The Largest Volcanic Eruptions in History

Ranking the largest volcanic eruptions in history depends on the ruler you pick. By volume, the winner of the past million-plus years is Toba, in Sumatra, about 74,000 years ago, with a commonly cited 2,800 cubic kilometers of material. In recorded history it is Tambora, in 1815, far smaller but strong enough to cool the Northern Hemisphere and help cause the 1816 "Year Without a Summer." Death toll and climate impact produce different rankings again. This article lays out the numbers behind each record and explains why they disagree.

How scientists rank eruptions: VEI, volume, and sulfur

The standard yardstick is the Volcanic Explosivity Index, or VEI, devised in 1982 by Christopher Newhall of the U.S. Geological Survey and Stephen Self. It assigns an explosive eruption a number from 0 to 8 using the volume of material thrown out, the height of the eruption column, and qualitative observations (Wikipedia summary of the index). Above VEI 2, each step up means roughly ten times more ejected material. For volumes above 0.001 cubic kilometers, the rule of thumb is VEI = floor(log₁₀ of the volume in km³) + 5.

Think of VEI as a measure of how much poured out of the spill, not how toxic the spill was. A VEI 6 eruption ejects between 10 and 100 cubic kilometers of material, ten times more than a VEI 5 and ten times less than a VEI 7. The U.S. Geological Survey defines a supereruption as one that ejects about 1,000 cubic kilometers of volcanic debris, which is the VEI 8 threshold (USGS). That is not lava flowing gently downhill. It is ash, pumice, and pulverized rock blasted skyward or sent racing across the ground.

VEI	Ejecta volume (bulk)	Plume height	Typical recurrence for this size or larger	Examples
5	1 km³ or more	Over 20 km	About every 12 years	Mount St. Helens, 1980
6	10 km³ or more	Over 30 km	About every 50 to 100 years	Krakatau, 1883; Pinatubo, 1991
7	100 km³ or more	Over 40 km	About every 500 to 1,000 years	Tambora, 1815; Samalas, 1257
8	1,000 km³ or more	Over 50 km	More than 50,000 years	Toba; Yellowstone's Huckleberry Ridge; Oruanui

Source: Volcanic Explosivity Index table, as summarized on Wikipedia from Newhall and Self (1982). Example eruptions are discussed, with their own sources, below.

The index has real limits. It treats ash, pumice, lava bombs, and ignimbrite (rock formed from hot, fast-moving ash flows) as the same thing, so it ignores density. It says nothing about how much sulfur an eruption releases, which matters more for climate than raw volume does. And it uses bulk volume, which is the loose, fluffy deposit, rather than dense-rock equivalent, or DRE, the volume the same magma would occupy as solid rock. Pinatubo, for example, ejected over 10 cubic kilometers of loose material, which is roughly 5 cubic kilometers DRE (Wikipedia; the USGS cites "more than 5 cubic kilometers").

That mismatch explains why you see conflicting figures for the same eruption. One author quotes bulk volume, another quotes DRE, and a third quotes the volume of one deposit type. When a list says Tambora ejected 100 or more cubic kilometers and another says 37 to 45, both can be correct if they are measuring different things.

Ancient eruptions add a second problem. Geologists never witnessed them, so they reconstruct them from deposits: map the ash layers, measure their thickness, estimate how much has eroded, and infer what must have been there. It is like reconstructing a crime scene after half the walls have been torn down. Toba's published volume estimates span from about 2,000 to 13,200 cubic kilometers, a sixfold range, for exactly this reason (Wikipedia, List of largest volcanic eruptions).

For the mechanics of how magma climbs and why some eruptions are explosive, see how volcanoes work and why volcanoes erupt.

Toba, 74,000 years ago: the biggest eruption of the past million years

Toba is a huge caldera complex in northern Sumatra, Indonesia. Lake Toba now fills the depression left behind when the ground collapsed. The two most precise argon-argon dates for the Youngest Toba eruption are 73,880 ± 320 years ago (Storey et al., 2012) and 73,700 ± 300 years ago (Mark et al., 2017), both reported in the Wikipedia article on the eruption.

