What Unique Forces Create Powerful Waves on the Shoreline?

Waves on a Lake

Part of the magic for me when visiting the beach is the sound of the waves lapping the shore.

The sound is rhythmical and mesmerizing.  Sitting on a chair or lying on a towel when I close my eyes all tension drains from my body.  From an evolutionary standpoint, it is said that all life originated in the ocean.  Perhaps we are programmed to feel at home at the beach.

I think the calming nature of waves is due to our evolutionary link to the ocean. Share on X My son loves the huge, crashing waves that pound the shore after a good storm. He prefers the thrill of riding and diving into the huge waves common after a good, Ontario thunderstorm.  Most summers we travel to Lake Huron, he is treated to at least one day of wild waves to play in.  Most years I am content to enjoy the sounds and sight of lapping waves.  This year my curiosity was peaked and I decided to investigate the science of waves.

How Waves Form?

Wind has energy.  That makes sense.  We can feel it push against our skin on a windy day.  Because we can feel the wind we can also understand that it is composed of matter – air molecules are composed of atoms of water, oxygen and nitrogen mostly.  As wind moves over water, the two are in contact and friction occurs between air and water molecules.  Energy from the wind is transferred to the water from this friction.  The water moves, fueled by this wind energy and waves are formed.

What Factors affect the size of Waves?

The height of a wave is affected mostly by three factors:

1. Wind speed has an obvious effect on wave height.  Faster winds have more energy.  More energy pushes the water faster giving the wave an opportunity to grow larger.
2. Wind duration also has an effect.  Some winds come in gusts meaning there is an interruption in the transfer of energy to the wave.  The longer the wind blows again the more energy is available to create a larger wave.
3. Fetch is probably the most important factor and involves the distance across water that the wind blows.  The longer that distance, the bigger the potential for creating big waves.

Now, these three factors do work together to determine how waves form:

Low wind speeds will not create large waves even if wind duration is high and there is a long fetch.

As well, if wind speed is high but only comes in short gusts, big waves will not form.

And finally, strong, consistent winds that blow over a short fetch will not produce large waves.

Fetch is really important in large lakes such as Lake Huron where the photos in this post were taken. Large waves are common in large lakes such as the Great Lakes.  Lake Huron waves have been recorded as high as 23 feet during Hurricane Sandy.

Some other more obvious facts about how waves form:

• waves travel in the direction of the wind
• when they meet a solid object such as docks much of their energy is reflected meaning they bounce back at an angle equal to that at which they hit the object
• if they enter shallow water, such as the shoreline of a beach, they are refracted
• waves on the shoreline break up in surf where the wave height is seen to decrease slightly, then increase followed by a the wave slowing before it breaks up
• where waves in the open ocean can reach over 100 feet, waves in big lakes such as Lake Huron have reached heights of only 23 feet – still a big wave!
• my son loves waves created by atmospheric disturbances which cause the waves to slosh back and forth between lake shores creating the big fluctuations in water levels and turbulent water

So there you have it. There is a lot of science in how waves form. Share on X I’ve only summarized and simplified the physics here.  Wave generation in water follows rules similar to those you may have learned about in science class about light and sound waves.  Physics at the beach – who would have thought?

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