Tsunami: Meaning, Formation and Characteristics

Tsunami is a Japanese term for ‘Harbor Wave’ which has been globally accepted to denote a huge seismically generated sea wave. Tsunami  is one of the most powerful natural forces that can create destruction on a massive scale. A tsunami can last for several hours to several days.

Definition: Tsunami is a series of waves of extremely long wavelength, initiated due to an impulsive displacement of water in a sea or ocean.

How is a Tsunami Generated?

Two conditions are required for a Tsunami to get initiated.

1. There should be an earthquake that can transfer the huge energy required.
2. There should be a vertical movement of the seafloor due to the earthquake.

While earthquakes are the most common cause, a tsunami can also get initiated due to landslides, undersea volcanoes, meteor or asteroid falling on earth and even anthropogenic factors like a nuclear explosion. But, in any case, the displacement of water need to be vertical. This is the reason that tsunamis are generated near the oceanic trenches where the plates are getting subducted. The vertical movement of the seafloor displaces large columns of water vertically, pushing them into waves of a gigantic wavelength that can travel very fast across great distances.

Propagation of the waves of Tsunami

Once a tsunami wave is created by the vertical displacement of water, the waves ripple outward at a great pace. The series of waves rapidly increase in height as they move away from their point of origin and approach the shore. Due to the shoaling effect, tsunami waves grow in height by several feet near the seashore which makes it devastating for the offshore people and properties. Due to their less steepness at the origin, tsunami waves pass unnoticed beneath the ships in a sea and hits the shore ferociously without a warning. The tsunami waves move at a very rapid pace which may go up to 650-900 km/h.

Characteristics of Tsunami

• Tsunamis are not very frequent and the majority of them are small and non-destructive as well.
• Tsunami waves travel in all directions like ripples and they can cover an entire ocean basin.
• They consist of a series of waves with periods ranging from few minutes to hours.
• There’s no fixed pattern for the occurrence of a tsunami and hence tsunamis cannot be predicted.
• A tsunami can affect different coasts differently at the same time.
• The wavelength of tsunami waves is extremely large in deep water. The wavelength gets reduced in the shallow water while the period remains the same. This results in an increased height of waves near the shore.

Frequently Asked Questions

Q. What was the tallest/biggest tsunami ever recorded?

A. The tallest Tsunami ever recorded was in Lituya Bay, Alaska. The highest wave recorded was 1,720 feet high. Interestingly, only 5 lives were lost due to this tsunami.

Q. What is the difference between a tsunami and a tidal wave?

A. A tidal wave is a shallow water wave that is caused by the gravitational interactions between the Earth, Sun and Moon. In contrast, tsunamis are caused due to the vertical displacement of water, generally initiated by the tremors of an earthquake.

Q. What do you mean by mega-tsunami?

A. Mega tsunami is an informal term that is used to denote a tsunami with a much larger wave amplitude than the usual tsunamis. (Lituya Bay tsunami is considered a mega-tsunami)

Q. How does a tsunami warning system work?

A. Tsunamis cannot be predicted. So, an early warning system is the only way to minimize any possible destruction. A tsunami warning system consists of seismic monitoring stations and sea-level gauges. The systems detect earthquakes and any abnormal changes in sea level. Scientists read these signs and decide upon the possibility of an upcoming tsunami.

Q. Where tsunami occurs most frequently?

A. 70% of the confirmed tsunami sources have been in the Pacific Ocean. Tsunamis are frequently observed along the pacific ring of fire.