The volume estimates deserve a closer look. Rose and Chesner's older figure was at least 2,800 cubic kilometers, which is the number most often repeated. A 2023 reassessment by Kutterolf and colleagues put it at about 3,800 cubic kilometers DRE, made up of roughly 1,800 of ash fall and 2,000 of ignimbrite. Across studies the range runs from 2,000 to 6,000 cubic kilometers on the low side to as much as 13,200 on the high side. The wide spread tells you how uncertain it is to reconstruct a deposit that old.

Toba's ash blanket was continental in scale. It fell as a layer at least 1 centimeter thick across more than 38 million square kilometers, about 7.5 percent of Earth's surface, with roughly 5 centimeters on the Indian subcontinent and about 10 centimeters in the central Indian Ocean. Microscopic glass shards from Toba have turned up in cores from South Africa, Ethiopia, Lake Malawi, and Lake Chala. Geologists treat that ash layer like a time stamp: wherever it appears, the sediment around it is the same age.

The Toba catastrophe theory and why it is contested

In 1998 the anthropologist Stanley Ambrose proposed that Toba triggered a volcanic winter of six to ten years, followed by a long cold spell that cut the human population to a few thousand survivors and left a genetic bottleneck. The idea drew on gene-coalescence evidence, but the physical evidence has not been kind to it.

Sediment cores from Lake Malawi show no sign of volcanic winter in East Africa around 75,000 years ago (Lane et al., 2013), and later work in the same lake by Jackson and colleagues in 2015 concluded that the environmental effects lasted less than a decade in East Africa, although Yost and colleagues in 2018 reported that cooling-driven aridity killed high-elevation montane forests there. In India, stone tools above and below the ash in the Jurreru Valley look very similar, which suggests that local people were not wiped out (Petraglia et al., 2012). Archaeologists working in South Africa found that people thrived through the eruption (Smith et al., 2018).

Not everything points the same way. Evidence from the Middle Son Valley in India suggests a significant population decline, and a 2024 study by Kappelman and colleagues linked a severe drought in Ethiopia to the ash layer and to changes in how early humans foraged. Whole-genome studies show non-African populations reaching a low point roughly 40,000 to 60,000 years ago, but most researchers attribute that mainly to the founder effect of small groups leaving Africa rather than to Toba. All of these points are summarized in the Wikipedia article on the Toba catastrophe theory.

Climate models add another constraint. Simulations that assume Toba released about 100 times Pinatubo's sulfur produced a peak global cooling of 3.5 °C, with recovery within about five years (Timmreck et al., 2010), and other emission scenarios in a separate model gave 2.3 to 4.1 °C. Newer work (McGraw et al., 2024) suggests that if sulfate particles grew larger, which makes them less effective at reflecting sunlight, cooling could have stayed below 1.5 °C. None of the models produces a 1,000-year ice age. The fair summary is that Toba was enormous, it had real regional effects, and whether it nearly ended our species is an unproven claim.

For a broader comparison of history's great blasts, see the biggest explosions in history.

Bigger still: La Garita and the flood basalts

Toba is not the largest explosive eruption in the geological record, only the largest in a window that is recent enough to leave good evidence. The Fish Canyon Tuff, erupted from the La Garita Caldera in Colorado about 27.8 million years ago, is estimated at about 5,000 cubic kilometers, nearly double Toba's usual figure (Wikipedia, Supervolcano). Geologists have identified at least 60 VEI 8 eruptions across Earth's history, and they stress that the count is incomplete, since older deposits are more likely to be eroded or buried.

There is a second category that makes "largest eruption" an even looser phrase: flood basalts. The Siberian Traps cover a region of northern Asia with roughly 4 million cubic kilometers of basalt, erupted around 251.9 million years ago, and they are widely believed to be the primary cause of the end-Permian extinction, the most severe in the geological record (Wikipedia, Siberian Traps). A flood basalt province differs from a supereruption in style. A supereruption is a burst pipe, a huge amount of material released in a short time. A flood basalt province is a river that stays in flood, with repeated outpourings of lava over a far longer period.

