Tsunami

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SHOBHIT SRIVASTAVA(026),M.Sc(EM),1ST SEM. 1

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TSUNAMIS:THE GREAT WAVES The phenomenon we call “TSUNAMI”(soo-NA hmee) is a series of travelling ocean waves of extremely long length generated primarily by earthquakes occurring below or near the ocean floor. Tsunami waves are distinguished from ordinary ocean waves by their great length. In the deep ocean ,the tsunami waves propagate at a speed exceeding 800 kmph. Tsunami is a kind of Coastal Hazard. 2

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PLATE TECTONICS Plate tectonic theory is based on an earth model characterized by a small number of lithospheric belts,70 to 250km,that float on a thick viscous under layer called the asthenosphere.These plates cover the entire surface of the earth & contain both continents & seafloor. The region where the two plates come in contact is called a plate boundary. When the two plates move away from each other ,it is called as Spreading. Where the two plates move towards each other &one slides beneath the other is called Subduction Where the two pates slide horizontally past each other, it is known as transform 3

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Subduction zones are characterized by Deep ocean Trenches, and the volcanic islands or mountain chains associated with many subduction zones around the Pacific Rim are known as “The Ring Of Fire” 4

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EARTHQUAKES & TSUNAMIS Not all earthquakes generate tsunamis. To generate a tsunami, the fault must be underneath or near the ocean. Shallow focus earthquakes (depth <70km) along subduction zone are responsible for most destructive tsunamis. Tsunami also called seismic sea wave are caused generally by earthquakes, less commonly by submarine landslides,infrequetly by submarine volcanic eruptions & rarely by large meteorite impacts in the ocean. 6

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In the deep ocean,destructive tsunamis can be small-often only a few tens of cms or less in height & cannot be seen nor felt on ships at sea. But as the tsunami reaches shallower coastal waters, wave height can increase rapidly.Sometime,coastal waters are drawn into the ocean just before the tsunami strikes. When this occurs, more shoreline may be exposed than even at the lowest tide. This major withdrawal of the sea should be taken as a warning of the tsunami waves . 7

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Where the ocean is over 6000 m deep, unnoticed tsunami waves can travel at the speed of a commercial jet plane, over 800kmph. Scientists can predict when a tsunami will arrive at various places by knowing the source characteristics of the earthquake that generated the tsunami and the characteristics of the seafloor along the paths to those places. Tsunamis travel much slower in shallower coastal waters where their wave-heights begin to increase dramatically. HOW FAST? 8

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HOW BIG? Offshore & coastal features can determine the size & impact of tsunami waves. When the tsunami reaches the coast & moves inland, the water level can rise many metres.In the extreme cases, water level has risen to more than 15m(50ft) for tsunamis of distant origin and over 30m(100ft) for tsunami waves generated near the earthquake’s epicenter. 9

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HOW DO VOLCANIC ERUPTIONS GENERATE TSUNAMIS? Although relatively infrequent, violent volcanic eruptions represent also impulsive disturbances, which can displace a great volume of water & generate extremely destructive tsunami waves in the immediate source area. According to this mechanism, waves may be generated by the sudden displacement of water caused by a volcanic explosion. One of the largest & most destructive tsunamis ever recoded was generated in August 26,1883 after the explosion & collapse of the volcano of Krakatau(Indonesia).This explosion generated waves that reached 135ft,destroyed towns &villages, and killing 36,417 people. 10

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VOLCANO CAUSING TSUNAMI 11

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HOW DO LANDSLIDES GENERATE TSUNAMI? Tsunami waves can be generated from displacements of water resulting from rock-falls, icefalls & sudden submarine landslides or slumps. Major earthquakes are suspected to cause many underwater landslides, which may contribute significantly to tsunami generation In the 1980’seath moving & construction work of an airport runway along the coast of Southern France,trrigered an underwater landslide, which generated tsunami waves in the harbor of Thebes. 12

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TSUNAMI WARNING CENTRES The Richard H. Hagemayer Pacific Tsunami Warning Centre(PTWC) serves as the international warning centre for tsunamis that pose a Pacific-wide threat. PTWC became a formal arrangement in 1965 as the operational centre for Tsunami Warning System in the Pacific(TWSP). The initial objective of PTWC is to detect, locate &determine the seismic parameters of potentially tsunamigenic earthquake occurring in the Pacific Basin. 14

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15 It continuously receives seismographic data from more than 150 stations around the pacific. If the earthquake location, depth,& magnitude criteria needed to generate a tsunami are met, a tsunami warning is issued to warn of an imminent tsunami hazard.

