In the afternoon of a working day, March 11, 2011, life changed for Japan.
The worst ever earthquake in Japanese history struck off the coast of the northeastern city of Sendai, on the island of Honshu.
The quake measured 8.9 on the Richter scale (a scale that measures earthquake intensity), powerful enough to shake buildings 400 km away in the capital city of Tokyo. But the nightmare was yet to come.
The nightmare from the sea
The earthquake happened out at sea and it triggered a tsunami.
Tsunami is a Japanese word meaning “harbor wave.” It is a body of water that is born near the epicenter of an earthquake. When it reaches land, this wall can be several meters high. In Japan's case, a 10-meter high wall raced towards the areas around Sendai.
The northeastern coastline of Japan was altered completely by the tsunami, as it swept inland taking everything – houses, cars, and boats – with it. More than the quake itself, the tsunami that followed has created untold damage. The full extent of Japanese loss is still unknown. Moreover, the tsunami and earthquake might have damaged nuclear reactors – and that is an ongoing story we are watching.
How is a tsunami formed?
Earthquakes, landslides, and volcanic activity – anything that displaces water, can cause a tsunami. Not all earthquakes generate tsunamis. First of all, it has to have its epicenter (the point where the earthquake actually happens) underwater. And even then, all underwater earthquakes do not result in tsunamis. This makes predicting tsunamis difficult.
The earth’s crust is full of “tectonic plates” on which continents sit and shift. When one tectonic plate butting up to the other moves and subducts (dives under the other plate) or pushes the other plate up, an earthquake is created.
If this happens underwater, the energy released by the movement of the earth's crust is transferred to the water. This could result in a wave. The wave is not very high at sea – but is very long. These waves have a lot of energy and can travel at almost 800 km per hour as they race towards land. When this “displaced water” reaches shallow coastal areas, the wall increases in height (all that water traveling from the deep ocean in a wave has to go somewhere). It slams onto land causing devastation and heavy flooding.
Tsunami warning: seek higher ground!
There are tsunami-warning stations all along the coast of Japan and throughout the Pacific Ocean. These warnings allow people in low-lying areas to escape to higher ground if there is the threat of a tsunami. It is likely that a lot of people in Japan on March 11, did that. But the tsunami that came was very, very big and powerful and has still managed to cause a whole lot of damage and loss.
How can we help?
The Japanese Prime Minister has called it the worst crisis Japan has faced since WWII, and has asked for help. People and countries around the world are helping. Ask your school or local community how you can join efforts to help the tsunami victims in Japan.