A supervolcano is defined as having the capacity to produce an eruption so big that it can eject around 240 cubic miles of volcanic material in the form of molten rock, hot gases, and ash. That’s roughly one thousand times more than the largest volcanic eruption ever recorded in modern human history. Supervolcanoes are formed when a momentous volume of super-heated magma rises from deep underground, but is unable to penetrate the Earth’s crust and creates a huge, high-pressure pool several miles beneath the surface. As time passes, pressures rise and this massive pool of magma grows, until a mega eruption takes place.
a large volcanic crater, especially one formed by a major eruption leading to the collapse of the mouth of the volcano.
10. The Apocalyptic Eruption of a Supervolcano
We have to make a couple of things clear right from the beginning. For starters, we know relatively little about how supervolcanoes are formed, and we know even less about what sets one off. However, recent geologic studies have shown us that super volcanoes are not like other ordinary volcanoes, especially when it comes to the causes that make them erupt. While an ordinary volcano is triggered by internal mechanisms, like magma pressure building up over time and eventually punching through the rock, a supervolcano is triggered by the above Earth’s crust which, due to the huge size of the magma chamber below, becomes highly unstable and forms cracks and faults. Through these faults, the magma can generate an unstoppable chain reaction that would lead to a devastating and inevitable explosion, the likes of which can extinguish most life on the planet. Because of this fact, it’s far more difficult to estimate when a supervolcano will erupt.
One such ancient eruption took place around the time of the extinction of the dinosaurs. Coinciding with another cataclysmic event (the meteor that struck the Yucatan Peninsula 65 million years ago), the area of what is now known as the Deccan Traps in central India was the site of a huge volcanic eruption. Even before India slammed into the Asian continent, one of the largest volcanic structures made its presence felt for nearly 30,000 years. It now consists of more than 6,500 feet of flat-lying basalt lava flows, covering an area of roughly 200,000 square miles (almost the size of the Washington and Oregon combined). It’s estimated that the original area was three times that size, but shrank due to erosion and plate tectonics. The present volume of volcanic material is somewhere around 122,835 cubic miles, as compared to the 1980 Mount St. Helens eruption, which spewed out only around 0.24 cubic miles of lava.
An even larger and more destructive event occurred some 235 million years ago in what’s now Siberia, which triggered the Great Dying event, where 75% of all land life and 95% of marine life went extinct. But the largest volcanic eruption in Earth’s past 300 million years took place underwater, and began 125 million years ago. It created a plateau 19 miles thick and 750,000 square miles wide (1% of the Earth’s surface), called Ontong Java, north of the Solomon Islands in the Pacific Ocean. It released about 24 million cubic miles of lava, and was 100 million times more powerful than the Mount St. Helens eruption.
9. The Hellish Pyroclastic Flows That Soon Follow
Immediately following a volcanic eruption, an equally, if not deadlier event takes place. This is a pyroclastic flow, which instantly killed many of the people in the ancient Roman town of Pompeii in 79 AD when Mount Vesuvius erupted. When a volcano goes off, besides the eruption column that forms above the crater, another, deadlier ash-cloud surge flows down the slopes in all directions and at incredibly high speeds (up to 450 mph). This is a fluidized mixture of solid and semi-solid fragments of rock, ash and incredibly hot expanding gases which act similarly to a snow avalanche. Everything that is caught in this flow will be killed instantaneously as temperatures inside it can reach 1,800 degrees Fahrenheit. If you find yourself on a path of one of these pyroclastic flows, there is absolutely nowhere to run or anywhere to hide. The gases are so toxic, they wreck the lungs almost instantaneously, while the water inside tissue is simply boiled off.
In a supervolcano, the ash in a pyroclastic flow would be so hot that it would turn into lava once it touched back onto the ground. This would lead to lava flows hundreds of miles away from the volcano itself. Because of the extremely high speeds an “avalanche” like this usually travels, a phenomenon known as “viscous heating” takes place. Basically, the force moving these solid volcanic materials through the air adds to their overall temperature, making them even hotter and thus turning them into lava midair. Any life found in the vicinity, but not caught in this hurricane of incandescent materials hurtling towards them, would be killed by the poisonous gases that are released after the pyroclastic flow dies off. The area engulfed by the flow would be covered by up to 700 feet of debris.
