the larger the wave generated.
A tsunami can be generated by four general ways: (1) an undersea earthquake; (2) landslide; (3) volcanic eruption; or (4) an extraterrestrial collision.