Volcanic Explosivity Index

The Volcanic Explosivity Index (VEI) is a logarithmic scale from 0 to 8 that ranks volcanic eruptions by explosiveness, using erupted tephra volume and eruption-column height.

Tephra: Tephra is fragmented material ejected into the air during a volcanic eruption, ranging from ash to large blocks. Its estimated volume is the main quantitative basis for assigning a VEI.
Logarithmic scale: A logarithmic scale represents multiplicative changes through equal increments. Adjacent VEI levels generally correspond to roughly tenfold changes in erupted volume.
1980 eruption of Mount St. Helens: The 1980 eruption of Mount St. Helens was a major explosive eruption in Washington State that began on May 18. Its deposits and eruption column provide a well-studied example of VEI classification.
Volcanic eruption intensity: Volcanic eruption intensity is the rate at which an eruption releases material. Intensity distinguishes eruptions with similar total volumes but different discharge rates.
Eruption column: An eruption column is a rising mixture of volcanic gas and particles produced by an explosive eruption. Column height supplements erupted volume when classifying an eruption.
Erupted volume: Erupted volume is the amount of volcanic material discharged during an eruption, often estimated from deposits. It is the central quantity used to distinguish VEI levels.
1991 eruption of Mount Pinatubo: The 1991 eruption of Mount Pinatubo in the Philippines was a large explosive eruption that injected substantial aerosols into the stratosphere. Its high VEI and global atmospheric effects show how eruption size can connect to climate.
Volcanic eruption duration: Volcanic eruption duration is the time an eruption remains active, including pauses under a chosen definition. VEI does not encode how long an eruption lasts.
Volcanic ash: Volcanic ash consists of fragments of volcanic rock and glass smaller than two millimeters. Fine ash contributes to tephra volume and can remain suspended far from the vent.
Volcanic eruption: A volcanic eruption is the release of magma, gas, and other material from a volcano. VEI classifies eruptions, though it does not describe every aspect of their behavior.

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