Tsunami vs. Tidal Wave: What’s the Difference?

Tsunamis and tidal waves have a lot in common. Both are powerful ocean surges that can cause death and destruction. While that remains true, tsunamis and tidal waves differ in major ways, including in their formation, size, and predictability.

A tidal wave is a relatively shallow wave caused by gravitational pulls between the sun, moon, and Earth. As Live Science writes, the phenomenon is predictable because it correlates to the moon’s phases. Tidal waves are also more common for this reason. Coastal areas have two high tides and two low tides every 24 hours and 50 minutes (the length of a lunar day).

These waves tend to be much smaller than tsunamis as well. The University of Alaska [PDF] states that the tallest tide ever recorded reached 52 feet at the Bay of Fundy in New Brunswick, Canada. Tides generally have longer wavelengths—also known as the distance between waves—spanning thousands of miles. 

Unlike tidal waves, tsunamis have nothing to do with gravitational pulls from celestial bodies. They result from natural disasters like earthquakes, volcanic eruptions, and coastal landslides—making them unpredictable. It’s also important to note that about 80 percent of tsunamis start in the Pacific Ocean. This is because of the “Ring of Fire,” an area surrounding most of the ocean where tectonic plates frequently shift and cause numerous volcanic eruptions and earthquakes.

While most tsunamis are less than 10 feet high upon reaching shore, the biggest ones tend to be much larger than tidal wives. The largest-ever tsunami wave was recorded in Alaska’s Lituya Bay in 1958 following an earthquake and a colossal landslide, and towered at a whopping 1720 feet. Their wave periods—or the time it takes for a wavelength to pass a specific point—can reach 15 minutes to an hour, an alarming rate compared to typical tidal wave periods of 12 to 24 hours. 

Tsunamis can be among the most devastating natural disasters due to their unpredictability, strength, and speed. One wave can cause thousands of deaths and injuries, as well as building destruction and flooding. Low-land areas—such as beaches, bays, lagoons, and harbors—are the most vulnerable.

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