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ASIA:LAGGING BEHIND 17 The National Oceanic & Atmospheric Administration(NOAA) of U.S & various international science agencies have indicated that there were few, if any tsunami early warning systems monitoring the Indian Ocean on 26thDec.,2004. However, nations bounded also by the Pacific Ocean, including Australia &Indonesia, had tsunami early warning system monitoring the Pacific shores where they perceived a threat While earthquakes couldn’t be predicted in advance, once the earthquake was detected it was possible to give about 3hrs advance notice of a potential tsunami, such a warning system is in place across the Pacific but not in Indian Ocean.

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On the contrary, scientists knew in advance that Southern Asia was going to be hit by the tsunami But attempts to raise the alarm were hampered by the absence of "EARLY WARNING SYSTEMS” in the region. Within 15min. of 26th Dec. earthquake, the PTWC in Hawaii had sent an alert to 26 countries, including Australia & Indonesia, but because of the lack of infrastructure to receive warnings rapidly, it had to face the havoc of tsunami. 18

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HOW IT ALL OCCURS? 20

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FACTORS OF DESTRUCTION Mainly there are three “FACTORS OF DESTRUCTION OR EFFECTS” of tsunami- Inundation Wave impact on structures Erosion. Strong tsunami-induced currents lead to erosion of foundations and the collapse of bridges & seawalls. Floatation & drag forces move houses &overturned railroad cars. Floating debris, including boats & cars become dangerous projectiles that may crash into buildings, break power line &may start fire 21

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Fires mainly come from damaged ships in ports or from ruptured coastal oil storage tanks & refineries, can cause damage greater than that inflicted directly by the tsunami 22

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TSUNAMI SAFETY If you feel an earthquake & you are near the sea or ocean you may need to do the following- DURING TSUNAMI Listen to a radio or television to get the latest emergency information, and be ready to evacuate if asked to do so If you hear an official tsunami warning, evacuate at once. Climb to higher ground. A tsunami warning is issued when authorities are certain that a tsunami threat exist. Stay away from the beach, NEVER go down to the beach to watch a tsunami come in. If you can see the wave you are too close to escape it!! 23

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Return home only after authorities advise it ids safe to do so. A tsunami is a series of waves .Do not assume that one wave means the danger is over. The next wave may be larger than the first one. Stay out of the area!! AFTER TSUNAMI Stay tuned to a battery-operated radio for the latest emergency information. Help injured or trapped persons. Give first-aid if you can. Do not move seriously injured persons unless they are in immediate danger of further injury. Call for help!!! 24

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CASE STUDY:26TH DEC.,2004 On Dec.26th 2004,a magnitude 9.0 undersea earthquake off the west coast of Northern Sumatra(Indonesia),unleashed a tsunami that affected more than 12 countries throughout south & southeast Asia & stretched as far as the northeastern African coast. Within 6 hrs. the deadly waves travelled more than 3,000 miles & carved a trail of death & destruction as they arrived on land. 25

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Current official estimates indicate that more than 160,000 people are dead,& millions of others are affected, including the injured, missing & displaced. The World Health Organization (WHO) indicates that an estimated 3-5 million people lack the basic necessities for survival; between 1-2 million people may be displaced. A massive, global relief & recovery operation is underway. After about 4 years of misery, their lives have started to come on track. According to the United Nations, the relief operation is the largest ever undertaken.Indonesia,Sri Lanka,India &Thailand have suffered some of the worst devastation. 26

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ORIGINATION OF THE DISASTER 27

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LOSS OF LIVES & PROPERTY 28

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PROPOSAL FOR EARLY WARNING SYSTEMS Development of such a system needs financial support from every country of the world. Developed countries have to bear most of the expenses, which includes, cost of procuring, operating &maintaining the system. United Nations Environment Program(UNEP) announced an international effort to develop an early warning system for the nations bounding the Indian Ocean. Expansion of the existing U.S tsunami early warning program in the Pacific is also on the cards, so as to include sites of the Indian & Atlantic Ocean in the system. 29

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HOPE WE WON’T GET ANOTHER 26th DECEMBER LIKE THIS,TILL THEN……………………. THANKS FOR YOUR COOPERATION 30