You may have heard of tsunamis, the enormous waves that crash into the coastline and flood entire towns, even cities. The 2011 Tōhoku tsunami, which slammed into Japan, caused billions of dollars worth of damage. Thousands of lives were lost. It even caused the meltdown of the Fukushima Daiichi Nuclear Power Plant.
But what exactly causes such waves to form in the first place?
The waves produced during the Tōhoku tsunami were, quite simply, huge. The tallest may have reached a height of 133 feet, scientists believe. In certain areas, these waves traveled as far as six miles inland, wiping out nearly everything in their path.
Waves of this size are usually caused by earthquakes. In the case of Tōhoku, the earthquake was classified as an “undersea megathrust earthquake,” and it is considered the biggest earthquake to ever have hit Japan. In fact, it was the fifth-largest earthquake ever measured, since humans began tracking the size of earthquakes in 1900.
The earthquake caused the ocean floor to be thrust upwards by as much as 15 feet. When the seabed rises, so does the ocean above it. And the more shallow the water is where the earthquake occurs, the larger the tsunami will be. Unfortunately for the inhabitants of Japan’s coastline, the earthquake happened just 45 miles off the coast.
Tsunamis behave differently than average ocean waves. For one thing, the type of waves you see at the beach are caused by wind. They tend to have a wavelength—that is, the distance between the crests of two consecutive waves—of around 330 feet. They also tend to average about 6.6 feet in height.