A guide to using the Volcanic Explosivity Index (VEI)
The concept of providing a relative measure of the explosiveness of a volcano, was developed and implemented by Chris Newhall of the US Geological Survey, and Steve Self of the University of Hawaii in 1982.
The term Volcanic Explosivity Index, was therefore birth through these brilliant pioneers, and embraces terminology like, volume of products, eruption cloud height, and quantitative observations, to determine whether to classify the explosivity as 0,1, 2, or at the maximum 8 on the index.
On a chart designed by these scientists, a column was set aside to describe the nature of the eruptions, and the terms were, non-explosive, gentle, explosive, severe, cataclysmic, paroxysmal, colossal, and super-colossal, to mega-colossal, to describe the increasing level of explosivity, the VEI should be able to measure.
Each level on the index is ten fold greater that the immediate level below. In order to measure the plume, the index had a section that tells you whether the volcanic dust was less than 100m in the air at the lowest grade, or greater than 25km at the highest level.
The scientists found a way to incorporate the volume of dust or ash released into the atmosphere, and incorporate into the index. Volcanoes with a VEI of I were expected to generate approximately a volume of 10,000sm³, mega-colossal with VEI of 8 would have as much as 100skm³ of ash and other particles prevailing in the atmosphere.
Historically, there was a section that could tell how long ago volcanoes of certain types occurred, so that future scientists, who would want to determine the explosive potential of a volcano, could use the information as a point of reference. Messrs Newhall and Self also made sure there was consistency in their measure, by treating volcanic bombs, ash, and ignimbrite the same manner.
According to www.agu.edu, VEI was a composite of the magnitude of past eruptions, and was used by the pioneers to develop a semi-quantitative compromise between poor data availability of the past, and the need in various disciplines to evaluate the records of past volcanism.
The scale was therefore able to cover volcanoes from the Ordovician age to the Pleistocene, and recorded 42 eruptions over a period of approximately 36million years.
In order to demonstrate the currency of the index, and the importance to present day scientists, Mount Kilauea which began in 1983 and is presently active, was given a VEI of 1, on the scale. Mount Vesuvius occurring between 1913 and 1944, fell into category 3 in terms of explosivity.
Krakatoa eruption in 1883 was graded 6, while YellowStone with its lava creek eruption almost 640,000 BP, received the maximum grade 8, indicating great consistency in the designing and implementation process of the pioneers.
The University of North Carolina has on its website a VEI chart that is also very informative. It covers the nature, volume, plume, as well as the historical aspects of volcanic eruptions. Starting at base 0, the volcanic explosivity increases along the same channel as that designed by Newhall and Self.
The work therefore that was done, to develop the VEI has certainly proved relevant and effective, to handle any present and future volcanic eruptions, because all the variables that are in place have been tried, proven, and replicated in higher learning institutions, and in government departments. Future scientists also, have a rich legacy to inherit in the fields of Geology, thanks to Messrs Newhall and Self.
Sources
www.agu.org
www.unc.edu
