Tectonic hazards

• Earth's surface is constantly moving as a result of the physical processes that occur beneath the surface. These processes lead to tectonic hazards such as earthquakes and volcanic eruptions
• Structure of the Earth

  • Solid inner core
  • Liquid outer core
  • Mantle
  • Crust
• The continental crust is thicker (30-60 km) and less dense, so it doesn't subduct
• The oceanic crust is thinner (5-30 km) and very dense, so it does subduct
• Plate tectonics theory


  1. Convection currents

  2. Slab pull

  3. Ridge push
• The global distribution of earthquakes and volcanic eruptions is concentrated at plate margins
• Some volcanoes form in the middle of plates on hot spots
• San Francisco sits on a conservative plate margin where the North American Plate and Pacific Plate move alongside each other, so there are no volcanoes
• Types of plate margin

  • Destructive
  • Constructive
  • Conservative
• Destructive plate margin


  • Plates move towards each other
  • Oceanic plate subducts beneath continental plate
  • Forms fold mountains
• Destructive plate margin


  Causes earthquakes and volcanic eruptions
• Constructive plate margin


  • Plates move away from each other
  • Hot fluid magma rises through cracks
  • Forms rift valleys and mid-ocean ridges
• Constructive plate margin


  Causes earthquakes and volcanic eruptions
• Conservative plate margin


  • Plates slide past each other
  • Friction builds up until rocks fracture
• Conservative plate margin


  Causes earthquakes but no volcanic eruptions
• Tectonic hazards


  Earthquakes and volcanic eruptions
• Earth's surface


  • Constantly moving as a result of the physical processes that lie beneath the surface
• Layers of the Earth


  • Inner core
  • Outer core
  • Mantle
• Inner core

  The solid centre of the Earth made up of iron and nickel with temperatures up to 5,500
• Outer core


  The liquid layer that surrounds the inner core. It is also made of iron and nickel
• Mantle


  The Earth's thickest layer. It can be split into further layers such as the asthenosphere (the semi-molten, upper layer of the mantel) and lithosphere (the rigid upper mantle and crust)
• Oceanic crust subducts underneath continental crust because oceanic crust is denser due to the heavier minerals that are part of its composition, whereas the continental crust is less dense due to it being more silica rich which is a lighter mineral
• focus is the point at wich an earthquake begins
• epicentre is the point at which the seismic waves reach the surface of the ground
• Earthquakes are formed at destructive boundaries due to pressure building and rocks fracturing
• Volcanic eruptions happen at destructive plate boundaries because newly formed magma rises through the crust
• composite volcanoes are formed at destructive boundaries
• Earthquakes form at constructive boundaries due to stretching and fracturing of rock at plate boundary
• Volcanic eruptions happen at constructive boundaries because fast flowing lava erupts gently upwards
• shield volcanoes form at constructive boundaries
• earthquakes form at conservative boundaries because plates moving builds up friction and plates lock. pressure builds up until rocks fracture