Volcanic Explosivity Index (VEI)

The Volcanic Explosivity Index (VEI) is the standard scale used by volcanologists worldwide to classify the explosive magnitude of volcanic eruptions. Developed in 1982 by Chris Newhall of the United States Geological Survey and Stephen Self of the University of Hawaii, the VEI assigns a number from 0 to 8 based primarily on the total volume of tephra (fragmented rock, ash, and pumice) ejected during an eruption, along with secondary criteria including eruption column height, eruption duration, and qualitative descriptors. The scale is logarithmic above VEI 2: each whole-number increase represents a tenfold increase in ejected volume.

A VEI 5 eruption ejects roughly 1 km3 of material; a VEI 6 ejects 10 km3; a VEI 7 ejects 100 km3; and a VEI 8 — a supereruption — ejects more than 1,000 km3. The Smithsonian Institution's Global Volcanism Program has assigned VEI ratings to 8,394 of the 11,079 eruptions in its database (the remaining 2,685 lack sufficient data for classification). The VEI has become the universal language for comparing volcanic eruptions across time and geography, and understanding the scale is essential for interpreting volcanic hazards, historical records, and the geological past.

The VEI is determined primarily by the volume of pyroclastic material (tephra) ejected during an eruption. For eruptions above VEI 2, each step up the scale represents a tenfold increase in volume — making the scale logarithmic, similar to the Richter scale for earthquakes or the decibel scale for sound.

For VEI levels 0 through 2, the scale is not strictly logarithmic. VEI 0 eruptions produce less than 10,000 m3 of tephra (0.00001 km3), VEI 1 produces 10,000 to 1,000,000 m3 (0.00001 to 0.001 km3), and VEI 2 produces 1,000,000 to 10,000,000 m3 (0.001 to 0.01 km3). Above VEI 2, each level spans exactly one order of magnitude in volume.

Secondary classification criteria include eruption column height (VEI 0–1 eruptions typically produce columns under 1 km, while VEI 5+ events produce columns exceeding 25 km into the stratosphere), eruption style descriptors (Hawaiian, Strombolian, Vulcanian, Plinian, Ultra-Plinian), and qualitative terms (gentle, explosive, cataclysmic, mega-colossal).

Importantly, VEI measures explosiveness, not total energy released or lava volume. Large effusive eruptions — like Hawaii's Kilauea, which can erupt enormous volumes of lava — may receive low VEI ratings because the lava flows gently rather than being explosively fragmented. Conversely, a relatively small but extremely explosive eruption can receive a higher VEI than a larger but less explosive one.

This is one of the scale's noted limitations: it does not fully capture the impact or hazard of all eruption types.

Descriptor: Hawaiian / Gentle. Volume: less than 10,000 m3. Column height: under 100 m.

VEI 0 eruptions are effusive, producing lava flows, lava lakes, and gentle fountaining rather than explosive fragmentation. They are characteristic of shield volcanoes like Kilauea and Mauna Loa. Though low on the explosivity scale, VEI 0 eruptions can still be destructive: Kilauea's 2018 lower East Rift Zone eruption destroyed over 700 structures despite being classified as VEI 0.

Recent example: Kilauea, Hawaii (2024).

Descriptor: Strombolian / Mild. Volume: 10,000 to 1,000,000 m3. Column height: 100 m to 1 km.

VEI 1 eruptions produce small explosive bursts, incandescent lava fragments, and modest ash emissions. They are common at persistently active volcanoes like Stromboli in Italy (which has been erupting near-continuously for roughly 2,000 years) and at many Ring of Fire volcanoes during routine activity. Recent example: Kikai, Japan (2025).

Descriptor: Strombolian to Vulcanian / Explosive. Volume: 0.001 to 0.01 km3. Column height: 1 to 5 km.

VEI 2 is the most commonly recorded eruption level in the Smithsonian database, accounting for nearly half of all VEI-rated eruptions. These events produce significant ash clouds, lava flows, and localized tephra fall but are generally not catastrophic. They are routine events at many of the world's most active volcanoes.

