The ocean is moving, but the water isn't really traveling
In short: When you watch a wave roll toward the shore, it looks like a wall of water migrating across the sea. In reality, the water stays almost exactly where it is. Waves are not bodies of water in motion; they are pulses of energy moving through a medium.
The fundamental mechanism of an ocean wave is the propagation of kinetic energy. As energy passes through seawater, it forces the water molecules to move in a circular or orbital motion rather than traveling forward from one point to another. If you were to track a single particle of water as a wave passes, it would lurch upward and forward, only to return to its original position once the wave has moved on.
This orbital motion isn't limited to the surface. A column of water beneath the surface follows this same circular path down to approximately half of the wave's wavelength. In the open ocean, these movements are relatively fluid because there is little interference from the seabed. However, as waves approach a coastline and enter shallow water, the seafloor begins to obstruct the lower portion of that orbital column.
This obstruction causes the bottom of the wave to slow down and compress. Because the energy must go somewhere, it forces the crest of the wave higher into the air. When this imbalance reaches a breaking point, the crest collapses, dissipating its energy into the surf as the dramatic crashing motion we see at beaches.
While most common waves are surface waves driven by wind blowing across the air-water interface, other phenomena exist. Storm surges result from high winds and low pressure, while tsunamis are triggered by submarine earthquakes or landslides that displace massive amounts of water quickly. These larger events often manifest as a massive rise in sea level rather than typical crashing waves. The scale of this energy is staggering. It is estimated that just 0.2% of the total energy contained within ocean waves could potentially power the entire world.
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Sources
- Summary by Intellect · source: How do Ocean Waves Work?
- Also: What causes ocean waves? - NOAA Ocean Exploration
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