The Volcanic Explosivity Index (VEI) Explained

Tap a level to see what it represents.

What the VEI Measures

A scale from 0 to 8 used to classify the explosive magnitude of volcanic eruptions, based primarily on the total volume of erupted material and the height of the eruption plume.

Why It's a Logarithmic Scale

Similar to the earthquake magnitude scale, each whole-number increase on the VEI represents roughly a tenfold increase in the volume of ejected material, meaning the difference between levels grows dramatically at higher numbers.

VEI 0-2: Frequent, Smaller Eruptions

The vast majority of volcanic eruptions worldwide fall into this lower range, including many of Hawaii's relatively gentle, effusive lava eruptions.

VEI 3-5: Significant Regional Impact

This range includes eruptions capable of causing major regional destruction, such as the VEI 5 eruption of Mount St. Helens in 1980.

VEI 6-8: Globally Significant Events

Eruptions at this level are exceptionally rare and can affect global climate — Mount Pinatubo's 1991 eruption (VEI 6) measurably cooled global temperatures for roughly a year afterward.

VEI 8: "Supervolcano" Eruptions

The highest classification on the scale, representing eruptions so massive they have occurred only a handful of times in the last several hundred thousand years, such as the Yellowstone supervolcano's prehistoric eruptions.

Why VEI alone doesn't determine an eruption's deadliness

While VEI is useful for comparing the sheer explosive scale of eruptions, it doesn't directly measure how deadly or destructive an eruption actually is — a lower VEI eruption near a densely populated area can cause far more casualties than a much higher VEI eruption in a remote, uninhabited region.

Frequently Asked Questions

How often do VEI 8 "supervolcano" eruptions actually occur?

Extremely rarely — geological records suggest VEI 8 eruptions occur roughly once every 100,000 years or less frequently, making them among the rarest and most significant natural events in Earth's geological history.

Is Mount Vesuvius's famous eruption that destroyed Pompeii considered a high VEI event?

The 79 CE eruption of Mount Vesuvius is generally classified as VEI 5, which, while significant and devastating locally, is well below the highest levels on the scale.