Volcanism is not confined to Earth. Jupiter's moon Io is the most volcanically active body in the solar system, heated by tidal flexing, and Mars carries Olympus Mons, the largest known volcano in the solar system. For other extremes beyond Earth, see the most massive objects in the universe and the most extreme temperatures in the universe.

Yellowstone's giant eruptions: real, huge, and often misunderstood

Yellowstone is the supervolcano of popular media, though many volcanologists dislike the word because it suggests a special kind of volcano rather than a size category of eruption. The system has produced three giant caldera-forming eruptions in the past 2.1 million years. They are not equal in size, which surprises many readers.

Eruption	Age	Ash-flow volume	VEI class by volume
Huckleberry Ridge Tuff	About 2.08 million years ago	More than 2,450 km³	8
Mesa Falls Tuff	About 1.30 million years ago	More than 280 km³	7
Lava Creek Tuff	About 631,000 years ago	About 1,000 km³	At the 8 threshold

Source: Christiansen (2001) for volumes, Singer et al. (2014), Rivera et al. (2016), and Matthews et al. (2015) for ages, as summarized in the Wikipedia article on the Yellowstone Caldera. The ash-flow volumes exclude distal fallout and buried deposits, so true totals are larger.

The Mesa Falls eruption, at a minimum of 280 cubic kilometers, was a VEI 7 event, not a supereruption, and the Lava Creek eruption sits right on the line. Only Huckleberry Ridge is clearly a VEI 8. The Lava Creek eruption formed the Yellowstone Caldera that exists today.

The real misunderstanding is about timing. Several popular accounts claim Yellowstone is "overdue" for a giant eruption. The USGS calls that idea mathematically inaccurate, noting that "it is not valid to calculate a recurrence period solely on two values" and that giant eruptions are not evenly spaced. It also says there is "no evidence that enough melt has accumulated in one place to feed a supereruption." Of the past 50 or so eruptions, almost all were simple lava flows, the most recent about 70,000 years ago (USGS: five things people get wrong).

What is certain is smaller. The USGS says hydrothermal explosions, in which superheated water flashes to steam and hurls out rock, are "certain to occur" at Yellowstone in coming decades, and earthquakes are expected too. Eruptions are "less likely, but are ultimately inevitable" in the region (USGS: Yellowstone volcanic hazards). Monitors track ground movement closely. Between 2004 and 2008 the caldera floor rose at almost 75 millimeters a year, more than three times any rate recorded since measurements began in 1923, then slowed. Respect is warranted, and panic is not. For a scenario-based walk-through, read what if Yellowstone erupted tomorrow.

The last supereruption, and a mystery that took until 2013 to solve

The most recent supereruption on Earth was Oruanui, from the Taupō volcano in New Zealand, dated to about 25,700 years ago (25,675 ± 90 years before present). It produced about 1,170 cubic kilometers of deposits and left the caldera that Lake Taupō now partly fills. Ash from it fell about 5,000 kilometers away in Antarctica, where it matches deposits in West Antarctic ice cores (Wikipedia, Oruanui eruption).

A subtler case is the eruption of 1257. Ice cores from both polar regions showed a huge sulfate spike around that year, which told scientists that a major eruption had occurred, but nobody knew where. In 2013, Lavigne and colleagues identified the source as Samalas volcano on Lombok, Indonesia, and rated the event as probably a VEI 7, with perhaps 40 cubic kilometers DRE (Wikipedia, Mount Samalas). Whether it helped bring on the cooling of the Little Ice Age is suggested, not established.

Tambora, 1815: the largest eruption in recorded history

Tambora, on Sumbawa Island in present-day Indonesia, had been rumbling since 1812 and reached its climax in April 1815. It is the most recent confirmed VEI 7 eruption. Estimates of the DRE volume run from 37 to 45 cubic kilometers, and the summit collapsed from about 4,300 meters to about 2,851 meters, losing roughly a third of its height (Wikipedia, 1815 eruption of Mount Tambora).

