Volcanic Hazards.

• Mudflows and Lahars:

  • lahars are mudflows but are so called in Indonesia and are now a specific term for flows of ash, soil and rock that have been changed to clay by acids in volcanic gases and hot-spring waters.
  • have destroyed more property than any other volcanic action and killed 1000s.
• Causes of lahars:

  • eruptions ejecting water from a crater lake, or through the broken crater walls.
  • rapid melting of ice or snow on the volcano's slopes.
  • eruption-induced heavy rainfall mixing with loose material on the volcano's slopes.
  • pyroclastic flows (nuees ardentes) entering streams.
• Colombian Armero tragedy of 1985:

  rising magma and gas and steam started melting the summit glacier of Nevado del Ruiz. The melting continued until the volcano erupted when all the slow melted. The meltwater (combined with torrential rain and raging flood water) mixed with ash from previous eruptions to send a 30m-high lahar over 8kmh towards the sleeping town of Armero resulting in 21,000 dead.
• Pyroclastic Flows:

  formed by a mixture of hot gas (over 800C) and tephra, after ejection the flow down the sides of a mountain at over 700km/h.

  Referred to as nuees ardentes when the cloud is formed with only hot gas.
• Pyroclastic Flows:

  • a mixture of super-heated gas, ash and volcanic rock that flows down the sides of a volcano.
  • at speeds over 80km/h.
  • generally travels around 10/15 km.
  • e.g. Pompeii and Herculaneum.
• Lava Flows:

  • flows from volcanism vents down the sides of a volcano.
  • viscosity and temperature decided distance and speed travelled, as well as steepness of the slope.
  • relatively slow so allow for evacuation.
  • destroy by burning, burying or knocking down anything in their path.
• Volcanic gases:

  • volcanoes release CO2 and sulphur dioxide when they erupt.
  • gases harmful to animals and humans if breathed in.
• Acid Rain:

  • volcanic gases react with water vapour in the atmosphere which falls as acid rain e.g. sulfur dioxide with water to sulphuric acid.
  • damage to ecosystems.
  • can cause stone and metal to deteriorate damaging infrastructure.
• Ash Fallout:

  material ejected during eruption which falls back to ground, when consisting mostly of ash named ash fallout.
• Ash Fallout:

  • material ranging in size, from tonnes to particles.
  • can travel 1000s of kms from volcano- heavier particles nearer volcano and smaller particles deposited further away.
• Tephra:

  • damage buildings and kill people.
  • finer material can form metres in thickness killing vegetation, hindering rail and road support and causing overall damage to infrastructure.
  • harmful if breathed in.