hazardousness


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  • Volcanoes: why are some more hazardous than others?
    • Viscosity of magma
      • 3 factors that determine the viscosity of magma
        • Temperature: higher temp means loer density of magma resulting in it to flow easily
        • Dissolved gases: greater the amount, the more fluid the magma
        • Chemistry: higher silica content, the more viscous the magma
    • Plate margins
      • exceptions
        • Hotspots, eg Hawaian volcanoes result from isolated plumesof rising magma which is basic
    • Explosiveness of eruption
      • measured by Volcanic Explosiveness Index (VEI). 0 for non-explosive to 8 for very explosive
    • The materials ejected
    • Proximity to population centres
      • Volcanoes located in areas of dense population or close to major cities are more hazardous than those located in remote region.
        • Mt Versuvius is a few kilometers away from Naples, Italy, which has a population of over 1 million and will erupt again in the future.
        • Japan: space is limited so there is little choice.
    • Frequency of eruptions and perception of risk
      • The frequencyof eruptions has an impact on peoples perceptions of the hazard
        • Mt Etna erupts frequently but is promoted by local tourism. due to the nature of the eruption, the volcano only poses a minor threat to property which is why hotels/cafes are set up on the flanks. these are considered worth the risk to maintain after they periodically get damaged.
    • Prediction, forecasts and reactions
      • Active volcanoes are monitored for infrared radiation, which indicates rising magma and ground instruments measure gas emissions. this enables scientists to predict eruptions and governments can evacuate areas. hazard maps can also be drawn and used to show who's at risk.
  • Constructive or destructive?
    • Constructive /divergent: basic magma is produced due to the partial melting of the mantle deep below the surface. has a low viscosity, meaning it flows easily.
    • Destructive/ convergent: an acidic magma chamber can form from the melting of the subducted plate. Very viscous and resistant to flow, build up of pressure... violent and dangerous eruptions involving ash and pyroclastics.
    • Plate margins
      • exceptions
        • Hotspots, eg Hawaian volcanoes result from isolated plumesof rising magma which is basic

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