| Tsunamis are gigantic waves that come ashore with little or no warning.
A tsunami is caused by earthquakes or volcanoes that move the land on the
bottom of the ocean. Movement of the earth's land is called an earth tremor.
When a tremor shakes the land under the sea, it causes the water at the
surface to rise up in a hump. This high swell of water starts moving away.
After a long trip, this swell finally reaches shore. It roars onto the beach
as a wave. This tsunami wave can be a wall of water 7 meters (21 feet) to
33 meters (100 feet) high. The name tsunami comes from two Japanese words.
Tsu means "port" and nami means "wave." Many tsunamis
hit the coasts of the Japanese islands. To understand why, look at Japan
on a world map. Its eastern and southern coasts face the whole Pacific Ocean.
A tsunami can form far away in the southern or eastern Pacific. It starts
moving towards Asia and builds up size and speed as the tsunami heads west.
For thousands of miles, there is no land to stop it or slow it down. Then
it hits the coast of Japan. This is why Japan has more tsunamis than anywhere
else in the world. Today scientists have more warning that a tsunami is
forming. They can find earthquakes under the ocean using a machine called
a seismograph. Also, photos taken from airplanes and images taken by space
satellites show ocean waves. Scientists send early warnings to port cities
that a big wave is on the way. |
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