Most ocean waves are created by wind. As moving air passes over calm water, friction and pressure differences between the two transfer energy from the atmosphere into the sea surface, producing ripples that can grow into the massive swells that crash onto coastlines thousands of miles from where they started. But wind isn’t the only source. Earthquakes, gravitational pull from the Moon and Sun, and storms all generate distinct types of waves through entirely different mechanisms.
How Wind Builds Waves
Wave formation starts small. When wind blows across flat water, it catches on the surface through friction, creating tiny ripples just millimeters high. Those ripples give the wind something to push against. Air flowing over a small bump in the water surface creates a zone of higher pressure on the windward side and lower pressure on the sheltered (leeward) side. That pressure difference nudges the water upward, making the ripple taller, which gives the wind even more surface area to work with. The process feeds on itself.
For this energy transfer to keep working, the wind must be moving faster than the wave crests. Once a wave moves as fast as the wind pushing it, it stops growing. How large waves ultimately get depends on three factors: wind speed, how long the wind blows (duration), and fetch, which is the uninterrupted distance of open water the wind travels over. This is why storms over the open Pacific Ocean produce much larger waves than equally powerful storms over smaller bodies of water. The Pacific simply offers more room for waves to keep building.
Water Doesn’t Actually Travel With the Wave
One of the most counterintuitive things about ocean waves is that the water itself barely moves forward. Waves are energy passing through water, not water moving across the ocean. As a wave rolls by, individual parcels of water trace a circular path: up and forward with the crest, then down and backward with the trough, ending up roughly where they started. If you’ve ever watched a seagull bob on the surface as waves pass underneath, you’ve seen this in action. The bird rises and falls but doesn’t get carried along with the wave.
This circular motion doesn’t just happen at the surface. It extends downward through a column of water reaching about half the wave’s wavelength deep. A wave with 100 meters between its crests moves water in circles down to about 50 meters below the surface. Below that depth, the water is essentially still.
From Choppy Seas to Organized Swell
Inside a storm, the ocean surface is chaotic, with waves of all different sizes, speeds, and directions crashing into each other. As these waves move away from the storm, they naturally sort themselves out. Longer waves travel faster than shorter ones, so they pull ahead and separate. Over hundreds or thousands of miles, this sorting process transforms a messy jumble into clean, evenly spaced swell.
Swell travels in groups called wave trains, typically containing 3 to 15 waves. Something odd happens within these groups: the train as a whole moves at half the speed of the individual waves inside it. The leading wave gradually loses energy and fades away, while a new wave forms at the back of the group. Energy essentially trades backward through the train, slowing its overall progress even as each individual wave moves fast.
Swell does lose energy as it crosses an ocean basin, mostly through friction and a phenomenon called spreading loss, where the wave front fans out like a flashlight beam. About 90% of a storm’s wave energy travels outward in a cone roughly 30 to 45 degrees wide. Even with that spreading, waves from a single storm system in the North Pacific can affect the entire western coastline of the United States.
What Makes Waves Break at Shore
Waves that have traveled cleanly across an ocean eventually hit shallow water near the coast, and that’s where they break. As the seafloor rises, the bottom of the wave drags against it, slowing down. The top of the wave, still moving at full speed, pitches forward and collapses. The classic rule of thumb is that a wave breaks when the water depth is roughly 1.3 times the wave’s height, though the actual ratio varies depending on the slope of the seafloor and other conditions. On gently sloping beaches, waves tend to crumble gradually. On steep underwater shelves, they pitch forward dramatically into the barrel shapes surfers prize.
Tides: Waves Driven by Gravity
Tides are technically very long, very slow waves created not by wind but by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Moon’s gravity tugs on the Earth’s oceans, creating a bulge of water on the side nearest the Moon. A second bulge forms on the opposite side of the planet, not because the Moon is pulling water there, but because its gravity pulls the solid Earth slightly away from the water on the far side. As the Earth rotates through these two bulges each day, coastlines experience two high tides and two low tides.
The Sun has about 27 million times the Moon’s mass, but it’s roughly 390 times farther away. That distance reduces its tide-generating force to a little less than half of the Moon’s. When the Sun and Moon align (during full and new moons), their forces combine to produce especially high and low tides, called spring tides. When they pull at right angles to each other, the result is more moderate neap tides.
Tsunamis: Waves From the Seafloor
Tsunamis have nothing to do with wind or tides. They form when an earthquake, volcanic eruption, or underwater landslide rapidly displaces a large volume of water. The most common trigger is an undersea earthquake of magnitude 6.5 to 7 or greater that causes the seafloor to shift vertically. When a slab of ocean floor suddenly drops or lifts, it pushes the entire column of water above it, from the bottom all the way to the surface. That displacement radiates outward as a wave.
In the open ocean, a tsunami may be less than a meter tall and completely unnoticeable to ships, because its energy is spread across a wavelength that can stretch hundreds of kilometers. But as it enters shallow coastal water, all that energy compresses. The wave slows, its height surges, and it can arrive onshore as a wall of water many meters high. Unlike wind waves, which only disturb the upper portion of the water column, tsunamis move water from the surface to the seafloor, which is what gives them such destructive force.
Storm Surge and Pressure Effects
During hurricanes and intense storms, extremely low air pressure at the storm’s center creates a slight dome of water, like a suction cup pulling the ocean surface upward. This effect accounts for about 5% of the total rise in water level during a storm surge. The other 95% comes from wind physically pushing water toward shore. The combination of both forces, often arriving on top of normal tides, is what makes storm surge the deadliest hazard in a hurricane.
How Big Can Waves Get
The largest verified wave height ever recorded by a buoy was 19 meters (62.3 feet), measured on February 4, 2013, by a sensor in the North Atlantic west of Scotland. The buoy sat south of an intense low-pressure system that drove sustained winds above 35 knots for 12 hours before the peak measurement, with gusts reaching nearly 44 knots. That record represents the “significant wave height,” which is the average of the tallest third of waves in a given period. Individual rogue waves can exceed that figure, though they are much harder to verify. Satellite and platform estimates of rogue waves exist but lack the ground-truth measurements needed for official records.