Vulcanicity

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  • Created by: Labake
  • Created on: 02-11-14 17:55
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  • Vulcanicity
    • Forms of Intrusive Activity
      • Dykes
        • Forms when magma solidifies in a vertical crack/fissure
        • Rock cools and crystallises slowly= large grained rock like granite/dolerite (horizonal cooling cracks)
        • Dyke cuts across bedding planes on country rock at a right angle
        • E.g. Isle of Skye
      • Sills
        • Horizontal intrusion along horizontal bedding planes e.g. sedimentary sandstone
        • Isle of Skye- Kilt Rock and Whin Sill
        • Rock cools and crystallises slowly= large grained rock (granite) with vertical cooling cracks
      • Batholiths
        • Deep below surface where large masses of magma cool, crystallise and solidify
        • Rock cools slowly= course grained igneous rock e.g. granite
        • Dome shaped and up to 100's of km diameter
          • Largeness, extreme heat and pressure alter surrounding rock
            • Called Metamorphism- rock affected called metamorphic aureole e.g. marble
        • Can be exposed on surface from erosion e.g. Isle of Arran
        • Batholiths feeds dyke/sill an forms smaller dome= laccolith
      • Magma moves into lithosphere by exploiting faults
        • Magma then cools, crystallises and solidifies= igneous rock
          • Forms intrusive features- surounding rock can be worn to expose feature on surface
      • Happens at plate margins and above hot spots
    • Minor forms of Extrusive Activity
      • Geysers
        • Explosive plumes of water and steam erupting from the ground
        • E.g Great Geyser in Iceland
          • Shortlived as groundwater conditions change, vents collapse and new geysers form
        • Surface water seeps down through fissures
          • Collects as conduits in underground caverns
            • Water boils from hot magma intrusions= bubbles
              • Bubbles rise with water to surface and expand closer to surface
                • Bubbles pop, pressure reduced and massive volumes of steam released quickly= explosion
                  • Geysers
                    • Explosive plumes of water and steam erupting from the ground
                    • E.g Great Geyser in Iceland
                      • Shortlived as groundwater conditions change, vents collapse and new geysers form
                    • Surface water seeps down through fissures
                      • Collects as conduits in underground caverns
                        • Water boils from hot magma intrusions= bubbles
                          • Bubbles rise with water to surface and expand closer to surface
                            • Bubbles pop, pressure reduced and massive volumes of steam released quickly= explosion
                        • E.g. Yellowstone
            • E.g. Yellowstone
        • Hot Springs and Boiling Mud
          • Hot spring is a release of hot water from underground to the surface- NOT under pressure
            • Forms pools (acidic to alkali)- near volcanic areas and near boiling point
              • E.g. Blue Lagoon Spa
              • Due to minerals dissolving in the water that seeps out of ground
                • Hot Springs- groundwater heated from hot rock/magma
          • Hot Springs- groundwater heated from hot rock/magma
          • Boiling mid pools= hot springs mix with surface sediment in steamy areas
            • H2S +O2= H2SO4- dissolves rock into clay and silica- mixes with water
        • Fumaroles
          • Patches of escaping steam from small vents in volcanic areas
            • Sometimes with sulphur around edges or a small cone of mineral deposit
            • Steam/CO2/H2S- (H2S = solfatara with sulphur deposits
              • Steam heated from water seeping in from pecipitation
          • Formed when water boils below surface to release steam/ magma degasses with SO2 etc
            • Often formed on volcano fissure when main vent is blocked
      • Major forms of Extrusive Activity
        • Types of Volcanoes
          • See Types of Volcano mindmap
      • Volcanic activity is the escape of magma from the mantle into the lithosphere (intrusive)/ earth's surface (extrusive)
      • Decompression Melting (forming magma)
        • Convection currents draw rock into asthenosphere from lower mantle
          • Pressure drops allowing the rock to melt
            • Happens at constrictive boundaries and Hotspots
      • Hydration Melting (forming magma)
        • In subducting zones where water and other volatiles escape from subducting plate
          • Lowers melting temperature of overlying rock in the lithosphere above

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