Luna Brooks

A trip to the ocean invokes images of sun, wind, and the endless rhythm of waves. They crash on the beach, lulling us to sleep at night and waking us in the morning. Surfers ride them, children play in them, and swimmers dive beneath them. But what exactly causes these constant undulations? The short answer is wind—but the root cause is the sun.

The story of a wave begins with sunlight. Solar radiation heats our planet unevenly; it is most intense at the equator and diminishes toward the poles. This thermal imbalance creates temperature differences across the globe. As hot air rises, cooler air rushes in to fill the void. This movement of air is wind, which acts as the primary energy source for most ocean waves.

Wind is a form of kinetic energy. When it blows across the water's surface, it transfers this energy to the water. However, the water particles do not travel horizontally toward the shore. Instead, they move in vertical circles.

If you have ever stood in the ocean, you have felt this motion: being pushed up as a wave crests and pulled down into the trough. If you were small enough to float freely, your body would complete a full circle. This orbital motion is why buoys appear to simply bob up and down rather than move horizontally with the waves.

In deep water, wind creates long, rolling waves known as swells. These do not resemble the crashing waves we see near the beach; instead, they look like smooth, rolling hills moving across the ocean surface.

The transformation occurs when these swells reach shallow water. As the circular motion of the water particles drags against the seafloor, friction slows the bottom of the wave down. The water at the surface, however, continues moving at its original speed. This causes the water behind it to pile up, eventually becoming too tall and unstable. The crest curls over the top and collapses, crashing onto the shore before retreating.

Not all waves follow the gentle breaking pattern caused by wind. Severe weather systems can generate storm surges, which are abnormal rises of water generated by a storm. Even more destructive are tsunamis, which are long-wavelength waves triggered by underwater earthquakes or mudslides. Unlike wind-driven waves, storm surges and tsunamis behave like towering walls of water, possessing immense energy capable of wiping out everything in their path.