Earth’s Active Supervolcanoes: The VEI-8 Eruptions and Their Restless Calderas

What is a VEI-8 Eruption?

Supervolcano eruptions are Earth’s most colossal volcanic events. They rate an 8 on the Volcanic Explosivity Index (VEI) – the highest value on that logarithmic scale – meaning they eject over 1,000 cubic kilometres of volcanic material in a single eruption. Such an eruption can blanket continents in ash and alter global climate. Geologically, any volcano that has produced a VEI-8 eruption is informally known as a “supervolcano.” These events are extremely rare. Based on the geologic record, at least 60 super-eruptions (VEI-8) have been identified throughout Earth’s history. The most recent occurred about 25,600 years ago in New Zealand (the Oruanui eruption of Taupō) – long before recorded history.

To put this in perspective, a VEI-8 “super-eruption” releases hundreds to thousands of times more ash and lava than a big eruption like Krakatoa (1883) or Mount St. Helens (1980). The widespread hazards of such an outbreak include pyroclastic flows scouring tens of thousands of square kilometres, ashfall capable of collapsing roofs even hundreds of kilometres away, and injections of sulphur aerosols into the stratosphere that can cool the global climate for years. Some scientists hypothesize that the Toba super-eruption (~74,000 years ago) induced a decade-long “volcanic winter” and nearly caused human extinction in some regions (though this remains debated). What’s certain is that a VEI-8 eruption is a planetary-scale event.

Criteria for inclusion: In this article, we focus on confirmed VEI-8 volcanoes that are still geologically active today – meaning their super-eruptions occurred in the Quaternary period and the volcanoes still show signs of life (seismicity, heat flow, gas emissions, or minor eruptions in the Holocene). That narrows the field to a few famous examples. We exclude “near-miss” cases like Tambora 1815 or Novarupta 1912 (VEI-7), as well as large caldera systems that haven’t produced a full VEI-8. While several other calderas – for example, Campi Flegrei in Italy and Long Valley in California – are often labelled “supervolcanoes” in the media, their known eruptive volumes (e.g. the ~39 ka Campanian Ignimbrite at Campi Flegrei was ~200–300 km³ DRE, and Long Valley’s Bishop Tuff ~600 km³) fall below the VEI-8 threshold. Below we highlight the truly super-sized eruptions and the volcanoes that created them, all of which remain under watch today.

Yellowstone Caldera (USA)

Name & Location: Yellowstone Caldera – northwestern Wyoming, USA (with parts in Montana and Idaho). This is the volcanic heart of Yellowstone National Park.

VEI-8 Eruption(s): Yellowstone has had multiple super-eruptions. The two largest were: Huckleberry Ridge (~2.1 million years ago) and Lava Creek (~640,000 years ago). The Huckleberry Ridge eruption unleashed about 2,450 km³ of material, while the Lava Creek eruption ~640 ka ejected roughly 1,000 km³, meeting the VEI-8 criterion. (An intermediate eruption, Mesa Falls ~1.3 Ma, was smaller at ~280 km³.) The Lava Creek super-eruption is the one that formed the current Yellowstone Caldera.

Caldera & Features: The Yellowstone Caldera is an enormous oval depression about 85 km by 45 km across. Essentially, the super-eruption emptied the magma chamber and caused the ground to collapse into a caldera roughly the size of a small state. Today much of this caldera is a high plateau studded with resurgent domes (uplifted regions marking the refilling magma chamber). It’s hard to “see” Yellowstone’s caldera from the ground because it’s so vast and its rim is partially eroded – but its outline can be traced by cliffs and the distribution of volcanic rocks. Notably, Yellowstone Lake straddles the southeastern caldera, and the West Thumb bay of the lake is itself a smaller caldera from a later eruption ~174,000 years ago.

One of the most remarkable features testifying to Yellowstone’s active magma system is its hydrothermal plumbing. The park contains over 10,000 geothermal features, including fumaroles, hot springs, mud pots, and over 500 geysers – the greatest concentration on Earth. Iconic geysers like Old Faithful owe their existence to the heat from the magma lingering a few kilometres below. The vivid hot spring pools and incessant steaming ground are visual evidence that Yellowstone is very much alive beneath the surface.

