volcanic activity

  • Created by: beaw18
  • Created on: 11-06-19 17:49

explosive eruptions

  • location - convergent plate boundaries
  • type of lava - rhyolite (more acidic) and andesite (less acidic)
  • lava characteristics - acidic, high viscosity, lowered temp at eruption
  • style of eruption - violent bursting of gas bubbles when magma reaches surface; highly explosive, vent and top of cone often shattered
  • materials erupted - gas, dust, ash, lava bombs, tephra
  • shape of volcano - steep-sided strato, caldera
  • products - composite cone volcanoes made up of layers of ash and acidic lava. internal lava flows form sills and dykes. the acidic magma does not flow easily and solidified magma plugs vents. calderas (deep craters) when the cone is destroyed by an explosive eruption
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effusive eruption

  • location - divergent plate boundaries
  • type of lava - basalt
  • lava characteristics - basic (low silica), low viscosity, higher temp at eruption
  • style of eruption - gas bubbles expand freely; limited explosive force
  • materials erupted - gas, lava flows
  • frequency or eruption - tend to be more frequent; an eruption can continue for many months
  • shape of volcano - gently sloping sides, shield volcanoes, lava plateaux when eruption from multiple fissures
  • products - basic magma flows freely and covers large areas: flood basalts
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hot spots

  • volcanic eruptions which do not occur at plate boundaries are associated with 'hot spots'
  • places where plumes of magma rise from the mantle and erupt at the surface
  • usually associated with intense volcanic activity and eruptions of basaltic lava
  • the Hawaiian chain of volcanic islands is an example
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types of volcano

  • icelandic lava eruptions: persistent fissure eruption. basaltic lava build up horizontal planes
  • hawaiian eruptions: more noticeable central activity than icelandic, runny basaltic lava, gases escape. occasional pyroclastic activity
  • strombolian eruptions: frequent gas explosions, blasts fragments of runny lava into air to form cones. large quantities of pyroclastic rock thrown out. white cloud of steam from crater
  • vulcanic eruptions: violent gas explosions blast sticky/cooled lava. fragments build cones of ash and pumice. viscous lava which solidifies rapidly after explosion. often explosion clears blocked vent - spews large quantities of volcanic ash into atmosphere
  • versuvian eruption: powerful blasts of gas pushing ash clouds high into the sky. more violent than vulcanic. lava flows occur. ashfall covers surrounding areas
  • plinian eruption: gas rushes through sticky lava and blasts ash and fragments into the sky in huge explosio. violent eruptions create immense clouds of gas and volcanic debris several kilometers thick. gas clouds and lava can rush down slopes. part of volcano may be blasted away in eruption
  • super volcanoes: volcanoes that erupt more than 1000 km cubed of material in a single event. example: Yellowstone's super volcano
  • volcanic explosivity index (VEI): amount of material erupted (magnitude) and the speed it is erupted (intensity) combined. 0- least, 8- most
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volcanic hazards - lava flows

  • flows or streams of molten rock that pour from erupting vent
  • speed of lava movement depends on:
    • type of lava - basaltic is free-flowing and runs considerable distances, acidic lava is thick and does not flow easily
    • viscosity
    • steepness of the ground
    • whether lava flows as a broad sheet, confined channel or a lava tube
  • highly destructive and will burn, bury or bulldoze infrastructure, property, natural vegetation and agricultural land
  • usually slow moving, and therefore easily controllable by road closures and fire services
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volcanic hazards - pyroclastic flows

  • flows of gas and tephra which are extremely hot (over 500 degrees)
  • flow down the side volcano at speeds of over 100 km/h
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volcanic hazards - gas emissions

  • carbon dioxide, carbon monoxide, sulphur dioxide and chlorine escape through fumaroles (openings in or near a volcano, through which hot sulphurous gases escape)
  • when sulphur dioxide combines with water, acid rain is produced
  • this leads to weathering and pollution
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volcanic hazards - tephra

  • volcanic bombs and ash ejected into the atmosphere. size ranges from ash to larger bombs
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volcanic hazards - lahars and flooding

  • lahars are a type of mud flow
    • snow and ice on volcano summit melt during eruption
    • rock ash and soil mix together and destroy and bury anything in the path of the rapid flow of material as they follow valleys
  • melting of snow and ice associated with volcanic eruptions can lead to flooding
  • in iceland these are known as jölkulhlaups
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volcanic hazards - tsunamis

  • violent eruption of an island/coastal volcano can displace oceanic water when the lava drops in
  • this can cause a tsunami
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