8. A Volcanic Winter is Coming!
Now you may be inclined to believe that, even though huge and deadly, supervolcanoes would wreak havoc on a local level. But this could not be further from the truth. While the popular image of volcanic destruction is that of molten rock engulfing everything in its path, far greater devastation takes place high in the air. A supervolcanic eruption column can rise up to 15 miles and the ash, which is dispersed by winds, can blanket the skies for years to come. The toxic gases react in the stratosphere, blocking out solar radiation and drastically cooling the atmosphere below. The resulting volcanic winter, along with other effects like acid rain, can affect the whole planet, disrupting natural cycles and annihilating plant life, on which other organisms, like us humans, depend.
In just several days after the blast, the skies would be dark and deadly, with fallout reaching distances of 1,750 miles from the volcano. Five hundred miles away, ash could settle up to 3 feet deep. Within this zone, movement would be impossible, roads invisible, air travel grounded and people outdoors would not be able to see where they were going, and would probably suffocate. Wet ash would collapse rooftops, short circuit power lines, and clog car engines and power station reservoirs. Nuclear power plants would be forced to close and lawlessness could take over.
Those living in the path of the ash cloud would need to protect themselves with masks and visors. This is because volcanic ash is in fact rock which has been blown apart into tiny pieces and transformed into minute shards of glass with jagged edges. In its fine powder form, this ash is easily inhaled into the lungs, and people and animals can suffer a slow and painful death caused by the rare Marie’s disease. As the lungs fail, the skeletal system goes out of control, rapidly depositing new bone on top of old. This will affect people living even one thousand miles away and within a month of the eruption.
A simulation conducted on what happened during the last time Yellowstone erupted, some 640,000 years ago, showed that in one month’s time, the cloud of fine ash and dust covered the entire Northern Hemisphere and within 18 months the average worldwide temperature dropped by 10 degrees C. As a result, sea ice rapidly grew in the Arctic, reflecting even more of the sun’s rays. This in turn led to a severe rainfall decline, and oceans and land areas retaining more CO2. All of these factors lead to a drop in biological productivity, with food supplies lasting just mere weeks in some areas. According to the analysis, it took roughly 20 years for the planet to recover to its pre-eruption period. So, if the blast and pyroclastic flow of a super volcano can kill millions of people (depending on where it is situated), the volcanic winter that follows will most likely kill billions all over the globe.
7. Aira Caldera, Kyushu, Japan
Now that you have an idea of what a supervolcano is and what devastating effects it can have, we’ll be talking about the seven such active volcanoes we currently know about. The first one is the Aira Caldera, located in southern Japan on the island of Kyushu. At first glance, the Sakura-jima volcano, at the northern half of Kagoshima Bay, looks like any other ordinary volcano. Even though it’s been in near continuous eruption since 1955, and threatening the nearby city of Kagoshima (population of 500,000 people), Sakura-jima doesn’t really stand out from the many volcanoes that dot the Pacific Ring of Fire.
This is highly misleading, as Sakura-jima is just the tip of a much larger and far more dangerous volcano. The fact that it’s positioned on an island in the middle of a bay is the first clue. This is because Kagoshima Bay itself is in fact the infamous Aira Caldera. A caldera, as opposed to a volcanic crater, is a huge depression in the ground which formed after a previous supervolcanic eruption. As the magma chamber emptied, the ground above sank in and partially filled the hole left behind. This caldera in particular formed after a huge eruption about 22,000 years ago, with Sakura-jima beginning to sprout 9,000 years later. Today this volcano acts as a mere vent for the much larger, 150 square mile caldera it sits on. When this supervolcano last erupted, it spewed out roughly 14 cubic miles of material.
Japanese scientists believe that a volcanic eruption big enough to disrupt the whole country has a 1% chance of happening in the next 100 years. With the many tremors that take place around Kagoshima Bay on a daily basis, the Aira Caldera is among the top on that list. If it were to erupt today, lava and pyroclastic flows, as well as ash clouds, could engulf areas where 5 million people currently live. Another 120 million people would be severely affected by ash fallout, which makes up pretty much the whole of Japan.
