Volcanic hazards

• Volcanoes


  Occur on plate boundaries where plates melt and magma erupts through a plate, or on hotspots
• Volcanic hazards


  • Lava flows
  • Lahars (mudflows)
  • Glacial floods (jökulhlaups)
  • Tephra
  • Toxic gases
  • Acid rain
  • Nuées ardentes/pyroclastic flows
• Lava flows


  • Can flow quickly or slowly depending on viscosity, silica makes lava viscous and slow which is common in explosive eruptions
• Lahars (mudflows)


  • Caused by a number of reasons, usually by melting ice at high latitudes
• Glacial floods (jökulhlaups)


  • When temperatures are high from magma, glaciers or ice sheets at high temperatures quickly melt and a large amount of water is discharged
• Tephra


  Any type of rock that is ejected by a volcano
• Toxic gases


  • Released during some eruptions, even CO₂ can be toxic as it is heavier than oxygen
• Acid rain


  • Caused when gases such as sulfur dioxide are released into the atmosphere
• Nuées ardentes/pyroclastic flows


  • Clouds of burning hot ash and gas that collapses down a volcano at high speeds, average speeds of around 60 mph but can reach 430 mph
• Effects of volcanic hazards

  • Environmental: Ecosystems damaged, wildlife killed
  • Economic: Businesses and industries destroyed or disrupted, jobs lost, profit from tourism industry
  • Social: People killed, homes destroyed, fires, trauma, homelessness
  • Political: Government buildings and other important areas destroyed or disrupted, conflicts concerning government response, food shortages, insurance etc.
• Responses to volcanic hazards

  • Preparedness: Risk assessment and mapping, community education and awareness, early warning systems, evacuation plans and drills
  • Monitoring and Prediction: Volcanic monitoring networks, remote sensing, research and scientific analysis
  • Emergency Response: Activation of emergency response plans, evacuation execution, provision of emergency shelters and supplies, temporary infrastructure
  • Recovery and Rehabilitation: Damage assessment, restoration of infrastructure, support services, review and refinement of plans
  • Mitigation: Land use controls, structural engineering, vegetative barriers
• Factors considered in risk management

  • Frequency and magnitude of volcanic activity
  • Population density of areas near volcanoes
  • Economic impact of disruptions and damage
• Primary effects of volcanic activity

  • Tephra
  • Pyroclastic Flows
  • Lava Flows
  • Volcanic Gases
• Tephra


  Material ejected by the volcano, varying in size from volcanic bombs (>64mm) to lapilli (2-64mm) and ash (<2mm)
• Pyroclastic Flows


  Very hot (>800 degrees Celcuis), gas charged, high velocity flows made up of gas and tephra, can flow at 700kmph, usually relatively close to the ground, wiped out the city of Pompeii in 79AD
• Lava Flows


  Streams of molten rock that pour or ooze from an erupting vent, erupted during either nonexplosive activity or explosive lava fountain
• Volcanic Gases


  • Carbon dioxide
  • Carbon monoxide
  • Hydrogen sulphide
  • Chlorine
• Secondary effects of volcanic activity

  • Lahars (volcanic mud flows)
  • Flooding
  • Volcanic landslide
  • Acid Rain
  • Climate Change
• Lahars (volcanic mud flows)


  Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move down the course of river valleys at high speed
• Volcanic eruption


  Melts glaciers and ice caps, causing serious flooding
• Volcanic landslide


  Large masses of wet or dry rock and soil that fall, slide, or flow very rapidly under the force of gravity
• Tsunamis


  Sea waves generated by violent volcanic eruptions, such as those formed after Krakatoa in 1883, estimated to have killed 36,000 people
• Acid Rain


  Sulphur emitted from the volcano mixes with moisture in the atmosphere, causing acid rain
• Volcanic eruption


  Ejects huge amounts of debris into the atmosphere, reducing global temperatures by blocking out sunlight, resulting in climate change
• Volcanic Hazards


  Most volcanic activity is associated with plate tectonic processes and is mainly located along plate margins
• Locations of volcanic activity

  • Oceanic Ridge
  • Subduction Zones
  • Rift Valleys
  • Hot Spots
• Volcanic eruptions


  Vary in both scale, frequency and magnitude
• Types of volcanic eruptions

  • Effusive eruptions - magma rises through the surface and flows out of the volcano as a viscous liquid called lava
  • Explosive eruptions - magma is torn apart as it rises and reaches the surface in pieces known as pyroclasts
• Volcanic Explosivity Index (VEI)

  A logarithmic scale from 0-8, quiet eruptions score 1 and increase in number as the volcano becomes more explosive
• A magnitude 7 has only been experienced in Tamboro, Indonesia (1815), so are relatively uncommon
• Frequency of volcanic eruptions

  The number of previous eruptions must be recorded and analysed
• Primary effects of volcanic activity

  • Tephra - Material ejected by the volcano, varying in size from volcanic bombs (>64mm) to lapilli (2-64mm) and ash (<2mm)
  • Pyroclastic Flows - very hot (>800 degrees Celcuis), gas charged, high velocity flows made up of gas and tephra
  • Lava Flows - streams of molten rock that pour or ooze from an erupting vent
  • Volcanic Gases - carbon dioxide, carbon monoxide, hydrogen sulphide and chlorine
• Secondary effects of volcanic activity

  • Lahars (volcanic mud flows): Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move down the course of river valleys at high speed
  • Flooding - The heat of the eruption melts glaciers and ice caps, serious flooding can occur
  • Volcanic landslide - These are large masses of wet or dry rock and soil that fall, slide, or flow very rapidly under the force of gravity
  • Tsunamis - These are sea waves generated by violent volcanic eruptions
  • Acid Rain - Sulphur is emitted from the volcano, when this mixes with moisture in the atmosphere and acid rain occurs
  • Climate Change - The huge amounts of debris that can be ejected into the atmosphere can reduce global temperatures as they can block out sunlight
• The frequency of volcanic eruptions depends largely upon their type
• Kilauea, on the island of Hawaii


  An active shield volcano which has erupted basaltic lava continuously since 1983
• Yellowstone caldera


  Has erupted three times in the last 2.1 million years, with an interval of between 600 000 and 800 000 years between each
• Basaltic lava


  Erupted from volcanoes at constructive plate boundaries and magma plumes
• Volcanoes at destructive plate boundaries

  Tend to erupt more viscous, andesitic or rhyolitic lava
• Predicting volcanic eruptions


  Vulcanologists need to know a volcano's eruption history and to be currently monitoring it, then interpret the data
• It is impossible to predict the exact size, nature and timing of an eruption