Current Activity: Yellowstone does not erupt often (its last magmatic eruption was a rhyolite lava flow ~70,000 years ago), but it is far from dormant. The caldera floor rises and falls in breathing-like cycles due to magma and hydrothermal fluids shifting below. Geologists have measured episodes of significant uplift: from 2004–2008, parts of the caldera rose ~20 cm as magma intruded shallow depths. This was three times faster than any uplift observed there since monitoring began in the 20th century. After 2008 the uplift slowed, and in some recent years the caldera has even subsided slightly – a reminder that these systems can deflate as well as inflate.

Yellowstone is also seismically active, experiencing hundreds to thousands of earthquakes a year (most very small). Occasional earthquake swarms punctuate this activity. For instance, in early 2010 a swarm of over 1,600 tremors occurred under the park in just a few weeks, the second-largest swarm recorded in the caldera. The largest of those quakes was modest (M~3.8), but swarms show how restless the volcanic system can be. These quakes typically indicate shifting fluids or minor fault adjustments; none so far have presaged an eruption.

All this activity is closely watched. The Yellowstone Volcano Observatory (YVO) – a partnership of the U.S. Geological Survey, University of Utah, and National Park Service – maintains a dense network of seismometers, GPS stations, satellite sensors, and geochemical sampling in the region. They track everything from quake patterns to ground deformation to hot spring chemistry. Currently, Yellowstone’s status is “Normal” (Green) on the volcano alert level; essentially, it’s at background activity with no signs of impending eruption. YVO scientists have repeatedly stated that there are no indications of an imminent super-eruption – or even a smaller eruption – on the horizon. In fact, they caution against the popular notion that Yellowstone is “overdue” for a cataclysm: volcanic systems do not erupt on schedule, and statistical recurrence intervals (like the often cited “~730,000 year interval” between Yellowstone’s big blasts) are not reliable predictors.

Monitoring & Alert Status: Yellowstone is one of the most intensively monitored volcanoes in the world. The alert level has remained at Green/Normal for decades. If any concerning changes occur – say, earthquake swarms intensifying, rapid uplift, or unusual gas emissions – scientists would quickly detect them and could raise the alert level. An interesting hypothetical project by NASA even investigated whether drilling to circulate water through the magma chamber could cool and depressurize Yellowstone to prevent an eruption, but this remains science fiction (and not without risk of its own). For now, the strategy is careful observation and research. Every year, YVO releases reports on Yellowstone’s seismicity, deformation, and geothermal activity, which continue to paint a picture of a dynamic yet non-eruptive system.

Potential Hazards: If Yellowstone were to have another super-eruption (again, extremely unlikely in any near time frame), the consequences would be severe regionally and globally. The entirety of the surrounding states (Wyoming, Idaho, Montana) would be blanketed in meters of ash and pyroclastic flow deposits. Ash could accumulate tens of centimetres thick as far away as the Midwest, crippling agriculture, clogging rivers, and shutting down infrastructure. The climate impact would also be global: an eruption on the scale of the Lava Creek Tuff (≈1000 km³) would inject vast quantities of ash and sulphur gases into the stratosphere, leading to significant sunlight reduction. Past super-eruptions are thought to have caused years of cooler temperatures (“volcanic winter” scenarios) due to sulfuric acid haze in the atmosphere. That said, smaller-scale events are more likely – e.g. a localized lava flow or a hydrothermal explosion (like the one that formed Mary Bay crater ~13,800 years ago) – which would still be hazardous within the park but far less apocalyptic than a super-eruption. Overall, Yellowstone’s volcano presents many hazards, but diligent monitoring and improved understanding mean we’re better prepared than ever to detect warning signs long before any future eruption.

Lake Toba (Indonesia)

Name & Location: Lake Toba – Northern Sumatra, Indonesia. Toba lies within the Sumatra subduction zone and is the site of Earth’s most recent super-eruption of truly staggering size.

