tsunami

A series of ocean waves generated by a sudden, large-scale displacement of the seafloor — most commonly by a submarine earthquake, but also by volcanic eruption, underwater landslide, or calving glacier. In open ocean, a tsunami is barely perceptible — a low, fast swell traveling at jet speed across the entire ocean basin. As it enters shallow water near shore, the wave slows, compresses, and rises, arriving as a wall of water that can be 100 feet tall and travel miles inland. The word is singular and plural — one tsunami, many tsunami — and it names not a single wave but a train of waves, the second or third often larger than the first.