volcanic explosivity index (VEI)
The volcanic explosivity index (VEI) is a method that vulcanologists use to classify the scale of volcanic eruptions. Devised in 1982 by Chris Newhall of the US Geological Survey and Stephen Self of the University of Hawaii it gauges the relative violence of different eruptions. Factors that go into determining the VEI are the volume of material thrown out, the height of the cloud of debris from the eruption, and qualitative observations about the nature of the explosion. The VEI range goes from 0, for a non-explosive, gentle burbling or spraying of lava, to 8 in the case of the most prodigious, cataclysmic supervolcanoes.