Stages of a Tsunami

A tsunami is one of the most destructive natural disasters that can occur to islands and coastal regions. It is a prime example of how much water can reshape or even destroy a landscape, and large tsunamis cause millions of dollars' worth of damage and take thousands of lives whenever they occur. Tsunamis are less like waves as most people know them and more like a sudden displacement of a large amount of water. They can be perceived as happening quickly, but they are actually formed in easily identifiable stages.

Initiation of a Tsunami

• A tsunami is often thought to be one large and very destructive wave that crashes into a coastal region, but it is really more like a series of waves. Whereas most waves are caused by the wind, tsunamis are usually formed by geological phenomenon such as an earthquake or volcanic eruption. They can also be caused by landslides or even meteor impacts. A tsunami is formed by such events whenever a column of water is pushed up and down; in the case of an earthquake it is caused by the sea floor being uplifted by tectonic plate activity. The incredibly potential energy of the water column is transferred into kinetic energy, which creates the series of waves known as a tsunami.

Tsunami Split

• After the initiation of a tsunami, the first wave that is formed by the displaced column of water splits into two waves. One wave is called a distant tsunami and is sent into the deeper ocean. The other wave is called the local tsunami. This is the one that moves toward shallower water and coastal regions that it often decimates. The speed at which both tsunamis travel is determined by water depth; distant tsunamis that move over deeper water move faster than local tsunamis.

Amplification

• As a tsunami travels into shallower water over the continental slope, its wavelength decreases dramatically as its amplification increases. In layman's terms, this means that the waves become shorter but more numerous. The leading wave also becomes taller and steeper, becoming essentially a destructive wall of water before it crashes into a coast.

Inundation

• Inundation is essentially when a tsunami reaches the coast. This stage is often referred to as "run-up" because of the way the water runs up the coast and raises the water level above sea level. A tsunami causes the ocean to overflow onto the land, which can be incredibly devastating to land not far above sea level. Since tsunamis can travel much farther inland than most wind-swell waves can, they can devastate places relatively far away from a coast. It is important to note, however, that it is not the water itself that causes so much damage as much as it is the energy moving through it.