Ocean waves form when wind drags across the water’s surface, transferring energy that stretches and lifts the water into swells. But “making” ocean waves can mean several things: understanding the physics behind natural waves, engineering artificial waves for surfing or recreation, or building a simple wave tank at home. This guide covers all three.
How Nature Makes Waves
Wind is responsible for nearly every wave you see at the beach. As air moves across smooth water, friction between the two stretches the surface upward, creating small ripples. Those ripples give the wind more surface area to push against, which builds the ripples into larger and larger waves. Three factors determine how big waves get:
- Wind speed. The wind must move faster than the wave crests for energy to keep transferring into the water.
- Duration. Strong wind blowing for a long, sustained period produces much larger waves than a brief gust.
- Fetch. This is the uninterrupted distance the wind travels over open water without changing direction. A fetch of hundreds of miles across the Pacific creates the massive swells that reach Hawaii and California.
What’s counterintuitive is that the water itself doesn’t travel with the wave. Water particles move in circles as a wave passes through, then return to roughly where they started. Picture a rubber duck bobbing in place as a swell rolls under it: the duck traces a small loop and ends up back where it began. The diameter of that loop equals the wave’s height at the surface, and the circular motion shrinks rapidly with depth. Below a depth equal to half the wavelength, there’s essentially no movement at all. This boundary is called the wave base, and it’s why submarines in deep water are unaffected by even violent surface storms.
Why Waves Break Near Shore
Waves travel across deep ocean without breaking because the water beneath them is deep enough for their circular motion to spin freely. As a wave approaches shore and the seafloor rises, the bottom of the wave’s orbit starts dragging against the ground. The top of the wave keeps moving forward while the base slows down, causing the wave to steepen and eventually topple over.
This happens at a fairly predictable ratio. Waves generally break when their height reaches roughly 70 to 78 percent of the water’s depth. A wave that’s 5 feet tall will break in water about 6 to 7 feet deep. The shape of the seafloor determines the type of break: a steep, sudden rise produces a hollow, crashing barrel, while a gradual slope creates a gentler, rolling break.
Waves From Earthquakes and Landslides
Tsunamis are a fundamentally different kind of wave. Wind waves only disturb the water near the surface, but tsunamis displace the entire water column from the seafloor to the surface. This happens when a geological event rapidly shifts a large area of the ocean bottom, most commonly an earthquake of magnitude 6.5 or greater that produces vertical displacement of the seafloor. Large underwater landslides and volcanic eruptions can also trigger them, and in rare cases, asteroid impacts or coastal landslides crashing into the water from above.
Because the energy extends through the full depth of the ocean, tsunamis travel at jet-plane speeds in deep water while appearing as barely noticeable swells at the surface. They only reveal their destructive size when they reach shallow coastal water and all that energy compresses upward.
How Wave Pools Create Artificial Waves
Modern wave pools use two main approaches to push water into rideable surf-quality waves.
Pneumatic Systems
Pneumatic wave pools line the back wall of a large pool with a series of air chambers. Blowers pressurize each chamber, and when the pressure is released in a carefully timed sequence, the air pushes water outward to form a wave. The more pressure released, the bigger the wave. By staggering the timing of neighboring chambers, operators can shape the wave’s angle, speed, and size. Each chamber contributes a small piece of energy that merges into a single, continuous wave front.
Underwater Foil Systems
The other major design, used in facilities like Kelly Slater’s Surf Ranch, works more like a plow. A large submerged foil is pulled along a straight track at high speed, displacing water to one side. That displaced water rolls over a carefully sculpted artificial reef (the pool’s bottom contour) and breaks just like an ocean wave would over a natural reef. Adjusting the plow’s speed changes the wave’s steepness and size. The system is bidirectional: it travels one direction to create left-breaking waves and the other for rights, with a three- to four-minute pause between waves as the foil resets.
Energy Costs
Generating artificial waves takes significant power. Pneumatic blower systems consume roughly 4,300 kilowatt-hours to produce 280 six-foot barreling waves in a one-hour session. Newer mechanical designs like the Wavegarden Cove use about one-tenth of that energy for the same output, around 450 kilowatt-hours for 280 comparable waves. For context, 4,300 kWh is close to what an average American home uses in four months. Energy efficiency is one of the biggest factors determining whether a wave pool project is financially viable.
Building a Simple Wave Tank at Home
If you want to demonstrate wave physics for a school project or just see wave behavior up close, you can build a functional wave tank with materials you probably already have. NASA’s Jet Propulsion Laboratory developed a straightforward design that requires:
- Two aluminum baking pans taped end-to-end (or one long, narrow pan)
- A stiff piece of plastic or wood cut to fit snugly across the short end of the pan
- Water
- Sand
- A ruler
- Duct tape and silicone caulking to seal the seam if using two pans
Fill the pan with a few inches of water. Pile sand at one end to create a sloped “beach.” At the opposite end, use the stiff plastic or wood as a paddle. Push the paddle steadily into the water, then pull it back, and you’ll generate a wave that travels down the tank. A single slow push creates a long, gentle swell. Quick, repeated pushes create shorter, choppier waves. You can watch the wave steepen and break as it hits the sand slope, demonstrating the same physics that make ocean waves crash on shore.
Experiment with different water depths, sand angles, and paddle speeds. You’ll quickly see the relationships that govern real ocean waves: steeper bottom slopes produce more abrupt, violent breaks, while gentle slopes create slow, rolling surf. Adding a few drops of food coloring near the surface lets you watch the circular orbital motion of water particles in action, confirming that the water moves in loops rather than traveling forward with the wave.
Tidal Bores: Rivers That Make Their Own Waves
One of nature’s stranger wave phenomena is the tidal bore, a single wave that travels upstream into a river mouth as the tide comes in. These form in estuaries with shallow, gradually sloping riverbeds and a tidal range greater than about 13 feet (4 meters). The incoming tide funnels into the narrowing river channel, and the water has nowhere to go but up, creating a wave that can reach 20 feet tall in extreme cases. Tidal bores occur in dozens of rivers worldwide, and surfers regularly ride them for miles in places like the Severn River in England and the Qiantang River in China.