Invented in 1982 by Chris Newhall and Stephen Self, the Volcanic Explosivity Index (VEI) is a bit like a Richter scale for volcanoes.
The VEI measures the “explosiveness” of a volcanic eruption, and takes into account the amount of material ejected, the height to which the material is ejected, and how long the eruption lasts. The scale runs from 0 (“effusive”) to 8 (“apocalyptic”), and is logarithmic from VEI-2 onwards (so VEI-3 is ten times more explosive than VEI-2, etc.).
|VEI||Classification||Material ejected /km3||Plume height /km|
|0||Effusive||< 0.000 01||< 0.1|
|1||Gentle||> 0.000 01||0.1-1|
|6||Colossal||> 10||> 30|
|7||Mega-colossal||> 100||> 40|
|8||Apocalyptic||> 1000||> 50|
Newhall and Self’s original paper contains a list of eruptions by VEI running back to 1500 (note their footnote about reporting at the bottom of the table).
The paper only lists one VEI-7 event, the “Mega-colossal” eruption of Mount Tambora in Indonesia in 1815 that caused The Year Without a Summer. They state that VEI-8 eruptions should occur with a frequency of ? 10 000 years, with the most recent being the eruption of New Zealand’s Taupo Volcano around 26 500 years ago.