Written by Olivier Guiberteau
A thick cloud of ash hangs ominously in the air. The sun’s rays are almost entirely blocked out causing temperatures to plunge well below normal levels. It’s only a matter of time until life on Earth begins to die off and it’s anybody’s guess how far it will go – or how long this bitter volcanic winter will last.
The effects of a volcanic winter, caused primarily by a supervolcanic eruption, can have devastating effects and can last years, if not decades. To really put it in perspective, a volcanic winter and a nuclear winter, caused by a nuclear detonation, would both provide eerily similar results and would certainly destroy vast swaths of the planet, while most likely causing the extinction of species on Earth.
Thankfully, volcanic winters are incredibly rare, but with between 10 and 20 supervolcanoes currently active around the world, and eruptions typically occurring every 50,000 years, the question is not will the Earth ever see another volcano winter, but when.
Recent Volcanic Eruptions
Before we look at volcanic winters themselves, let’s begin with the monstrous beasts that create them, volcanoes. Over the last few thousand years, Earth has experienced several massive volcanic eruptions which were large enough to not only destroy on an almost biblical scale but also dramatically affect weather patterns around the world.
We recently did a post here on Into the Shadows about the long-term effects of the Krakatoa eruption in Indonesia in 1883, and how the shockwaves from that particular eruption continued for several years, potentially affecting weather patterns, lowering sea temperatures, and causing the kind of vivid explosive sunsets that are difficult to imagine.
The Krakatoa eruption was truly massive but still paled in comparison to what happened in New Zealand in 1815 when the colossal Tambora stratovolcano – a volcano composed of alternate layers of lava and ash – let rip.
The Tambora eruption is without question the largest we have seen over the last 10,000 years, sending 10 meter (32.8 ft) high tsunamis barreling across the oceans and killing an estimated 100,000 people in the process. We’ll be coming back to this particular eruption a little later on when we talk specifically about volcanic winters but before that, there is the small matter of the giant raging mountains, which, if they were ever to erupt, could spell doom for humanity and much of Earth along with it.
Both the Krakatoa and Tambora eruptions were titanic in their strength and devastating in their effects, and yet, in the grand scheme of volcanic eruptions, neither come anywhere near to being the largest the Earth has ever seen.
There are thought to be roughly 40 supervolcanoes around the world, but many have long become extinct. The exact number of live supervolcanoes is difficult to calculate exactly, but most estimates lie between 10 and 20, with one in Yellowstone National Park, one close to Taupo in New Zealand, and another lying beneath the picturesque Lake Toba on Sumatra in Indonesia, to mention just a few.
Around 40 VEI-8 magnitude eruptions have occurred within the last 132 million years, with 30 in the past 36 million years. To give you a very rough average, Earth typically sees a supervolcano eruption every 50,000 or so – and yes it’s been well over 50,000 years since our last planet shattering eruption – 75,000 years to be exact.
When one of these volcanoes rears its ugly head back and roars with all its might, the effects on the planet and the species that inhabit it can be devastating. Many of the major extinction events that we know about are believed to have at least been linked to a supervolcano eruption.
Today, we are actively developing plans for how to deflect a comet on a collision course with Earth, but the eruption of a supervolcano is not only beyond our rather simple human imagination, its effects would be so devastating we would be almost powerless to address them. To put it bluntly, if a supervolcano erupts, all bets are off for humanity.
A supervolcano eruption would follow a series of steps, beginning with the eruption itself, and ending with a protracted volcanic winter. With our knowledge and experience of an eruption on this scale entirely limited, it can be difficult to fully imagine what happens when these underground brutes unleash their furious anger.
The Krakatoa eruption has long been cited as being one of the loudest sounds ever heard by modern humans. The blast was loud enough to rupture eardrums close by and was thought to have reached 310 dB, loud enough to be heard 5,000 kilometers (3,100 mi) away. But bear in mind that Krakatoa was small fry compared to what still lurks underground, and it’s safe to assume that a supervolcano eruption would produce a sound that could potentially be heard around the world.
Magma and Ash
Next up comes the ash and magma that pours out from the newly broken caldera. The Tambora eruption resulted in roughly 50-150 cubic km (12-36 cubic miles) of magma spilling out in all directions, while a giant plinian column – an ash and smoke column that heads straight up into the stratosphere – reached an astonishing 40-50 km (25-30 miles) altitude – at least 4 times as high as a cruising passenger airliner.
