tsunami

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TSUNAMI Name - Ravi Hasyagar Class - 10th ‘A'

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Introduction A tsunami or a tidal wave is a series of water waves (called tsunami water trains) caused by displacement of a large volume of a large volume of a body of water usually an ocean. These are caused due to Earthquakes , volcanic eruptions or underwater explosions. In this presentation we will discuss about this natural disaster , its mitigation strategies and also see how the 2004 Tsunami destroyed asian countries…

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Causes of Tsunami Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water.  Tectonic earthquakes are a particular kind of earthquake that are associated with the earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, due to the vertical component of movement involved. Movement on normal faults will also cause displacement of the seabed, but the size of the largest of such events is normally too small to give rise to a significant tsunami. Drawing of tectonic plate boundary before earthquake. Overriding plate bulges under strain, causing tectonic uplift. Plate slips, causing subsidence and releasing energy into water. The energy released produces tsunami waves

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Characterstics While everyday wind waves have a wavelength (from crest to crest) of about 100 meters (330 ft) and a height of roughly 2 meters (6.6 ft), a tsunami in the deep ocean has a wavelength of about 200 kilometers (120 mi). Such a wave travels at well over 800 kilometers per hour (500 mph), but due to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 meter (3.3 ft).This makes tsunamis difficult to detect over deep water. Ships rarely notice their passage. As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its velocity slows below 80 kilometers per hour (50 mph). Its wavelength diminishes to less than 20 kilometers (12 mi) and its amplitude grows enormously, producing a distinctly visible wave. Since the wave still has such a long wavelength, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not break (like a surf break), but rather appears like a fast moving tidal bore. Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front. When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed 'run up'. Run up is measured in meters above a reference sea level. A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run up. About 80% of tsunamis occur in the Pacific Ocean, but are possible wherever there are large bodies of water, including lakes. They are caused by earthquakes, landslides, volcanic explosions, and bolides.

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Drawback If the first part of a tsunami to reach land is a trough—called a drawback—rather than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas. A drawback occurs because the water propagates outwards with the trough of the wave at its front. Drawback begins before the wave arrives at an interval equal to half of the wave's period. Drawback can exceed hundreds of meters, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed. During the Indian Ocean tsunami, the sea withdrew and many people went onto the exposed sea bed to investigate. Photos show people walking on the normally submerged areas with the advancing wave in the background. Few survived. Drawback in Sri Lanka

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Intensity Scale Intensity scales The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity scale, used in the Pacific Ocean. The latter scale was modified by Soloviev, who calculated the Tsunami intensity I according to the formula where Hav is the average wave height along the nearest coast. This scale, known as the Soloviev-Imamura tsunami intensity scale, is used in the global tsunami catalogues compiled by the NGDC/NOAA and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami.

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Magnetic Scale The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on the potential energy.[ Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale Mt, calculated from, where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicenter, a, b & D are constants used to make the Mtscale match as closely as possible with the moment magnitude scale.

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Tsunami 2004 Indian ocean The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred at 00:58:53 UTC on December 26, 2004, with an epicenter off the west coast of Sumatra, Indonesia. The quake itself is known by the scientific community as the Sumatra-Andaman earthquake. The resulting tsunami is given various names, including the 2004 Indian Ocean tsunami, Asian Tsunami, Indonesian Tsunami, and Boxing Day Tsunami. The earthquake was caused by subduction and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing over 230,000 people in fourteen countries, and inundating coastal communities with waves up to 30 meters (100 feet) high.  It was one of the deadliest natural disasters in recorded history. Indonesia was the hardest hit, followed by Sri Lanka, India, and Thailand. With a magnitude of between 9.1 and 9.3, it is the third largest earthquake ever recorded on a seismograph. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm (0.4 inches)  and triggered other earthquakes as far away as Alaska.  Its hypocenter was between Simeulue and mainland Indonesia.[8]

