- Written by Nadia O'Carroll
Most ocean waves are caused by wind blowing over the surface of the ocean; friction between the air and the water transfers energy from the wind into the ocean and pushes the particles of water into a circular movement that creates the shape of a wave. Ocean waves appear to be movements of water, but they are really movements of energy, and although ocean waves can travel great distances, there is actually very little forward movement of the water particles themselves.
Waves organise themselves into sets, because energy is transferred from the leading and trailing waves to the central waves it is these waves that become the largest in the set.
Surf is a breaking wave and it is created when a wave makes contact with the seabed and friction slows the velocity of the wave base, but the top of the wave continues to move at the same speed. Eventually this speed difference causes the wave to tip forward, break apart and release its energy.
Breaking waves exist in a highly variable environment influenced by wind, tides and currents but it is basically the profile of the seabed which creates different types of breaking waves. These have been classified into different types based on changes to the wave surface profile during the breaking process.
Surging waves are found in deep water, they are stable and do not break.
Spilling waves are found where there is a sloping or gentle gradient of seabed, the crest of the wave crumbles at the top and spills down the front of the wave, dissipating energy uniformly. Spilling waves are usually predictable with waves breaking when their height is one to point seven times the water depth eg 1 metre wave will break in 1 to 1.4 metres of water.
Plunging or dumping waves occur where the seabed is steep or shallow, and the base of the wave is slowed abruptly, the crest of the wave curls forward and plunges over the front of the wave, releasing energy suddenly.
The fluid dynamics of broken waves are complex, but most obviously the mass of water released by the waves must quickly return seawards to maintain the water level, and this forms an undertow or rip which tends to end at the last line of breakers.
The familiar sound of the surf is thought to be primarily caused by the bursting, splitting and oscillations of plumes of bubbles.
Although, as yet, we still do not fully understand the complex mechanics of the surf zone, it remains a source of enjoyment, excitement, relaxation and inspiration for many people.