Waves definitely exist in the middle of the ocean, but they look and behave far differently than the crashing surf familiar to coastal observers. The open ocean is constantly in motion, driven by a complex interplay of forces that create waves of varying scales, from visible undulations on the surface to massive, unseen movements deep within the water column. These waves are largely driven by wind, gravitational forces, and tectonic activity. The waves in the deep expanse are more organized and subtle, representing pure energy traveling across the globe.
The Generation and Travel of Ocean Swell
The most common visible wave in the open ocean originates from wind interacting with the surface, initially creating disorganized waves known as “sea.” The size and energy of these initial waves are determined by the wind speed, the duration the wind blows, and the “fetch,” which is the distance over which the wind travels unobstructed across the water. When the wind stops or the waves move out of the storm’s immediate area, they begin to travel away from their point of origin as organized energy called “swell.”
This process of transformation is governed by dispersion, where waves separate according to their wavelength and speed. Longer-wavelength waves travel faster and move ahead of the shorter, choppier waves, resulting in the smooth, long-period undulations characteristic of open-ocean swell. Swell can travel across entire ocean basins, often covering thousands of kilometers, carrying the energy from a distant storm to a far-off coastline.
Understanding Deep Water Wave Dynamics
In the middle of the ocean, surface waves operate under “deep water” conditions, defined as a water depth greater than half the wave’s wavelength. Under this condition, the energy of the wave moves forward, but the water itself does not travel horizontally over long distances. Instead, water particles near the surface move in distinct circular orbits as the wave crest passes.
These circular orbits are entirely contained within the water column and do not interact with the seabed. The diameter of a water particle’s orbit decreases exponentially with depth, becoming virtually negligible at a depth equal to half the wavelength. This means that the wave motion does not affect the deepest parts of the ocean floor. The speed of these deep-water waves is also directly related to their wavelength, with longer waves moving faster, which reinforces the dispersive sorting of swell.
Waves Beneath the Surface: Internal Waves and Tides
Beyond the visible surface swell, the deep ocean hosts massive, unseen movements known as internal waves, which occur within the water column rather than on the surface. These waves form along density boundaries, called pycnoclines, where layers of warmer, less dense water meet colder, denser water. Internal waves can have amplitudes significantly larger than surface waves, sometimes reaching hundreds of meters in height, but they cause only a slight ripple on the surface.
Tides act as massive, planetary-scale waves generated by the gravitational pull of the moon and the sun. These forces create two bulges of water that travel across the ocean basin as extremely long-period waves. When these tidal flows encounter seafloor features like mid-ocean ridges or seamounts, they can generate powerful “internal tides,” which are internal waves with a tidal frequency that transmit large amounts of energy vertically and horizontally through the ocean depths.
The Extremes: Tsunamis and Rogue Waves
The deep ocean is also the birthplace of two dramatic wave phenomena: tsunamis and rogue waves, both driven by non-atmospheric forces. Tsunamis are generated by sudden, massive displacements of water, typically from underwater earthquakes or landslides. Due to their immense wavelength—often hundreds of kilometers long—a tsunami behaves as a “shallow-water wave” even in the deepest parts of the ocean, meaning its energy extends from the surface to the seafloor.
In the open ocean, a tsunami travels at speeds exceeding 800 kilometers per hour (500 miles per hour) but has a wave height of less than one meter, making it nearly imperceptible to a ship. Rogue waves are unpredictable, massive surface waves that appear suddenly and are defined as being more than twice the height of the surrounding significant wave height. They are often formed through constructive interference, where multiple smaller wave systems temporarily align their crests to create a single, towering wall of water.