Содержание
- 2. What is a volcano? A volcano is a vent or 'chimney' that connects molten rock (magma)
- 3. How and why do volcanoes erupt? Hot, molten rock (magma) is buoyant (has a lower density
- 4. Explosive Eruptions Mt. Redoubt Explosive volcanic eruptions can be catastrophic Erupt 10’s-1000’s km3 of magma Send
- 5. Three products from an explosive eruption Ash fall Pyroclastic flow Pyroclastic surge Explosive Eruptions Pyroclastic flows
- 6. Direct measurements of pyroclastic flows are extremely dangerous!!!
- 7. Effusive Eruptions Effusive eruptions are characterised by outpourings of lava on to the ground. Hawaii
- 8. Practical Exercise 1. What controls the violence of an eruption? How fast is magma ejected out
- 9. Volcano Monitoring and Hazard Mitigation
- 10. 92,000 Tambora, Indonesia 1815 36,000 Krakatau, Indonesia 1883 29,000 Mt Pelee, Martinique 1902 15,000 Mt Unzen,
- 11. Pyroclastic flow Lahars/Mud flows Pyroclastic fall Lava flow Noxious Gas Earthquakes Volcanic Hazards Courtesy of www.swisseduc.ch
- 12. Pyroclastic Flow For example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii
- 13. Pompeii (79AD) On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten
- 14. Pompeii (79AD) Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii,
- 15. Pompeii (79AD) The cities remained buried and undiscovered for almost 1700 years until excavation began in
- 16. Vesuvius today Vesuvius remains a hazardous volcano with heavily populated flanks: around 1.5 million people live
- 17. An eruption of Mt Peleé in 1902 produced a pyroclastic flow that destroyed the city of
- 18. 29,000 people died…. Only 2 survived! Why?
- 19. How do pyroclastic flows cause devastation?
- 20. Pyroclastic Flow - direct impact Courtesy of www.swisseduc.ch
- 21. Pyroclastic Flow - burial
- 22. Pyroclastic Flow - burns
- 23. Pyroclastic Flow - lahars Hot volcanic activity can melt snow and ice Melt water picks up
- 24. Pyroclastic Fall Ash load Collapses roofs Brings down power lines Kills plants Contaminates water supplies Respiratory
- 25. Lava Flow It is not just explosive volcanic activity that can be hazardous. Effusive (lava) activity
- 26. Lava Flow - Heimaey, Iceland Iceland, January 23,1973. Large fissure eruption threatened the town of Vestmannaeyjar.
- 27. Lava Flow - Heimaey, Iceland The lava flows caught the inhabitants by surprise Before the eruption
- 28. Lava Flow - Heimaey, Iceland However, the potential damage was reduced by spraying seawater onto the
- 29. Practical Exercise 2. Assessing Volcanic Hazards
- 30. So…. How do we minimize the risk of active volcanoes?
- 31. Volcano Monitoring Volcano Observatories are set up on all active volcanoes that threaten the human population.
- 32. Volcano Monitoring Seismicity Deformation Gas Output (on volcano and remote sensing techniques) These three things are
- 33. Seismic Activity Earthquake activity commonly precedes an eruption Result of magma pushing up towards the surface
- 34. Seismic Activity Earthquake activity is measured by Seismographs Seismographs are stationed on the flanks of the
- 35. Deformation Monitoring “Tiltmeters” are used to measure the deformation of the volcano The tiltmeters measure changes
- 36. Deformation Monitoring Tilltmeters can tell you when new material enters the magma chamber. Note the presence
- 37. Gas Monitoring Commonly gas output from a volcano increases or changes composition before an eruption. As
- 38. Gas Monitoring Gas samples are collected from fumaroles and active vents. Gas levels may also be
- 39. In Summary.. Volcanoes are extremely hazardous. However, the volcano can be studied, monitored and understood. Each
- 40. Post-lecture Question: What should geologists do about volcanic eruptions in the future? Study volcanoes to find
- 41. Additional (Optional) Material
- 42. Are there other volcano related hazards?
- 43. Noxious Gas 1,700 people living in the valley below Lake Nyos in northwestern Cameroon mysteriously died
- 44. Noxious Gas Lake Nyos is a crater lake inside a dormant volcano. The lake had become
- 45. Noxious Gas A management plan has been developed to remove gas from the lake to prevent
- 46. Noxious Gas
- 47. Noxious Gas
- 48. Noxious Gas The Lake Nyos incident was not unique. Two years earlier, Lake Monoun, 60 miles
- 49. Earthquakes Large volumes of magma moving through the shallow crust can cause large earthquakes. This can
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