Tuesday, March 11, 2008

Ocean Science 101: How our surf is made

OK this will probably review for a lot of you, but I thought I would go back and cover some of the basics in surf forecasting. I have been posting forecasts, reports, maps, and other random nonsense for a while now and I started to realize that a lot of the stuff that I have been throwing at you assumes that you have an idea of how our surf is generated. It isn’t really that hard to find on the interweb, (I mean, come on, that is what Wikipedia was invented for people), but I decided to throw it up here too so that you didn’t have to hunt around for it.

Why it matters

I am sure that there are some of you out there that don’t really care about where the waves come from and are fine with just knowing if the surf is going to be good tomorrow. That is totally cool…I hope that I keep my forecasts simple enough that you can keep scoring…or at least save some gas money now and then.

Personally I think that you become a better surfer, and a better waterman, if you get in tune with the ocean, the weather, and the processes that create the conditions that we, as surfers, are looking for. You don’t need to be a forecaster or anything but I do think that knowing the general principles behind how waves are made will keep you a step ahead of other surfers, which is nice, particularly when that step could mean the difference between scoring empty surf and slogging it out with the rest of the crowd that is a day late and a dollar short.

Types of Waves

There are actually 3 types of waves that occur in the ocean.

1. Tsunamis
2. Tidal Waves
3. Wind Waves


Tsunamis, if you were living under a rock or something, are waves that are usually generated by earthquakes. They actually used to be called “Tidal waves” because of the way they behaved as they hit an area. The true definition is that a Tsunami is actually caused by anything that quickly displaces a large amount of water. That could be anything from a volcanic eruption, a collapse of an undersea cliff or shelf, an asteroid/meteor hitting the ocean, or even something man made like a nuclear weapon. It just so happens that all of those other things are rare and earthquakes are fairly common. Also Tsunamis don’t have to occur in the ocean…they can occur in any large body of water.

Tsunamis are not actually surfable…in fact the characteristics of tsunamis are very similar to a low-to-high tide swing, albeit much larger and much more violent. In general the tsunami “wave” is moving much too fast and the swell period is measured in hundreds of miles, both of which do not allow the wave to take a “rideable shape”.

Tidal Waves (aka the tides)

Tidal Waves are the high and low tide that your beach experiences each day. These waves are caused by the gravity of the sun, the moon, along with the spin of the Earth in relation to those celestial bodies. The basics behind it is that there are 2 bulges of water in the ocean, one of which points to the sun, the other to the moon. As the Earth spins these bulges eventually get ran into land…as these causes them to reflect back and bounce all around the various ocean basins.

What is really crazy is that there are almost 200 different factors that have to be accounted for when you predict a high and low tide for a location. What is even crazier is that almost all of those factors are fairly stable so once you take them into account all you have to do is change the date on the forecast and the numbers fall into place. It is possible, though I am not sure why you would want to, to get a tidal forecast for a particular location 10, 20, or 200 years in advance…I guess it is probably something that oceanographers do when they are really bored.

These waves are also not-surfable but since the tide plays an important roll in surfing you definitely want to keep track of how it is behaving.

Wind Waves

Wind Waves are another properly named type of wave (I love some of the terminology in Oceanography, much of it is amazing straightforward). Winds waves are generated by wind blowing over the ocean. The more intense the wind, the longer the duration, and the bigger the area that the wind is blowing over, the bigger the wind waves will be.

These are the waves that we actually surf…from an energy/swell period perspective they are actually the weakest type of waves with the shortest swell periods…not that it matters much…a 20’ wave at Jaws can kill you just as fast as a tsunami.

Continued in these posts
Part 2: Wave Creation and Swell Generation
Part 3: Characteristics of swells
Part 4: Breaking waves

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