The death toll is uncertain and depends on what you count. Oppenheimer (2003) put it at at least 71,000. Tanguy and colleagues (1998) estimated about 11,000 killed directly by the eruption and 49,000 more by famine and disease, and some other estimates reach about 100,000. The direct victims died in pyroclastic flows and ashfall. The rest died when the volcano wrecked crops and water supplies across the region.

Then came the climate effect. Tambora's sulfur, with estimates ranging from 10 to 120 teragrams and an ice-core-based average of about 25 to 30, spread through the stratosphere and cooled the Northern Hemisphere. Estimates of the global cooling range from 0.4 to 0.7 °C, with the 1816 Northern Hemisphere summer about 0.53 °C below normal. That does not sound like much, but the Tambora article on Wikipedia describes 1816 as the second-coldest Northern Hemisphere year since about 1400.

The Year Without a Summer

The consequences of that fraction of a degree were large because agriculture then ran on narrow margins. Frosts hit New England and northern New York in early June 1816, and snow fell in Albany on June 6. New England corn ripened so poorly that no more than a quarter was usable for food, and oat prices rose from 12 cents to 92 cents a bushel between 1815 and 1816. Vermont lost an estimated 10,000 to 15,000 people to emigration in 1816 and 1817 (Wikipedia, Year Without a Summer, summarizing historians).

In Europe, the same cooling produced the worst famine of the century, with food riots in 1816 and 1817 that were the most violent since the French Revolution, and typhus epidemics that killed more than 65,000 people between 1816 and 1819. The historian John D. Post called it "the last great subsistence crisis in the Western world." In Asia, a famine in Yunnan is credited with helping weaken the Qing dynasty, and a delayed monsoon in India aggravated a cholera outbreak.

Tambora also left cultural fingerprints. The cold, wet weather kept Mary Shelley, Percy Shelley, and Lord Byron indoors at Lake Geneva that summer, and Byron proposed a ghost-story contest that led to Frankenstein. But the global story often romanticizes the European weather while underplaying the catastrophe in Indonesia. Tambora is not the largest eruption by volume, but it happened in a world with written records, trade networks, and cities, so its effects were documented.

Krakatau, 1883: not the biggest, but the loudest

Krakatau's 1883 eruption is often remembered as history's largest, but by volume it was smaller than Tambora. It was a VEI 6 event that deposited about 20 cubic kilometers of tephra, with the climactic phase running from about 1 p.m. on August 26 through the major explosions on August 27 (Wikipedia, 1883 eruption of Krakatoa). The official death toll was 36,417, largely attributed to tsunamis, with wave heights reported up to 46 meters at Merak.

The sound is what made it famous. It was heard 3,110 kilometers away in Perth and 4,800 kilometers away near Mauritius, and accounts describe the third explosion as the loudest sound ever measured. The pressure wave was recorded on barographs worldwide and circled the globe more than three times. For the physics of loudness and the competing records, see the loudest sounds ever recorded.

Ash and sulfur in the stratosphere reddened sunsets worldwide for months, vividly enough that fire engines were called out in New York to what looked like blazes. Northern Hemisphere summer temperatures fell about 0.4 °C in the year after. The lesson of Krakatau is that location matters as much as size. The eruption took place in shallow seawater between two heavily populated islands, which made tsunami generation the main killer.

The same volcanic system produced another warning in December 2018, when the southwestern flank of Anak Krakatau, the "child of Krakatau," collapsed during an eruption and triggered a tsunami. It killed 437 people and injured 14,059, according to the disaster agency's count at the end of the year, and the volcano lost more than two-thirds of its volume (Wikipedia, Anak Krakatau). It was far smaller than 1883, but it showed that the system remains dangerous.

Pinatubo, 1991: the eruption we measured best

Mount Pinatubo in the Philippines erupted on June 15, 1991, after centuries of quiet. It was a VEI 6 event, with more than 5 cubic kilometers of material and nearly 20 million tons of sulfur dioxide injected into the stratosphere (USGS Fact Sheet 113-97). Satellites, aircraft, and ground instruments captured its atmospheric effects in unprecedented detail, which turned Pinatubo into a natural experiment in how aerosols affect climate.