Recent example: Cotopaxi, Ecuador (2023).

Descriptor: Vulcanian to sub-Plinian / Severe. Volume: 0.01 to 0.1 km3. Column height: 3 to 15 km.

VEI 3 eruptions can cause significant damage within 10 to 20 km of the vent and disrupt regional aviation. The 1985 eruption of Nevado del Ruiz in Colombia was only VEI 3, yet it generated lahars that killed approximately 23,000 people — demonstrating that even moderate eruptions can be catastrophic when secondary hazards (mudflows, tsunamis) are triggered. Recent example: Klyuchevskoy, Russia (2023).

Descriptor: Plinian / Cataclysmic. Volume: 0.1 to 1 km3. Column height: 10 to 25 km.

VEI 4 eruptions are major explosive events capable of devastating areas within 25 km and producing ashfall across hundreds of kilometers. The 2010 eruption of Eyjafjallajokull in Iceland was VEI 4 and caused widespread disruption to European air travel for weeks. The 1944 eruption of Vesuvius — the most recent activity from Europe's most dangerous volcano — was also VEI 4.

Recent example: Ruang, Indonesia (2024).

Descriptor: Plinian / Paroxysmal. Volume: 1 to 10 km3. Column height: over 25 km.

VEI 5 eruptions are major events with regional to global impact. The 1980 eruption of Mount St. Helens (VEI 5) killed 57 people and flattened 600 km2 of forest.

The 79 AD eruption of Vesuvius that buried Pompeii was VEI 5. The 2022 eruption of Hunga Tonga-Hunga Ha'apai (VEI 5) produced an atmospheric shockwave detected worldwide. VEI 5 events occur roughly once per decade.

Most recent example: Hunga Tonga-Hunga Ha'apai, Tonga (2022).

Descriptor: Plinian to Ultra-Plinian / Colossal. Volume: 10 to 100 km3. Column height: over 25 km.

VEI 6 eruptions are catastrophic events with global climatic impact. The 1991 eruption of Mount Pinatubo (VEI 6) lowered global temperatures by approximately 0.5 degrees C for two years. The 1883 eruption of Krakatau (VEI 6) killed over 36,000 people and produced the loudest sound in recorded history.

The 1912 eruption of Novarupta (VEI 6) was the 20th century's largest. VEI 6 events occur roughly once every 100 years. Most recent: Pinatubo, Philippines (1991).

Descriptor: Ultra-Plinian / Super-colossal. Volume: 100 to 1,000 km3. Column height: over 40 km.

VEI 7 eruptions are civilization-altering events. The 1815 eruption of Mount Tambora (VEI 7) was the largest in recorded history, killing approximately 71,000 people and causing the 'Year Without a Summer' in 1816. The Holocene record includes seven VEI 7 events, roughly one every 1,000 to 2,000 years.

Other examples: Santorini (~1610 BCE), Crater Lake (~5680 BCE), Kikai (~4350 BCE). Most recent: Tambora, Indonesia (1815).

Descriptor: Ultra-Plinian / Mega-colossal. Volume: over 1,000 km3. Column height: over 50 km.

VEI 8 events are supereruptions — the most powerful explosive events on Earth. No VEI 8 eruption has occurred in the Holocene (last 11,700 years). The most recent was the Oruanui eruption at Taupo, New Zealand, approximately 26,500 years ago (roughly 1,170 km3).

The largest Quaternary supereruption was Toba in Indonesia (~74,000 years ago, approximately 2,800 km3). The estimated recurrence interval is roughly 100,000 years.

The distribution of eruptions across VEI levels in the Smithsonian database reveals important patterns about volcanic activity on Earth. Of the 8,394 eruptions with assigned VEI ratings (out of 11,079 total), the distribution is heavily skewed toward lower magnitudes — as expected for a logarithmic natural phenomenon.