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Countries affected

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Aftershocks and other earthquakes Numerous aftershocks were reported off the Andaman Islands, the Nicobar Islands and the region of the original epicenter in the hours and days that followed. The largest aftershock, which originated off the coast of the Sumatran island of Nias, registered a magnitude of 8.7, prompting debate among seismologists as to whether it should be classified as an aftershock of the December 2004 quake or as a "triggered earthquake" (which typically differs from an aftershock in that it is not located along the same fault line and may be as large or larger than the earthquake which triggered it).This earthquake was so large that it produced its own aftershocks (some registering a magnitude of as great as 6.1) and presently ranks as the 7th largest earthquake on record since 1900. Other aftershocks of up to magnitude 6.6 continued to shake the region daily for up to three or four months . As well as continuing aftershocks, the energy released by the original earthquake continued to make its presence felt well after the event. A week after the earthquake, its reverberations could still be measured, providing valuable scientific data about the Earth's interior.The 2004 Indian Ocean earthquake came just three days after a magnitude 8.1 earthquake in an uninhabited region west of New Zealand's sub-Antarctic Auckland Islands, and north of Australia's Macquarie Island. This is unusual, since earthquakes of magnitude 8 or more occur only about once per year on average .Some seismologists have speculated about a connection between these two earthquakes, saying that the former one might have been a catalyst to the Indian Ocean earthquake, as the two earthquakes happened on opposite sides of the Indo-Australian Plate. However, the U.S. Geological Survey sees no evidence of a causal relationship in this incident. Coincidentally, the earthquake struck almost exactly one year (to the hour) after a 6.6 magnitude earthquake killed an estimated 30,000 people in the city of Bam in Iran on December 26, 2003.[ Some scientists confirm that the December earthquake had activated Leuser Mountain, a volcano in Aceh province along the same range of peaks as Mount Talang, while the 2005 Sumatran earthquake had sparked activity in Lake Toba, an ancient crater in Sumatra.[ Geologists say that the eruption of Mount Talang in April 2005 is connected to the December earthquake

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Condition of India after 2004 Tsunami

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Mitigation Things to know about Tsunami Tsunamis that strike coastal locations in the Pacific Ocean Basin are most always caused by earthquakes. These earthquakes might occur far away or near where you live. Some tsunamis can be very large. In coastal areas their height can be as great as 30 feet or more (100 feet in extreme cases), and they can move inland several hundred feet. All low-lying coastal areas can be struck by tsunamis. A tsunami consists of a series of waves. Often the first wave may not be the largest. The danger from a tsunami can last for several hours after the arrival of the first wave. Tsunamis can move faster than a person can run. Sometimes a tsunami causes the water near the shore to recede, exposing the ocean floor. The force of some tsunamis is enormous. Large rocks weighing several tons along with boats and other debris can be moved inland hundreds of feet by tsunami wave activity. Homes and other buildings are destroyed. All this material and water move with great force and can kill or injure people. Tsunamis can occur at any time, day or night. Tsunamis can travel up rivers and streams that lead to the ocean.

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What to do when you are on land Be aware of tsunami facts. This knowledge could save your life! Share this knowledge with your relatives and friends. It could save their lives! If you are in school and you hear there is a tsunami warning, you should follow the advice of teachers and other school personnel. If you are at home and hear there is a tsunami warning, you should make sure your entire family is aware of the warning. Your family should evacuate your house if you live in a tsunami evacuation zone. Move in an orderly, calm and safe manner to the evacuation site or to any safe place outside your evacuation zone. Follow the advice of local emergency and law enforcement authorities. If you are at the beach or near the ocean and you feel the earth shake, move immediately to higher ground, DO NOT wait for a tsunami warning to be announced. Stay away from rivers and streams that lead to the ocean as you would stay away from the beach and ocean if there is a tsunami. A regional tsunami from a local earthquake could strike some areas before a tsunami warning could be announced. Tsunamis generated in distant locations will generally give people enough time to move to higher ground. For locally-generated tsunamis, where you might feel the ground shake, you may only have a few minutes to move to higher ground. High, multi-story, reinforced concrete hotels are located in many low-lying coastal areas. The upper floors of these hotels can provide a safe place to find refuge should there be a tsunami warning and you cannot move quickly inland to higher ground. Local Civil Defense procedures may, however, not allow this type of evacuation in your area. Homes and small buildings located in low-lying coastal areas are not designed to withstand tsunami impacts. Do not stay in these structures should there be a tsunami warning. Offshore reefs and shallow areas may help break the force of tsunami waves, but large and dangerous wave can still be a threat to coastal residents in these areas. Staying away from all low-lying areas is the safest advice when there is a tsunami warning.

