Disaster Management: Tsunami | UPSC Mains: Internal Security & Disaster Management PDF Download

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.

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.

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

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. 

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
• Indian National Center for Ocean Information Services (INCOIS) is an autonomous organization of the Government of India, under the Ministry of Earth Sciences, located in Pragathi Nagar, Hyderabad.
• INCOIS was established as an autonomous body in 2007 under the Ministry of Earth Sciences (MoES) and is a unit of the Earth System Science Organization (ESSO).

History of INCOIS

• Under the guidance of Dr A. Narendra Nath, the Ministry of Earth Sciences initiated a project called PFZ Mission during the 1990s. It was handed over to National Remote Sensing Centre (NRSC) Hyderabad
• The project was separated as a result form NRSC and a new organisation was created to look after it. Indian National Centre for Ocean Information Services (INCOIS) and was placed under reputed scientist Dr A.Narendra Nath, Who was also the founder-director for INCOIS.
• The services of the INCOIS led to its recognition as one of the key International Oceanic Organisation.

Services Provided by INCOIS

The following are the services provided by INCOIS

1. Potential Fishing Zone (PFZ)

• The identification of Potential Fishing Zones was one of the first advisory services started by INCOIS. The PFZ uses real-time data for ocean colour and imagery provided by OCEANSAT. OCEANSAT is a satellite built by ISRO for ocean applications. This service was started to help fisherman identify high-quantity fishing zones in order to maximise their catch. 
• This service was started by the Ministry of Earth Sciences with the help of the Department of Space and several institutions under the Ministry of Agriculture. These organizations are collaborating with the State Governments of the beneficiary states to offer these services to the end-users.

2. Tsunami Early Warning System (TEWS)

• Following the devastating Tsunami of December 26, 2004, and frequent storm-surgest that occur from time to time, the Government of India wanted to set up an early warning centre for tsunami and other storm surges in the Indian Ocean region. On October 15 2007, a centre housing the Tsunami Early Warning System was set up in INCOIS by the Ministry of Earth Sciences through the collaboration of Department of Science and Technology (DST, Department of Space (DOS) and Council for Scientific and Industrial Research (CSIR)
• The data obtained from a network of equipment is used to run models to provide maps that describe inundation scenarios for the entire coastal belt. Based on these scenarios, potential danger zones ate identified to generate advisories for various stakeholders. In the event of a Tsunami, advisories are generated at intervals that show the location of storm surges which helps local authorities to evacuate people from the region likely to be affected.

3. Indian Ocean Forecasting System (INDOFOS)

• Since India is a peninsula, surrounded by water on its three sides, thus it is important to know the state of the oceans in advance for carrying out various commercial activities.
• Thinking about all these factors, a new service was rolled out to forecast the ocean state, which is capable of predicting the surface and sub-surface features of the Indian Ocean in advance. It is called the Indian Ocean Forecasting System (INDOFOS).

The generated forecasts fall under four categories. They are

• Global, 
• Regional, 
• Location-specific 
• Coastal forecasts. 

For the coastal forecast, the models are set up with the concept of “coarse grid” with coarse resolution in open ocean region whereas very fine resolution is used for location-specific forecasts.

4. Ocean Observation Group (OOG)

• The Ocean Observation Group measures and monitors the temperature and salinity of the upper 2000 metres of the ocean. This is done through a global array of 3000 free-drifting, profiling floats that relay the measurements data to agencies, which in turn make the data publicly available up in hours of receiving the data.
• This system was named as Argo, which emphasizes the strong complementary relationship between the free-drifting floats and Jason altimeter mission.
• The Argo system helps to study quantitatively the evolving state of the upper ocean and the patterns of its climate variability, including heat, freshwater storage and transport.

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