Usually the phrase, “Holy cow!” gets the point across that a volcanic eruption was impressive, but it does not accurately portray how much material a volcano belched out, or how violent the eruption was. Scientists have developed a scale for measuring how large a volcanic eruption is. This is called the Volcanic Explosivity Index and eruptions are rated on a scale of one to eight. Why stop at 8? Because the scale is created on exponential increases (much like the Richter Scale) and, at that rate, a 9 has never been recorded. Does the Earth have the capability to produce an eruption of this magnitude? I’m sure it could muster the mojo if it wanted to, but not much would survive.
The scale is based on the following:
- Amount of material ejected
- Height of eruption column
- Style of eruption
- Duration of the eruption
Each step up on the scale represents an increase of 10x in the amount of material ejected. Because these are such large steps, occasionally a “+” will be added to the end of a number if the amount ejected is at the upper end of its rating scale.
I’ve drawn up a chart for you that explains the VEI (click for a bigger, badder image):
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