Volcanoes types structure and effects


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Endogenic processes

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Volcanoes types structure and effects

  1. 1. Volcanoes
  2. 2. What is a volcano?• A point on the earth’s crust where magma forces its way to the surface• Ash and gases may also escape
  3. 3. Where do they occur?• On subduction zones• On constructive plate boundaries• On hot spots
  4. 4. What types of volcanoes are there?Acid volcanoes Basaltic volcanoes• Highly explosive • Less explosive*• Magma/lava is viscous • Magma/lava less viscous (thick) (runny)• Found where oceanic • Found at rift zones crust is subducted under (constructive boundaries) continental crust and hotspots * Continental hotspots are basaltic but potentially highly explosive
  5. 5. Acid (rhyolitic) volcanoesLava domes Stratovolcanoes• Formed of layers of lava • Also called composite high in silica volcanoes• Lava is viscous and does • Formed of layers of lava not run very far and ashes• Rounded form • Lava is viscous• composed completely of • Distinct cone shape lava
  6. 6. Example – lava dome• Mount St Helens - Washington state, USA before during after
  7. 7. Example - stratovolcano • Mount Pinatubo, Luzon, Philipinesbefore During… after
  8. 8. Other famous stratovolcanoes Fuji, dormant Vesuvius, active Kilamanjaro,Krakatoa, dormantactive
  9. 9. Location of stratovolcanoes• Along subduction zones• Often found in volcanic arcs*• E.g. Cascade range, USA *not to be confused with Island chains formed over hotspots
  10. 10. Basic (basaltic) volcanoes• Also known as shield volcanoes• Formed of widespread layers of lava low in silica – low viscsity, lava travels very far• Low form spread over a great distance
  11. 11. Example – basic volcano• Eyjafjallajökull, Iceland
  12. 12. Example 2• Kilauea, Hawaii
  13. 13. Calderas• Collapsed volcanoes• Magma chamber has emptied and the ground has sunk• Often becomes a lake• New volcanoes can form, or pressure can build from below, lifting the ground• If acidic, this can cause a catastrophic eruption in the form of a ”super-volcano”
  14. 14. Caldera - Santorini • Destroyed the Minoan civilization due to tsunamis circa 1600BC • May have given rise to the Atlantis myth
  15. 15. Yellowstone national park
  16. 16. Yellowstone is a hotspot
  17. 17. Hotspots• Tectonic plate moves over a magma ”plume”• Occasionally erupts, creating a volcano• Hawaii – basic• Yellowstone - acid
  18. 18. Major hotspots
  19. 19. Volcanic Explosivity index (VEI)• 1 – Hawaiian gentle (Kilauea)• 2 – Strombolian explosive (Stromboli)• 3 – Vulcanian severe• 4 – Peléan cataclysmic (Mt.Pelée)• 5 – Plinian paroxysmal (St.Helens)• 6 – plinian/ultra-plinian colossal (Krakatoa)• 7 – ultra-plinian super-colossal (Tamb.)• 8 – supervolcanic mega-colossal (Y.st)Number 8 has never been experienced in human historyThe list has been simplified. See correct details here: http://www.unc.edu/~rowlett/units/scales/VEI.html
  20. 20. Volcanic hazards• Most hazards during eruptions are caused by what comes out of a volcano• In worst case scenarios then a volcano may violently explode
  21. 21. Volcanic hazards – lava flows• Mostly associated with basic volcanos• Slow moving 1 – 5 kmh• Low risk to human life• Cover large areas and destroy large amounts of infrastructure
  22. 22. Hazards – pyroclastic flows• Hot clouds of ash and gas• Move downhill, close to the ground, following valleys• High speed – up to 500 kmh• As far as 30 km• Up to 7000 C• Highly dangerous
  23. 23. Hazards - lahars• Occur on high volcanos covered in snow and ice, or wet mud/soil• Eruption causes snow to melt, or lava mixes with mud• Flows downhill like wet concrete
