What Causes Waves in the Ocean?
Most waves in the ocean are caused by the wind. Somewhere over the ocean, wind ruffles the surface of the water. Ripples form and grow into swells, and finally into waves. The wind transfers some of its energy to the water, through friction between the air molecules and the water molecules.
The longer and harder the wind blows, the bigger the waves get. They travel one after another across the sea. Far out from the shore, ocean waves are usually rounded and smooth. But closer to land, they become taller and more pointed. As a wave rolls toward the shore, the shallow bottom forces the wave higher and higher, until it finally breaks, and spills over onto the beach.
Waves of water do not move horizontally, they only move up and down (a wave does not represent a flow of water). You can see a demonstration of this by watching a floating buoy bob up and down with a wave; it does not, however, move horizontally with the wave.
Tsunamis (sometimes called tidal waves) are different from surface waves; they are usually caused by underwater earthquakes, volcanic eruptions, or landslides.