Global temperatures dropped by about 0.5 °C, roughly 1 °F, between 1991 and 1993. Because sulfur makes up half of sulfur dioxide's mass, the 20 million tons of SO₂ corresponds to about 10 million tons (10 teragrams) of sulfur, which makes Tambora's ice-core average of 25 to 30 teragrams roughly two and a half to three times larger, though Tambora estimates range widely.

The eruption is also a case study in saving lives. Scientists from the Philippine Institute of Volcanology and Seismology and the USGS recognized the warning signs and forecast the eruption, and the USGS estimates that the forecast saved "at least 5,000 lives." Even so, about 847 people died, mostly when roofs collapsed under the weight of wet ash, because Typhoon Yunya struck the island on the same day, with its center passing about 75 kilometers north of the volcano (Wikipedia, 1991 eruption of Mount Pinatubo). Rain mixed with ash also produced lahars, mudflows of volcanic debris that buried valleys.

Two modern eruptions that broke the pattern

Mount St. Helens, which erupted on May 18, 1980, is a VEI 5 event by the usual accounting. Its ash, before rain compacted it, had a volume of about 1.3 cubic kilometers, and the commonly cited death toll is 57. Its ash column rose about 24 kilometers.

The 2022 eruption of Hunga Tonga-Hunga Ha'apai, on January 15, 2022, was stranger. The Smithsonian Global Volcanism Program rates it VEI 5, though other estimates run from 4 to 6, and its plume reached about 58 kilometers into the mesosphere, a height the VEI chart associates with the largest eruptions. It injected what researchers describe as unprecedented amounts of water vapor into the stratosphere, which one study estimated could linger for up to eight years. The eruption raised a tsunami that reached Japan and the Americas, killing four people in Tonga and two in Peru (Wikipedia, Hunga Tonga-Hunga Ha'apai). The lesson is that a single number can hide very different physics. A modest ejected volume can still do unusual things to the atmosphere if the water and the geometry are right.

What makes a supereruption different?

A supereruption is not simply "a big volcano blowing up." It is typically a caldera-forming eruption, in which a large magma reservoir empties so quickly that the ground above it collapses. Think of the roof of a cellar when the contents are pulled out from under it: the eruption is the emptying, and the caldera is the collapse.

The deposits include pyroclastic density currents, ground-hugging avalanches of hot gas, ash, and pumice that flatten and scorch everything in their path, and fallout that can blanket regions thousands of kilometers away, as Toba's ash did. That is the difference between a supereruption and an ordinary large one: the footprint is continental, not regional.

The word "supervolcano" can mislead. Many supereruption sites are broad calderas rather than steep cones, and their magma systems are crystal-rich and only partly molten. Yellowstone, Toba, and Taupō are landscapes, not peaks. A large caldera does not mean a giant eruption is near. Humanity has never witnessed a VEI 8 event, so planning for one means relying on deposits and models, not direct experience.

How volcanoes change the climate

Large explosive eruptions affect climate mainly through sulfur dioxide. When it reaches the stratosphere, it reacts with water to form sulfate aerosols, tiny droplets that reflect incoming sunlight and cool the surface. The stratosphere is dry and stable, so the droplets can persist for a year or more, while ash, though visually dramatic, falls out much faster.

That is why the VEI is an imperfect guide to climate. The Wikipedia summary of the index notes that sulfur dioxide emissions are more significant than the VEI for assessing atmospheric and climatic impact. Two eruptions of similar size can differ greatly in how much sulfur they release.

