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Natural Hazards

Natural Hazards. Are all “natural” hazards natural?. Introduction to Natural Hazards. What is a “Geohazard”? Earth processes (involving the lithosphere, hydrosphere & atmosphere) that, upon interaction with human populations, cause loss of life and property.

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Natural Hazards

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  1. Natural Hazards

  2. Are all “natural” hazards natural?

  3. Introduction to Natural Hazards • What is a “Geohazard”? • Earth processes (involving the lithosphere, hydrosphere & atmosphere) that, upon interaction with human populations, cause loss of life and property. • It is important to understand the human element. • Without it, there would be no hazard! • Because of it, the science of geohazards becomes more important every year… • Mitigation - reduction/prevention Hazardousconditionor result geo-process humanprocess

  4. Why is the human element so critical? • The Earth’s population is increasing. • More people living in hazard-prone areas. • Populations are becoming more concentrated. • For example: • Currently ~6 billion people on Earth ( ~50% live in cities). • By 2025, estimated ~8 billion people (~66% in cities). • Of these cities, 40% are coastal locations… • prone to severe storm and tsunami damage! • And many major cities lie in areas subject to other geohazards (for example volcanoes and earthquakes). • E.g., 12% of Earth’s population (720 million) lives within 100 km of a volcano that has erupted in the past 10,000 years.

  5. Global distribution of population vs location of Holocene volcanoes

  6. We CANNOT stop the geologic processes! • We CANNOT stop our population growth… • Therefore, we must try to mitigate (reduce or prevent) the hazards through: • Scientific study of the geologic processes. • Population education initiatives. • Improvements in engineering/building practices. • Management plans and hazard response scenarios.

  7. Types of Natural Hazards Volcanoes, floods, earthquakes, tornadoes, hurricanes, tsunamis, landslides, forest fires…. • Can adversely affect human populations. • Can occur: • Without warning (e.g. earthquakes). • With warnings (precursors) (e.g. satellite monitoring of hurricane tracks, or the presence of ground deformation at a volcano before an eruption).

  8. To help forecast an event and thus mitigate the hazard we need to know: • Frequency vs. Magnitude • Frequency (F) = how often a given event occurs in a certain region. • Magnitude (M) = how powerful (amount of energy released) an event is. • For example, high M hazards happen with low F, but are much more destructive. • Scope • Scope (S) = area affected by a given hazard. • Local - landslides, floods, earthquakes, fire … • Regional - tsunamis, small volcanic eruptions, larger earthquakes, hurricanes … • Global - large volcanic eruptions, global warming, large meteorite impacts …

  9. Earthquakes and Tsunamis

  10. Frequency vs Magnitude Richter Scale Magnitudes

  11. San Francisco – Great 1906 Earthquake • Magnitude 7.8 earthquake. • Epicenter only 3 km offshore. • San Andreas fault ruptured over nearly 500 km. • Considered one of the worst natural disasters in U.S. history.

  12. Earthquake Hazards • Earthquakes are important hazards to understand because: • The natural hazard that, on average, kills the highest number of people per year (>1 million during the past century). • Commonly strikes without warning. • No time for evacuation. • No predictable trend to earthquake numbers, magnitude or location. • 1000's of earthquakes every year worldwide. • ~20 are > M7.0 and these account for 90% of the energy released and 80% of all the fatalities.

  13. How do we mitigate the hazard from earthquakes? • Reinforce buildings (earthquakes don’t kill people – buildings do!) • Education • Disaster plan

  14. Earthquakes and Tsunami’s • An earthquake on the seafloor has the potential to form a tsunami. • The earthquake must vertically displace overlying water (extensional or compressional faults - not transform). Extension Compression Transform

  15. How does an earthquake form a tsunami?

  16. 2004 South Asian Event • Biggest earthquake since 1960 event in Chile. (M9.5) • Magnitude 9.2 • 150 km off the west coast of Northern Sumatra • Generated a disastrous tsunami that affected 12 countries around the Indian Ocean. • Travel time for the tsunami was ~15 minutes to as long as 7 hours. • So, there is the possibility of warning people ahead of time, but not by much!

  17. A village near the coast of Sumatra lays in ruin after the tsunami. - Estimated that 1,600 km of faultline slipped about 15 m (a LOT of rock moved!). - The earthquake released 20 x 1017 Joules of energy, which is like setting off 475 million kilograms of TNT or 23,000 atomic bombs!

  18. How do we mitigate the hazard from tsunamis? • Monitoring • The process is very technology-intensive (satellite monitoring, seismograph arrays, computer modeling and tracking of tsunamis). • Costs are simply too high for many poorer countries. • Often no technology is available to monitor local tsunamis. • E.g., Papua New Guinea has no monitoring stations. • Reliant on the Pacific Tsunami Warning Center (in Hawaii). • Tsunami in 1998 was not detected because it originated locally.

  19. How do we mitigate the hazard from tsunamis? • Establish building restrictions in hazard prone areas. • In Hawaii, Hilo harbor and downtown were destroyed by the tsunamis of 1946 and 1960. • The town is now rebuilt on higher ground and the devastated area is a park.

