Synopsis
A tsunami is not a single wave but a series of them, typically described as a wave train, generated when a sudden and massive displacement of water sends energy propagating outward through the ocean in concentric rings.
What distinguishes a tsunami from every other type of ocean wave is not its height when it reaches the shore — though that can be extraordinary — but its origin, its physics, and its relationship to the entire column of water through which it travels. While most ocean waves are born at the surface, animated by the friction of wind against water, a tsunami draws its energy from deep geological forces, and it carries that energy through the full depth of the ocean, from seabed to surface.
This distinction matters enormously. An ordinary wind-driven wave involves only the upper portion of the ocean. Its energy is shallow, dispersed, and relatively easily absorbed. A tsunami, by contrast, mobilises the entire water column. In parts of the Pacific Ocean where the water depth exceeds eight kilometres, this means an unimaginable mass of water is set in coordinated motion simultaneously. When that motion finally encounters a coastline, the energy concentrated in hundreds of kilometres of open ocean is compressed into a matter of metres. The results can be catastrophic beyond anything a wind-driven wave could produce.
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