1.3B

• Major volcanic eruptions frequently have more than one hazard associated with them, especially violent volcanic eruptions at destructive plate margins. There may also be secondary hazards, which are an indirect consequence of the eruption. This is especially the case with the violent eruptions associated with volcanoes at destructive plate margins. 
• Primary Hazards

  Lava Flow

  Pyroclastic Flow

  Ash Fall

  Gas Eruption
• Lava flow

  Extensive areas of solidified lava, which can extend several kilometres from volcanic vents if the lava is basaltic and low viscosity. It can flow at up to 40 km/h. 

  Occurs at:

  subduction zone volcano (composite)

  hot-spot volcano (shield type)
• Pyroclastic Flow

  Very large, dense clouds of hot ash and gas at temperatures of up to 600'C. They can flow down the flanks of volcanoes and devastate large areas. 

  Occurs at:

  Subduction zone volcano (composite)
• Ash Fall

  Ash particles, and larger tephra particles, can blanket large areas in ash, killing vegetation, collapsing buildings and poisoning water sources. 

  Occurs at:

  Constructive plate margin volcanoes (cinder cone, fissure eruption)

  Subduction zone volcano (composite)
• Gas Eruption

  The eruption of carbon dioxide and sulphur dioxide, which can poison people and animals in extreme cases. 

  Occurs at:

  Subduction zone volcanoes (composite)

  Hot-spot volcano (shield)
• Secondary Hazards

  Lahars

  J​ökulhlaups 
• Lahars

  Volcanic mudflows, which occur when rainfall mobilises volcanic ash. They travel at high speed down river systems and cause major destruction. 

  Occurs at:

  Subduction zone volcanoes (composite)
• J​ökulhlaups

  Devastating floods caused when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of meltwater. They are common in Iceland. 

  Occurs at:

  Constructive plate margin volcanoes (cinder cone, fissure eruption)

  In most cases, only large composite volcanoes found at destructive plate margins represent a significant tectonic hazard. These eruptions often have lava flows, pyroclastic flows, lahars and extensive ash and tephra fall that can affect areas up to 30 km from the volcanic vent