volcanoes - natural hazards

• natural hazards


  any natural event that impacts humans in a negative way such as death and damage to property.
• Tectonic hazards

  • earthquakes
  • volcanic eruptions
  • tsunamis
• weather hazards

  • tropical storms (typhoons, hurricanes, cyclones)
  • flooding
  • drought
• Factors affecting hazard risk

  • population density
  • poverty
  • farming
  • climate change
• natural event

  is a natural event like a earthquake but does not affect human activity therefore there is no hazard/risk.
• Divergent plate boundary


  when 2 tectonic plates move away from each other.

  e.g. Pacific and Nazca plate
• Convergent plate boundary 


  when 2 tectonic plates move towards each other.

  e.g. Pacific and Indo-Australian plate
• Transform plate boundary 


  when 2 tectonic plates slide past each other in opposite directions or the same direction but at different speeds.

  e.g. Pacific and North America plate
• Cross section of the earth

  Consists of crust/lithosphere, mantle, molten outer core, solid inner core
• Crust

  • keeps the Earth's temperature stable
  • it is made of different materials like granite and basalt
  • thinnest layer and is around 10-80km thick
• Mantle

  • made up of semi-molten rock called magma
  • makes up 85% of the earth's weight
  • largest layer and is around 3000km thick
• Molten outer core

  • made up of liquid iron and nickel
  • helps aid the movement of the tectonic plates
  • controls the earth's magnetic field
• Solid inner core

  • it is 2400km wide (almost size of the moon)
  • 5000 Celsius hot
  • it is solid from the surrounding pressure
• Continental drift


  a theory Alfred Wegener created where the all the continents were connected.

  • coal was a type of rock which was distributed all around the world formed in prehistoric climatic conditions.
  • mesosaurus fossils (freshwater dinosaur) were found in the coast of South America and Africa - which led to the belief they were once connected.
• Lava


  when magma is no longer in the mantle and is above the earth's surface.
• convection current theory


  magma from the mantle rises upwards because it is hot, as it rises towards the crust it cools down and sinks back to the core (where it is reheated). The repeated process causes circular motions called convection cells.

  • when magma is moving outward creates divergent plate boundaries (constructive)
  • when the magma is moving inwards it causes convergent plate boundaries (destructive)
• slab pull and ridge push


  Slab pull is when the plate is subducted, the weight of the plate pulls itself into the mantle.

  Ridge push is where magma erupts from a rip in the crust and pushes the plates away from each other.

  These 2 mechanisms happen at the same time to help move the plates.
• Destructive plate margin


  Happens at a convergent plate boundary, where the younger but heavier oceanic plate is subducted beneath the lighter but older continental plate when the 2 plates move towards each other.

  Forms composite volcanoes, prone to volcanic eruptions and earthquakes.
• Constructive plate margin 


  Happens at a divergent plate boundary, where 2 tectonic plates move away from each other causing magma to rise to the surface through gap between the splitting plates.

  Forms shield volcanoes, prone to volcanic eruptions and earthquakes.
• Transform plate margin


  Happens at a conservative plate boundary, where the plates move side by side to each other, no new land is created.

  Prone to earthquakes.
• Collision plate margin


  Mountains are formed as 2 continental plates slam into each other.
• Shield volcano

  • low, mound shaped dome
  • wide base
  • gentle relief
  • constructive plate margins (hot spots)
  • fast and runny lava type (due to less silica/sand)
  • hotter lava than composite
  • quite frequent eruptions
  • less violent eruptions
  • Mauna Lao, Hawaii
• Composite volcano

  • tall and pointy shaped
  • narrower base
  • steep relief
  • destructive plate margins
  • slower and sticky lava type (due to more silica)
  • cooler lava than shield
  • less frequent eruptions
  • more violent eruptions
  • Mt.Mayon, Philippines
• Why does a volcano erupt?

  1. an oceanic and continental collide each other in a destructive plate margin.
  2. As the oceanic plate is being subducted, it melts into magma and builds up pressure under the continental plate causing the magma to force through the cracks.
  3. Overtime, magma builds up inside a plate forming a huge and pressurised magma chamber.
  4. The magma nears the surface of the main vent and eventually burst through the crust resulting in an eruption.
  5. Many eruptions happen over time, new layers of ash and lava form on the sides, increasing its size.
• Benefits of living in tectonically active areas.

  • Fat - farming
  • Mothers - mining
  • Eat - energy
  • Their - tourism
  • Children - constructions
• Volcanic hazards

  • tephra and ash - debris like lava bombs which are released from volcanoes
  • volcanic gases - carbon dioxide and sulphur dioxide
  • lava flow - magma which is on the surface of the crust
  • pyroclastic flow - a very hot mixture of rock, gas and ash which travels rapid downhill
  • lahars - very cold or hot mixtures of slow moving mud containing debris
  • tsunamis - series of enormous ocean waves
• Tephra and ash


  a volcanic hazard where debris produced by a volcano.

  • the ash blocks the sun causing it to be very dark, it obscures roads and causes traffic whilst people are evacuating.
  • ash smothers on the leaves of plants which destroys crops and trees as it stops them from photosynthesising.
  • ash is very heavy and when settles on buildings can cause it to collapse.
  • ash is made of small bits of rock and glass, breathing it in can serrate your lungs causing them to bleed.
• Volcanic gases


  a volcanic hazard where gas like carbon dioxide, sulphur dioxide, hydrogen fluoride is produced by a volcano

  • sulphur dioxide can condense into acid rain which can damage buildings and crops (leading to crop failure).
  • organisms exposed to volcanic gases through contact of skin, eyes or lungs can cause irritation or kill you.
  • volcanic gases can suffocate organisms (happens in Lake Nyos).
• Lava flow


  a volcanic hazard, lava with low concentrations of silica usually flow faster therefore it allows less time for people to be evacuated posing a greater risk.

  lava flow destroys everything in its path like buildings and roads.
• Pyroclastic flows


  a volcanic hazard where very hot dense mixtures of rock fragments, gas and ash travels rapidly downhill. they are extremely destructive and deadly because of its high temperature and mobility. It will carbonise living organisms, an example which has happened in Pompeii.
• Lahars


  a volcanic hazard where usually very hot or cold mixtures of mud, debris and rock fragments flow down the slopes of the volcano entering a river valley. They are triggered after volcanic eruptions and can solidify like concrete.
• Tsunamis


  a series of enormous ocean waves caused by earthquakes, underwater landslides, volcanic eruptions or asteroids.
• Farming (benefit in tectonic areas)


  Lava weathers over time to improve land fertility which encourages agriculture, for example rice, tea and coffee made in Indonesia. As ash breaks down it releases minerals and nutrients acting as a natural fertiliser for plants.
• Mining (benefit in tectonic active areas)

  lots of raw sulphur is produced. and many raw materials and precious metals like copper and diamonds are located in South Africa (Mt.Kimberly )
• Energy (benefit in tectonic active areas)


  25% of Iceland's energy is geothermal which is used for heating (underfloor heating in streets), hot water and agriculture.

  Heat from the earth is converted to electricity by turbines.
• Tourism (benefit it tectonic active areas)


  Also known as disaster tourism, attracts people after an natural event. Mt St Helens has 3 million visitors a year after it has erupted creating a huge crater.
• Construction (benefit in tectonic active areas)


  A lot of rocks and materials are erupted out of the volcano, like granite which is used for building walls.