6. Taupo Caldera, North Island, New Zealand
Lying beneath the surface of one of the most beautiful landscapes on Earth sits the Taupo supervolcano. Located on the North Island in New Zealand, this caldera is currently covered by the country’s largest lake, Lake Taupo. This volcano began forming some 300,000 years ago, with the present caldera coming into existence around 25,000 BC, in what is called the Oruanui Eruption. It ejected somewhere around 288 cubic miles of volcanic material to the surface when it erupted. Today the magma chamber is situated some 5 miles beneath the surface, and is responsible for the largest eruption in the past 5,000 years.
This last major eruption at Lake Taupo took place around 200 AD from vents near Horomatangi Reefs (now submerged). The eruption plume reached heights of 30 miles into the air, well into the stratosphere. The pyroclastic flows that followed engulfed the surrounding area, 55 miles in all directions. This was the largest such event in recorded history, with the Kaimanawa mountains climbing one mile in a matter of minutes. The lake itself was blocked at its mouth, raising the water levels by 112 feet. This natural dam eventually broke out in a huge flood, the effects of which can be traced for over 125 miles downstream, and which include boulder beds and buried forests. It is quite possible that this eruption was the cause for the red sunsets the ancient Romans and Chinese recorded at that time.
5. Toba Caldera, Sumatra, Indonesia
The Toba caldera in Indonesia is responsible for producing the largest volcanic eruption in the past 2 million years. It is also the largest at 18 by 60 miles, which makes a total surface area of over 1000 square miles. This caldera probably formed in stages after eruptions occurred about 840,000, 700,000, and 75,000 years ago. This last one was the largest, spewing out a whopping 670 cubic miles of lava, ash and gas. Pyroclastic flows covered an area of at least 7,700 square miles, with the island of Samosir being engulfed by a thick, 1,800 foot blanket of tuff (pyroclastic debris). The resulting ash from the eruption covered an area at least 1.54 million square miles, and reached distances some 4,350 miles away.
Many scientists believe that this Young Toba Tuff eruption from 75,000 years ago put an incredible strain on the early human population still living in East Africa. So much so that it created a bottleneck from which only a mere couple of thousand people managed to survive. While this close call with extinction humanity faced back then actually happened, recent discoveries seem to point out that Toba wasn’t the main contributor. Archaeological investigations indicate that East Africa’s climate wasn’t so severely affected by the blast and its aftermath as to kill off almost all of humanity. What did it, however, is still a matter of debate. Nevertheless, it seems that the volcanic winter that ensued dropped Earth’s climate by at least 5 degrees C. and may have triggered a new ice age.
4. Valles Caldera, New Mexico, United States
Despite a very green, tranquil and inviting landscape present in New Mexico’s Valles Caldera National Reserve, the presence of hot springs, gas seeps and occasional tremors indicate a disturbing presence hiding underground. The volcanic caldera found there is relatively small compared to others here on this list, but at 14 square miles, it’s quite a hike to walk it from one end to the other. It’s also not the first here, as it collapsed over and buried the older Toledo caldera, which in turn covered previous ones.
This volcano had two mega eruptions in the past 2 million years, one 1.7 and the other 1.2 million years ago, piling up to 150 cubic miles debris and spewing ash as far away as Iowa. The last eruption here took place roughly 50 to 60,000 years ago, but this blast was far smaller in comparison. Though unlikely to erupt in the near future, the Valles Caldera lies above the intersection of the Rio Grande rift and the Jemez lineament, and its volcanic activity is due to tectonic movement along this crossroads. This makes this particular volcano highly unpredictable and hard to pinpoint a future eruption. With nearly 40 deep wells that have resulted in extensive subsurface data, the Valles caldera is the best explored caldera complex in the United States.
3. Campi Flegrei Caldera, Naples, Italy
Everybody knows that the residents of the city of Naples in Italy have always lived in the shadow of Mount Vesuvius, which completely wiped off the map the town of Pompeii in 79 AD. What most people don’t know, however, is that on the other side of the city rests a 13 square mile caldera known as Campi Flegrei (burning fields). This caldera makes part of the city’s westernmost outskirts, as well as the Gulf of Pozzuoli. This volcano went through two major eruptions in the past, 47,000 and 36,000 years ago, with smaller periods of activity at relatively regular intervals of roughly 4,000 years. Two eruptions have occurred in recent history, one in 1158 at Solfatara and the other in 1538, which formed the Monte Nuovo cinder cone we see today.
