VEI Scale Table
| VEI | Ejecta volume (bulk) | Classification | Description | Plume height | How often | Named examples |
|---|---|---|---|---|---|---|
| 0 | < 104 m³ | Hawaiian | Effusive | < 100 m | constant | Kilauea, Fagradalsfjall |
| 1 | ≥ 104 m³ | Hawaiian / Strombolian | Gentle | 100 m – 1 km | daily | Yakedake (1995), Dieng (1964) |
| 2 | ≥ 106 m³ | Strombolian / Vulcanian | Explosive | 1–5 km | 2 weeks | Mount Etna, Stromboli (since 1934) |
| 3 | ≥ 107 m³ | Strombolian / Vulcanian / Peléan | Severe | 3–15 km | 3 months | Surtsey (1963-67), Nevado del Ruiz (1985) |
| 4 | ≥ 0.1 km³ | Peléan / Plinian / Sub-Plinian | Catastrophic | > 10 km | 18 months | Bandai (1888), Pelée (1902), Lamington (1951) |
| 5 | ≥ 1 km³ | Peléan / Plinian | Cataclysmic | > 20 km | 12 years | Vesuvius (79), Fuji (1707), Tarawera (1886) |
| 6 | ≥ 10 km³ | Plinian / Ultra-Plinian | Colossal | > 30 km | 50–100 years | Lake Ilopango (~450), Paektu (946), Huaynaputina (1600) |
| 7 | ≥ 100 km³ | Ultra-Plinian | Super-colossal | > 40 km | 500–1,000 years | Campi Flegrei (~37,000 yr), Crater Lake (~5677 BC), Tambora (1815) |
| 8 | ≥ 1,000 km³ | Ultra-Plinian | Mega-colossal | > 50 km | > 50,000 years | Wah Wah Springs (~30 Mya), La Garita (~26.3 Mya) |
The Volcanic Explosivity Index (VEI) rates eruptions from 0 to 8 by the volume of material they eject, and it is a logarithmic scale: each step up means roughly ten times more ejecta, so a VEI 6 is not a bit bigger than a VEI 5 - it is a whole order of magnitude, in the same way a magnitude 7 earthquake dwarfs a 6. The scale bundles that volume with eruption style and plume height, which is why the same chart runs from Hawaiian fountains under 100 meters to Ultra-Plinian columns more than 25 kilometers into the stratosphere.
The historical calibration surprises most readers: Vesuvius, the eruption that buried Pompeii and defined volcano in the Western imagination, is a VEI 5. Krakatoa and Pinatubo are 6s. Tambora in 1815 - the largest eruption in recorded history, the one that caused the Year Without a Summer - is a 7. VEI 8, the mega-colossal caldera-formers like the one that resurfaced Yellowstone hundreds of thousands of years ago, has never occurred in the roughly 10,000-year span of human written records.
How to use
- Read the volume column as powers of ten: VEI 1 starts at ten thousand cubic meters, VEI 2 at a million, VEI 3 at ten million, and by VEI 6 the scale switches to cubic kilometers (ten of them). A bump of one VEI level multiplies the eruptive output about tenfold - there is no meaningful 'a little VEI 7'.
- Use plume height in the field sense: eruption columns above about 10 kilometers punch into the jet stream and the stratosphere, where ash spreads across continents and climate. That is the physical reason VEI 4 and up make international aviation and climate news while VEI 1-2 barely leave the volcano observatory's bulletins.
- Check the periodicity column before worrying: the common eruptions are constant-to-daily at VEI 0-1, while the continent-shaking VEI 7 class averages half a millennium to a thousand years apart, and nothing like a VEI 8 has appeared in written history. Frequency, not just size, is why the small end dominates the news.
Frequently asked questions
What VEI was Mount St. Helens?
VEI 5 - the 1980 lateral blast ejected about one cubic kilometer of material, a cataclysmic event by the chart's wording and a human catastrophe, yet only halfway up the scale. The same VEI 5 class holds Vesuvius in 79 AD and Fuji in 1707. The comparison is the point of the scale: St. Helens, which emptied a whole mountainside, ejected roughly one ten-thousandth of the volume of a VEI 8 super-eruption.
Why is the scale logarithmic?
Because eruption volumes span an unchartable range otherwise - from Hawaiian fountains that add a few thousand cubic meters of lava to caldera collapses that move thousands of cubic kilometers, nine or ten orders of magnitude in one phenomenon. Linear plotting would flatten every eruption below VEI 6 into a single pixel; the log scale keeps each step visible and matches how geologists estimate size from deposits. Each +1 VEI means roughly ten times the ejecta, which is why deposits, not eyewitness drama, set the number.
Which volcanoes are VEI 8 supervolcanoes?
By the chart, VEI 8 means at least a thousand cubic kilometers of ejecta with Ultra-Plinian columns above 50 kilometers - caldera-forming events whose recurrence interval exceeds 50,000 years. Named candidates in the geologic record include La Garita (Colorado, about 28 million years ago) and the Wah Wah Springs deposit in Utah, along with the Toba super-eruption about 74,000 years ago, the largest in the Quaternary. Yellowstone's past caldera-forming eruptions reached this class; none has occurred within recorded human history, and the scale caps at 8 partly because nothing bigger is known.
How is VEI determined after an eruption?
Mostly from the deposits, not the drama. Volcanologists reconstruct the bulk volume of tephra - the fallen ash, pumice and rock fragments - map its thickness over the dispersal area, and read the resulting volume against the scale, with plume height and eruption style as corroboration. That is why historical VEI values are sometimes revised as field mapping improves, and why the famous eruptions sit comfortably on the chart only decades or centuries after the event: the volcano writes the number in ash, and the survey takes centuries to read it all.