What is a tsunami? | What causes tsunamis? | What are some useful facts about tsunamis? | What kind of damage does a tsunami cause? | How can tsunamis be prevented?

  What is a tsunami?   [Top]

  A tsunami is a large wave of water, originated at sea, that cause massive amounts of damage to coastlines. Tsunamis can be caused by earthquakes, volcanoes, hurricanes, or other strong forces. Tsunamis occur in a series of waves that surface the ocean when close enough to a shoreline. Tsunamis are often confused with tidal waves, but the two are actually quite different. Even though tsunamis can be affected by the tides, they have little to do with them. In the open ocean, wave height of a tsunami is generally small (usually only a few feet). As the tsunami travels the distance to the shore, the wavelength (distance between wave crests), increases. The wavelength can be hundreds if miles apart! This also increases the actual height of the wave. Initially, the depth of the water determines the speed at which the tsunami travels. Some have been known to travel up to 500 miles per hour! As the tsunami reaches the shore, it slows down. This decrease of speed greatly increases the height of the wave. The reverse fault causes the part of the tsunami that is away from the shore to be pushed down. This is what causes the dramatic damage done to the shoreline. The longer it takes for a tsunami to reach the shore, the larger it will be when it reaches it.

Tsunami Characteristics:

1. Time between the wave crests can range from 5 minutes to 90 minutes.
2. In the open ocean, tsunamis can reach speeds of up to 450 miles per hour.
3. Near the shore, tsunami waves can reach heights up to 100 ft.
4. Tsunamis can form up to thousands of miles away from a coastline.

  What causes tsunamis?   [Top]

  Tsunamis are caused by very fast movements in the Earth's crust. Sudden movements made by the sea floor (such as an earthquake or landslide) can result in a tsunami. Rarely, the collapse of an island volcano or a meteorite impact can generate a tsunami. The wave originates when the major fault moves rapidly and pieces of the oceanic crust move vertically. This movement displaces large amounts of water, creating the wave that can travel for up to 10,000 miles. Blocks of the Earth's crust are separated by a tilted fault plane, which is one block resting above the fault plane, the other resting below it. Reverse faults, or thrust faults, move the overlying blocks upward. These reverse faults are caused by compressive forces. When the fault 'slips', the lower block moves down as the upper block moves up. When the rock breaks along the fault, an earthquake occus. This fault motion causes waves, which can cause tsunamis.

  what are some useful facts about tsunamis?   [Top]

  - A fault scarp (where the fault breaks the surface of the Earth) must be produced for a tsunami to occur. Thus, not all ocean originated earthquakes cause tsunamis.

- The Pacific Ocean Ring has the highest occurance of a tsunami. Tsunamis are not known to occur along the coast of the Atlantic, but are far less frequent.

- Monitoring the sea floor's activity helps warn people of a potential tsunami. This warning can be as much as a few hours.

- When a tsunami is approaching, it gives warning by retracting sea water from the coast in order to supply the wave.

- Some of the worst damage caused by a tsunami is not from the arrival of the wave itself, but from the undertow it creates as it leaves land and heads back to the sea, carrying objects and people with it.

- A tsunami in deep ocean water is not always noticable. The height increases only in shallow water, due to a decrease in depth.

- Tsunamis have four main causes. Production of fault scarp in the ocean; the eruption of an oceanic volcano; an avalanche either on land or in the sea; or an asteroid impact.

  What kind of damage does a tsunami cause?   [Top]

  Because tsunamis occur so suddenly, they cause a greater number of deaths and a greater degree of damage. Tsunamis can cause damage to ships at sea, and the land that the wave floods. Most tsunamis occur along the coast of the Pacific Ocean, but in the last 100 years, one tsunami was recorded along the Atlantic coast. More people have been killed by tsunamis in the United States than the direct result of an earthquake.