But again, we need to remember that a supervolcano eruption would be significantly bigger. For example, the Youngest Toba eruption, which was the largest event in the last one million years and occurred around 75,000 years ago, is thought to have been at least 12 times as powerful as the Tambora eruption.
It’s thought it may have unleashed a staggering 13,200 km3 (3,200 cubic miles) in total bulk volume – enough to fill the Grand Canyon three times – and deposited ash 15 centimetres (6 inches) thick over the whole of South Asia, as well as across the Indian Ocean, the Arabian Sea, and the South China Sea.
Needless to say, this amount of magma and ash can fundamentally reshape enormous areas of the world. The Siberian Traps eruption, which occurred around 251.9 million years ago, was one of the largest eruptions of the last 500 million years and is widely blamed for the Permian–Triassic extinction event in which over 90% of species on Earth became extinct.
Now, remember earlier how I said that some aspects of supervolcanoes were difficult to get your head around for the simple reason that eruptions on that scale are difficult for modern humans to picture, well, this is where that really becomes apparent. The Siberian Traps eruption created a flood basalt event in which large tracts of land are covered with basalt lava. And in this case, by large I mean 7 million sq km (3 million sq miles) – which is around 80% of Brazil’s total landmass – with a volume of around 4 million cubic km (1 million cubic miles).
As astonishing as that is, it’s still not the fact that’s going to leave you scratching your head in bewildered puzzlement. Very few volcanic eruptions are simply a single loud boom and it’s common for multiple eruptions to occur in a short period. In the Siberian Traps, however, the eruptions carried on for an unbelievable two million years. It’s no surprise then, that this monstrous event, coupled with another supervolcano eruption occurring in China, was responsible for the closest Earth has ever come to being left completely devoid of life. An event that is known entirely appropriately as ‘the Great Dying’.
The tallest tsunami ever recorded was not quite the catastrophe that you’d imagine. A relatively small earthquake close to Alaska in 1958 caused a huge chunk of rock to plunge into Lituya Bay resulting in a 524 meter (1,720 ft) tsunami that tore through the bay. Quite miraculously, only five people died in the event, which devasted the local area.
This tsunami, which itself was an enormous slice of bad luck, luckily hit in a sparsely populated area, but we don’t need to go back far to see just how horrifying they can be. On December 26th, 2004, an earthquake with an epicentre off the west coast of northern Sumatra, Indonesia, spread a wall of watery death around the Pacific Ocean, killing an estimated 230,000 people.
This was a vicious earthquake that devastated vast areas, but still, the entire event from start to finish was relatively short – especially compared to what might happen after a supervolcano erupts.
We need to do a bit of guesswork when estimating the size of the waves that would emanate from a massive eruption, but between 30 and 60 meters 100 – 200 ft) is generally discussed. Scientists predict that at some point over the next few thousand years or so, the Cumbre Vieja volcano, on the southern half of La Palma, one of the Canary Islands, will see a huge eruption that will likely carve off an enormous chunk of the volcano’s western flank which will then drop into the ocean and send massive tsunamis mostly westward, towards the U.S Eastern coast and the Caribean, but also in other directions.
Off the coast of Naples in Italy lies Campi Flegrei, a vast underwater supervolcano that comes with a slightly worrying 24 craters and edifices. Even more worrying is the half a million people who live within what is considered the ‘Red Zone’ that would have little to no warning if Campi Flegrei saw one of its bigger eruptions.
It’s clear that the tsunamis that would accompany a supervolcanic eruption would be immense and would most likely cause enormous damage and loss of life to those living in coastal areas. But for those further inland, it would be what came next that could completely destroy life.
All of the factors that we’ve mentioned wouldn’t necessarily mean the widespread destruction of humanity and other life on earth. If they were to occur all at the same time during a supervolcano eruption, they might well kill hundreds of thousands and possibly even millions, but most of their damage would be constricted to specific areas.
However, what had survived the massive eruption, might not stay that way for very long. A volcanic winter is described as a reduction in global temperature brought on by a supervolcano eruption, where volcanic ash and droplets of sulfuric acid mixed with water obscure the Sun and raise Earth’s albedo – the quantity of solar radiation the planet normally reflects.
We have evidence that this occurred after the Krakatoa and Tambora eruptions and may have lasted for a few years. This essentially causes chaos to weather patterns around the world, with some areas seeing much more rain than normal, and others seeing none at all. This devastated crops and caused famine in certain regions, but humans quickly recovered. As we’ve seen, these were big eruptions, but a long way off from being the biggest.
