What VEI was the Pinatubo 1991 eruption?

VEI 6 — the largest eruption of the 20th century. It erupted about 10 km³ of bulk tephra, the lower end of the VEI 6 bracket, and cooled global temperatures by roughly 0.5°C for two years.

Volcanic Explosivity Index

Six steps from a sigh to the colossal.

Q: Is the VEI a single number per eruption?

No. Each VEI step labels a logarithmic range of erupted-tephra volumes, not a single value. Successive upper bounds differ by 10×.

Pick a Philippine volcano, drag the VEI slider, and watch the ash plume, pyroclastic zone, and lahar paths scale together. Pinatubo 1991 was the big one.

Pyroclastic flow

Lahar path

Ash plume / fall

Volcano

Mayon

Scenario

VEI 3

Ash plume

15 km

Ejecta (bracket)

0.01–0.1 km³

Population at risk

Volcano

Eruption scenario

Volcanic Explosivity IndexVEI 3

123456

Severe — Mayon 2018-class.

VEI 1 = gentle · VEI 6 = colossal (Pinatubo 1991). Each step is ~10× more ejecta at its upper bound.

How to use

Pick a volcano — Taal, Mayon, or Pinatubo. Drag the VEI slider from 1 to 6. The ash plume height, pyroclastic-flow radius, lahar reach, and estimated population at risk all scale with the scenario. Watch how a single step up the index transforms the hazard footprint.

The VEI scale, step by step

VEI 1 — "gentle," <0.01 km³, plume <5 km. Most Mayon background activity.
VEI 2 — "explosive," ~0.01 km³. Taal 2020 phreatic eruption.
VEI 3 — "severe," ~0.1 km³. Mayon 2018 (PDC fatalities).
VEI 4 — "cataclysmic," ~1 km³, plume 25 km. Mt St Helens 1980.
VEI 5 — "paroxysmal," ~10 km³. Vesuvius 79 AD.
VEI 6 — "colossal," up to 100 km³, plume 35+ km. Pinatubo 1991 — largest eruption of the 20th century.

Pinatubo 1991 in context

On 15 June 1991, Pinatubo's VEI 6 eruption ejected ~10 km³ of magma and ash, carved a 2.5 km-wide caldera, sent ash plumes 35 km high, and pumped ~20 megatonnes of SO₂ into the stratosphere.

The aerosol veil reflected enough sunlight to cool global average temperature by ~0.5°C for the following two years. PHIVOLCS and USGS evacuated 60,000+ residents — the warning saved tens of thousands of lives.

Lahars kept coming for years afterward, choking rivers and burying communities under hot mudflows during typhoons.

What kills people in eruptions

Pyroclastic density currents — gas, ash, and rock at 100–700°C racing downslope at 80–700 km/h. Unsurvivable in range. Mayon 1814 killed ~1,200 at Cagsawa.
Lahars — volcanic mudflows from rain on ash deposits. Pinatubo's killed hundreds after the main eruption ended.
Ash fall — collapses roofs, ruins crops, grounds aircraft.
Volcanic gases — SO₂, H₂S, CO₂ pooling in low ground.
Tsunamis — caldera collapse into water (a Taal-specific risk, sitting in a lake).

About the VEI scale

The VEI is logarithmic, but bracketed: each step labels a range of erupted-tephra volumes, not a single value. The canonical Newhall & Self (1982) ranges are: VEI 1 ≈ 10⁴–10⁶ m³ (10⁻⁵–10⁻³ km³), VEI 2 ≈ 10⁶–10⁷ m³ (0.001–0.01 km³), VEI 3 ≈ 10⁷–10⁸ m³ (0.01–0.1 km³), VEI 4 ≈ 0.1–1 km³, VEI 5 ≈ 1–10 km³, VEI 6 ≈ 10–100 km³, VEI 7 ≈ 100–1000 km³, VEI 8 ≥ 1000 km³.

The "10× per step" rule of thumb describes the ratio between successive upper bounds, not individual eruptions. Pinatubo 1991 erupted ~10 km³ of bulk tephra — the lower end of VEI 6. The 100 km³ figure on the VEI 6 chip is the upper bound of that bracket, not the Pinatubo eruption itself.

Citations

Newhall & Self (1982) — "The Volcanic Explosivity Index: an estimate of explosive magnitude," JGR Solid Earth 87, 1231.
Newhall & Punongbayan (eds., 1996) — Fire and Mud: Eruptions and Lahars of Mount Pinatubo, PHIVOLCS/USGS.
PHIVOLCS — official volcano monitoring & hazard assessments (Taal, Mayon, Pinatubo).
Smithsonian Global Volcanism Program — eruption history database.
Mason et al. (2004) — "The size and frequency of the largest explosive eruptions on Earth," Bull. Volcanol. 66, 735.

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