Tsunami and Seismic Sea Waves

Have you ever heard the true meaning for the word tsunami? In Japanese, the word tsunami actually means harbor wave. Why? Probably because these dangerous waves create a lot of damage when they wash into enclosed areas. Many people have incorrectly called them tidal waves. This is incorrect because these waves are not created by tides or related to the tides in anyway. Instead, tsunami are seismic waves, which are caused by a geological event that sends energy out that makes the Earth's crust tremble.

In March 2011, Japan was hit by a major tsunami that was caused by an underwater earthquake about 250 miles north of the major city of Tokyo, Japan. What else can cause tsunami? Anything that causes water to be displaced can create these waves. Landslides, underwater landslides, volcanic eruptions, or even a large iceberg falling off of a glacier can all create this type of wave, but earthquake-generated tsunami are the greatest offender and most dangerous!

How Tsunami and Plate Tectonics Relate

Earthquakes and volcanoes occur because of the movement of plate boundaries. Plate Tectonics explains that the Earth's crust is made of sections or plates that move. Movement along faults, or breaks in the Earth's crust, can cause earthquakes, volcanoes, and even changes in the ocean basins. When earthquakes take place along plate boundaries in the ocean, a tsunami can result because of the energy produced and the displacement of water. Some of the largest earthquakes occur along deep ocean trenches; however, earthquakes can result from movement at any of the three plate boundaries: divergent (where plates spread apart), convergent (where plates come together and may even overlap), or transform (where plates slide past each other or grind).

A volcano in the ocean can also cause displacement of water as magma rises from an opening in the Earth's crust. Volcanoes erupt from plate subduction (when a plate bends downward into the Earth) at a convergent plate boundary, rifting (when plates spread apart), or sea floor spreading (when plates spread apart and new magma rises and solidifies to create new seafloor). Earthquakes and volcanic activity in the ocean cause seismic waves or resulting tsunami, thus providing evidence of the structure of the Earth's crust and that which lies beneath it.

What Makes a Tsunami Different?

What makes a tsunami wave that is generated from an earthquake or volcano so much different from a regular wind-generated progressive wave? The answer to that lies within the anatomy of a wave. Earthquake-generated tsunami have an extremely long wavelength. In fact, they are so long that they can travel through the ocean undetected. Tsunami, however, always act as shallow-water waves because there is no point in the ocean deep enough to not cause some bottom drag with the wave. Once the wave is created, it can travel very quickly and go undetected until it arrives at shore.

When the tsunami reaches shore, it becomes much higher. The wave surges ashore, breaks, and floods a tremendous amount of land. A few minutes before the tsunami comes washing into shore, the water near the shoreline recedes. This causes a lot of curiosity for beach goers, subsequently causing some people to put themselves in even more danger. After the receding water has lured people to the beach, the tsunami wave washes in quickly and the people are all at risk for drowning or for being crushed by the wave. If they survive the first wave, they face others waves to follow. Tsunami almost always travel in a wave train with three to five destructive waves.

Tsunami Warning Signs

In this interactivity, you will learn the key warning signs you can look for if you feel an approaching tsunami is coming. Click the player button to get started.

View a printable version of this interactivity.

 

 

 

Tsunami and Seismic Sea Waves Review

Now that you have investigated tsunamis and seismic sea waves, check your knowledge. In this non-graded interactivity, follow the instructions on each question slide. Click SUBMIT to check your response. Click the player button to begin.