VEI 2 dominates the record with 4,020 entries (47.9% of all rated eruptions), reflecting both the genuine frequency of moderate explosive events and a detection bias: VEI 2 eruptions are large enough to be noticed and recorded, but small enough to occur frequently. VEI 0 and VEI 1 eruptions are undoubtedly far more numerous in reality, but many go unrecorded because they occur at remote volcanoes, beneath the ocean, or without significant impact on human populations.

At the upper end of the scale, the numbers drop precipitously: 514 events at VEI 4, 181 at VEI 5, 52 at VEI 6, and just 7 at VEI 7. No confirmed VEI 8 eruption has occurred during the Holocene epoch. This exponential decline is consistent with the fundamental physics of magma accumulation: the larger the eruption, the more magma must accumulate and the longer the recharge period.

The 2,685 eruptions without VEI assignments (24.2% of the total) are predominantly older events for which insufficient evidence survives to estimate eruption volume. This data gap is particularly acute for pre-historical eruptions, submarine eruptions, and eruptions in regions with limited geological investigation.

The VEI is sometimes compared to other scales of energy and destruction to convey the power of volcanic eruptions in more familiar terms.

**TNT equivalent and nuclear weapons** — The thermal energy released by volcanic eruptions can be compared to nuclear weapons, though the comparison is imperfect because volcanic energy is released over hours to days rather than microseconds. The Hiroshima atomic bomb released approximately 63 terajoules (TJ) of energy. The 79 AD eruption of Vesuvius (VEI 5) released energy estimated at roughly 100,000 times the Hiroshima bomb.

The 1883 eruption of Krakatau (VEI 6) released approximately 840 petajoules — roughly equivalent to 200 megatons of TNT, or about four times the energy of the largest nuclear weapon ever detonated (the Tsar Bomba, 50 megatons). A VEI 8 supereruption would release energy equivalent to roughly 10,000 to 100,000 megatons of TNT.

**Earthquake comparison** — The moment magnitude scale for earthquakes is also logarithmic, but measures different phenomena (seismic energy vs. ejected volume). Major volcanic eruptions are typically accompanied by earthquakes of magnitude 4 to 6, though the relationship is not direct. The 1815 Tambora eruption (VEI 7) was accompanied by earthquakes felt hundreds of kilometers away.

**Richter context** — While both VEI and the Richter/moment magnitude scales are logarithmic, they are not interchangeable. A VEI 6 eruption does not correspond to a magnitude 6 earthquake. The scales measure fundamentally different processes, and comparing them requires converting between tephra volume and energy release — a calculation with large uncertainties.

Despite its widespread use, the VEI has several recognized limitations that volcanologists keep in mind when interpreting the scale.

First, VEI measures only explosive tephra volume, not total eruption energy or impact. Large effusive eruptions — like the 1783 Laki fissure eruption in Iceland, which produced 14.7 km3 of lava and killed roughly 9,000 Icelanders — receive relatively low VEI ratings (VEI 6, based on the tephra component alone) despite being among the most impactful eruptions in recorded history. Similarly, the 2018 Kilauea eruption destroyed over 700 homes but was classified as VEI 0 because it was entirely effusive.

Second, VEI does not account for eruption duration. A VEI 4 eruption lasting several months may produce the same total tephra volume as a VEI 4 eruption lasting hours, but their instantaneous hazards are very different.

Third, VEI does not capture secondary hazards such as lahars, tsunamis, gas emissions, or famine — which are often the primary causes of death in volcanic disasters. The 1985 Nevado del Ruiz eruption (VEI 3) killed approximately 23,000 people through lahars, far more than many higher-VEI events.

Fourth, the scale has a significant historical bias. Pre-modern eruptions are often assigned VEI ratings based on incomplete tephra deposits, leading to systematic uncertainty. Many Holocene eruptions, particularly in poorly studied regions, lack VEI assignments entirely.

Volcanologists have proposed alternative scales — such as the magnitude scale (M) based on erupted mass and the intensity scale (I) based on mass discharge rate — but the VEI remains the most widely used and publicly recognized metric.