VEI (Volcanic Explosivity Index)
"A logarithmic scale (0-8) used to measure the explosive magnitude of a volcanic eruption, similar to the Richter scale for earthquakes."
The Volcanic Explosivity Index (VEI) is the standard “ruler” geologists use to measure how powerful a volcanic eruption is. Developed in 1982, it is not determined by the lava flow, but by the volume of tephra (ash and rock) ejected and the height of the plume.
How the Scale Works
The scale is logarithmic, meaning each step is 10 times more powerful than the previous one (except from VEI 0 to VEI 1, and VEI 1 to VEI 2, which are increments of 100).
- VEI 0 (Effusive): Gentle lava flows. Example: Fagradalsfjall (Iceland), Mauna Loa.
- VEI 1 (Gentle): Small explosions. Example: Stromboli (Italy).
- VEI 2 (Moderate): Ash columns 1-5 km high. Example: Whakaari (2019).
- VEI 3 (Catastrophic): Severe damage. Example: Ruiz (1985).
- VEI 4 (Cataclysmic): Massive disruption. Example: Eyjafjallajökull (2010), Mount Pelée (1902).
- VEI 5 (Paroxysmic): Global cooling possible. Example: Mount St. Helens (1980), Vesuvius (79 AD).
- VEI 6 (Colossal): Global climate impact. Example: Krakatoa (1883), Pinatubo (1991).
- VEI 7 (Super-Colossal): Civilization-altering. Example: Tambora (1815).
- VEI 8 (Mega-Colossal): Extinction level. Example: Yellowstone, Toba (74,000 years ago).
Why It Matters
Understanding VEI helps emergency planners predict the “blast radius” of a volcano. While a VEI 0 eruption might destroy a few houses with slow lava, a VEI 6 can alter the global climate for years by injecting sulfur into the stratosphere.