Specification

Hazards have an impact on people and environments. Measuring earthquakes: the volcanic explosivity scale.

A. The Volcanic Explosivity Index (VEI)

The Volcanic Explosivity Index (VEI) is a measure of the explosiveness of volcanic eruptions.

It was devised by Chris Newhall of the United States Geological Survey and Stephen Self at the University of Hawaii in 1982.

The index is based on a scale of 1 to 8, 1 being very small, and 8 being huge and very rare. The level of an eruption is based upon:

• Volume of products
  
• Eruption cloud height
  
• Qualitative observations (using terms ranging from "gentle" to "mega-colossal")
  

A value of 0 is given for non-explosive eruptions, defined as less than 10,000 m3 (350,000 cu ft) of tephra ejected; and 8 representing a mega-colossal explosive eruption that can eject 240 cubic miles of tephra and have a cloud column height of over 20 km (12 mi).