This week, the world learned of the devastating effects of giant, powerful waves known as tsunamis. But what causes such waves? And how are they able to wreak such death and destruction thousands of miles from their source?
For some answers, English to Africa reporter Joe De Capua spoke with Jose Carlos Borrero, research professor at the Viterbi School of Engineering at the University of Southern California in Los Angeles. He says, “Tsunamis are long water waves that are caused by an impulsive motion of the sea floor. So, anything that pushes the sea floor up or pulls it down violently can generate a tsunami. So, that can be either an earthquake underwater, a volcano under water or a landslide underwater or even a landslide that starts above land and falls into the water.”
Tsunamis are known to travel hundreds of miles an hour, but is there any evidence of this on the surface before the wave makes landfall? Professor Borrero says, “Not very much. It is measurable, but the amplitude in deep ocean is very low, on the order of just a few inches. They move very fast in deep water. The speed of these waves is related to the depth of the water, so the deeper the water the faster they go.”
The size and strength of the tsunami isn’t really known until it reaches shore. The University of California professor says, “As the front end of the wave enters shallower water it begins to slow down, whereas the back part of the wave is still in deep water going very fast. So the result is kind of like a train wreck. The back end of the wave piles up into the slowing down front end of the wave.“ The result is a massive wall of water.
The reason it can do so much damage as racing across the deep ocean for thousands of miles is that its energy has not dissipated. That happens when a wave actually breaks. Professor Borrero says, “Areas that have large earthquake fault systems that are known as subduction zones, that’s where you have the most tsunamis.”
While there are none reported off the coasts of Africa, the continent, as witnessed this week, is vulnerable to tsunamis that begin in Asia.
There is no early waning system in the part of the world struck by this week’s tsunami. The United States operates such systems in Hawaii and Alaska.