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What Causes Tsunamis

Updated on March 14, 2011

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What Causes Tsunamis
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What Causes Tsunamis

Most people know the devastating damage and destruction tsunamis cause as they travel swiftly across the open ocean eventually turning into fatal waves in the shallow shorelines, but many do not know exactly what causes tsunamis.

Tsunami is a Japanese term that roughly translates to mean “harbor waves.” Tsunamis are not tidal waves; tidal waves are an entirely different natural phenomenon. Tsunamis are also not just one gigantic wave, but a series of waves known as a tsunami wave train. Imagine what happens when you toss a stone into the water and how the waves ripple out continuously. This is the same principle in tsunamis formation and the idea of the tsunami wave train.

Tsunamis are not always massive, destructive waves once they reach the shore. Sometimes, they occur as a series of continuous strong, destructive and amazingly quick tides that result in fast rising water levels inland, wreaking havoc and destruction on life and property.

What Causes Tsunamis to Occur

There is more than one type of disturbance that causes tsunamis, but all are related to an abrupt movement along the ocean floor. These sudden movements can be caused by earthquakes, underwater landslides, volcanic eruptions, and conceivably large meteoric impact.

The most commonly occurring cause of tsunamis are brought on by earthquakes occurring along the ocean's floor. It's all about how earthquakes occur that forms tsunamis. If you're wondering how do earthquakes occur, then here is a brief explanation: the initiation of an earthquake occurs as the oceanic plates move into the Earth's mantle by natural plate movement called plate tectonics, immense friction is produced. This tremendous friction causes the plate to become stuck.

As the stuck plate continues to sink into the mantle, a malformation of the overlapping plate forms and continues to build up massive amounts of energy over geologic periods of time. Eventually the overlapping plate snaps back, which provides the sudden movement that pushes the overlying water up abruptly, initiating the tsunami. Simultaneously, inland areas of the overlying plate lower.

This lowering of the shoreline is what causes flooding as water quickly moves inland. At the same time, waves are moving out and across the ocean. Across the open ocean, these smaller wave heights travel at incredibly quick speeds of more than 500mph, although the height of the wave correlates to speed.

As the height of the waves increase as the wave nears the shoreline, the speed slows drastically to around 30-200mph, but wave heights reach fifty feet or higher because in the more shallow water, the energy builds up wave size as it acquires more force with the lesser volume of water to spread its energy throughout.

Any time there is displacement of large rocks and material beneath on the ocean's surface, such as from large-scale underwater landslides or volcanic activity, there can also be the sudden necessary movement for tsunamis to form. The movement of the rocks and debris to the ocean floor can push up the overlying water suddenly, producing catastrophic waves. Underwater landslides are often caused by earthquake activity, but tsunamis causes can also happen from rock and debris plummeting into the ocean from the land. Even typical landslides are often caused by some sort of seismic activity.

Volcanic activity that spurs tsunamis can either be from undersea volcanic eruptions or from volcanic eruptions adjacent to the ocean as in volcanic islands. When a land volcano's base crumbles, it can push more ash and debris into the ocean causing waves of certain amplitude.

The severity and sizes of the eruption determines whether or not the eruption will cause tsunamis. Of course, with large enough volcanic eruptions, earthquakes in the surrounding area may result from the magnitude of the eruption thus forming tsunamis. Underwater volcanoes can cause tsunamis by collapsing downwards or if they cause the surrounding water to heat quickly due to hot lava flow.

While nearly 85% of all tsunamis occur in the “Ring of Fire” in the Pacific Ocean, they can happen anywhere, although some areas they occur very rarely. To understand what causes tsunamis and what causes tsunamis to form is a step in preventing some of the loss associated with one of the most catastrophic forces produced naturally by our planet. Although property and land loss is inevitable with tsunamis, the loss of life is preventable. The more people become aware of the signs of tsunamis and develop their own evacuation techniques in the higher risk areas, the more human lives can be spared.


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