Difference between a Tidal Wave and Tsunami

Discussions of tidal waves, seismic waves and tsunamis can be confusing when all three are referred to as the same thing. There are differences between tidal waves and tsunamis that will help to understand the ways in which they are similar but not the same.

A tidal wave is the unusual incursion of water along a sea shore. These unusual events occur as the result of offshore winds or storms, or a combination of wind and normal tides.

A tsunami is the result of some major upset in the ocean floor. A major volcanic eruption, earthquake, submarine landslide, or most commonly, a major upward shift in an underwater tectonic plate can cause tsunami. The term tsunami is both singular and plural and comes from the meaning “large harbor wave” in Japanese.

A tidal bore occurs when open water passes through a constriction and into shallower depths. The Cook Inlet, southeast of Anchorage, Alaska, has tidal bores.

With tsunamis, the same effect as lifting one end of a shallow pan filled with water will occur. Water in tsunamis can travel across entire oceans, with the deepest parts showing no indication of a wave at all. As water piles up when the ocean floor becomes shallower, the wave reaches enormous size by the time that it reaches land. Tsunamis build up as they approach the shore.

The Aleutian chain, East of Alaska, is possibly the most prolific source of tsunamis.

Tidal waves are also called rogue waves, freak waves, killer waves, monster waves or open surface waves. One standard is to consider a wave that is more than twice the “significant wave height” as a tidal wave. Significant wave height is calculated as the mean of the largest third of waves in a wave record.

Instead of being the largest waves in the ocean, these are waves that are unusually large in relation to the normal state of the sea. Open ocean tidal waves can form when strong winds hit the point where currents converge. In some cases, several waves are joined together into one large wave.

Tidal waves are also called hundred year waves because they are rare. But there is a statistical wave called a “hundred year” wave which is a calculation of the biggest wave that might occur, based on calculations and probability.

Once believed to be the stuff of myth, tidal waves have been observed by satellite technology, and are related to damage and ships that have otherwise inexplicably gone missing.

“Tidal Waves, Tidal Bores and Tsunamis”

Wikipedia: Rogue Wave