Geography - Earthquakes and Volcanos

• What comes out of a volcano

  • Gases
  • Liquids
  • Solids
• Gases emitted by a volcano

  • Water vapor
  • CO2
  • Sulfur dioxide
• Water vapor is the main gas emitted (50-80%)
• Gases can get trapped in viscous (thick) lava, which can lead to explosion
• Magma

  Liquid rock inside the Earth
• Lava

  Liquid rock outside the Earth
• Ash


  Smallest particle (± 4mm) from a volcano

  Ash can stay suspended in the atmosphere for a long time
• Rocks thrown by eruptions are known as ‘volcanic bombs’
• Types of volcanoes

  • Shield volcanoes
  • Stratovolcanoes/Composite
• Shield volcanoes


  • Rise from the deep ocean floor
  • Gentle upper slopes (angle about 5 degrees)
  • Steeper lower slopes (angle about 10 degrees)
  • Little pyroclastic material
• Stratovolcanoes/Composite


  • Steeper slopes than shield
  • More viscous (thicker) lava
  • Alternating layers of lava and pyroclastic material
  • Can remain dormant for hundreds or thousands of years
• Dormant stratovolcanoes can lead to explosive eruptions
• Features of volcanoes


  • Craters
  • Calderas
  • Parasitic cones
  • Lava domes
• Dangers of volcanic eruptions

  • Ash
  • Pyroclastic flow
  • Lateral blast
  • Mudflows (lahars)
  • Volcanic gases
  • Acid rain
  • Post-eruption, famine and disease
  • Tsunamis
  • Lava flows
• Ash can stay in the atmosphere for long periods, affecting planes and buildings (weather)
• Pyroclastic flow


  Mixture of extremely hot and toxic gas, ash, and volcanic bombs
• Lateral blast occurs when a volcano erupts sideways
• Mudflows (lahars)


  Mixture of ash and rainwater that moves quickly down the slopes
• Volcanic gases

  CO2 is non-toxic but can suffocate people; other gases are very toxic
• Acid rain is caused by sulphur dioxide and other gases mixing with raindrops, which can damage crops, buildings, and aquatic life
• Post-eruption, famine, and disease may be difficult to deliver aid due to infrastructure damage
• Lava flows can damage infrastructure but not people
• Reducing risk from volcanic eruptions

  • Lava flow diversion
  • Mudflow barriers
  • Building designs
  • Volcanic monitoring
  • Remote sensing
  • Hazard mapping and planning
• Lava flow diversion

  Mechanical excavators are used to channel lava flows away from buildings
• Mudflow barriers


  Walls are built across valleys to trap mudflows and protect settlements
• Building designs

  Stronger roofs can be built to stop them from collapsing when covered with ash
• Volcanic monitoring


  Measuring features that happen before an eruption (e.g., earthquakes, ground deformation, and gas emissions)
• Remote sensing

  Monitoring the location of ash clouds from satellites is useful for warning aircraft
• Hazard mapping and planning


  Looking at patterns from previous eruptions to predict future eruptions
• Earthquakes happen when two plates try to move past each other, building up pressure along the way
• Causes of earthquakes


  Caused by plate movement, plates move either towards each other, away from each other, or sliding past each other

  When plates stick to each other it builds up pressure, and the pressure is released when the plates break free

  Huge amounts of energy are released

  They send shock waves and vibrations throughout the earth as an earthquake
• When plates stick to each other, it builds up pressure, which is released when the plates break free
• Huge amounts of energy are released during an earthquake
• Earthquakes send shock waves and vibrations throughout the earth
• Focus


  The point at which the earthquake originates
• Epicentre


  The point on the earth’s surface directly above the focus
• Assessing earthquakes


  The effects of an earthquake can be assessed on a 12-point scale
• Mercalli Scale


  Used to show the effects of an earthquake on a map
• Richter Scale


  Measures the total amount of energy released by an earthquake
• Factors affecting earthquake damage

  • Amount of energy released
  • Depth of the focus beneath the surface
  • Density of the population in the area of the earthquake epicentre
  • Building resilience
  • Solid bedrock quality