How do scientists measure the size of volcanic eruptions?

The Volcanic Explosivity Index is a relative measure used to quantify the size of explosive volcanic eruptions. Devised in 1982 by Christopher G. Newhall and Stephen Self, the scale evaluates the volume of products, eruption cloud height, and qualitative observations. It is an open-ended logarithmic scale ranging from magnitude 0 for non-explosive events up to magnitude 8 for supervolcanoes.

What we know

• The Volcanic Explosivity Index is a relative measure of explosive volcanic eruption size based on product volume and eruption cloud height. [1, 2]
• The Volcanic Explosivity Index was devised in 1982 by Christopher G. Newhall of the United States Geological Survey and Stephen Self. [2]
• The scale determines explosivity using the volume of products, eruption cloud height, and qualitative descriptive terms ranging from gentle to mega-colossal. [2]
• The VEI scale is logarithmic, with each interval representing a tenfold increase in observed ejecta criteria, except between VEI-0, VEI-1, and VEI-2. [2]
• A value of 0 is assigned to non-explosive eruptions ejecting less than 10,000 cubic meters of tephra, while magnitude 8 represents supervolcanic eruptions ejecting 1.0 trillion cubic meters. [2]

Where to go next

• whoWho created the Volcanic Explosivity Index?
• a case in pointWhat happens during a supervolcano eruption?
• what caused itHow do tectonic plates cause different types of volcanoes?
• compared withWhat scale is used to measure earthquakes?
• what followedHow do massive volcanic eruptions affect Earth's climate?
• an unexpected connectionWhy is a caldera with VEI 7 eruptions not classified as a supervolcano?Popular media often calls the Phlegraean Fields a supervolcano despite its largest eruptions measuring VEI 7, because the accepted scientific definition strictly requires a VEI of 8.

Sources

• [1]Volcanic Explosivity Index (Wikidata Q210510) · CC0 1.0
• [2]Volcanic explosivity index · CC BY-SA 4.0
• [3]Mount Vesuvius · CC BY-SA 4.0
• [4]Volcano · CC BY-SA 4.0
• [5]Phlegraean Fields · CC BY-SA 4.0