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Chapter 3

Chapter 3 - Tsunamis

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Rob Milne

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Risks and Disasters – Chapter 3  Catastrophe in the Indian ocean o December 2004 – countries around Indian ocean  230 000 people killed, hundreds of thousands injured, millions displaced  Source was from Magnitude 9.1 quake off Sumatra  Third largest in recorded history  Movement of faults produced massive waves that reached Indonesian islands within minutes and other countries later  People were caught by surprise due to lack of tsunami warning  Tsunami took more than 7 hours to cross entire Indian ocean to east African coast  More than ¾ of deaths were in Indonesia, which suffered from the earthquake and the tsunami  Sri Lanka, India, Thailand also suffered a great deal Country Number of deaths Indonesia 167 540 Sri Lanka 35 322 India 16 269 Thailand 8 212 Somalia 289 Maldives 108 Malaysia 75 Burma 61 Tanzania 13 Bangladesh 2 Yemen 2 Kenya 1  Much less common in Indian ocean compared to Pacific ocean  Effective warning systems needed in all countries near ocean basins  Also need emergency protocols that are effective and efficient  Earthquake and tsunami education necessary for people living along coast lines  Introduction to tsunami o Tsunami – produced by sudden displacement of water due to other trigger events o Major Tsunami  1755 – Lisbon – 20 000 people  1883 – Krakatoa – 36 000 people  1946 – Hawaiian Islands– 160 people  1960 – Hawaii – 61 people  1964 – Alaska/California – 130 people  1993 – Japan – 120 people  1998 – Papua New Guinea – 2 100 people  2004 – Indian Ocean – 230 000 people o Earthquake-triggered tsunami  Causes tsunami by displacing ground or triggering landslides  Takes M >7.5 to trigger damaging tsunami  4 stage process  Displacement of seafloor transmits energy upward and outward , creating a ripple wave effect  Deep ocean – waves move more rapidly and spaced farther apart o Spacing between crests may be more than 100km and height less than 1m  Water depth and tsunami decrease it gets close to land, forward speed about 45 km/hr o Decreases in wave crest spacing and increase in height 1 Risks and Disasters – Chapter 3  As it approaches shore, tsunami heights are several tens of meters high o Destroying everything in its past  Multiple surges of turbulent of waves  Series of waves, not single wave  Waves can be separated by minutes to hours  Can produce distant or local tsunami  Local tsunami can be more dangerous because of the lack of warning o Landslide-triggered tsunami  Landslides can happen on seafloor or from mountains  Many landslides caused by earthquakes o Volcanic-triggered tsunami  Tsunami due to volcanoes less common  Second most deadly tsunami in history caused by Krakatoa explosion  smaller tsunami can be triggered by lahars and pyroclastic flows  Less hazardous as they slow down and decrease in size as they get farther from volcano  Regions at risk o All ocean/lake shorelines are at risk  Some coasts at higher risk  Coasts close to a subduction zone are at a greater risk o Areas along the Pacific Basin are greatest risk  Includes Japan, Kamchatka, Hawaii, Chile, Peru, Mexico, pacific coast from Alaska to N. California o Japan and Hawaii experience frequent tsunami  Effects of tsunami and linkages of other natural hazards o Have primary and secondary effects  Primary  Related to impact of onrushing water and entrained debris and resulting flooding and erosion  Tear up beaches, vegetation and buildings  Majority of deaths from drowning and physical impact to debris/stationary objects  Secondary  Occur after the tsunami  May start fires, water pollution and disease outbreaks o Natural hazards  Closely linked to a trigger (earthquake, landslide, volcanoes, asteroids/comets)  Trigger event /waves can change coastlines  Natural service functions of tsunami o Very few benefits, may be advantageous to some coastal ecosystems and contribute to coastal dunes  Minimizing the tsunami hazard o Detection and warning  First warning of possible tsunami comes from M7.5 earthquake  Able to detect and accurately estimate arrival time to within minutes  Three types of warning systems in Pacific Ocean  Pacific wide system o Located in Hawaii  Regional system o Includes West Coast an Alaska Tsunami Warning system o Located in Alaska  Local system o Located in Chile and Japan 2 Risks and Di
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