TsunamiWhat is a Tsunami?Slide 3How a Tsunami FormsSlide 5Slide 6How a Tsunami Forms Earthquake Generated TsunamiSlide 8Velocity and Wave HeightCoastal EffectsSlide 11Chile Tsunami May 1960Slide 13Slide 14Slide 15Slide 16Slide 17Tsunami HazardsThe Relevance of Hazard Prediction and Mitigation for the 2004 TsunamiTsunami from Great Earthquakes in the Pacific NorthwestHow a Tsunami Forms Volcano Generated TsunamiHow a Tsunami Forms Landslide and Rockfall Generated TsunamiHow a Tsunami Forms Tsunami from Volcano Flank Collapse and Submarine LandslidesHow a Tsunami Forms Tsunami from Asteroid ImpactSlide 25Slide 261TsunamiChapter 5Tsunami The Great Wave2What 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.3TsunamiThe 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)4How a Tsunami Forms(Refer to pg. 99, 114-116)5How a Tsunami FormsWhen 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)6How a Tsunami FormsAs 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)7How a Tsunami FormsEarthquake Generated Tsunami(Refer to pg. 104-105)Most tsunami are generated during shallow focus underwater earthquakes associated with sudden rise or fall of the seafloor, most commonly along subduction zones. Tsunami Animation8Most destructive tsunamis occur in Pacific Ocean. The borders of the Pacific Ocean are dominated by active subduction zones that produce frequent violent earthquakes .9Velocity and Wave Height(Refer to pg. 115-116)1957 Aleutian TsunamiTsunami 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.10Coastal 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. The inundation can extend inland by 1000 feet (305 m) or more, covering large expanses of land with water & debris. run-up animationAbove: 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.11As 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.12Chile TsunamiMay 1960On 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. 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. (Refer to pg. 87-88, 102-104)13Left: 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.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)Above: tsunami in Hilo, Hawaii, 1960.14On December 26, 2004 at 07:58:53 local time in the Indian Ocean there was an undersea earthquake; known as the Sumatra-Andaman earthquakeAs 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.South East Asia TsunamiDecember 26, 20041516Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours to reach the various coastlines (Left).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). NYTimes Animation ASIA'S DEADLY WAVES17The 2004 tsunami was the deadliest in recorded history.The U.S. Geological Survey records the toll as 283,100 killed, 14,100 missing, and 1,126,900 people displaced.2004 Tsunami Satellite Images18Tsunami 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)19The Relevance of Hazard Prediction and Mitigation for the 2004 TsunamiThe water line suddenly retreatedA simple program of public education and awareness of the potential hazards could have saved many
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