Earth Science for Kids
What are tsunamis?
Tsunamis are large and powerful ocean waves that grow in size as they reach the shore. They can cause major damage as they rush inland flooding cities and destroying homes.
What can cause a tsunami?
Tsunamis are caused by a large displacement of water. Think of when you are sitting in the bathtub and you move forward in the tub. This can cause a relatively large wave. The same thing happens in the ocean when a large amount of water is suddenly moved. A number of events may cause this kind of movement including earthquakes, landslides, volcanic eruptions, glaciers breaking off, and even meteorites.
Most tsunamis are caused by earthquakes. An earthquake occurs when a large area of the Earth's crust suddenly moves. When this happens underwater, big gaps may appear on the ocean floor. When water moves in to fill this gap, a tsunami is born.
What happens during a tsunami?
- Once the water is moved by an earthquake or other event, large waves like ripples spread out from the point where the water first moved.
- These waves can move quickly and for very long distances. Some tsunamis have been known to travel for thousands of miles across the ocean and travel at speeds of up to 500 miles per hour.
- As the waves travel through the deep parts of the ocean, their crest is usually short, only a few feet tall. This makes it difficult to detect a tsunami as they are not necessarily visible in the deep ocean.
- When the waves approach land and shallow water, they pile up and grow in height.
- At the coastline, a trough of the wave may appear. This will cause drawback to occur on the shoreline. The water may recede for some distance. This can be dangerous as people may be tempted to walk out into the open area.
- When the wave arrives on the shore, it will usually be a tall wall of water. The water will rush inland, sometimes for some distance and with great speed and power. The height of the tsunami wave will depend on the topography of the shoreline. Some tsunamis have been known to reach heights of 100 feet.
- More waves may arrive. The time period between waves may be several minutes.
Where do tsunamis occur?
Tsunamis can occur in any major body of water. They are most common in the Pacific Ocean where there are lots of underwater earthquakes and volcanoes. Countries with long coastlines on the Pacific Ocean such as Japan, Chile, and the United States are all at risk of being hit by a tsunami. However, tsunamis can happen anywhere. In 2004 a massive earthquake in the Indian Ocean caused a devastating tsunami that killed over 230,000 people.
Why are tsunamis dangerous?
Even though tsunamis slow down as they approach the shoreline, they can still be travelling at highway speeds of over 50 miles per hour. A huge wall of water traveling at this speed can cause major damage. A large tsunami can travel many miles inland and wiping out entire coastal cities.
Many coastal areas have tsunami warning systems in place. If an earthquake occurs that may cause a tsunami, people are warned to leave the area or find high ground.
Interesting Facts about Tsunamis
- Although tsunamis are sometimes called tidal waves they have nothing to do with the ocean's tides.
- The series of waves generated by a tsunami is called a wave train.
- The first wave of a tsunami may not be the biggest. There may be bigger and stronger waves to come.
- The word "tsunami" means "harbor wave" in Japanese.
- The warning system in the Pacific Ocean is called the DART system which stands for Deep-ocean Assessment and Reporting of Tsunamis.
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