VEI-8 Eruption: Approximately 74,000 years ago, Toba produced the eruption of the Youngest Toba Tuff, which was the largest volcanic eruption on Earth in the past 2 million years. This colossal event is estimated to have erupted about 2,800 km³ of magma (dense rock equivalent) – an unimaginable volume. For comparison, that’s roughly 7 times the material ejected by the Tambora 1815 eruption. The Toba super-eruption registers as VEI-8 by any measure. It created a global layer of Toba ash that serves as a marker in geological sediments. According to volcano researchers, the Toba eruption may even have had worldwide ecological and climate impacts – it has been theorized (though debated) that it caused a severe “volcanic winter” and a genetic bottleneck in human populations. What’s certain is that Toba’s outburst was cataclysmic in its immediate footprint.

Caldera & Features: The eruption emptied Toba’s magma chamber so completely that the ground collapsed into a giant caldera, now filled by Lake Toba, the largest volcanic lake in the world. Toba’s caldera measures roughly 100 km by 30 km across – about the size of a large metropolitan area. Steep caldera walls ring the lake, reaching up to 500–700 meters above the lake surface, evidence of the colossal subsidence. The lake itself is about 505 meters (1,660 ft) deep. In the middle of Lake Toba lies Samosir Island, a large island ~45 km long that is actually a resurgent dome – the floor of the caldera pushed back up by slowly refilling magma. Along with the Uluan Peninsula on the caldera’s south side, these form uplifted blocks inside the caldera. Geological studies found that lake sediments on Samosir Island have been lifted about 450 m (1,350 ft) since the cataclysm, indicating significant magmatic resurgence underneath.

Even after the super-eruption, Toba’s volcanic system wasn’t completely finished. There is a smaller stratovolcano (Mt. Pusukbukit) on the western caldera edge that formed after the big eruption. Around the caldera, especially on the north side, one can find active solfataras and hot springs – vents where sulphur-rich steam and gas escape. These fumaroles show that heat from magma still permeates the system. Lake Toba today is a scenic highland lake attracting tourists, but it’s also a massive volcanic scar, still thermally active.

Current Activity: No eruption has occurred at Toba in recorded history (the past few thousand years). In that sense, Toba has been quiescent for a very long time. However, “geologically active” doesn’t require recent eruptions – Toba exhibits ongoing geothermal and tectonic unrest. The presence of hot springs and fumaroles around the caldera (e.g. in the north at Sipoholon and along the Uluan Peninsula) indicates a magma heat source beneath. Importantly, geophysical research in recent years has imaged magma still present under Toba. A 2021 study of zircon crystals, for example, estimated that about 320 square kilometres of semi-molten magma could be lurking under Lake Toba today. The continuing slow uplift of Samosir Island – effectively a giant piston being pushed up – “indicates that the volcano is active and that magma is accumulating underneath”.

Seismic activity around Toba is notable, though much of it is related to the regional tectonics (Sumatra’s active faults and the subduction zone offshore). The area has experienced major earthquakes (for instance, a M8.6 quake struck offshore of northern Sumatra in 2005). These quakes sometimes “rattle” the Toba region but haven’t been linked to any magma movement triggering eruptions. In 2016, clusters of shallow earthquakes directly under the lake raised some concern, but no volcanic eruption ensued. Indonesia’s Centre for Volcanology and Geological Hazard Mitigation (PVMBG) keeps watch on Toba’s activity with a monitoring network – though Toba is not as instrument-heavy as some more frequently erupting Indonesian volcanoes. As of now, Toba’s alert level is at Level I (normal) or equivalent, reflecting no immediate unrest beyond background geothermal venting.

Ongoing Research: Scientists worldwide are intrigued by Toba and have drilled into lake sediments and studied its crystal formations to understand the timing and conditions of super-eruptions. One interesting finding is that the magma that fed Toba’s big eruption may have accumulated over hundreds of thousands of years quietly, without obvious precursors right before the eruption. This suggests that traditional warning signs (like a huge influx of fresh magma or escalating smaller eruptions) might not always precede a supervolcano blast – a sobering idea, and an impetus for very close monitoring of any subtle changes.

