Gate 2011 1.7

1.7 Tsunamis are

(A) gravity waves

(C) Capillary waves

(D) internal waves

(B) acoustic waves

Tsunami: When the ocean floor is abruptely lifted droppped by a submarine earthquake or land slides the entire water column is pushed up and down more than 95% of the potential energy of displaced water is gravitational and less than 5% is elastic energy resulting from compression of ocean floor and water column. The potential energy of the vertical motion is converted to kinetic energy and propogates away from the source as a tsunami

    In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium.  A gravity wave results when fluid is displaced from a position of equilibrium. The restoration of the fluid to equilibrium will produce a movement of the fluid back and forth, called a wave orbit. Gravity waves on an air–sea interface of the ocean are called surface gravity waves or surface waves, while gravity waves that are within the body of the water (such as between parts of different densities) are called internal waves. 

    Wind-generated waves on the water surface are examples of gravity waves, as are tsunamis and ocean tides.

    Wind-generated gravity waves on the free surface of the Earth's ponds, lakes, seas and oceans have a period of between 0.3 and 30 seconds (frequency between 3.3 Hz and 33 mHz).