Without waves there would be no surfing. A lot of surfers already know how waves are formed, and they will probably have skimmed over the title to this article and snorted with derision before moving on to something else; but they had to learn that knowledge from somewhere at some point. Plenty of surfers just go surfing and have no real care or interest in what causes the waves that they’re enjoying to break the way that they do, a situation that is perpetuated by surf forecast websites and webcams that allow surfers to stumble on blindly should they so choose. But it wasn’t all that long ago, before star ratings and tweeting wave buoys, when surfers were required to have at least a basic knowledge of how waves form in order to ensure that their trip to the beach was going to bear fruit.
So, where do waves come from, why are they sometimes “here today and gone tomorrow” and how come there’s such a huge variety of different waves? Chapters of oceanography tomes and numerous books have been written on the subject of wave formation and it’s a lot to distill down into just a few paragraphs, but here goes:
Waves are energy being moved from one place to another. In physics the law of conservation of energy states that energy cannot be created or destroyed, but it can be transferred. A wave is caused when wind blows over the surface of the water and the friction between the wind and the water causes the surface of the water to become ruffled. Ripples (known as capillary waves) form as energy is transferred from the wind to the water’s surface, and these little bumps begin to grow as their existence alters the flow of air over the water and small vortices form behind each wave. The capillary waves become gravity waves (the type of waves that you and I surf) as the ripples grow larger and the wind is therefore able to “grip” them, so the waves start to grow exponentially; the larger the wave becomes, the more the wind can exert force on it and cause it to grow still further. The stronger and longer the wind blows over a patch of ocean, the bigger the waves will be. This wave energy radiates from the source storm and swells travel outwards in the same way that ripples do when you throw a stone into a lake. The water stays in the same place, but the energy moves through it in much the same way as a wave travels along a slinky toy. If it didn’t and the water travelled rather than the energy then many high latitude coasts would enjoy the warm water of the regions where tropical storms generate the swells that travel to break on their shores. This wave energy travels across a sea or ocean until it reaches a coast upon which it breaks, transferring and dispersing its energy. The greater the distance between the storm that created the waves and the shore upon which the waves break, the more chance the swell has to organise itself into trains or “sets” (as surfers call them) of evenly spaced and similarly sized waves. If the wind or storm is close to the coast then the unorganized, unpredictable and different sized waves are called a wind-sea, and they are often accompanied or followed closely by strong winds. If the waves have been generated hundreds or thousands of miles away and travelled a long way then they are groundswell. It is long distance groundswells that surfers are on the hunt for, as they deliver evenly spaced and powerful waves to our beaches, reefs and points. Few of us would mind if a groundswell day were to become a groundhog day.