Potential Impacts: A future super-eruption at Toba, while extremely improbable on human timescales, would be catastrophic. Northern Sumatra and neighbouring areas would be devastated by pyroclastic flows extending tens of kilometres beyond the caldera. Ashfall would inundate all of Southeast Asia – the Toba eruption covered an area of at least 20,000 km² in pyroclastic flows near the volcano, and ash 15 cm thick (6 inches) fell as far away as the Indian subcontinent. For context, a 15 cm ash layer was spread over the entire Indian subcontinent – thousands of kilometres from Toba – by the last eruption. If repeated today, such an ash blanket would collapse roofs, poison water supplies, and shut down transportation over an immense region. Globally, the climate cooling from millions of tons of sulphur gases could depress temperatures for years, affecting world agriculture. Some climate models suggest a volcanic winter scenario with temperature drops of several degrees Celsius. However, it’s important to stress that volcanoes like Toba give us long repose periods. Toba might erupt again someday, but current evidence – gradual magma accumulation and modest geothermal venting – suggests no sign of an impending catastrophe. The supervolcano will likely slumber for millennia more, and if that changes, scientists expect to see telltale signs (ground deformation, seismic swarms, gas changes) well in advance.

Taupō Volcano (New Zealand)

Name & Location: Taupō Volcano – central North Island, New Zealand. It lies in the Taupō Volcanic Zone, a highly active volcanic region that also includes volcanic neighbours like Ruapehu and Tongariro. Taupō is a sizeable caldera volcano currently filled by Lake Taupō, New Zealand’s largest lake.

VEI-8 Eruption: Taupō’s claim to supervolcano status comes from the Oruanui eruption ~25,500 years ago. This was the world’s most recent confirmed VEI-8 super-eruption. During the Oruanui event, an estimated 1,170 km³ of tephra was ejected (about 430 km³ of ash fall, 320 km³ of pyroclastic flows, plus intracaldera material – equivalent to ~530 km³ of solid magma). This titanic eruption devastated a large swath of New Zealand. It is credited with creating the modern Taupō caldera shape and depositing the widespread Oruanui ignimbrite sheet. For context, Oruanui was the largest eruption on Earth since the Toba event; it was hundreds of times larger than the 1815 Tambora eruption. Notably, Oruanui’s fallout blanketed much of New Zealand – ash deposits 10–15 cm thick can be found even 850 km away on the Chatham Islands in the Pacific. The eruption likely caused short-term climate perturbations as well, though on a lesser scale than Toba due to the smaller sulphur output and different latitude.

Caldera & Features: The Lake Taupō we see today (about 616 km² in area) occupies the collapse crater from Oruanui. The caldera is roughly oval, ~35 km across at its widest. The eruption and caldera collapse fundamentally reshaped the landscape: thick ignimbrite (welded tuff) up to 200 m thick covers the central North Island. Unlike Yellowstone or Toba, Taupō’s caldera is largely flooded, creating a picturesque lake with bays and a central depression. The only prominent intra-caldera features are small islands (such as Motutaiko Island) and a submerged rhyolite dome complex (the Horomatangi Reefs) – likely remnants of post-Oruanui lava eruptions. Indeed, Taupō Volcano has erupted multiple times since the super-eruption, but these were much smaller events. The most notable was the Hatepe eruption (also called the Taupō eruption) around 232 CE (1,800 years ago). Though not VEI-8, the Hatepe eruption was enormous in its own right (VEI 7, perhaps ~120 km³ of ejecta) – it is considered the most violent eruption worldwide in the last 5 millennia. The Hatepe eruption caused devastating pyroclastic flows that rafted across the lake and sent ash clouds high into the atmosphere. It provides a stark example of Taupō’s potential for highly explosive activity, even at less-than-supervolcano scale.

Today, Lake Taupō’s waters obscure much of the caldera’s geothermal expression, but around its shores and the broader region, there are numerous hot springs, fumaroles, and geothermal fields (e.g. the Craters of the Moon thermal area near Taupō town). These indicate ongoing heat flow. Also, at the lake’s bottom, scientific surveys have found hydrothermal venting and hot, gassy water – evidence Taupō’s volcanic vents are not entirely silent beneath the lake surface.

