How Waves Are Made
20 commentsWaves are generated by wind. Offshore storms generate winds which blow on the surface of the sea and create ripples, much in the same way as the ripples in your post surf cuppa are made when you blow on it to cool it down. The wind can be seen on weather maps as low pressure areas. The more tightly packed the isobars are on the weather map the stronger the winds will be. Small waves (capillary waves) are initially generated in the direction that the wind is blowing.
Wind blowing on the Flat Sea Surface
The stronger and longer the wind blows, the more effect it has on these ripples and the larger they become. Initially the waves will just be small chop, but these will soon increase in size.
Constant Wind Creates a Larger Swell
As the wind continues to blow and the waves generated remain under the influence of the wind, the smaller waves will increase in size. The wind will get hold of the small waves much more easily than the calm sea surface.
The wave size is dependent on the wind speed generating it. A certain wind speed will only be able to generate a wave of certain size. Once the largest waves that can be generated for a given wind speed have formed, the seas are "fully formed."
Large Groundswell
Waves being generated have differing speeds and wave periods. (See wave terms explained for more detail.) The longer period waves are faster and move farther ahead of the rest of the slower waves. As the waves travel farther away (propagate) from the wind source, they start to organise themselves into swell lines. "Wave trains" form and these inevitably hit the beach at the same time. You may have heard of sets already!
Waves that are no longer affected by the wind that generated them can be referred to as ground swell, gold dust for surfers!
What Affects the Size of Swell
There are three main factors that affect the size of a wave in open sea.
- Wind speed - The greater the wind speed is, the larger the wave will be.
- Wind duration - The longer the wind blows, the larger the wave will be.
- Fetch - The greater the area the wind affects the wave, the larger the wave will be.
Once waves are no longer affected by wind, they'll start to lose their energy. They'll travel as far as they can while being decreased by friction on the sea bed and obstacles in the way. (A big island for example)
There are different factors affecting the wave size at a certain surf break. Examples include:
- Swell direction - Will the break be "open" to the current swell direction?
- Ocean floor - A swell coming straight from deep sea up onto a reef will generate big, barreling waves. A long, shallow ledge up to the shore will slow down the waves and they'll lose their energy, causing the waves to have less oomph.
- Tide - Some spots are totally tide dependant.
Find out what makes the best waves here.
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Comments
 | Guest on Aug 25, 2011 | This Helped so Much thanks |
| Conny Riakardsson on Aug 31, 2011 | Hi I also like your description of "How the waves are made". But you miss one important part. That is the difference between hi and low pressure over the sea... That also creates waves. The differences creates a swell and that is a stronger wave that comes out from that. Depending on how low the low-pressure is and what direction it has, related to where your surf break is, together with wind speed. It is really obvious when you follow up how waves appears in a limited sea like the Baltic sea. I can follow the wether-forcast and see how the wind waves and how the swell appears. Right in front and on both sides of the low-pressure direction. The wind is not going straight forward as you know. It rotates against the clock direction if it is a low pressure and with the clock direction if it is a Hi pressure. Check the satellite forecast videos. Cheers Conny R |
| Guest on Sep 1, 2011 | Waves come from the wind, and the wind blows strongest when isobars are close together in a low pressure system. High pressures don't tend to have the same wind strength. The wind direction in a low pressure and high pressure system is the opposite way in the southern hemisphere. |
| logan on Sep 22, 2011 | I surf and I like it. |
| Logan on Sep 27, 2011 | Surfing is a good sport . I a`m 8 years old.I have a little brother and he is 5 and he can stand up.His name is Henrik.Surfing is awesome !!!!!!!!!!!!!!! |
| freek on Nov 10, 2011 | Hello! I have a question. In the picture the wind is blowing over the sea towards the land to create waves. The more wind (lo-pressure-area)the bigger the waves will get. BUT, this site says also that the best wind for surf is an offshore wind!? Now why is that? Offshore winds blow towards the sea, so in your picture will that stop the wave... or blow them away... Please help! |
| Guest on Nov 10, 2011 | A light offshore wind will not be enough to blow the waves away, it ensures that the waves that break are clean and do not close out. If the offshore wind is really strong, it will indeed ruin the waves. The offshore wind only needs to blow locally, compared to strong winds far off the shore that generates good swells. |
| Felix on Jan 13, 2012 | Aloha, this has definitely helped me with my science fair project. |
| guest on Jan 20, 2012 | i did not get it:P |
| Guest on Feb 23, 2012 | what about the moon gravitational pull?????????? |
 | surf patrol on Feb 23, 2012 | Gravitational pull does not have an effect on the creation of swell. It only effects the tides. Gravitational pull may indirectly effect the size and quality of the waves when they reach the shore. Many surf spots are dependent on the tide level. |
| Guest on Mar 29, 2012 | This should help me get an A on my project.:p |
| excusemwa on Jun 19, 2012 | what do the 2 type of numbers mean on a weather map |
| surf patrol on Jun 19, 2012 | One is the pressure, one is the wind speed. |
| joe on Aug 6, 2012 | yo me name is joe, how are waves formed ;) |
| Guest on Aug 9, 2012 | what waves do you get at Bells Beach Victoria Australia?? kawabunga |
| Gabriel on Sep 12, 2012 | The moon in fact does have an effect, though it may be indirect or minimal. As the planet orbits the sun and the moon the Earth, the moon releases it's gravitational hold on different parts of the Ocean at different times. The rotation of the Earth in turn(with all of it's variously sized land masses and creviced sea-floor topography)causes mild agitation in the hydrological cycle, both on land and at sea. Imagine being able to grab a hand full of water as though it were a bed sheet, when you let go, you'd get massive ripples. Same thing(much bigger scale). Later |
| eddiek@icon.co.za on Oct 29, 2012 | Is South Africa's Jeffrey's Bay with offshore winds one of the best surfing spots in the world? |
| surf patrol on Oct 30, 2012 | @eddiek: Yes, it's a world class wave. |
| angie on Apr 28, 2013 | I always thought that waves were made only by the moon and that surfing would disappear forever when the moon disappear in space forever :3 |