More recently however, back in 2013, a series of earthquakes put the residents of Naples in a state of unrest. Satellite imagery has indicated that the land on top the seemingly dormant caldera had risen by 1 inch in the course of a month, with some regions raising as much as 4 inches. Since the land hasn’t yet receded back to its original state, scientists believe that the chamber beneath the city has filled with about 148 million cubic feet of magma. This is not nearly enough magma to be a major cause for concern, as a super eruption needs a lot more in order to occur. Nevertheless, volcanologists need to keep a very close eye on Campi Flegrei, as these tremors can cause major faults throughout the city of Naples. But if it ever erupts to its full potential, all life in Europe could be lost.
2. Long Valley Caldera, California, United States
Close to the Nevada state line, in east-central California, lays the 200 square mile Long Valley caldera, just south of Mono Lake. The biggest eruption that occurred here took place some 760,000 years ago and unleashed around 3,000 times more lava and other volcanic material than Mount St. Helens in 1980. The ash that ensued reached as far away as Nebraska and the ground above the magma chamber dropped by approximately one mile. What is most worrisome here is that in 1980, after a swarm of earthquakes, roughly half of the caldera had risen by about 10 inches. Ten years later, CO2 and other poisonous gases began to seep through the ground, killing off trees and other vegetation in the Mammoth Mountain part of the caldera.
What sets aside the Long Valley caldera from all others is the fact that, as volcanologists like to put it, this volcano has a split personality. By this they mean that this supervolcano can generate two distinct types of eruptions at once. The first style is a gloppy, not very explosive lava called basalt that poses little blast danger unless it contacts groundwater or snow. The other is richer in glass, called silicic magma, which tends to be more explosive in nature. The official prognosis puts an eruption on any given year at less than 1%, which is somewhat equal to the San Andreas Fault letting loose another magnitude 8 earthquake like the one that destroyed San Francisco in 1906 on any given day.
1. Yellowstone Caldera, Wyoming, United States
Unbeknownst to many tourists who visit Yellowstone National Park in Wyoming is the fact that they are actually walking on probably humanity’s biggest natural threat. Several miles beneath their feet lies the largest pocket of magma we currently know about. It is estimated that there’s enough magma in there to fill the Grand Canyon to the brim, eleven times over. The entire national park and the surrounding area form the huge caldera. The caldera is about 1,500 square miles and can fit the entire city of Tokyo in its perimeter.
Yellowstone has been active for a very long period of time and has erupted on different sites, as North America moved over it on its tectonic journey west. Its last three eruptions took place 2.1 million years ago, 1.2 million years ago and 640,000 years ago and were about 6,000, 700 and 2,500 times larger than the St. Helens eruption, respectively. Last time it erupted, it released around 600 square miles of lava on the continent and covered most of the present-day United States in a thick layer of ash. Looking at the pattern of previous eruptions, it looks like Yellowstone could be preparing itself for a new one. However, volcanologists believe that it’s not quite there yet. Nevertheless, the grounds of the caldera have been rising and falling for thousands of years, which clearly indicate that the volcano is still brewing. If and when it finally decides to blow, it is fairly possible that all of the above mentioned catastrophes will happen. Most of the country would be covered in ash, with three feet of ash falling more than 500 miles away, as far as Denver.
A volcanic winter will probably ensue and it could last for up to 20 or more years, lowering overall temperatures by at least 11 degrees C. Together with the humongous amount of poisonous gases like CO2, the planet will then begin to warm up exponentially, similar to the Great Dying event of 235 million years ago. As the planet and oceans back then began to heat up, the vast quantities of methane hydrate (30 trillion tons), which lie frozen on the ocean floor even to this day, began to surface and heat up the planet by another 5 degrees in a positive feedback cycle.
The most frightening thing here, and far more probable than an imminent super eruption, is that what that ancient volcano managed to do in some 500,000 years, in terms of CO2 production and an initial warming of the planet, we humans can achieve in maybe two centuries. One of which has already passed.