Current Activity: Taupō is an active but quiescent volcano – there have been no eruptions in ~1,800 years, but it regularly exhibits unrest. Geologic records and oral histories of the Maori indicate occasional eruptions over the past 5,000 years aside from Hatepe (several smaller ones formed lava domes or short-lived explosions within the lake). In the modern era (last ~150 years), no eruptions have been witnessed, but Taupō has shown significant seismic and geodetic activity. Scientists have documented at least 17 episodes of volcanic unrest since 1872. These unrest episodes typically involve swarms of small earthquakes under the lake, often accompanied by ground deformation (uplift or subsidence) of the caldera floor.

One very recent episode occurred from mid-2022 to early 2023. Starting in May 2022, Taupō was hit by increased earthquake activity – over 1,800 micro-earthquakes were recorded under the lake in that period. Residents around the lake felt some of the larger quakes (up to about M4-5). In addition, GPS instruments detected that parts of the caldera were uplifting by several centimeters, and one under-lake slope even slumped, causing a small local tsunami (wave) in the lake in 2022. This heightened unrest led New Zealand’s monitoring agency (GeoNet) to raise the Volcanic Alert Level to 1 (indicating minor volcanic unrest) on 20 September 2022 – the first time ever that Taupō’s alert level had been raised. The public was alerted, though officials emphasized there was no sign of an impending eruption, just unusual activity. The unrest eventually waned by May 2023; earthquakes subsided and ground deformation paused. Consequently, the alert level was lowered back to 0 (no unrest) in May 2023 as the volcano returned to background levels.

These unrest episodes underscore that Taupō’s magma system is still active. Scientific studies estimate that Taupō’s crustal magma reservoir currently holds on the order of 200–250 km³ of magma, of which perhaps 20–30% is liquid melt. (The rest is crystalline “mush.”) For context, that partially molten zone is large – roughly on par with Yellowstone’s upper magma chamber in size – but it doesn’t mean a large eruption is imminent. It does mean, however, that Taupō still has magma available and heat to drive unrest.

Monitoring & Preparedness: Taupō volcano is closely watched by the GeoNet program run by GNS Science. There are multiple seismographs around the lake, continuous GPS stations tracking ground movement, lake level gauges, and periodic airborne gas measurements over Taupō. With the raising of the alert level in 2022, local civil defense also increased preparedness messaging for communities around the lake. New Zealand has a well-defined alert level system (0 to 5) and contingency plans for volcanic crises, given that the country hosts many active volcanoes. Taupō’s current status (Alert Level 0, Aviation Color Code Green) indicates no sign of eruptive activity at present.

Crucially, volcanologists point out that super-eruptions are extraordinarily infrequent at Taupō. In the last 30,000 years since Oruanui, the volcano has had 28 known eruptions, all of which were much smaller than the caldera-forming one. Many were lava dome effusions or moderate explosive events confined to the volcano’s vicinity. This suggests that Taupō’s typical behavior is on a smaller scale, and the giant Oruanui-type events are extremely rare. The recent unrest, while noteworthy, likely reflects minor readjustments in the magma system rather than a build-up to anything massive. GeoNet volcanologists have assessed the probability of a large eruption from Taupō in any given year as very low (on the order of fractions of a percent).

Potential Hazards: Given Taupō’s active nature, the primary hazards are twofold: 1) Future smaller eruptions – which could still be dangerous locally – and 2) The ever-present but very remote possibility of another super-eruption. For the smaller-scale scenario, an eruption at Taupō might involve pumice-forming explosions within the lake (which could cause pyroclastic surges and tsunamis on the lake) or possibly a lava dome extrusion that could result in localized ashfall (like its eruptions ~1,100 and ~1,800 years ago). These would significantly impact the central North Island – for example, air travel could be disrupted, and ash could affect pastoral farming – but would not be globally catastrophic.

