4. What is the cause of tsunami?
Answers
What is Tsunami?
A tsunami is a powerful series of waves caused by a disturbance under water. This is usually an earthquake under the sea.
CAUSES:
Tsunamis are caused by sudden movements of the earth that happens under the sea. Often the most destructive Tsunamis are caused by earthquakes but causes can also include volcanic eruptions, landslides or even a comet hitting the sea.
Landslides cause tsunamis when the debris falls into the water. This has the same effect of dropping a large stone into a pool - big ripples are created. But when this happens in the sea and it is thousands of tonnes of rock and earth falling into the sea a very large ripple, more like a tidal wave is created. This travels across the sea until it comes into contact with land and a tsunami is formed.
Volcanoes cause tsunamis when there is an eruption. The volcano can either be on land or under the sea, in which case it is known as a submarine volcano. If the volcanic eruption happens on land, the tsunami is caused by debris and lava from the volcano flowing into the sea, which once again causes a bug ripple.
If the eruption happens under water, the enormous power of the eruption sends shudders through the earth and disrupts the water. The water in the sea then breaks into waves which travel across the ocean until they come into contact with a coast. Here, a tsunami is formed.
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Answer:
A tsunami is a series of waves caused by earthquakes or undersea volcanic eruptions.
Causes are:
Subduction Zones are Potential Tsunami Locations
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Most tsunamis are caused by earthquakes generated in a subduction zone, an area where an oceanic plate is being forced down into the mantle by plate tectonic forces. The friction between the subducting plate and the overriding plate is enormous. This friction prevents a slow and steady rate of subduction and instead the two plates become "stuck."
Accumulated Seismic Energy
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As the stuck plate continues to descend into the mantle, the motion causes a slow distortion of the overriding plate. The result is an accumulation of energy very similar to the energy stored in a compressed spring. Energy can accumulate in the overriding plate over a long period of time - decades or even centuries.
Earthquake starts tsunami-Earthquake Causes Tsunami
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Energy accumulates in the overriding plate until it exceeds the frictional forces between the two stuck plates. When this happens, the overriding plate snaps back into an unrestrained position. This sudden motion is the cause of the tsunami - because it gives an enormous shove to the overlying water. At the same time, inland areas of the overriding plate are suddenly lowered.
Tsunami waves Races Away From the Epicenter
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The moving wave begins travelling out from where the earthquake has occurred. Some of the water travels out and across the ocean basin, and at the same time, water rushes landward to flood the recently lowered shoreline.
Tsunamis Travel Rapidly Across Ocean Basin
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Tsunamis travel swiftly across the open ocean. The map on this page shows how a tsunami produced by an earthquake along the coast of Chile in 1960 traveled across the Pacific Ocean, reaching Hawaii in about 15 hours and Japan in less than 24 hours.
Tsunami "Wave Train"
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Many people have the mistaken belief that tsunamis are single waves. They are not. Instead tsunamis are "wave trains" consisting of multiple waves. The chart on this page is a tidal gauge record from Onagawa, Japan beginning at the time of the 1960 Chile earthquake. Time is plotted along the horizontal axis and water level is plotted on the vertical axis. Note the normal rise and fall of the ocean surface, caused by tides, during the early part of this record. Then recorded are a few waves a little larger than normal followed by several much larger waves. In many tsunami events, the shoreline is pounded by repeated large waves.
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