Eruption	Sulfur release	Cooling	Source
Tambora, 1815	10 to 120 Tg of sulfur; ice-core average 25 to 30 Tg	About 0.4 to 0.7 °C globally; Northern Hemisphere summer 1816 about 0.53 °C	Wikipedia, citing Robock and ice-core studies
Krakatau, 1883	Not stated in the source	About 0.4 °C in Northern Hemisphere summers the following year	Wikipedia, 1883 eruption
Pinatubo, 1991	Nearly 20 million tons of SO₂ (about 10 Tg of sulfur)	About 0.5 °C, 1991 to 1993	USGS Fact Sheet 113-97
Toba (model, not observed)	8.5 × 10¹⁴ g of sulfur assumed	Up to 3.5 °C in one model; under 1.5 °C if particles grew large	Timmreck et al.; McGraw et al., as summarized on Wikipedia

The cooling is temporary. After Pinatubo, temperatures recovered as the aerosols settled out within a few years, whereas carbon dioxide from human activity persists far longer in the atmosphere, which is why volcanic cooling does not offset warming. For the longer-term picture, see climate change science. Volcanoes do show that aerosols can cool the planet briefly, and that observation features in debates about deliberately injecting aerosols, but a one-to-two-year effect says nothing about whether such a scheme would be wise.

The deadliest is not always the largest

The biggest eruptions by volume are mostly prehistoric. The deadliest in human records are often smaller but better placed to kill.

Eruption	VEI	Deaths	Main cause of death
Tambora, 1815	7	At least 71,000 (Oppenheimer, 2003); some estimates about 100,000	Pyroclastic flows, then famine and disease
Krakatau, 1883	6	36,417 (official)	Mostly tsunamis
Nevado del Ruiz, 1985	3	More than 23,000	Lahars from melted glacier ice
Pinatubo, 1991	6	About 847	Roofs collapsing under wet ash
Mount St. Helens, 1980	5	57 (most commonly cited)	Blast, ash, and debris flows
Anak Krakatau, 2018	Not rated here	437	Tsunami from flank collapse

Sources: Wikipedia articles on each eruption, citing Oppenheimer (2003), Tanguy et al. (1998), and disaster-agency counts; Pinatubo lives-saved figure from USGS Fact Sheet 113-97.

The most striking row is Nevado del Ruiz in Colombia. On November 13, 1985, a VEI 3 eruption, three VEI steps (roughly a thousandfold) below Pinatubo, sent pyroclastic flows across the summit ice and snow and melted them into four large lahars. They buried the town of Armero, where only about a quarter of the 28,700 residents survived (Wikipedia, Nevado del Ruiz). An eruption that would barely register on a global list killed more than 23,000 people because of where it was and what it melted.

That mismatch is important for risk communication. People hear "supervolcano" and picture the largest possible event, but practical preparedness more often depends on moderate eruptions meeting water, snow, cities, and infrastructure. Ash on roofs can collapse buildings, ash in jet engines can stop aircraft, and lahars can follow river valleys long after an eruption ends. The task is to match the hazard to the place, which is why our ranking of the deadliest volcanoes in history looks so different from this one. The broader picture of lethal events is in the deadliest natural disasters in history, and for volcanoes defined by size rather than eruption, see the largest volcanoes in the world.

Could a Toba-sized eruption happen again?

Geologically, yes. In terms of anything you could schedule, no. VEI 8 events recur on timescales of more than 50,000 years on average, and the last one, Oruanui, was about 25,700 years ago. A VEI 7 event like Tambora happens about every 500 to 1,000 years on average, and the last confirmed one was 1815. Averages are not appointments. These events arrive irregularly, and USGS stresses that recurrence cannot be computed from a few data points.

No monitoring agency has identified an imminent supereruption. Volcanologists watch for earthquake swarms, ground deformation, gas changes, heat flow, and hydrothermal shifts, as described in how scientists predict volcanic eruptions. None of these signals alone means a giant eruption is coming. Many restless volcanoes show unrest for years without erupting, and some eruptions escalate quickly. Monitoring reduces uncertainty without turning volcanoes into scheduled machines.

The most useful preparation is broad: maintain volcano observatories, map hazard zones, plan evacuation routes, protect water systems, reinforce roofs where ashfall is plausible, and coordinate aviation warnings. It is less cinematic than planning for the biggest eruption ever, and it is how lives were saved at Pinatubo.

