The combined gravitational pulls of the sun and the moon draw up the earth’s ocean into a hump, called a tidal wave. This wave moves across the water as the earth rotates, and though it is only a low lump (unnoticed by seafarers), its effect when it reaches the shallower waters near land is to create the to and fro surges which we call Tides. It may be worth mentioning that the expression ‘tidal wave’ is commonly misused for a phenomenon which should be called a ‘Tsunami’.