Tectonics , earthquakes/ volcanoes

• Plate Tectonics


  The study of the structure and movement of the Earth's crust and underlying mantle
• Layers of the Earth


  • Crust
  • Mantle
  • Outer core
  • Inner core
• Crust


  • The outer layer, broken into sections called tectonic plates
  • The thinnest layer and the one which we live on
• Mantle


  • The thickest layer and consists of molten rock
• Outer core


  • Molten and about 3000 degrees C
• Inner core


  • Solid due to the immense pressure and is about 5000 degrees C
  • Consists of iron and nickel
• Tectonic plates


  Sections of the Earth's crust that are slowly moving about
• Plate movement


  1. Convection currents in the mantle distribute the heat from the core

  2. This movement drags the plates in different directions

  3. Responsible for earthquakes and volcanoes
• Over millions of years the land masses have moved around the planet as the tectonic plates shifted about
• Where the different sections of tectonic plate meet the movement causes geographical features such as mountains, volcanoes and earthquakes
• Constructive boundaries


  1. Convection currents in the mantle drag the plates apart

  2. Magma rises to fill the gap and solidifies to form new crust

  3. This creates a ridge that slowly gets wider as the plates continue to separate
• Constructive boundary


  • The Mid-Atlantic Ridge
• Constructive boundary volcanoes


  • Fissure volcanoes which are long cracks, they are less explosive
• Destructive boundaries


  1. Oceanic and continental plates collide

  2. The oceanic plate is denser and so sinks under the continental plate

  3. As the oceanic plate sinks it takes some sand, water and other material from the sea bed with it

  4. This melts and is gaseous which causes it to force its way up to the surface as a volcano

  5. The continental plate crumples at the edge creating fold mountains
• Collision boundary


  1. Convection currents in the mantle pull two plates of continental crust together

  2. Since both crusts are made of the same material and have equal density neither subducts

  3. They crumple up creating fold mountains

  4. There are no volcanoes at these boundaries but earthquakes occur
• Collision boundary


  • The Himalayas
• Shield volcano


  • Gentle sloping, created by basic lava (travels along way before solidifying)
  • Found at constructive boundaries
• Composite volcano


  • Alternating layers of acid lava and rock/ash create the classic conical shape
  • Found at destructive boundaries
• Ash and cinder volcano

  • Alternating layers of ash and cinder compacted
• Fissure volcano


  • Volcanoes running along a crack in the crust, usually a constructive boundary
• Caldera


  • Crater volcano created after volcano collapses in on itself having emptied the magma chamber
• Dome volcano


  • Steep sided volcano created by acid lava which cools before it has travelled far
• Destructive boundary volcanoes are often cone shaped and explosive
• Constructive boundary volcanoes are often more gently sloped and have less violent eruptions
• Volcanoes vary in shape and structure depending on the reason for their existence
• Secondary vents (fumaroles)


  • Occur when magma and gases force their way through weaknesses in the main volcanic structure
• Lava, ash, cinders and smoke may be ejected from the vent
• Negative impacts of volcanic eruptions


  • Lava flows destroy vegetation, buildings and roads
  • Ash can smother plants, cut out light in the atmosphere, disrupt air travel and cause respiration problems for people
  • Eruptions often cause earthquakes as pressure is released
  • Volcanoes with ice near the peak, or crater lakes can cause devastating mud flows as the water mixes with loose ash
  • Gas released from volcanoes can travel down the slopes silently killing people and animals
• Montserrat is an island in the Caribbean that unexpectedly suffered devastating eruptions
• Positive impacts of volcanoes


  • Fertile soils as ash and lava contain many minerals and nutrients that weather to form fertile soils which can be used very effectively for farming
  • Sulphur deposits that can be mined and sold
  • Volcanic scenery, crater lakes, hot springs and geysers that attract tourists and create many job opportunities
• Focus


  The exact point at which the earthquake occurred, often deep in the ground
• Epicentre


  The point on the surface of the earth directly above the focus
• Seismic waves


  The shockwaves that move outwards from the focus, their energy dissipates the further they travel
• Seismometer


  Instrument that measures the magnitude of earthquakes
• Seismograph


  The print out/graph produced by the seismometer
• Richter scale


  The scale traditionally used to record the magnitude of an earthquake
• Moment Magnitude Scale


  The scale often used currently to record the magnitude of earthquakes, more accurate for large earthquakes than the Richter scale