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Natural Disasters

Natural Disasters. Earthquakes Floods Storms Cyclones. © Karen Devine 2010. Earthquakes. Earthquakes occur due to movements in the continental plates of the earth’s crust. This is known as tectonic movement.

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Natural Disasters

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  1. Natural Disasters Earthquakes Floods Storms Cyclones © Karen Devine 2010

  2. Earthquakes • Earthquakes occur due to movements in the continental plates of the earth’s crust. This is known as tectonic movement. • Earthquakes have a focal point known as an epicentre where the greatest shocks occur. © Karen Devine 2010

  3. Earthquakes • Earthquakes can result in: • significant property damage • damage to infrastructure • damage to services • landslides and mudslides • tsunamis • land subsidence • injury or death. © Karen Devine 2010

  4. Earthquakes • An earthquake’s strength or intensity is measured by the Modified Mercali Scale. • Earthquake rates are generally very low in Australia because it is situated in the middle of the continental plate. © Karen Devine 2010

  5. Earthquakes • Nations which are located on the fault lines are more likely to experience earthquakes as the continental plates move against each other. © Karen Devine 2010

  6. Floods • Whilst Australia is prone to droughts, it can also be subject to flooding. • There are 3 types of floods: • Flash floods: result from periods of extreme rainfall and occur very quickly. • Slow onset floods: also result from heavy rains, yet the water takes significantly longer to reach properties. • Rapid onset floods: result from waters flowing quickly out of steep inland rivers. © Karen Devine 2010

  7. Floods • Floods occur naturally when rivers overflow their banks. • The waters run over their floodplains and eventually cover roads, properties and towns. • A floodplain is a flat area adjacent to a river. © Karen Devine 2010

  8. Floods • Floodplains consist of alluvial deposits which are fine materials eroded by the river. • Floodplains are highly fertile areas. © Karen Devine 2010

  9. Floods • The rains which contribute to flooding result from: • low pressure systems which move across Australia • cold fronts or the front of a cold air mass which causes very heavy rainfall • storms which may be cyclones or thunderstorms. © Karen Devine 2010

  10. Floods • Communities can contribute or cause flooding by: • removing vegetation near river zones • farming on floodplains • failing to develop levees • building towns in low-lying areas or below sea level • constructing low-lying roads • failing to build appropriate drainage. © Karen Devine 2010

  11. Thunderstorms • A thunderstorm is an atmospheric disturbance which may result in: • thunder • lightning • torrential rain • hail • cyclones • tornadoes or water spouts. © Karen Devine 2010

  12. Thunderstorms • Cumulonimbus clouds are responsible for thunderstorms. • Thunderstorms develop when the following conditions occur: • high humidity • very hot ground surfaces • cold fronts pushing under warmer, humid air masses. © Karen Devine 2010

  13. Thunderstorms • Thunderstorms can have the following features: • Lightning: which can cause loss of life or start bushfires. • Hail: caused by the freezing of rain droplets • Flash floods: very heavy rain is associated with thunderstorms • Gusty winds: often caused by rainfall generating downdraughts • Tornadoes: not a common occurrence in Australia. Result from rotating or funnel shaped descending air flows. © Karen Devine 2010

  14. Thunderstorms • Thunderstorms can have significant impacts such as: • death • property damage agricultural losses or damage • large insurance claims. © Karen Devine 2010

  15. Tropical Cyclones • Tropical cyclones are types of storms. • A cyclone has the following features: • a low pressure system • warm waters over 27° C • tropical location • exists over oceans or occurs near coastal areas • occurs between January and March. © Karen Devine 2010

  16. Tropical Cyclones • A cyclone exists when warm air rises and rotates around a central core followed by very gusty winds and heavy rains. © Karen Devine 2010

  17. Tropical Cyclones • Tropical cyclones can result in: • heavy rains > 2000 mm/day • wind speeds > 300 km/hr • storm surges when sea levels rise due to wind pressure on the ocean’s surface • property loss due to fierce winds, flooding or storm surges • erosion of beach sands by large waves • damage to coral reefs. © Karen Devine 2010

  18. Tropical Cyclones • Australia experiences approximately 10 cyclones per year. • Most move inland or away from the tropical zones where they lose their intensity. © Karen Devine 2010

  19. Tropical Cyclones • Cyclone Tracy is Australia’s most well known cyclone. • It struck Darwin on Christmas Day 1974. © Karen Devine 2010

  20. Pause Point • Play Cyclone Tracy Newsreel. © Karen Devine 2010

  21. Question Time? • How are cyclones named? © Karen Devine 2010

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