Types of volcanoes

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NCEA Level 1 Geography AS 1.1 "Extreme Natural Events" - how volcanic eruptions affect the natural environment

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Types of volcanoes

  1. 1. 11 GeographyDifferent types of Volcanic Landforms
  2. 2. There are many different types of volcanic landforms.Often these are caused by the different types oferuptions that we looked at previously.So first… what were the main types of eruptions?Ex_________________ Magma is ___________ because it contains a lot of ___ Eg…r________________________________Ef_________________ Magma is ___________ because it doesn’t contain so much _________ eg b__________________________ UNLESS the magma meets ______________________ Then it may cause a __________-________________Ex________________ ← eruption
  3. 3. Two main categories of landforms• Cone = a hill, mound, mountain, dome, peak, cone etc – a new or altered landform that sticks up out of the ground• Crater = a basin, hollow, depression in the ground that will probably get filled up with freshwater (eg a lake)or saltwater
  4. 4. 3 Main types of volcanic cones• Scoria Cone (or cinder cone)• Shield Volcano• Stratovolcano (or composite cone)
  5. 5. Scoria Cone• Otherwise known as a cinder cone• Sides are quite straight with steep slopes• Large summit crater• The lava and tephra are usually basalt (or sometimes andesitic) which means it is quite runny
  6. 6. Scoria Cone continued• The eruption type is usually Strombolian which means it has fire fountains
  7. 7. Strombolian Eruption
  8. 8. Scoria Cone continued• A good example around Auckland is Maungawhau (Mt Eden) – steep, straight sides, crater in centre
  9. 9. Shield Volcano• Very gentle slopes; convex upward• Basalt lava flows - the lava flows easily away from the vent in large sheets, or follows existing stream valleys• Sometimes caves or tubes form in the lava, other times large columnar basalt formations
  10. 10. Shield Volcano continued• The eruption type is known as hawaiian,• producing lava flows known as aa or pahoehoe
  11. 11. Shield Volcano continued• Rangitoto is a good example of this type of volcano• Gentle slopes • “Aa” lava flow on Rangitoto
  12. 12. Stratovolcano or Composite Cone• Gentle lower slopes, but steep upper slopes; concave upward;• small summit crater• Highly variable lava types; alternating basaltic to rhyolitic lava and tephra with an overall andesitic composition.• This means that the lava often has a lot of trapped gas, so it is very sticky• The cone is built up over a long period of time by many eruptions of various types
  13. 13. Stratovolcano continued• This eruption type is known as Plinian or Vesuvian• These eruptions can be huge, long-lasting and extremely dangerous
  14. 14. Stratovolcano continued• When these volcanoes erupt they emit volcanic products that also have major impacts on the land and natural environment:• Pyroclastic flows• Lahars• Ash showers• In New Zealand volcanic activity has built up a huge volcanic plateau (area of upraised land) in the Central North Island.
  15. 15. Pyroclastic flows• huge clouds of ash, rock and hot gas that sweep downhill at incredible speed, flattening anything in their way
  16. 16. Lahars• A flow of liquid mud down a mountain or valley• NZ’s most famous is the Whangehu River lahar, Christmas Eve 1953, causing the Tangiwai Disaster
  17. 17. Ash showers• Thick layers of gritty, acidic volcanic ash fall in a thick blanket, choking the landscape
  18. 18. Craters• A caldera forms when a huge stratovolcano collapses in on itself after a major eruption sequence, creating a massive crater• Usually this fills with water to form a lake• Rotorua and Taupo both formed in this way
  19. 19. Lake Taupo – a caldera
  20. 20. Maar• A crater caused by a phreato-magmatic eruption• This is when hot magma encounters groundwater and explodes out of the ground• Auckland has several examples, such as Lake Pupuke, Tank Farm, Onepoto Basin, Panmure Basin and Orakei Basin• A maar is often surrounded by a tuff ring = a ring around the edge of the crater made of layers of ash, soil and scoria• Maars usually fill up with freshwater or seawater
  21. 21. 3D map of Auckland volcanoes
  22. 22. A really useful website about volcanic eruptions • http://www.squidoo.com/volcano-glossary

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