Waves
The surface of the Ocean is almost always in a state of motion. Wind waves and swells are most often observed. Wind waves are directly related to the wind, and when the winds decrease or die, swells are observed. Swells also originate from adjacent Ocean regions under the effects of winds. Waves spreading in the absence of wind are called dead swells. As a result of the interaction of wind wave and swells, mixed waves may occur. The apparent motion of water masses is caused by the forward movement of waves.. The shape (profile) of a wave is the only part that actually moves. The particles of water in a wave move on circular orbits and have no forward movement. The wind disturbs the uppermost layer of water. With an increase in depth, the radii of the orbits decrease, and at a depth equal to one wavelength on the surface, the disturbance is practically non-existent. The basic elements of a wave are the crest and trough: the highest point is the crest and the lowest point is the trough. The wave height is the vertical distance from the crest to the trough. The wave length is the horizontal distance between two crests or two troughs. The period is the time it takes for a wave to pass until the next wave takes its place.
The size of wind waves depends on the speed, the duration of the wind and length of the fetch. Fetch is the distance a wave travels from the moment of its generation under the effect of a steady wind. The largest waves have been observed in the middle latitudes, where storm winds may blow at speeds of up to 30-50 m/s. The largest wave ever recorded had a height of 34 m and was observed in the North Pacific Ocean. Waves of up to 30 m have been observed in the Atlantic and Indian Oceans. The impact force of storm-generated waves can reach 50-60 t/m2.
As a wave approaches the coast, it becomes shorter in length and more abrupt, increasing its height. Friction with the bottom causes the trough of the wave to disappear, the crest to slow its movement, and, when the depth causes the wave height to become 1.3 times the depth, the crest falls, forming a breaker. Breakers can be observed above elevated placed on the shallow sea floor (reefs and shoals), and can be seen from shore. At an abrupt shoreline, the breakers become stronger, making large splashes and have great destructive power.
The constant action of waves for millennia shape of the coasts throughout the world. As can be seen in the photo, even after major pieces of headlands fall to the see below, the waves continually act upon them turning them into grains of sand. Click on Rocky Shores Images for a larger picture (200 kb) and browse to Rocky Shores.