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How Tall Is the Average Tsunami Wave?

The height of a tsunami wave gives little indication of the raw destructive power that lies beneath the waters. While tsunamis often originate in the ocean, they can form in lakes as well. Barreling at high speeds across the water, these waves can deliver enough force to devastate communities on shore. A tsunami's average wave height depends on the point in its life cycle.

Wave Height Varies
- Most tsunamis are not powerful and only reach a few centimeters (or inches). When strong tsunamis occur, they might reach heights of several meters. As tsunamis move away from their originating sources and encounter deep ocean water, they get shorter and can shrink to 0.3 meters (1 foot) or less. When tsunamis move close to shore or over shallow water, they get taller again and can cause significant damage when they make landfall. Using computer models, the National Oceanic and Atmospheric Administration showed that tsunami heights in states such as Oregon and California could reach 21 meters (70 feet).
Wave Height on Land
- A tsunami's life eventually ends after it moves onto land, interacts with objects and fades away. Scientists define run-up as the height of a tsunami at its furthest point inland. That height could differ from the height the tsunami had when it moved across the water. Run-up heights on land are often twice the tsunami's height at its landfall point. It's common to see run-up heights of 10 meters (30 feet), but on rare occasions those heights may reach 90 meters (300 feet).
Tsunamis Change on Shore
- When a tsunami crosses shore and moves across land, its height and direction may change at different locations along its path. Some regions could experience effects that differ from those in neighboring regions. Investigators who study a tsunami's aftereffects use a variety of techniques to estimate a tsunami's height on land. For example, they can look for debris in tree branches and measure the distance from the ground to the debris.
Silent, Invisible Killers
- A tsunami consists of a series of waves that have long periods and wavelengths. Even though a tsunami may travel at speeds of over 970 kilometers per hour (600 miles per hour), you can't detect them from the air or aboard a ship that might be in the area. Many people may think these destructive waves only occur during earthquakes, but other forces, such as landslides and volcanic eruptions, can generate them as well. Any disturbance that displaces a large amount of water from its equilibrium point can create a deadly tsunami.

Nature