Tectonic Hazards

• Lithosphere

  Includes the crust and the top layer of the mantle, it is about 80-100km thick (thinner under the oceans). This part is broken up into tectonic plates which float on the asthenosphere below
• Asthenosphere


  A denser, more mobile layer in the upper part of the mantle (100-300km deep). The temperature is much higher here so the rock is partially melted allowing plate movement
• The lithosphere and asthenosphere make up the upper mantle and are involved in tectonic activity
• Crust

  • Thinnest layer
  • Two types: Oceanic (ocean) - thin 5-8km and is denser (heavier) and made of basaltic rock, Continental (land) - 30 - 40km, however thickness varies, lighter as it's made of granite rock
• Mantle

  • Thickest layer - nearly 2,900km
  • Temperature ranges from 1000°C (near the crust) to 3,700°C (near the core)
  • Can be divided into two layers: Upper mantle is mostly solid and slow moving, Lower mantle - solid, it gets hotter and denser with depth
• Continental crust

  Thicker and lighter than oceanic crust
• Oceanic crust

  Thinner and denser than continental crust
• Continental lithosphere

  Includes the continental crust and upper mantle
• Oceanic lithosphere

  Includes the oceanic crust and upper mantle
• Core

  • Centre of the Earth
  • Very hot and dense
  • Two types: Outer Core - Hot (4,500-5,000°C), made of iron and nickel, Inner core - Hot (6000°C), solid ball of iron and nickel
• What drives movement in the mantle

  1. Rock is heated in the lower mantle and rises

  2. When it reaches the asthenosphere it cools and is forced sideways by the lithosphere above

  3. It continues to cool and sinks back towards the core

  4. This process continues as it's reheated by the core
• Convection currents

  The driving force behind tectonic plate movement
• Convection currents

  • Move in a circular motion
• Tectonic plates

  Large areas of rock that make up the Earth's crust
• Tectonic plates are sometimes called lithospheric plates
• Tectonic plates

  • They float on the asthenosphere in the mantle below
  • They are moved by the convection currents acting in the mantle
• How tectonic plates move

  Driven by the convection currents in the mantle
• Convection currents in the mantle

  Give us different types of plate boundaries
• Different types of plate boundaries

  Can lead to earthquakes, volcanoes etc.
• Types of plate boundaries

  • All controlled by the convection currents in the mantle
• Plate boundaries

  • Different boundaries give different features
• Volcanoes and earthquakes

  Tend to be found along plate boundaries
• Types of Plate Boundaries

  • Convergent
  • Divergent
  • Conservative
• Convergent Boundary

  • Trench
  • Compression due to collision of plates
  • Volcanoes and earthquakes
• Convergent Boundary

  • Chile Trench
• Divergent Boundary

  • Convection ends and the plates move apart
  • Upwelling of magma
• Volcanoes and earthquakes tend to be found along plate boundaries
• Volcanoes

  Formed when molten rock from a magma chamber inside the earth erupts through a vent in the lithosphere
• Magma

  Molten rock below the surface
• Lava

  Molten rock when it erupts
• What volcanoes erupt

  • Lava
  • Steam
  • Gas
  • Ash
• Main types of volcanoes

  • Type 1
  • Type 2
• Composite Volcanoes

  Formed along convergent plate boundaries
• Composite Volcanoes

  • Tall, steep sided, conical and have a narrow base
  • Made of alternating layers of ash and lava
• Andesitic lava

  Has a high silica content making it more viscous (so it runs like sticky toffee), it is unable to travel very far
• Eruptions of Composite Volcanoes

  • Infrequent but violent
• Primary hazards of Composite Volcanoes

  • Lava bombs
  • Pyroclastic flows
• Lahars


  Mudflows (secondary hazard of Composite Volcanoes)
• Shield Volcanoes

  Formed along divergent plate boundaries and hotspots
• Shield Volcanoes

  • Gently sloping domes with a wide base
  • Made of lava only
  • Basaltic lava is erupted - low in silica so it is less viscous (so it runs like runny honey), it is able to travel long distances before cooling
  • Eruptions tend to be frequent and gentle