Tectonic hazards

• This work by PMT Education is licensed under CC BY-NC-ND 4.0
• Tectonic hazard


  Hazards caused by the physical processes that tectonic plates undergo, such as earthquakes and volcanic eruptions
• Tectonic plates


  • They are huge slabs of rock that make up the Earth's crust
  • They range from tens to hundreds of kilometres thick
  • They are either continental crust or oceanic crust
• Convection currents in the Earth's mantle

  1. The core heats up the magma

  2. Hot magma rises upwards

  3. Magma cools and sinks back down

  4. The cycle continues

  5. Plates are pushed and pulled by the convection currents
• Plate tectonic movement has been happening for hundreds of millions (if not billions) of years
• The continents we see today are not still, plate tectonic movement happens all the time
• The Atlantic Ocean is growing, and we are moving away from the USA about 2-5cm a year
• Tectonic hazards


  • They occur along plate margins
  • There is a clear pattern of volcano and earthquake distribution along plate margins
• The Ring of Fire


  • An area with high volcanic and earthquake activity located in the Pacific Ocean
• Earthquakes occur along plate margins


  Due to plate movements causing vibrations
• Volcanoes occur along certain plate margins


  As magma feeds volcanoes and can get to the surface
• Volcanoes do not always occur on plate margins, they can also occur at hotspots where magma breaks through the middle of a plate
• Plate margins


  • Constructive: Plates move away from each other
  • Destructive: Plates move towards each other
  • Conservative: Plates move alongside each other
• Constructive plate margins


  1. Magma rises in the gap between the separating plates

  2. Lava pours out onto the surface, forming volcanoes

  3. This process can happen on continental or oceanic crust

  4. New land is formed on the ocean floor through sea floor spreading
• Destructive plate margins


  1. One plate subducts (sinks) below the other into the mantle

  2. Friction between the plates causes strong, deep earthquakes

  3. The subducting plate is melted, creating magma that causes volcanic eruptions
• On continental crust, a constructive plate margin causes huge fractures in the land, creating a rift valley
• Conservative plate margins


  1. Parallel plates move in different directions or at different speeds

  2. Friction builds up over time and is then released suddenly, causing earthquakes

  3. On oceanic crust, this can displace water and cause tsunamis
• There are no volcanoes on conservative plate margins because no magma is being generated
• Primary effects


  The direct effects caused by the natural hazard itself
• Secondary effects


  The effects that are a result of the primary effects
• Immediate responses


  Actions taken as soon as the hazard happens and in its immediate aftermath, to reduce loss of life and provide vital aid
• Long-term responses


  Actions taken after the immediate responses, to restore normality and reduce risk in the future
• In 2015, it was reported that 2.7 billion people live in seismically active areas and more than 400 million people live near one of the 220 most dangerous volcanoes
• There are many reasons why people choose to live in hazardous places, including economic benefits, the risk seeming small compared to the advantages, or not being able to afford to move
• Tectonic hazards can bring positive effects, such as volcanic ash enriching soil for agriculture
• Many people choose to live in hazardous places despite the very real risk that exists when living in these areas
• Reasons why people live in hazardous places


  • It may be economically beneficial
  • The risk may seem small in comparison to the advantages
  • Some may not be able to afford to move
• Tectonic hazards


  Hazards related to the movement of tectonic plates
• Volcanic eruptions emit ash and material into the air, which eventually settles on the surrounding slopes and its base
• Volcanic material contains lots of nutrients that make the soils fertile
• Agriculture is a major source of income for people living in these areas
• Hazardous areas with a well developed tourism industry

  • Iceland
  • Volcanic areas
• There have been major advances in monitoring technology for tectonic hazards, which have enabled warning systems to be developed
• Large earthquakes in the ocean can also be monitored to tell people when there will be a tsunami
• Building designs to withstand tectonic hazards


  • Buildings in Japan with carbon fibre 'curtains' to minimise earthquake shaking effects
• Some of the largest cities are near tectonic margins
• The last time there was a major earthquake on the San Andreas Fault in California was 1857
• Mount Vesuvius in Italy has not erupted since 1944 so people do not see it as a high risk
• In less wealthy countries, the top priority for many households is having an income, food, and necessities, so the risk of a hazard is a less pressing issue
• In some countries there is a lack of education about the tectonic hazards that pose a risk to the population