Volcanic eruptions can be violent, passive, or anywhere in between. When a people are told that a volcano is going to erupt, many imagine an explosive eruption with a giant ominous cloud of ash and red hot lava flowing down a mountain. However, since volcanic eruptions can vary greatly in size and intensity, volcanologists use the Volcano Explosivity Index, or VEI, to classify the size of an eruption.
The Volcano Explosivity Index
The VEI scale has been used in modern volcanology as a way to forecast the possible size of a volcanic eruption based on that volcano's historical eruptions.
It first debuted in 1982 as a paper titled "The Volcanic Explosivity Index (VEI): An Estimate of Explosive Magnitude for Historical Volcanism," written by Christopher Newhall and Steve Self and published in the Journal of Geophysical Research.
The VEI of a volcano depends mostly on the volume of material ejected during the eruption and the height of the ash column or plume. The VEI scale breaks down volcanic eruptions into nine classifications ranging from a VEI of zero to eight - zero being a non-explosive eruption and eight being a mega-colossal eruption. There are no known explosive events with a VEI greater than eight.