Tsunamis

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What are tsunamis?
Giant sea waves generated by shallow-focus underwater earthquakes, volcanic eruptions, underwater debris slides and large landslides under the sea.
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What is the most common cause of a tsunami?
A shallow-focus underwater earthquake.
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What does the earthquake have to cause to generate a tsunami?
A vertical displacement of the sea bed. This in turn displaces water upwards which generates a tsunami at the ocean surface.
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What are the characteristics of tsunamis in the sea?
Long wavelength (100 km), low wave height (700 kmph).
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How long can it take for a tsunami to cross the Pacific Ocean?
Less than one day.
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What is often the first warning sign given to coastal populations?
The wave trough in front of the tsunami which results in a reduction in sea level, kwown as drawdown. Behind this comes the tsunami, reaching 25 m high.
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What does a tsunami event usually consist of?
A number of waves, with the largest not necessarily being the first. Many tsunamis reach 500 to 600 m inland, depending on the geography of the area.
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When a tsunami reaches land, what does its characteristics depend on?
The height and distance travelled by waves, the length of the event, coastal geography, both offshore and in the coastal area.
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What are the characteristics in the coastal area?
As water depth decreases, friction increases and slows the wave down. As it slows, wavelength dramatically decreases and wave height increases, producing a series of huge waves, metres high.
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How many tsunamis are generated within the Pacific Basin, with tectonic activity taking place around the edges?
90% of all tsunamis.
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Which type of plate margin are most tsunamis generated at?
Destructive, where subduction is taking place. This is especially true for the Japan-Taiwan island arc, where 25% of all tsunamis occur.
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What must be remembered with tsunamis?
They don't just affect the surface of the water, they affect the whole column from the sea bed. Also, the greater the volume of water displaced, the larger the tsunami wave.
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Give an example of a tsunami in the Atlantic Ocean.
In 1775, an earthquake in Lisbon killed 60,000 around the area, and caused a 7 m high wave in the Caribbean.
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What can help to protect a coastal area from a tsunami?
Coral reefs, as they dissipate energy.
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Other cards in this set

Card 2

Front

What is the most common cause of a tsunami?

Back

A shallow-focus underwater earthquake.

Card 3

Front

What does the earthquake have to cause to generate a tsunami?

Back

Preview of the front of card 3

Card 4

Front

What are the characteristics of tsunamis in the sea?

Back

Preview of the front of card 4

Card 5

Front

How long can it take for a tsunami to cross the Pacific Ocean?

Back

Preview of the front of card 5
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