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5th Session: Earthquakes. Video: What is a Tsunami?

Lesson 2: Internal forces of the Earth: earthquakes and volcanoes

5th session: Earthquakes

3. Watching the video: “What is a Tsunami?”

Watch this video paying atention to the explanation. You have enough time to watch the video two times if you want.

You have 15 minutes.

What is a Tsunami?

 

Hi! I'm Emerald Robinson and in this “what is” video we're going to discuss earth's most powerful waves: tsunamis.

A tsunami is a series of fast-moving waves triggered by an underwater shock. Tsunamis are usually caused by earthquakes or volcanic activity, but landslides or underwater explosions can also be the cause.

Tsunamis were once called tidal waves, but this name isn't very accurate, because tsunamis aren't related to the Earth's normal tides. Instead tsunamis form when water is somehow displaced by force. Let's look at an example. Shifting lava beneath the earth's crust can cause the ocean floor to bulge, and then suddenly flatten as this occurs energy is released into the water creating a series of waves.

In deep water the waves have a small height or amplitude a very long length and move at an extremely high rate of speed up to 500 miles per hour. Because these waves are usually less than a foot high, tsunamis are barely noticeable at this stage.

Tsunamis gain their power when they get close to shore, as the water gets shallower the rapidly moving waves are forced to suddenly slowed down, and the energy that has been carrying the tsunami causes the way to increase in amplitude. Most tsunamis reach heights of about 10 feet but some can be up to 100 feet tall. When a tsunami makes landfall, it usually takes the form of a sudden and rapidly rising tide that moves at about 50 miles per hour.

Tsunamis are very unpredictable not all undersea earthquakes cause tsunamis and about 75% of tsunami warnings turn out to be false alarms. Still scientists continue to monitor areas of high earthquake or volcanic activity such as the Pacific Oceans Ring of Fire where color about eighty-five percent of the world's tsunamis occur. There studies will improve our ability to predict these natural disasters officially warned areas at risk.

 

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