Surf science of wave formation: Where do waves come from?

Jun 25, 2018 BY AWE365 Team

Have you ever walked along the beach and wondered where do waves come from and how they are formed? If you fancy learning about the surf science of wave formation you can do a little experiment.

Surf science: Where do waves come from? flickr CC image in Maldives by Bruno Ahlgrimm

Return to the same beach every few weeks and make some observations about the size and shape of the waves. I guarantee that they’ll be very different from day to day. It blows my mind to think that most waves that we observe on the coast have travelled hundred or thousands of miles to get there.

Where do waves come from?

There is a great science in understanding where waves come from. First off, it is important to understand that waves are not moving water. A wave is simply energy that is passing through the water.

To understand this, picture a boat floating on the ocean. As a wave passes underneath the boat, the boat will rise and fall vertically with the swell of energy (the wave), but it will not move in a horizontal manner. In other words, a wave or swell is a pulse of energy that travels through a body of water.

The simple answer to ‘where do waves come from?’ is that nearly all are formed by either seismic activity (earthquakes) or by the wind. But surf science is way more complex than that!!

Surf science: Where do waves come from? Todos Santos in Mexico CC Google (wikimedia) image by Boone Speed

Seismic waves: Tsunamis

Imagine an earthquake under a body of water. This powerful activity will cause energy to be dispersed or pushed away in all directions. In this case, a massive amount of energy is transferred through the water.

This is more of a surge of water that is usually accompanied by a small number of waves. This is how tsunamis are created. Remember throwing rocks in the water and seeing the ripples spread out in all directions?

Wind waves: surfs up!

The most common and less destructive way that waves are formed is from wind. When wind blows over the surface of water, it creates friction passing energy into the water which creates waves. This friction is called fetch.

An ocean storm that makes waves is called a low-pressure system. The determining factor of the size of the resulting wave(s) is a storm’s size, the speed of the wind and how long the wind blows. A storm with sustained winds of 35 knots will make larger waves than a storm with winds of 20 knots, assuming both storms are the same size and last for the same amount of time.

Surf science: Where do waves come from? Flickr image of Maui windsurfing in Hawaii by Mauishooter

As the wind blows, energy is pushed through the water and away from the storm. In the midst of the storm, wave formation is usually choppy, disorganized and all messy.

As the energy moves away from the eye of the storm, it organizes itself into groups of waves called sets. Travel and surf your way around the world and you’ll learn to spot them wherever your board takes you.

Surf science

This is an amazing science in itself. The waves form sets for the same reason that birds fly in “v” formations – because it is more efficient and requires less energy. The collections of waves that are pushed away from a storm are usually called a “swell”.

This is why you will observe different sizes of waves at your local beach. Beach conditions are dependent on the storms that have happened at sea. The fascinating thing is that by the time most swells reach a coast, the storm that generated the waves has long since dissolved.

Surf science: Where do waves come from? Diani beach kitesurfing in Kenya Wikimedia image by Grierhh

It’s once the wave reaches the cost that things get interesting for us surfers. The speed the wave is moving reduces due to friction from the seafloor as the water becomes shallower. This makes the wavelength shorter which forces the peaks higher.

Once the wave height is more than 1.3 times the depth of the water the wave will usually break. This happens because the friction in greater closer to the seafloor than at the peak, so the peak overtakes the base and brings the wave crashing down.

Ground or wind swell?

The further that a swell travels, the more organized and clean that the waves become. Surfers and other ocean people measure swell by its period. In surf science this is simply the time that passes between the wave peaks.

A swell that travelled 2000 miles (or so) is called a “ground swell”. Its period between waves is greater than 10 seconds. So in this case the answer to ‘Where do waves come from?’ could be somewhere very exotic such as a storm in the Caribbean.

Surf science: Where do waves come from? Flickr image of Hawaii Billabong Pro Pipeline Masters 2008 by surfglassy

A storm that forms closer to shore forms waves that are called “wind swell” because their period is less than 10 seconds. Remember that the further a wave travels, the greater that its period becomes.

Wave formation

Another massive factor that goes into determining the wave formation you experience and the size and shape of a wave breaking on the shore is the direction the waves come from. This is determined by the direction the storm pushed waves toward the coast. So if a storm creates swell in a westerly direction, a beach facing north will usually have smaller waves than a beach that faces west.

The depth of water along the shoreline is also very important. The more shallow a coastline is offshore, the more energy that is dissipated as the swell reaches the coast. The profile (bottom of the sea) of the beach also makes an incredible difference in the power and the shape of the wave.

We hope you enjoyed this brief lesson about the surf science of wave formation!! As you now know where do waves come from, you can better plan your surf trips. Just be sure to check out our surfing holiday discounts as you could save a packet!

 

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