Vulcanicity

• What are the layers of the earth?

  • inner core
  • outer core
  • mantle
  • asthenosphere
  • lithosphere
  • crust
• describe the inner core

  • 1270km thick
  • iron/nickel
  • solid
  • 5000 degrees celsius
  • heat generated by radioactive decay
• Describe the outer core

  • semi molten
  • iron/nickel
• Describe the mantle

  • 2900km thick
  • silicate rocks
• What is the asthenosphere?

  the semi molten layer above the mantle
• What is the lithosphere?

  crust + upper mantle
• Describe continental crust

  • thicker
  • less dense
  • granitic
  • silica/magnesiun
• Describe oceanic crust

  • younger
  • densser
  • thinner
  • basaltic
  • silica/aluminium
• What is the evidence for plate tectonic theory?

  • jigsaw theory - continents match up
  • mountain ranges match up between continents
  • fossils e.g trillabites
  • rock type
  • pollen type (different latitudes effect vegetation type)
• What is the theory of plate tectonics?

  the idea that the earths lithosphere is made up of plates that move
• Describe the process of convection currents

  1. the earth’s mantle is hottest closest to the core - this heats the lower parts of the asthenosphere which causes the magma to heat up, become less dense, and rise
  2. as the magma moves towards the top of the asthenosphere it cools, becomes less dense and sinks
  3. the circular movement of the magma is called convection currents - this drags on the base of tectonic plate, causing them to move
• Describe the process of slab pull

  1. at destructive plate margins, denser crust is subducted under the less dense crust
  2. the sinking plate pulls the rest of the plate towards the boundary and gravity causes it to slide downwards
• Describe the process of ridge push

  1. at constructive plate margins, magma rises to the surface and forms a new crust - it heats surrounding rocks which expand and rise above surface of crus, forming a slope
  2. new crust cools and becomes denser - gravity causes denser rock to move downslope, away from the plate margin
  3. this puts pressure on the plates - causing them to move apart
• Describe sea floor spreading

  1. tectonic plates diverge - magma rises up to fill gap - cools to form new crust
  2. over time new crust dragged apart and more crust forms between
  3. if this occurs under the sea then the sea floor gets wider
  4. this creates mid ocean ridges
• Describe the characteristic processes at conservative plate margins ?

  Tectonic plates sliding next to each other - can slide in one direction or different directions - can be at different speeds
• What are the characteristic landforms at conservative plate boundaries?

  no volcanoes, shallow focus earthquakes
• What are examples of conservative plate boundaries?

  • Haiti - caribbean plate and North American plate
  • san Andrea’s fault in California - many earthquakes
• Describe the characteristic processes at Oceanic destructive plate margins

  • converging plates
  • faster/denser plate subducts
• What are characteristic landforms at oceanic destructive plate margins?

  • deep sea trenches e.g marianna trench
  • volcanic island arch
  • explosive volcanoes
  • intermediate and deep focus earthquakes
• What are named examples of oceanic destructive plate boundaries?

  japan and Aleutian Islands - both have curved lines of volcanoes
• Describe the characteristic processes at destructive continental meets oceanic plates

  • oceanic subducts - area of subduction creates ocean trench
  • when plate melts it forces molten material to the surface - volcanoes
• What are characteristic landforms at oceanic meets continental destructive plate boundaries

  • composite volcanoes
  • high magnitude earthquakes
  • fold mountain chains
• What are named examples of oceanic meets continental destructive plate boundaries?

  chile - Nazca plate subductws under NA plate
• Describe the characteristic processes at continental destructive plate margins

  • neither subducts as similar density - crumple upwards to form fold mountains
• What are characteristic landforms at continental destructive plate margins?

  fold mountains, no volcanoes, violent earthquakes
• What are named examples of continental destructive plate margins?

  the Himalayas
• Describe the characteristic processes at Constructive plate margins

  • two plates diverge
  • mantle under pressure -plates move - pressure released at margin - release of pressure melts mangle - magma
  • some parts move away faster
• What is the benoiff zone?

  where the plate melts after it is subducted at a destructive plate boundary
• What are characteristic landforms at constructive plate boundaries?

  shield volcanoes, ocean ridges, rift valleys, earthquakes
• What is a named example of a constructive plate margin?

  iceland - where NA and SA plates diverge
• How are magma plumes formed?

  1. radioactive decay heat’s core and mantle
  2. decay is concentrated - hotspots form
  3. hotspots heat lower mantle - creating localised thermal currents - magma plumes rise vertically
  4. plumes rise within centre of plates and burn through lithosphere to create volcanic activity on surface
• Describe shield volcanoes

  • basaltic lava - low viscosity
  • effusive eruptions
  • low magnitude
  • constructive plate margins
  • gentle slopes
  • e.g. Maunakea and Maunaloa around Hawaii
• Describe composite volcanoes (stratovolcanoes)

  • andesitic/rhyolitic lava - viscous
  • intermittent
  • explosive eruptions - gas building up in viscous magma
  • steep sides/cone shaped
• Describe lava domes

  • large dome shaped mass of material
  • viscous lava cannot flow away from vent easily - piles on top of vent
• what does viscous mean?

  thick and sticky
• Describe a caldera

  • magma stored beneath volcano in magma chamber - roof of chamber collapses during explosion - creates depression with steep walls
• What is an example of a caldera?

  Mt Tambora 1815 - following year called year without a summer as there was a global blackout and global temps dropped by 1 degree
• How much volcanic activity occurs in the ring of fire?

  75%
• What are primary hazards of volcanic eruptions?

  pyroclastic flows, lava flows, tephra
• What are the secondary hazards from volcanic activity?

  volcanic gases, lahars, acid rain