  20. How do we mitigate the hazard from tsunamis? • Construction of seawalls. • Cause early wave breaking away from populations. • Thus prevent wave run up into urban areas.

  21. How do we mitigate the hazard from tsunamis? • Public education: • Warning systems. • Evacuation plans. • Promote a general understanding of the hazards involved. Punishment From God 45% Natural event 35% Bomb 20% Population reaction: Papua New Guinea (1998)

  22. Tropical Storms

  23. Atlantic and eastern Pacific Oceans – Hurricanes - average 10 named storms/year, 6 become hurricanes • Western Pacific Ocean – Typhoons - average 16 named storms/year, 9 become typhoons • Indian Ocean – Cyclones (best term to describe these storms) • Coriolis effect – causes storms to circulate counterclockwise (northern hemisphere) or clockwise (southern hemisphere) • Western Pacific – warm waters, few land masses, major storms…

  24. Hurricane Katrina (August 2005, Category 3) had gale force winds extending 120 miles (190 km) from the storm center (“eye of the storm”) – since these are circular storms this one was approximately 240 miles (380 km) from one side to the other – and they can get much larger….

  25. Hurricane Ike (category 4) – photo taken from 220 miles altitude in the space station. This hurricane was 600 miles in diameter – the largest ever recorded.

  26. How do cyclones form? • Tropical cyclones form only over warm ocean waters near the equator. • Warm, moist air rises upward from the surface. As this air moves up it leaves less air near the surface. This causes an area of lower air pressure below. • Air from surrounding areas with higher air pressure moves in to the low pressure area. Then this new “cool” air becomes warm and moist and rises, also. The cyclone is beginning to build… • As the warmed, moist air rises and cools the water in the air forms clouds. The whole system of clouds and wind spins and grows, fed by the ocean’s heat and water evaporating from the ocean surface. • As the storm system rotates faster and faster, an eye forms in the center. It is very calm and clear in the eye, with very low air pressure. Higher pressure air from above flows down into the eye. • When the winds in the rotating storm reach 39 mph (63 kmph), the storm is called a “tropical storm”. • When the wind speeds reach 74 mph (119 kmph), the storm is officially a “tropical cyclone” (or hurricane or typhoon). • Tropical cyclones weaken and eventually die out when they hit land, because they are no longer being “fed” by the energy from the warm ocean waters.

  27. How do cyclones form? This figure shows the motions of air within cyclones. The green arrows show where warm air is rising. The red arrows indicate where cool air is sinking.

  28. Classification of Cyclones The Saffir-Simpson Scale

  29. Hurricanes – Typhoons - Cyclones • The most widespread and destructive weather hazard that we face. • - Example: Hurricane Floyd (1999) • Was only a moderate level hurricane (category 3 at landfall). • But, it caused $5.6 billion in damage in the Bahamas and North Carolina and 57 fatalities. • 2.6 million coastal residents had to evacuate. • Most rivers in Florida reached high-water levels equivalent to a 500-year flood. Hurricane Floyd just before landfall.

  30. Cyclone Gorky - 1991 • Struck coast of Bangladesh. • Wind speeds 250 km/hr (156 mph – a category 5 storm). • A 6 meter (~20 ft.) storm surge wave traveled several km’s inland. • Estimated 138,000 killed, and 10 million homeless. • 2 billion dollars (2007) damage.

  31. Children attend class in what remains of their school…

  32. Homes in rural areas of poor countries are not built to withstand 156 mph winds…

  33. Hurricane Katrina - 2005 • Hurricane Katrina was the most costly and most deadly hurricane in the history of the USA. • Category 5 • At least 1,836 fatalities. • Damage estimated at $81.2 billion.

  34. Hurricane Katrina Collapsed bridge in New Orleans Suburbs in New Orleans Boats washed onshore by the storm surge

  35. What type of damage is produced? • Storm Surge • Water that is pushed onshore by the force of the cyclone winds.

  36. What type of damage is produced? • Wind… of course. • Responsible for the loss of power and utilities. • Wind damage affects much larger areas than surge. • Flying debris is a serious hazard.

  37. What type of damage is produced? • Flying debris • Can be propelled at very high speeds…

  38. How do we mitigate the hazard from a cyclone? • Monitoring • Early warning systems. • Infrastructure • Cyclone walls. • Communal shelters. • Building codes. • Education and planning

  39. Natural Hazards Summary Graph showing the number of deaths per year due to natural hazard events…

  40. Economic losses due to major disasters are increasing due to population growth and land-use changes…

  41. Number of major catastrophes are increasing due to population growth and land-use changes… are there other reasons?

  42. http://maps.grida.no/go/graphic/trends-in-natural-disasters Apparent exponential increase – Why? Improved information transfer worldwide. Population growth. No change in number of volcanic eruptions, earthquakes, etc… However, a statistically significant increase in cyclones and floods. Global warming???

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