vulcanicity

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  • vulcanicity
    • minor forms of extrusive activity
      • hot springs and boiling mud
        • a release of hot water from under the surface without a build up of pressure.
          • often form pools
            • can contain lots of dissolved minerals
          • like geysers water seeps underground and is heated by vulconicty
        • mud pools formed through the water emerging in soft rock
          • hydrogen sulphide created in steam making it acidic thus dissolving the surrounding rock further
            • makes clay and mud that mix with water making the mud pool
              • e.g.: blue lagoon spa iceland
      • geysers
        • explosive plumes of water and steam erupting from the ground
          • due to water seeping through fissures collected in caverns
            • heated by vulconicity through hot rock from magama intrusions
              • water reaches boiling point resulting into a build up of pressure
                • the steam created rises through the vent thus making the geyser
                  • the vent then refills with water and the process starts again
        • e.g.: the great geyser in Iceland
      • fumeroles
        • patches of escaping gas  from small vents can deposite sulphur around its edge
          • gas usually co2 or hydrogen sulphide
        • fromed by boiling water below the surface releasing steam or when magma releases vapours such as so2
          • gases escape through the surface through the vents
          • feature of both active and dormant volcanoes
    • volcano hazards
      • factors effecting hazard
        • the direction of blast
        • the energy of blast
        • type of eruption explosive/ effusive
        • lava viscosity (thickness)
        • surface conditions
      • lava flows
        • Generally not dangerous though causes serious damage though one example of a stpsided lava flow Myirangones in the Congo.
      • tephra
        • solid material blasted into the atmosphere (blocks or lava bombs) that are larger than 64mm can get to 8-30 tonnes smaller stuff is lapilli and fine stuff smaller than 2mm is ash
      • gasses
        • gasses emitted from an eruption can be toxic/ corrosive and flow down the volcano acting as a silent killer a common toxic a=gas is CO2 can lead to form acid rain
      • pyroclastic flows
        • avalanches of hot rock and ash that can reach speeds of 450mph can be formed from a dome collapse or a ash cloud loosing heat and collapsing
      • explosive blasts
        • measured on the volcanic explosion index (EPI)
      • lahas
        • mudflows from melted ice/snow can be fast flowing  and travel along valleys heavy rain too can form lahars from the steam of a volcanic eruption
      • tsnamiis
        • a section of volcano falling into the sea displacing it
      • flooding
        • melting glaciers/ snow can carry huge blocks of ice
      • climate change
        • volcanic debris can reduce global tempratures
    • forms of intrusive activity
      • batholiths
        • a cooled magma chamber made up from igneous rock from the cooling of magma
        • domed shape hundreds km in diameter the extreme heat of its formation alters the surrounding rock through metamorphism changing the rock type e.g. marble is metamorphosed lime stone
        • e.g. Dartmoor and the isle of arran
      • sills
        • horizontal inclined magma intrusion along the bedding planes of rock
          • formed like the dyke and also like the dyke surrounding rock can be eroded away revealing the more resilient igneous rock exposed on the surface
      • dykes
        • vertical crack or fissure in filled with magma that has solidified
          • magma exploits any weaknesses in the rock
            • when it intrudes into the lithosphere cutting through the country (natural rock) it cools
              • the magma crystaslises forming igneous rock
                • surrounding rock types can erode over time leaving the more resilient dyke exposed on the surface
    • the forming of magma
      • hydration melting where water escapes as steam that lowers the melting temperature of the overlying rock
      • decompression melting due to a drop in pressure allowing the rock to melt

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