  24. 24. Hazards – ash clouds• Slow moving• Weight of ash can collapse buildings• Destroys crops, pollutes water• Affects air traffic• Can enter high atmosphere and cause cooling – disrupting climate
  25. 25. Hazards – lava bombs• Molten rocks thrown out of volcano• Pummice – smaller rocks• Travel short distances• Can start fires
  26. 26. The Decade Volcanoes• 16 volcanoes identified as potentially highly hazardous to humankind
  27. 27. So why live near a volcano?• Aesthetic beauty e.g. Mount Fuji, Japan• Mining of minerals and diamonds• Geothermal energy and hot springs
  28. 28. So why live near a volcano?• Highly fertile soils – soft rocks and high mineral content
  29. 29. So why live near a volcano?• Poverty – cheap marginal land• Overcrowding and population pressure – nowhere else to live• Common problems in LEDCs
  30. 30. So why live near a volcano?• Complacency or naivete – ”nothing will happen”• Confidence – ”we will be warned and have time to get away”• Tradition/family – ”we have always lived here”
  31. 31. Predicting volcanic eruptions• Monitoring seismic disturbances (tremors)• Changes in volcano profile (shape)• Chemical changes in groundwater• Emissions of gases• Thermal monitoring (temperature)
  32. 32. Vesuvius
  33. 33. Mount VesuviusMount Vesuvius is an active volcano in Italy It is the only volcano on the European mainland to have erupted in the last 100 years It is not currently erupting It is dormant, not extinct
  34. 34. • Vesuvius is in southern Italy near Naples• Location: 40°49′N 14°26′E
  35. 35. NaplesVesuvius
  36. 36. Vesuvius is a composite volcano (strato-volcano)
  37. 37. Vesuvius - data• Height (elevation) 1,281 metres (4,203 ft) above sea level• Has a collapsed caldera from a previous eruption
  38. 38. Formed at the collision of two tectonic plates – the African and the Eurasian• A converging, destructive boundary, with very little movement• Several volcanoes nearby, none active
  39. 39. An acid volcano• Potential for violent eruptions• Slow moving lava• Explosions• Hot ash/cinders• Pyroclastic flows• Real danger!
  40. 40. History of eruptions• 1800 BC – destruction of Bronze age settlements – then several more times• 79 AD – destruction of Pompeii• At least 40 times until the last eruption in 1944 – witnessed by allied troops towards the end of WWII• = once every 40-50 years
  41. 41. Pompeii Ad79
  42. 42. Pompeii AD79• Massive eruption of Vesuvius buries the towns of Pompeii under a thick layer of burning ashes and pumice up to 2.8 metres deep and Herculaneum under 23 metres of ash and pumice• Eruption lasted for two days• Deaths unknown – estimates from 5000 to 25000
  43. 43. Causes of deaths• Burial under ash and pumice• Killed by pyroclastic flows• Collapsing building• Rain of lava bombs• Starvation• Disease• Drowning (many fled to the sea for rescue)
  44. 44. Buried alive!
  45. 45. The population of Naples is 960,000(as of 2012)The centre of Naples is 15km fromVesuviusthe population of the Naples suburbanregion is nearer 3 million
  46. 46. Reducing the risks• Round-the-clock monitoring of the volcano – Tremors, gasses, changes in water• Identifying hazard areas – Weak spots, secondary vents, predicting routes of pyroclastic flows• Creating an evacuation plan – Zoning, warning systems, public education
  47. 47. Evacuation plans?• Red zone – immediate risk from pyroclastics• Blue zone – secondary zone of floods and lahars• Yellow zone – mostly ash and other debris
  48. 48. Useful links• http://greenfieldgeography.wikispaces.com/IG CSE+Plate+Tectonics+and+GCSE+Plate+Te ctonics• http://volcano.oregonstate.edu/• http://www.physicalgeography.net/fundament als/chapter10.html• http://volcanoes.usgs.gov/hazards/index.php