Hyderabad: By 2030, an estimated 50 percent of the world's population will live in coastal areas exposed to flooding, storms and tsunamis. Scaling up international cooperation to developing countries will help ensure that 100 percent of communities at risk of tsunami are prepared for and resilient to tsunamis by 2030.
Tsunamis are rare events but can be extremely deadly. In the past 100 years, 58 of them have claimed more than 2,60,000 lives, or an average of 4,600 per disaster, surpassing any other natural hazard. The highest number of deaths in that period was in the Indian Ocean tsunami of December 2004. It caused an estimated 227,000 fatalities in 14 countries, with Indonesia, Sri Lanka, India and Thailand hardest-hit.
Just three weeks after that the international community came together in Kobe, in Japan’s Hyogo region. Governments adopted the 10-year Hyogo Framework for Action, the first comprehensive global agreement on disaster risk reduction. They also created the Indian Ocean Tsunami Warning and Mitigation System, which boasts scores of seismographic and sea-level monitoring stations and disseminates alerts to national tsunami information centres.
What are tsunamis?
• The word "tsunami" comprises the Japanese words "tsu" (meaning harbour) and "nami" (meaning wave). A tsunami is a series of enormous waves created by an underwater disturbance usually associated with earthquakes occurring below or near the ocean.
• Volcanic eruptions, submarine landslides, and coastal rock falls can also generate a tsunami, as can a large asteroid impacting the ocean. They originate from a vertical movement of the sea floor with the consequent displacement of water mass.
• Tsunami waves often look like walls of water and can attack the shoreline and be dangerous for hours, with waves coming every 5 to 60 minutes.
• The first wave may not be the largest, and often it is the second, third, fourth or even later waves that are the biggest. After one wave inundates, or floods inland, it recedes seaward often as far as a person can see, so the seafloor is exposed. The next wave then rushes ashore within minutes and carries with it many floating debris that were destroyed by previous waves.
What are the causes of tsunamis?
Earthquakes
It can be generated by movements along fault zones associated with plate boundaries. Most strong earthquakes occur in subduction zones where an ocean plate slides under a continental plate or another younger ocean plate. All earthquakes do not cause tsunamis. There are four conditions necessary for an earthquake to cause a tsunami:
• The earthquake must occur beneath the ocean or cause material to slide into the ocean.
• The earthquake must be strong, at least magnitude6.5 on the Richter Scale
• The earthquake must rupture the Earth’s surface and it must occur at shallow depth – less than 70km below the surface of the Earth.
• The earthquake must cause vertical movement of the sea floor (up to several metres).
Landslides
A landslide which occurs along the coast can force large amounts of water into the sea, disturbing the water and generate a tsunami. Underwater landslides can also result in tsunamis when the material loosened by the landslide moves violently, pushing the water in front of it.
Volcanic eruptions
Although relatively infrequent, violent volcanic eruptions also represent impulsive disturbances, which can displace a great volume of water and generate extremely destructive tsunami waves in the immediate source area.
One of the largest and most destructive tsunamis ever recorded was generated in August 26, 1883 after the explosion and collapse of the volcano of Krakatoa (Krakatau), in Indonesia. This explosion generated waves that reached 135 feet, destroyed coastal towns and villages along the Sunda Strait in both the islands of Java and Sumatra, killing 36,417 people.
Extraterrestrial collisions
Tsunamis caused by extraterrestrial collision (i.e. asteroids, meteors) are an extremely rare occurrence. Although no meteor/asteroid-induced tsunamis have been recorded in recent history, scientists realize that if these celestial bodies should strike the ocean, a large volume of water would undoubtedly be displaced to cause a tsunami.
2004 Indian Ocean tsunami - Recalling Post Development
The nation will never forget December 26, 2004 when the deadly tsunami triggered by an earthquake of magnitude 8.6 off the coast of Sumatra snatched away thousands of precious lives and caused huge damage to the agriculture, livestock and infrastructure.
The Nation shared the grief along with other countries in the Indian Ocean namely – Indonesia, Sri Lanka, Maldives and Thailand for more than 3,00,000 human lives lost of which 12,405: 107 in Andhra Pradesh, 177 in Kerala, 8009 in Tamil Nadu, 599 in Pondicherry and 3513 in Andaman & Nicobar Islands were in India. 14 Indians abroad; 13 in Sri Lanka and 1 in Maldives also lost their lives.
The tsunami tidal waves traveled at a speed of 700-800 km per hour and reached as far as the coast of Africa. The Nicobar Group of Islands being in the immediate vicinity of the Sumatra coast suffered maximum damage. The coral reefs, the beautiful coastline, the agriculture and coconut plants were all washed away.
What India learnt
• The Sumatra earthquake and tsunami are considered to be an eye-opener for India as it introduced the Indian coastline to tsunami and its destructible power.
• Learning from the unprecedented natural disaster that led to such heavy damage to life and property, the Ministry of Earth founded the Indian Tsunami Early Warning System (ITEWS) at Indian National Centre for Ocean Information Services (INCOIS), Hyderabad in October 2007.
• In a major development in India’s capability to assess dangers following a tsunami event, the Indian National Centre for Ocean Information Services (INCOIS) has now developed a system which will be able to predict risk to coastal areas, height of waves that can hit them and even pinpoint vulnerable buildings, all in ‘realtime’.
• Scientists in India are now able to predict and project movements in Indian ocean through real-time seismic monitoring with Bottom Pressure Recorders (BPR), tide gauges and 24x7 operational tsunami warning system to detect tsunamigenic earthquakes as to provide early advisories to the most vulnerable.
• A community performance-based programme known as Tsunami Ready has also been started by the Intergovernmental Oceanographic Commission (IOC) of UNESCO to promote tsunami preparedness by actively involving the public, community leaders, and national and local emergency management agencies. As part of the UNESCO-IOC framework, the ITEWC now offers advisories to all Indian Ocean rim countries.
• India is the first country to establish an early warning system for tsunami detection, while Odisha is the first state in the country to get Tsunami Ready recognition.
State-wise impact
• A total of 27.92 lakh people: 1.96 lakh in Andhra Pradesh, 13.00 lakh in Kerala, 8.97 lakh in Tamil Nadu, 0.43 lakh in Pondicherry and 3.56 lakh in A & N Islands were affected in 1,089 villages.
• The tsunami destroyed over 2.35 lakh dwelling units; 481 in Andhra Pradesh, 13735 in Kerala, 1,90,000 in Tamil Nadu, 10061 in Pondicherry and 21,100 in A & N Islands.
• Apart from their homes people lost their livelihoods-83,788 boats; were damaged; 39,035 hectares of cropped area: 302 ha. in Andhra Pradesh, 7763 ha in Kerala, 19168 ha. in Tamil Nadu, 792 ha. in Pondicherry and 11,010 in A & N Islands and 31,755 livestock were lost.
• The social infrastructure of schools, primary health centres, drinking water supply, anganwadis, and other community assets in these areas was totally destroyed.
• There was widespread damage to the infrastructure including the shipping sector particularly in the Islands where harbours and jetties which were the lifelines to the Islands, were destroyed; as also to the roads and bridges, power and communication.
• In monetary terms, the damage was estimated at about Rs.11,544.91 crore - Rs. 342.67 crore in Andhra Pradesh, Rs. 2371.02 crore in Kerala, Rs.4528.66 crore in Tamil Nadu, Rs. 466.00 crore in Pondicherry and Rs. 3836.56 crore in Andaman & Nicobar Islands.
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