In the deep ocean, tsunamis are often less than 3 feet high and can pass beneath ships completely unnoticed.

Tsunamis differ fundamentally from wind-driven waves because their energy extends through the entire water column to the ocean floor. In the open ocean, where depths exceed 13,000 feet, wave heights are typically less than 3 feet. With wavelengths often exceeding 100 miles, the wave slope is so gradual that sailors aboard ships frequently don't even feel it passing beneath them.These waves travel at extraordinary speeds, often exceeding 500 miles per hour—comparable to a commercial jet aircraft. This speed is determined by water depth according to the formula: wave speed equals the square root of the product of gravitational acceleration and depth. As long as the water remains deep, the energy stays kinetic and horizontal rather than vertical.The transformation occurs through a process called wave shoaling as the tsunami enters shallow water near a coastline. As ocean depth decreases, the front of the wave slows significantly while the back continues at high speed. This compression causes the wave to grow dramatically in height, a phenomenon documented extensively by the National Oceanic and Atmospheric Administration (NOAA).The 2004 Indian Ocean tsunami provides a tragic illustration. Deep-sea sensors recorded the wave as merely a minor rise in sea level, yet when that same energy reached the shores of Indonesia and Thailand, it surged into waves exceeding 100 feet tall. This dramatic difference underscores why deep-water detection systems, such as the DART buoy network, are essential for early warning.