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Slide 4: 4 These are the most destructive and common tsunamis; When a quake is colossal, at least 7.5 in magnitude, it displaces enough water to case a huge wave; Such quakes often occurs at a thrust fault. Earthquakes cause Tsunamis! Past Earthquakes and Tsunamis in the Indian Ocean– note the magnitude of the 1883 and 2004 earthquakes/tsunamis Slide 5: 5 VOLCANOES (1) A classic aboveground eruption can disturb the ocean floor and generate a tsunami. can cause tsunamis! Slide 6: 6 - contd. (2) submarine events like eruptions, cascades of ash or the collapse of a volcanic flank, can also be the cause of a tsunami. In 1883, the volcanic eruption of Krakatau and the collapse of its caldera stirred up 130-foot high waves and killed 36,000 people. VOLCANOES Slide 7: 7 Usually set off by Earthquakes or Rock and icefalls Highest such wave was recorded in Lituya Bay, Alaska in 1958: a quake-triggered rock fall threw up a 500+m wave. LANDSLIDES can cause tsunamis! Slide 8: 8 ASTEROIDS 35 million years ago an asteroid blasted an 80 km wide crater under what is now the southern tip of Chesapeake Bay. The resulting waves are known to have roared inland for hundreds of miles! can cause a tsunami! ChesapeakeBay Slide 9: 9 Asteroids Artist’s impression of the impact of an asteroid on Earth – an asteroid of a few kilometres in diameter may release as much energy as several million nuclear bombs detonating! Let us hope that the next asteroid falls on some other planet! contd. Slide 10: 10 The Development of a Tsunami - a simplified diagram applicable to the 26.12.04 Asian Tsunami Slide 11: 11 happened in the Indian Ocean effected 12 countries around Bay of Bengal and beyond triggered by a quake of magnitude 9.3 with its epicentre west of Sumatra The 26.12.04 Tsunami Slide 12: 12 chronology of the 26.12.04 Asian tsunami Wave started when a 960km stretch of fault line off Sumatra’s coast finally snapped. The 9.3 quake lifted the seabed by about 5 metres. Minutes later the tsunami split sending energy pulses east towards the Sumatra coast and west across the open ocean. As the leading tsunami raced towards Sumatra and shallower water, its speed slowed, its wavelength shortened and its height rose to around 30metres. Slide 13: 13 Effects of the Asian Tsunami of the 26.12.04 300 000 dead Thousands of houses destroyed Loss of property Tourist resorts and coastline buildings destroyed Slide 14: 14 $ The costliest quakes, 1900-2004 $ Slide 15: 15 ? Where Next ? This map showing epicentres of earthquakes is very eloquent – it is at the places where continental plates meet that it is more likely that tsunamis will occur! Slide 16: 16 At Risk from Tsunamis! At particular risk are those places which are found at the juncture of tectonic plates Slide 17: 17 The Kamchatka Peninsula in Russia sits on the Kuril-Kamchatka Trench and is flanked by volcanic ranges. 29 of the 160 volcanoes which surround it are still active. This makes the area a prime candidate for a tsunami! The Kamchatka Peninsula is shown in red. Its relief is shown at right. The Kamchatka Peninsula, Russia Slide 18: 18 Hawaii-a volcanic island is very prone to a tsunami. The East coast of Japan is also very closely watched. Slide 19: 19 California & N Carolina These two N American states sit on continental shelves where sediments collect and the unstable flanks of volcanoes are landslide prone. Slide 20: 20 Prone to Earthquakes The San Andreas fault in California is closely watched. It is the cause of many earthquakes like the one shown above in San Francisco. Slide 21: 21 The Mediterranean The Mediterranean sits on the junction of the Eurasian and African Plate and is therefore prone to earthquakes and tsunamis. In 1630 a volcano on the Greek Island of Santorini exploded and sped the Minoan civilisation demise. Slide 22: 22 Conclusion Here’s hoping that none of us is ever in the path of a tsunami. GOOD LUCK to us all! © Joan Pace May 2005 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.