In the figure above, the volumes of several past explosive eruptions and the corresponding VEI are shown. Numbers in parentheses represent total volume of erupted pyroclastic material (tephra
, volcanic ash, and pyroclastic flows) for selected eruptions; the volumes are for uncompacted deposits. Each step increase represents a tenfold increase in the volume of erupted pyroclastic material. A series of small to moderate explosive eruptions from Mono-Inyo Craters Volcanic Chain, California
, during the past 5,000 years ranged from VEI of 1 to 3. The 18 May 1980 eruption of Mount St. Helens
was a VEI 5 with an erupted volume of about 1 km3. The 1991 eruption of Mount Pinatubo
had a volume of about 10 km3 and a VEI of 5 to 6. The 1815 eruption of Tambora
, had a VEI of 7 and a volume in excess of 100 km3. The eruption of Long Valley Caldera about 760,000 years ago had a VEI of 7 and a volume of 600 km3 of material. The largest explosive eruption on the figure occurred at Yellowstone
about 600,000 years ago with a VEI of 8 and a volume of about 1,000 km3 of material.
The Volcanic Explosivity Index
, or VEI, was proposed in 1982 as a way to describe the relative size or magnitude of explosive volcanic eruptions. It is a 0-to-8 index of increasing explosivity. Each increase in number represents an increase around a factor of ten. The VEI uses several factors to assign a number, including volume of erupted pyroclastic material (for example, ashfall, pyroclastic flows, and other ejecta), height of eruption column, duration in hours, and qualitative descriptive terms.
- ↑ VEI, Photo glossary of volcano terms: U.S. Geological Survey