What is a tsunami?

The word tsunami comes from the Japenese word for harbour wave. A tsunami is made from a series of waves in the sea that is made by an underwater earthquake or an underwater volcanic eruption. Tsunami's happen along the coastline of countries and islands. When an earthquake or volcanic disruption happens, ripples spread out from that point through the ocean and can travel up to 450 mph. When the waves get closer to the shallow shore, they grow in height (referred to as "run-up") and can get as tall as 100 ft. When the waves become this tall, they will cause a large amount of destruction and death to anything along the shorelines.They move rapidly but quickly run out of water as they proceed inland and uphill.Tsunamis don't stop once on land. After they break on shore, part of the tsunami energy is pushed back to the open ocean. As a tsunami hits, they can generate a type of wave called edge waves that travel back-and forth, parallel to shore. Because of the behavior of tsunami waves are unpredictable, the first wave that hits shore are not the largest. There will always be another wave that will come ashore and will be larger than the first wave and will cause the most destruction. In an area where a tsunami hits, the people in that area are told not to return after the first wave hits.

Important Facts to Know about Tsunamis

  • Tsunamis that strike coastal areas are most always caused by earthquakes may occur far or near where the earthquake starts.
  • Some tsunamis can be very large the height of them can be as great as 30-100 feet, and can travel inland several hundred feet.
  • Tsunamis can strike all low-lying coastal areas and travel up rivers and streams that lead to the ocean.
  • Tsunami are made up of a series of waves and the danger from one can last for several hours after the first wave comes ashore.
  • Sometimes a tsunami can cause the water by the shore to come back, exposing the ocean floor.
  • Tsunamis have alot of power and can move boats hundreds of feet inland destroying buildings.
  • Tsunamis can happen any time, day or night and can move faster than a person can run. tsunamisign1.jpg


This is a tsunami breaking on shore. These people didn't even see it coming.One minute they were driving to work and then the next they were completely underwater.

How are tsunamis tracked?

In 1965, after a tsunami hit the pacific coastline in the United States, a warning sytem was created. The headquarters for this is known as the Pacific Tsunami Warning Center (PTWC) located in Honolulu, Hawaii. Its responsibility is to issue warnings on any tsunami like activity to any Pacific Ocean emergency centers. Although the risk of tsunamis are possible in the Atlantic and Indian Oceans, the Mediterrean, Caribbean, and Black Seas, there are no warning systems for these oceans!

The first step of a tsunami warning system is keeping track of seismic waves and the sea level. The next step is to compare all data on any previous tsunamis that may have happened in the area before.The last step is to make sure there is good communication between monitoring stations, the warning centre and at-risk states.

A good example of needing tsunami warning systems all over the world is when the tsunami hit Sri Lanka in December 2004. By chance, this tsunami was recorded by the Jason satellite that was flying over the Indian Ocean. Scientists did not know that the satallites could pick up low wave amplitudes of the tsunamis until that day. The satallite is designed for ocean research so it was not able to send warning before the tsunami hit Sri Lanka. This tsunami was caused by a major shift in a well known fault lnecausing increased pressure on other parts of the fault. This tsunami had the same amount of energy as 23,000 atomic bombs and caused 150,000 people to die in one day.

Go to fullsize image
Go to fullsize image

This diagram illustrates the difference between tsunamis and wind waves when they come ashore.

This is a wind wave
tsunami speed and facts
tsunami speed and facts

This is a Tsunami wave.

How do earthquakes generate tsunamis?
Tsunamis can be created when the sea floor quickly changes and pushes the wate up. Waves start to form as the gravity works against them causing the sea floor to rise creating a tsunami. When vertical movements on the earth's crust occur at plate boundaries plates are joined together along the faultlines causing subduction. Subduction earthquakes cause the most tsunamis.

How do landslides, volcanic eruptions, and cosmic collisions generate tsunamis?

A tsunami can be created by a disturbance that moves a large water mass from its balanced position. A violent submarine volcanic eruption can create an strong force that lifts up the water column and creates a tsunami. Supermarine landslides and cosmic collisions disturb the water from above, as momentum from the falling debris is transferred to the water and the debris falls to the ocean floor. Tsunamis created from these objects, quickly end and rarely affect coastlines distant from the source area.

What happens to a tsunami as it approaches land?

When a tsunami leaves deep water in the ocean and goes into the shallower water near the coast, it takes on a new form. A tsunami travels at a speed that is the same as the water depth so when the water depth gets shallow the tsunami slows. The tsunami's energy relies on its wave speed and wave height to be at the same level. When a tsunami's speed slows down as it travels into shallower water, its height grows. Because of this it may grow to be several meters or more in height near the coast. When it finally reaches the shore, the tsunami may look like fast rising and falling tides or a lot of breaking waves. The tsunamiss will lose energy while they move inland and the energy is pushed back out to sea, while the wave energy builds on shore form friction causing the waves to get stronger and grow. This energy level causes the waves to move hundreds of feet inland causing a lot of desrtuction.

There is no tsunami season: We have discussed on our page about the dangers of tsunamis. Tsunami season is all year round. Tsunami mostly start from earthquakes.

There is normal size tsunami: There is usually more than one wave and the first wave is not the largest or the worst. The tsunami can last for hours with waves spaced 10-60 mins. apart.

Tsunami are not just big surf: These waves are not tidal waves and don't start from off shore storms. They are not good for surfing.

You can't outrun a tsunami: You can't outrun a wave. Sometimes the water recedes but the beaches are not safe for hours or days.

what causes a tsunami
what causes a tsunami

The diagram above shows the plates moving, causing an earthquake, which causes a tsunami.

You have been reading a page about tsunamis.

By: Connor Hogeston &
Jacob McClure