Measuring and Assessing Volcanic Activity

• Volcanic eruptions


  • Can vary in duration
  • Can vary in the amount of material released
  • Can vary in type (explosive/effusive)
• It is difficult to compare one volcanic eruption from another
• Factors to consider for volcanic eruptions

  • Magnitude - the amount of material erupted from the volcano
  • Intensity - The speed material erupts from the volcano
• Volcanic explosivity index (VEI)

  Combines magnitude and intensity into a single figure on a scale of 0 (least explosive) to 8 (most explosive)
• Each VEI number represents a 10 fold increase in explosivity
• The VEI scale is logarithmic
• Eruptions with a small VEI are far more common than those with a high VEI
• VEI


  Not particularly useful for effusive eruptions such as those on Hawaii
• VEI


  Valuable in predicting the relative impacts volcanoes may have at different points on the scale