Classification of volcanic eruptions

• Since 1982 the magnitude of volcanic eruptions has been measured using a logarithmic scale from 0-8 called the Volcano Explosivity Index (VEI)
• Volcanic classifications based upon the violence of the eruption may include a VEI rating, but are more useful if related to tectonics by including details of the type of magma and even frequency. 
• What is dormant?


  They classify a dormant volcano as one that hasn’t erupted in the past 10,000 years, but which is expected to erupt again. The term is used to describe a volcano which is presently inactive but which may erupt again. Most of the major Cascade volcanoes are believed to be dormant rather than extinct.
• What is active?


  An active volcano is one that has erupted since the last ice age (i.e., in the past ~10,000 years). That is the definition of active used by the Global Volcanism Programme. A volcano that is erupting. Also, a volcano that is not presently erupting, but that has erupted within historical time and is considered likely to do so in the future.
• What is extinct?


  An extinct volcano would be one that nobody expects to ever erupt again. These are human definitions of natural things – there have been a number of eruptions from “extinct” volcanoes! Perhaps a better definition would be - A volcano that is not presently erupting and is not likely to do so for a very long time in the future.
• Primary hazards (impacts)

  • Ash 
  • Tephra
  • Lava flows
  • Nuées ardentes/Pyroclastic flows
  • Volcanic gases
• Secondary hazards (impacts)

  • Acid rain
  • Climate change
  • Flooding
  • Tsunamis