What this means

The headline question has three honest answers. The largest eruption of at least the past million years is Toba, with volume estimates that depend on the method. The largest in recorded history is Tambora. The most lethal in terms of death per unit of volume is something like Nevado del Ruiz, a VEI 3 that killed more than 23,000 people.

The pattern behind the three is that volume is only one input. Sulfur decides the climate effect, geography and water decide the death toll, and the quality of the record decides how well we know any of it. Toba is huge but poorly constrained. Pinatubo is modest but exquisitely measured, and it taught volcanologists more about aerosols and forecasting than any ancient supereruption could.

For readers, the practical lesson is to distrust single-number rankings. Ask which measure is being used, whether it is bulk or dense-rock volume, and whether the claim is about size, climate, or casualties.

Frequently Asked Questions

Q: What was the largest volcanic eruption ever?
A: It depends on what you count. Among the largest known explosive eruptions is the Fish Canyon Tuff in Colorado, about 27.8 million years ago and roughly 5,000 cubic kilometers. The largest of at least the past million years is Toba, about 74,000 years ago, with common estimates near 2,800 cubic kilometers. Flood basalts like the Siberian Traps are larger still but are not single explosions.

Q: What was the largest volcanic eruption in recorded history?
A: Tambora in 1815, a VEI 7 eruption in Indonesia with a DRE volume of about 37 to 45 cubic kilometers. It killed at least 71,000 people by most estimates and cooled the Northern Hemisphere enough to cause the 1816 "Year Without a Summer." The 1257 Samalas eruption may have been comparable, but it is known only from geology and ice cores.

Q: Is Yellowstone overdue for a supereruption?
A: No. The USGS calls the "overdue" claim mathematically inaccurate and says there is no evidence of enough melt accumulating to feed a supereruption. Almost all of Yellowstone's last 50 or so eruptions were lava flows. Hydrothermal explosions are the more realistic hazard in coming decades.

Q: What does VEI 8 mean?
A: It is the top of the Volcanic Explosivity Index, applied to eruptions that eject 1,000 cubic kilometers or more of material. These are called supereruptions. At least 60 have been identified in the geological record, and the most recent, Oruanui in New Zealand, was about 25,700 years ago.

Q: Did Toba almost wipe out humanity?
A: Probably not. The "Toba catastrophe theory" proposed a bottleneck of a few thousand survivors, but sediment cores in East Africa show no volcanic winter, and archaeological sites in India and South Africa show continuity across the ash layer. Models suggest cooling of up to a few degrees for about five years, and some evidence of regional hardship, such as drought in Ethiopia, exists.

Q: Why do volcanoes cool the climate?
A: Big eruptions inject sulfur dioxide into the stratosphere, where it forms sulfate aerosols that reflect sunlight. After Pinatubo in 1991, global temperatures fell about 0.5 °C for roughly two years. Ash falls out quickly, so sulfur drives most of the global effect, and the cooling fades as the aerosols settle.

Q: Which eruption killed the most people?
A: Tambora in 1815 had the highest estimated toll, at least 71,000, most of it from famine and disease after the eruption. Krakatau in 1883 killed 36,417 according to the official count, mostly through tsunamis. Nevado del Ruiz in 1985, a VEI 3 event, killed more than 23,000 through lahars.

Sources

• USGS Fact Sheet 113-97, Pinatubo (volume, sulfur dioxide, cooling, lives saved)
• USGS, Five things most people get wrong about Yellowstone volcano (supereruption definition, "overdue," eruption history)
• USGS, Yellowstone volcanic hazards (hydrothermal explosions, likelihood)
• Compiled summaries with citations to the primary literature: Wikipedia articles on the Volcanic Explosivity Index, the Youngest Toba eruption, the Toba catastrophe theory, the 1815 eruption of Mount Tambora, the 1883 eruption of Krakatoa, the 1991 eruption of Mount Pinatubo, the Yellowstone Caldera, and the Year Without a Summer

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