What Is a Tsunami?

A tsunami is a series of extremely large and often devastating ocean waves typically caused by sudden movements on the ocean floor. Usually, these sudden movements are caused by earthquakes, strong volcanic eruptions, or underwater landslides. Tsunamis are dangerous not only because of their size but also because of their speed. In fact, according to the National Oceanic and Atmospheric Administration (NOAA), tsunamis travel faster than 500 miles per hour (mph) in deep regions of oceans, and some of them can last for several days.

Image Credit: David Rydevik (Wikimedia Commons)

How Fast Is a Tsunami?

The speed of a tsunami is determined by the depth of the region in which it originates and the regions it travels to. In short, the deeper the water, the faster and more devastating the tsunami. What’s more, it is very difficult to spot a tsunami in deep waters, which makes it all the more dangerous. Nonetheless, tsunamis lose speed as they approach shallow coastal waters. In fact, they can strike land at speeds as low as 20-30 mph. This, however, does not make them any less dangerous. The 2004 Indian Ocean tsunami, widely regarded as the deadliest tsunami in human history, killed and displaced over 150,000 people in 11 countries. The tsunami was caused by a massive earthquake near Sumatra, an Indonesian island.

The 2004 Indian Ocean Tsunami

Famously, National Geographic reported that, according to the U.S. Geological Survey (USGS), the tsunami may have released energy equivalent to the detonation of over 23,000 Little Boys—the nuclear bomb that was dropped on Hiroshima during the Second World War. The massive earthquake occurred on December 26, 2004, and unleashed a series of killer waves that reached the coasts of Africa and Thailand the very same day. The tsunami killed almost 150,000 people—the official death toll—across 11 countries on December 26th itself. Although tsunamis slow down as they approach shorelines, they strike with deadly impact velocity. These killer waves carry large volumes of water and can permanently damage coastlines, as was indeed the case with the 2004 Indian Ocean tsunami. In fact, the tsunami also led to the permanent submersion of entire islands in the Indian Ocean. In addition to human deaths, the tsunami also caused heavy property damage. Remarkably, however, there were very few animal deaths.

Some Characteristics of a Tsunami

Since tsunamis can travel faster than 500 mph in the deep ocean, they can cross entire oceans over the course of a single day! Moreover, tsunamis typically have a wavelength (the distance between successive waves) of over 100 miles in the deep ocean. This explains the interval between waves that strike shorelines.

Although tsunamis lose speed rapidly as they approach coastlines, they grow significantly in height. The killer waves are typically around 10 feet tall when they strike land. On the other hand, they can be more than 100 feet tall if they originate near coastlines.