The recent earthquake and tsunami in Japan have caused not only a lot of damage but also tremendous loss of life. How do earthquakes and tsunamis occur?

On Friday, March 11, 2011, Japan experienced a very severe earthquake just 130 km off its north-eastern coastal city of Sendai, at 2:46pm Japan Standard Time (11:16am IST). The US Geological Survey says this was the seventh most powerful earthquake ever recorded.

Within minutes after this, a tsunami (Japanese word; tsu = harbor, nami = wave) hit the north-eastern coast of Japan. A huge wall of water, several storeys tall, and stretching for many kilometres, rushed on to land and engulfed everything — and almost everyone — in its path. This quake and tsunami's effects are being felt both locally and worldwide.

The latest quake occurred where the North American plate and the Pacific Plate meet. Here, the Pacific plate goes under the North American Plate, pushing it up. This process is called subduction. It generates tremendous force. On March 11, the North American Plate jerked up with such force that it pushed the ocean water up with tremendous violence. The water rose about 10 metres and came back down. This up and down movement happened for a while. The waves travelled away like ripples in a pond. When the first major wave hit land, along the north-eastern coast, the water flooded inland and washed away objects and people.

After-shocks (earthquakes that occur as the plates settle down again) are occurring and are expected to continue for some time. This makes matters worse.

The Pacific Plate is a major plate. Its margins touch many countries of North America, South America, Asia, and Australia and New Zealand (there was an earthquake here recently). All around this plate, at its margins, there is always a lot of volcano and earthquake activity. Hence it is called the ‘Pacific Ring of Fire.' All countries along this Ring are vulnerable. Japan is one of them.

The immediate impact has been the loss of lives. The death toll is still being calculated, but it is expected that it may be several lakhs. It is difficult to reach many places. So, rescue became very difficult very quickly. Japan is in the higher latitudes and it is still cold there; snow is falling. Snowfall is also slowing rescue and relief efforts. Japan's economy is mainly in the manufacturing sector. So, from automobiles to computer chips all industries have suffered. The Japanese economy is suffering badly. This means, the global economy also suffers. India and Japan have significant investments in each other's economies. These are also seriously affected.

Most importantly, Japan's nuclear power plants have been damaged quite severely. There are very serious worries about severe nuclear radiation affecting both Japan and the entire world, including India, is at risk of nuclear radiation. It's geography: winds circulate around the world, carrying radioactive material. This is why India and many other countries are very worried and are carrying out safety inspections of their own nuclear power plants. The U.S. has sent experts and materials to help reduce the nuclear risks.

In nature, there are no ‘disasters.' Earth is still undergoing change. It is a ‘restless' planet. Earthquakes, tsunamis, severe weather, etc. are all part of this process. We are very tiny and powerless against these forces of nature. When we get in their way, we are in severe danger. Often, we get killed. WE call these ‘disasters.' Nature does not discriminate for or against anyone or anything.

What is an earthquake?

The earth's crust consists of many large and small ‘tectonic plates' which have been floating about on a very hot, thick, gooey mass for millions of years. In some places, the boundaries of the plates rub against each other as they move. At some point, the pressure is so much that one (or both) of the plates suddenly jerks. This happens several kilometres underground. On the surface, where we live, we feel the ground shaking under us. This is what we experience as an earthquake.

What is a tsunami?

Earthquakes also occur underground below the ocean floor. When this happens, the ocean is jolted. This causes the water above the earthquake point to be violently and suddenly pushed with a tremendous amount of force. A huge wave forms out on the open ocean. When this wave travels and encounters a coast, it bumps into the land. Coastal areas are very shallow. When this bump occurs, the water rises high and crashes on to the land. If the land is flat, the water floods inland with extreme force and wipes out everything in its path.

Most of us in India first heard the word ‘tsunami' when one hit our east coast on December 26, 2004.

Want to know more?

No one knows for sure what the full impact will be, for how long, or how long it will take for Japan to recover. Watch the news on TV, in newspapers, and online to keep yourself informed of what is happening.

Visit http://tiigs.org for more detailed and interactive information.