What Happens When a Deep-Water Wave Strikes the Bottom of the Ocean?

Deep-water waves form in the open ocean because of the transfer of wind energy. Wave size typically depends on a combination of three specific conditions: wind velocity, duration and fetch. When deep-water waves approach the shoreline, they strike the bottom of the ocean. Friction from the seafloor slows the water near the base (bottom) of the wave, causing the water near the crest (top) to surge ahead and break.

  1. Deep-Water Waves

    • Deep-water waves are generated in the ocean when wind moves across the water's surface. Wind velocity, duration and fetch (length of water over which the wind has blown) determine the size of resulting waves. The greater these three factors are, the larger a wave will become. The highest point of a wave is known as its crest, and the lowest point is known as its trough. The distance from a wave's upper crest to its lower trough is known as wave height. The distance from one crest to another or one trough to another (in a sequence of waves) is known as wavelength. Deep-water waves are waves that form in water deeper than 0.5 wavelengths.

    Horizontal Movement of Energy, Not Water

    • When looking at deep-water waves from a boat, the water appears to be moving across horizontal distances. This, however, is untrue. As waves pass through water deeper than 0.5 wavelengths, water molecules flow in circular patterns, oftentimes remaining in the same area. Energy, not water, moves horizontally across the ocean's surface. Deep-water waves do not move objects like boats or surfboards horizontally; instead, they move the objects up and down and back and forth.

    Wave Behavior Near Shore

    • Wave behavior changes when energy approaches the shallow water of a shoreline. In water less than 0.5 wavelengths deep, the seafloor intercepts the wave by slowing down the motion of water near the wave's base. Because the water at the crest of the wave continues to move at its original speed, the water begins to pile up. This process continues until the water at the crest can no longer be supported by the base. When waves break, they fall over and result in whitecaps. Waves break near the shore when they reach a depth that is only one-seventh the wavelength.

    Effect of Abnormal Wind Conditions

    • Hurricanes and tropical storms can lead to abnormally violent wind conditions. Under these circumstances, large amounts of energy enter the water, forming abnormally large waves. As these waves slow down and break near the shoreline, they typically have a devastating impact on regional wildlife and coastal communities. During the 2004 hurricane season, waves more than 90 feet tall were recorded in the open ocean by seafloor-based measuring devices.