Throughout recent history, we have seen several instances of a volcanic winter but nothing on such a massive scale. The Hekla 3 Eruption in Iceland around 1000 BC, caused a drop in temperature across the Northern Hemisphere, with scientists estimating eighteen years of global cooling, thanks to carbon dating in Irish bog oaks. There have also long been whispers that the Hekla 3 eruption may also have had something to do with the Bronze Age Collapse that occurred during a span of 100 years or so after the eruption. It’s difficult to say for sure here and there were almost certainly other factors at play, but the fact that large numbers of seemingly desperate people descended on the Eastern Mediterranean a few decades after such a massive eruption might not be a coincidence.
By the way, if you’re enjoying the end of the world vibe in this post and fancy learning more about the Bronze Age collapse, we have already done a whole post on it, so why not check it out after.
The volcanic winter of 536 AD was a result of an unknown eruption that caused summer temperatures to drop by 2.5 degrees Celsius (4.5 degrees Fahrenheit) below normal in Europe and caused widespread famine as a result. This was the most significant period of cooling in the last 2,000 years that led one contemporary writer to describe the sun’s strength as “feeble” for many years.
In 1452 or possibly 1453, a mystery volcano eruption led to a devastating period that saw temperatures drop for around 3 years causing crops to fail across the world. There is evidence of stunted tree growth from Europe all the way to China, while 40 days of constant snowfall south of the Yangtze River at the start of the year killed thousands.
These types of large eruptions can have significant effects on farming and crop production around the world, but in a few years, Earth’s natural cycle usually prevailed and things reverted to normal. However, that almost certainly won’t be the case when a supervolcano goes off.
A Supervolcano Winter
A volcanic winter that follows a supervolcano eruption would most likely signal the end of most, if not all of human life. Only those with specially designed underground habitats capable of growing food and sustaining life would survive. You might be tempted to think that with our modern technology we might have a fighting chance, but that may well be wishful thinking.
The Toba eruption 75,000 years ago led to a volcanic winter that may have lasted decades and saw the global mean surface temperature drop by 3–5 °C (5.4–9.0 °F). This event has been used to explain the human genetic bottleneck that occurred around the same time, that saw the human population around the world fall from between 50,000 and 100,000 to 3,000–10,000 people in a relatively short period.
This is certainly just a theory at this point and many argue against it, but few would deny that there was a significant drop in population and that a volcanic winter happened around the same time. Regardless of what exactly happened and why, humans did survive, and there is even some evidence to suggest that population growth actually sped up after the Toba eruption.
However, while the Toba eruption was certainly significant, it still pales in comparison to what happened around 251.9 million years ago that led to the Permian–Triassic extinction event. When the cataclysmic eruption of the Siberian Traps was followed shortly after by another, at the Emeishan Traps in China, they created an environment that is beyond even the wildest fantastical imagination.
The extinction event that followed, as I said earlier, was as close as the Earth has ever come to having all of its life stripped away. The ‘Great Dying’ killed up to 96% of all marine species and around 70% of terrestrial species, including plants and insects. Ironically, considering most major eruptions seemed to be followed by a volcanic winter, what happened after the eruptions was a rise in temperature that led to oceanic anoxia and ocean acidification due to the large amounts of carbon dioxide being pumped into the atmosphere.
The effects of this were unimaginable, and while some species made a struggling comeback in as little as 3 million years, it was around 10 million years until we could say that life was even beginning to get back to normal.
The Waiting Beasts
Supervolcanoes are something we nonchalantly dismiss as events that happen rarely, but rare is simply a matter of perspective. The truth is that many of these titans could go off at any time and as we’ve seen, the effects across the world would be apocalyptical.
At best we may experience years of affected weather, poor harvests, and probably a hefty price laid at the feet of the poorest in the world. At worst we might see the kind of eruption that led to one of the many extinct events that have occurred on Earth. A brutal eruption that sends 30 meter (100ft) tsunamis around the world, enough lava and ash to cover vast swaths of the planet, and a protracted volcanic winter that would slowly starve the rest of the planet and gradually choke life on Earth.
We might be able to alter the course of an incoming comet, we may be able to reverse the course of our current climate struggles or even fend off an invading alien force, but a supervolcano eruption is a very different matter. What stirs angrily below ground might well spell the end.