How Does a Tsunami Start?

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Tsunamis generally begin with the vertical movement of the earth's crust on the ocean floor. The movement displaces the water above, creating a wave. As the wave reaches shore, its amplitude increases.

Tsunamis may reach shore as either a breaking wave or as a fast, strong tide. Either form can cause catastrophic damage to property and destroy lives. Powerful tsunamis can reach as much as 1000 feet inland in an area called the inundation zone. Thus, earthquake warning systems are an important factor in preventing tsunami-related deaths.

The earthquake that triggers a tsunami may last only a few seconds. Moving at speeds of up to 500 miles per hour, tsunamis can travel the width of the Pacific in 24 hours and the residual waves can last for several hours or even weeks (in extreme cases) as the displaced water travels back and forth across the ocean.

Tsunamis often occur in the Pacific Ocean in the area known as the Ring of Fire. Many continental plates converge in this area, resulting in a higher-than-average number of earthquakes. Besides the movement of the earth's crust, ocean water can be displaced by other methods. Landslides and volcanoes may thrust objects into the ocean, resulting in a tsunami. Volcanoes, both underwater and on land, are also common in the Ring of Fire.