volcanic hazards

• Most active volcanoes


  • Occur at or near plate boundaries
• Many (about 75%) active volcanoes


  • Occur around the 'Ring of Fire' surrounding the Pacific Ocean
• Vulcanicity (volcanic activity)


  • Focused on constructive and destructive plate margins
• Eruptions at constructive margins

  • Tend to be small and effusive
  • Basaltic lava
  • Low gas content
  • Low viscosity
  • Higher temperature
• Eruptions at destructive margins

  • Tend to be explosive as the magma is forcing its way to the surface
  • Often andesitic or rhyolitic lava
  • High gas content
  • High viscosity
  • Lower temperature
• Volcanoes can also be found at hot spots in the middle of plates, like Hawaii in the central Pacific
• Volcanic Explosivity Index (VEI)

  • Used to measure the magnitude of an eruption
  • Logarithmic scale from 0-8
  • Cannot be measured on a scientific instrument, calculated based on measurements and observations
  • Includes height of material ejected, volume of material, duration of the eruption
• Primary volcanic hazards


  • Tephra (solid material of varying sizes)
  • Ash fallout
  • Pyroclastic flow
  • Lava flow
  • Volcanic gases
• Tephra


  • Ash (less than 2mm in diameter)
  • Volcanic bombs (more than 64mm)
• Ash fallout


  • Caused respiratory problems, injuries, damage, deaths and disruption to transport
  • E.g. 2010 Eyjafjallajökull eruption in Iceland
• Pyroclastic flow


  • Speeds of up to 700 km per hour
  • E.g. Fuego volcano eruption in Guatemala in 2018
• Lava flow


  • Speeds up to 60 mph
  • E.g. 2021 eruption of Mount Nyiragongo in the Democratic Republic of Congo
• Volcanic gases


  • Sulphur dioxide and carbon dioxide
  • E.g. Kilauea in Hawaii (USA)
• Secondary volcanic hazards


  • Lahars
  • Jökulhlaups
  • Acid rain
• Lahars


  • E.g. Mount Pinatubo eruption in the Philippines in 1991
• Jökulhlaups


  • E.g. 2010 eruption of Eyjafjallajökull
• Acid rain


  • Forms when sulphur dioxide reacts with water vapour in the atmosphere to form sulphuric acid
  • Can damage crops, forests and aquatic ecosystems
• Shield volcanoes


  • Found at constructive plate margins
  • High frequency, low magnitude eruptions
• Stratovolcanoes


  • Found at destructive plate margins
  • Low frequency, high magnitude eruptions
• Primary impacts of volcanic eruptions

  • Deaths and injuries
  • Displacement of people
  • Damage to properties and infrastructure
• Secondary impacts of volcanic eruptions

  • Mental health issues
  • Homelessness
  • Disruption to services
  • Loss of cultural heritage sites
  • Destruction of property and infrastructure
  • Disruption of trade and economic activity
  • Loss of income and employment
  • Slower economic growth and development
  • Increased economic inequality
  • Increased costs of insurance and hazard management
  • Poor air and water quality
  • Loss of biodiversity
  • Destruction of habitats and ecosystems
  • Acid rain
  • Release of greenhouse gases
  • Ash clouds
  • Pressure on governments
  • Social unrest and political instability
  • Conflicts over government response and food shortage
  • Changes in government policy and regulations
• Long-term responses to volcanic hazards

  • Hazard mapping and land use zoning
  • Building codes
  • Education and training
• Short-term responses to volcanic hazards

  • Evacuation
  • Search and rescue
  • Emergency aid
• Responses can also be categorised as prevention, preparedness, mitigation and adaptation