Tsunami - Meaning, Characteristics & Mitigation Measures

The word ‘Tsunami’ literally means ‘harbour waves’. These are the series of waves and the characteristic feature that differentiates these waves are is their long wavelength.

The information about the Tsunami is important for the general studies paper of the most coveted IAS Exam.

What is a Tsunami?

1. The series of extremely long waves, Tsunami are very long wavelengths of water caused by a large and sudden displacement of the ocean due to earthquakes, volcanic eruptions etc.
2. These are also called seismic sea waves and are one of the most powerful and destructive natural forces. 
3. When they reach the coast, they can cause dangerous coastal flooding and powerful currents that can last for several hours or days.
4. Most tsunamis are caused by large earthquakes. Though, not all earthquakes cause tsunamis.

Know in detail about the Earthquake in the given link. 

Characteristics of Tsunami

• Tsunamis are among Earth’s most infrequent hazards and most of them are small and nondestructive. 
• Over deep water, the tsunami has very long wavelengths (often hundreds of kilometres long) when a tsunami enters shallow water, its wavelength gets reduced and the period remains unchanged, which increases the wave height.
• Tsunamis have a small amplitude (wave height) offshore. This can range from a few centimetres to over 30 m in height. However, most tsunamis have less than 3 m wave height.
• It radiates in all directions from the point of origin and covers the entire ocean.
• It generally consists of a series of waves, with periods ranging from minutes to hours.
• These are the waves generated by tremors and not by earthquakes themselves.
• There is no season for tsunamis and not all tsunamis act the same. It cannot be predicted where, when and how destructive it will be. A small tsunami in one place may be very large a few miles away.
• An individual tsunami may impact coasts differently. A tsunami can strike any ocean coast at any time. They pose a major threat to coastal communities. The effect of Tsunami would occur only if the epicentre of the tremor is below oceanic waters and the magnitude is sufficiently high.
• The speed of the wave in the ocean depends upon the depth of water. It is more in the shallow water than in the ocean deep. As a result of this, the impact of a tsunami is more near the coast and less over the ocean

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Causes of Tsunami

How are Tsunami generated?

A Tsunami can be generated only through the vertical movement of the seafloor. Most Tsunamis are generated by earthquakes. Volcanic eruption, underwater explosion, landslides and meteorite impacts are some other causes of Tsunami. 

The details of causes of Tsunami is explained below-

Earthquake – Tsunami is generated by the earthquake because of the disturbance of the seafloor and is formed generally with vertical displacement. Most Tsunami is generated by earthquakes that occur along the subduction boundaries of plates along the ocean trenches. The size of the Tsunami is related to the size of the earthquake.

Underwater explosion – A Nuclear Testing by the US generated Tsunami in 1940 and 1950s in Marshall island.

Volcanic eruption – Volcanoes that occur along the Coastal waters can cause several effects that can cause a tsunami. 

Landslides – Earthquake and volcanic eruptions generally generate landslides, these landslides when moving into the Oceans, bays and lakes can generate Tsunami.

Meteorite Impacts – Though no historic example as such of meteorite impact has caused Tsunami, the apparent impact of a meteorite about 5 million years ago produced Tsunami leaving deposits along the Gulf Coast of Mexico and the United States. 

Tsunami is a geography topic. To aid your geography preparation for UPSC Exam, check the below-mentioned links:

1. Geography NCERT Notes for UPSC
2. Previous Year Geography Questions of UPSC Mains GS 1
3. Download compilation of Geography Questions in UPSC Prelims 

How Often Does Tsunami Occur?

• On average, every 15 years a tsunami occurs in the Pacific Ocean.

• Example a be taken from India itself which was the tsunami on Dec 26th, 2004 on the Indian Coast. It caused huge damage to life and property.

 How is Tsunami different From a Wind – Generated Wave?

 Tsunami should not be confused with the huge wind-generated waves. A wind-generated wave lasts for some seconds whereas a tsunami remains for minutes to hours. A tsunami can be disastrous which a wind-generated wave is not.

 Tsunami Vulnerability in India

INCOIS is the body that is vigilant regarding tsunamis on the Indian coast. To know more about the Indian National Centre for Ocean Information Services – INCOIS.

 The possible zones are Andaman – Sumatra or Makran (Pakistan).

Tsunami Risk, Hazard & Mitigation Measures

The main damage from the Tsunami comes from the destructive nature of waves. The second effect of the Tsunami includes debris acting as projectiles and the tertiary effect includes the loss of crops and water which leads to famine and disease.

Mitigation Measures

1. Effective Planning
2. The building of walls was done by Japan.
3. Planting trees as done in Tamil Nadu by a village
4. Proper relief and rehabilitation preparedness
5. Awareness among the masses

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