In the extreme case of a super-eruption (again, considered extremely unlikely in the foreseeable future), the North Island of New Zealand would face devastation. Thick ash and ignimbrite flows could cover tens of thousands of square kilometres, which would be an unprecedented natural disaster for the country. The global climate would also take a hit: a Taupō-scale VEI-8 eruption would inject enough ash and gas to cool global temperatures, perhaps for a few years, and dramatically affect weather patterns. However, given Taupō’s lengthy repose since Oruanui and the extensive monitoring in place, scientists are confident that any reawakening would be detected well in advance. In sum, Taupō remains a fascinating and dynamic system – a supervolcano that sleeps beneath a tranquil lake, occasionally stirring, but likely to give us ample warning before any future roar.

Conclusion and Other Notable Supervolcanoes

In summary, VEI-8 supervolcano eruptions are among Mother Nature’s rarest and most titanic events. We have highlighted three locations – Yellowstone, Toba, and Taupō – that have unleashed confirmed super-eruptions in the past and remain geologically active today. Each features a vast caldera and ongoing signs of subterranean heat and magma: from Yellowstone’s geysers and uplift, to Toba’s resurgent island and hot springs, to Taupō’s seismic swarms and inflation episodes. These systems are not erupting right now, but they are not extinct – their magma chambers persist, and thus they merit close scientific vigilance.

It’s important to note that not every large caldera is a VEI-8 supervolcano. For instance, Campi Flegrei (Phlegraean Fields) near Naples had a huge eruption ~39,000 years ago (the Campanian Ignimbrite) but its eruptive volume (perhaps 200–300 km³ DRE) was a high-end VEI-7, below the super-eruption threshold. Campi Flegrei is very much active – it has shown significant ground uplift and seismic tremors in recent years, prompting elevated concern – but it is excluded here because it hasn’t produced a confirmed VEI-8 event. Similarly, the Long Valley Caldera in eastern California, Aira Caldera in Japan (Kagoshima), and others have had tremendous eruptions in the past (VEI-7), yet not quite reaching the size of the true supervolcanoes. They are nonetheless volcanoes of great concern and are heavily monitored. In fact, in terms of immediate risk, an active VEI-7 caldera under a populated area (like Campi Flegrei) can be more threatening than a quiescent VEI-8 system. But the distinction made here is strictly about the geologic record of size: only those that definitively passed the ~1000 km³ ejecta mark is counted as “supervolcano” eruptions.

Looking back to our three supervolcanoes, it’s heartening to emphasize that no signs point to an impending super-eruption at any of them. At Yellowstone, scientists openly address doomsday speculations to clarify that there’s “no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future”. At Toba, the long dormancy and slow magma recharge mean any resurgence would likely take many millennia (and would be preceded by smaller eruptions or intense unrest). Taupō, while more frequently restless, mostly produces moderate events; a full-scale caldera eruption would be a massive outlier and, based on past patterns, extremely improbable on human timescales.

Each of these volcanoes is under continuous surveillance by local and international scientists. The global scientific community has learned much from studying supervolcanoes: drilling projects, geochemical analysis of crystals, and sophisticated computer models are all being used to figure out how these giant magma systems work and what warning signs they give off before mega-eruptions. Interestingly, research suggests that supervolcano magma chambers can take hundreds of thousands of years to accumulate enough melt for a super-eruption, and they may not always announce themselves with extreme precursor events. This means we must pay attention even to subtle signals. Organizations like the USGS, PVMBG, GeoNet, and others cooperate through the World Organization of Volcano Observatories to share data and best practices for monitoring these sleeping giants.

In the end, while supervolcanoes capture the imagination (and often, alarmist headlines), the reality is that they erupt infrequently and are under watch by experts who strive to maintain accuracy over hype. The potential hazards – from local devastation to global climate effects – are unquestionably severe, but our growing understanding provides reassurance that we won’t be caught completely off guard. By studying Yellowstone’s breathing caldera, Toba’s towering caldera walls, and Taupō’s restless lakebed, scientists are piecing together the complex story of how our planet releases its immense internal heat in rare, violent paroxysms. For the general public and geology students alike, these supervolcanoes are a profound reminder of Earth’s power – but also a lesson in how science, preparation, and clear communication can help us face even the most extraordinary natural events without undue sensationalism or fear. In short: supervolcanoes can indeed erupt again, but they give us long intervals of peace, and through vigilant monitoring we aim to keep it that way for generations to come.