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What to do when you are on boat Since tsunami wave activity is imperceptible in the open ocean, do not return to port if you are at sea and a tsunami warning has been issued for your area. Tsunamis can cause rapid changes in water level and unpredictable dangerous currents in harbors and ports.If there is time to move your boat or ship from port to deep water (after a tsunami warning has been issued), you should weigh the following considerations: Most large harbors and ports are under the control of a harbor authority and/or a vessel traffic system. These authorities direct operations during periods of increased readiness (should a tsunami be expected), including the forced movement of vessels if deemed necessary. Keep in contact with the authorities should a forced movement of vessel be directed. Smaller ports may not be under the control of a harbor authority. If you are aware there is a tsunami warning and you have time to move your vessel to deep water, then you may want to do so in an orderly manner, in consideration of other vessels. Owners of small boats may find it safest to leave their boat at the pier and physically move to higher ground, particularly in the event of a locally-generated tsunami. Concurrent severe weather conditions (rough seas outside of safe harbor) could present a greater hazardous situation to small boats, so physically moving yourself to higher ground may be the only option. Damaging wave activity and unpredictable currents can effect harbors for a period of time following the initial tsunami impact on the coast. Contact the harbor authority before returning to port making sure to verify that conditions in the harbor are safe for navigation and berthing.

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Other Ways Education Public Awareness Information Risk Communication Training to all concerned (Govt. officials, search and rescue workers, volunteers, women, children, elderly, local community as a whole) Non Structural Mitigation Non-Structural Mitigation Measures Coastal regulations Zone Act –Strict implementation (no development within 500 m of the high tide line with elevation ofless than 10 m above m.s.l) Land use Zoning in accordance with CRZ Natural Bioshields(Mangroves) and shelterbelt plantations (Casuarina) Maintaining Natural Sand dunes Maintaining and promoting beach development

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CONCLUSION The 26 December 2004 tsunami - one of the most natural disastrous events in human recorded history has caused enormous damage and loss to human societies. Apart from unrecoverable losses in human lives, the tsunami would cost us billions of dollars and decades to restore its damage. However, it also provided us a chance to look back at the serious mistakes we have made when promoting development without considering the natural forces that sustain us. From the lessons given by the tsunami, we recognised that many vital links which connect human societies together have been broken or missing. Without repairing these links, the sustainable future of human beings would be threatened.   In this paper we have pointed out and discussed the weaknesses of five links which we consider as the most vital knots that should unify us together in emergency situations. We also stated that all these five broken or missing links are closely related and mutually supported each other. The missing of one links strongly influences the existence of the other. In other words, one of the links cannot be reconnected without repairing the other.   The problems caused by tsunami are large in scale and complex in nature. To deal with these problems, we need to establish an international mechanism in which more prosperous countries are obliged to help the poorer ones and the poor countries are obliged to show strong commitments in improving their capacity.   Human societies are a unity. Without unifying efforts, especially in the cases of emergency and great natural disasters, collective strength of mankind will not be maximised and we would become vulnerable to natural threats.

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Acknowledgements I am very thankful to all the contributors who have helped me to complete this project effectively and on Time.. Wikipedia (almost all the information) Google Images rsta.royalsocietypublishing.org Washington State Department of Natural Resources National Disaster Management Authority(Government of India) www.geophys.washington.edu Windows Office 2007

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Thank You