Tsunami Chapter 5 Tsunami The Great Wave 1 What is a Tsunami A tsunami is a series of waves called a wave train generated in a body of water by an abrupt disturbance that vertically displaces the water column Earthquakes landslides volcanic eruptions volcanic flank collapse submarine landslides and large asteroid impacts all have the potential to generate a tsunami 2 Tsunami The term tsunami comes from the Japanese language meaning harbor wave Tsunamis are also called seismic sea waves Tsunamis have been historically referred to as tidal waves Refer to pg 99 3 How a Tsunami Forms Refer to pg 99 114116 4 How a Tsunami Forms When the water is displaced water from the surrounding rushes in to fill the depression forming a series of high speed up to 870km hr flat spread out waves average wavelength of 360km In deep water tsunami waves are nearly undetectable Refer to pg 99 114 116 5 How a Tsunami Forms As the leading waves of a tsunami approach a shoreline friction with the sea floor slows the waves down This compresses the wavelength and increases the wave height The waves surge onto shore as a rapidly rising flood of water with great destructive power Refer to pg 99 114 116 6 How a Tsunami Forms Earthquake Generated Tsunami Most tsunami are generated during shallow focus underwater earthquakes associated with sudden rise or fall of the seafloor most commonly along subduction zones Refer to pg 104 105 Tsunami Animation 7 Most destructive tsunamis occur in Pacific Ocean The borders of the Pacific Ocean are dominated by active subduction zones that produce frequent violent earthquakes 8 Velocity and Wave Height Refer to pg 115 116 Tsunami waves in the open ocean are low and far apart but move at velocities of several hundreds of kilometers per hour They slow and build much higher in shallow water near the coast especially in coastal bays 1957 Aleutian Tsunami 9 Coastal Effects Refer to pg 114 116 Run up is the height to which a tsunami wave rushes up onshore Driftwood trees and the remains of boats houses and cars are swept up by the incoming wave and commonly mark the upper limit of tsunami run up The first run up of a tsunami is often not the largest run up animation The inundation can extend inland by 1000 feet 305 m or more covering large expanses of land with water debris Above Katukurunda South of Kalutara on the West Coast Tsunami run up height of over four meters near the beach Left The Indian Ocean coastline near Phuket Thailand The changes along the coast from the 2004 tsunami are obvious where the vegetation has been stripped away 10 As the wave recedes into the trough before the next wave the onshore water and its debris flow back offshore The time between the trough and the next tsunami wave is often more than a half hour Below Maximum recession of tsunami waters at Kata Noi Beach Thailand before the 3rd and strongest tsunami wave Above A broad offshore beach is exposed at Kalutara Sri Lanka as the first wave of the tsunami drains back to the ocean 11 Chile Tsunami May 1960 On May 22 1960 the largest earthquake on record struck the coast of Chile with a Mw of 9 5 The earthquake ruptured along a 1 000 km length of the subduction zone In Chile the earthquake and the tsunami that followed took more than 2 000 lives From Chile the tsunami radiated outward killing 61 people in Hilo Hawaii and 122 on the island of Honshu Japan Refer to pg 87 88 102 104 Left Stuck to the subducting plate the overriding plate gets squeezed This movement goes on for decades or centuries slowly building up stress Right An earthquake along a subduction zone happens when the leading edge of the overriding plate breaks free and springs seaward raising the sea floor and the water above it This uplift starts a tsunami 12 Left This tide gauge record shows the tsunami waves in Hilo Hawaii fifteen hours following the Chilean Earthquake Right This low lying area of downtown Hilo was destroyed by the Chilean tsunami Above tsunami in Hilo Hawaii 1960 Left The tide gauge at Onagawa Japan recorded a dramatic drop in sea level as the Chilean tsunami arrived Refer to pg 102 104 118 13 South East Asia Tsunami December 26 2004 On December 26 2004 at 07 58 53 local time in the Indian Ocean there was an undersea earthquake known as the Sumatra Andaman earthquake As the pictures illustrate the Indian Plate subducts under the Burma Plate at the Sunda Trench With the earthquake an estimated 745 miles of faultline slipped along the subduction zone The vertical rise of the seafloor by several meters during the earthquake produced the tsunami 14 15 As the map shows the tsunami devastated the shores of Indonesia Sri Lanka Thailand India Malaysia Burma and Bangladesh with waves up to 100 feet Maldives Somalia Kenya and Tanzania were also affected Right The total energy of the tsunami waves was about five megatons of TNT more than twice the total explosive energy used during all of WWII including the two atomic bombs Because of the distances involved the tsunami took anywhere from fifteen minutes to seven hours to reach the various coastlines Left NYTimes Animation ASIA S DEADLY WAVES 16 The 2004 tsunami was the deadliest in recorded history 2004 Tsunami Satellite Images The U S Geological Survey records the toll as 283 100 killed 14 100 missing and 1 126 900 people displaced 17 Tsunami Hazards Drowning in the incoming waves Being thrown against solid objects Being carried back out to sea in the outgoing wave Being hit by debris carried by the wave Refer to pg 117 118 18 The Relevance of Hazard Prediction and Mitigation for the 2004 Tsunami A simple program of public education and awareness of the potential hazards could have saved many lives The water line suddenly retreated The magnitude of the tsunami disaster could have been mitigated with a proper disaster preparedness plan and a functioning early warning system Human destruction of coral reefs coastal mangrove trees and sand dunes that had formerly protected some coastal areas was believed to be a significant factor in the loss of life and damage Northern part of Banda Aceh Sumatra before above and after right the tsunami 19 Tsunami from Great Earthquakes in the Pacific Northwest Refer to pg 119 122 Above and Right A sequence of peat sand and mud are a geologic record of tsunami Radiocarbon dating of organics in buried soils along the coast of the Pacific Northwest indicate tsunami with recurrence intervals ranging from 300 to 900 years Radiocarbon dating places the
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