Barely a month goes by these days without the Yellowstone supervolcano hitting the headlines somewhere or other, and this one is no exception.
It might be a swarm of Earth tremors or a minor steam-driven explosion that sets the hearts of news editors and disaster preppers racing. Or, on occasions like this, a new piece of research that sheds light on prospects for the next big bang.
Sometimes it can seem as if the entire world is waiting for Yellowstone to blow – in a sense, almost willing it.
So, what do the latest findings tell us – and do they bring good news or bad? Let’s dig a bit deeper.
A new study about Yellowstone
In January 2025, researchers from the United States Geological Survey (USGS) published a new analysis in the journal Nature that reveals exactly what’s going on underneath Yellowstone.
By measuring and mapping the electrical conductivity of the rocks, they were able to paint a three-dimensional picture of how much magma there is, and where it’s located.
This is because molten rock can be up to a thousand times more conductive than its solid equivalent, so is pretty easy to pick out.
The bad news is that there is one hell of a lot of magma down there. The good news is that it’s not all in one place, nor is it filling some great subterranean void.
Most of the magma, in fact, is contained in pockets, each making up 2–30 per cent (by volume) of the hot, solid, rock within which they are contained.
Furthermore, the areas of magma-hosting rock are not all joined up, so even if the volcano did blow, it couldn’t all come out in one go.
The most interesting revelation, however, lies in what the study tells us about where the next volcanic action might be centred.
It turns out that the magma is not evenly distributed. Most of it is concentrated under the north-east of the Yellowstone Caldera – the huge crater left by the last super-eruption 630,000 years ago.
Somewhere between 400 and 500 cubic kilometres (95–120 cubic miles) of sticky, silica-rich rhyolite magma is squatting here. That’s significantly more than the volume of magma that erupted in Yellowstone’s huge Mesa Falls blast around 1.3 million years ago.
Furthermore, hot basalt magma rising from the mantle below is pumping more and more heat into this part of the volcano, keeping the rhyolite magma hot and, over time, ramping up the total volume of molten rock.
This may sound disconcerting, to say the least, but remember that the magma is spread around. All these pockets of molten rock would need to connect up and pool together before there is sufficient volume to come out in one hefty eruption.
Nevertheless, the authors of the Nature paper have hypothesised that this part of the volcano will be the most likely place for the next big outburst. The big question is – when?
No, a super-eruption isn’t overdue
There is a great deal of talk about the next Yellowstone super-eruption being due, but this – as the latest research also bears out – simply isn’t the case.
Alongside the aforementioned Mesa Falls eruption, there have been two other much bigger blasts, the Huckleberry Ridge eruption a little over two million years ago, and the 630,000-year-old Lava Creek outburst.
The average return period of the three eruptions is 735,000 years, so notwithstanding the lack of any statistical rigour, given such a small sample size, there’s no reason to think that another super-eruption is in any way imminent.
It’s also worth observing that the Mesa Falls eruption, while massive, wasn’t deserving enough to be awarded the epithet ‘super’, as the volume of its deposits fell below the 1,000 cubic kilometres threshold required.
Consequently, the return period between the two really big ones is nearer one and a half million years. The reality, then, is that the next Yellowstone super-eruption could be a very long time coming – but it will come.
And, when it does, its impact on the United States and the entire planet will be immense.
What happened when Yellowstone erupted all those years ago
To get some idea of what a future Yellowstone super-eruption might look like, we need to look back in time at those earlier explosions, which have many features in common.
All involved a detonation so great that the erupted magma was torn apart, creating colossal quantities of ash.
In addition, each eruption was followed by the collapse of the crust above the emptied magma reservoir, leading to the formation of a giant caldera.
The current 60-kilometre-wide (35-mile) Yellowstone Caldera was formed during the most recent Lava Creek eruption.
While each super-eruption marked the climax of an eruption cycle that was terminated by collapse, this was both preceded and followed by volcanic activity on a smaller scale.
This highlights an important point that doesn’t get much airing in discussions about the Yellowstone threat, and that is that there have been plenty of smaller eruptions between the three biggest, and many of these have not been explosive.
In fact, the last eruption at Yellowstone involved the relatively quiet extrusion of lava around 70,000 years ago.
Trying to look out for the warning signs
But let’s zero in on the big ones which, let’s face it, is what everyone wants to know. What would we experience as Yellowstone girded itself for volcanic cataclysm, and during the eruption itself?
One thing we don’t know too much about is how long the build-up to a big one takes, and what the warning signs would be.
Even today, there are hot springs, bubbling mud pools and swarms of Earth tremors. Meanwhile, the land surface continually rises and falls as if a giant slumbers below, which, in a sense, it does.
It might seem logical to expect a super-eruption to be preceded by more of the same warning signs we see in smaller eruptions – just on a larger scale, possibly with growing unrest over decades or longer.
However, research on past eruptions at another supervolcano, Mount Toba in Indonesia, suggests otherwise.
The findings indicate that warning signs could be minimal, offering little to suggest that a world-changing eruption was on its way.
This is very bad news for anyone living within 100km (60 miles) or so of the Yellowstone volcano, because once all hell breaks loose, there will be little chance of escape.
This isn’t to say that a Yellowstone super-eruption will explode onto the scene unannounced. Recent fieldwork by geologists has revealed that the 630,000-year-old Lava Creek event was preceded by two smaller-scale explosive eruptions, probably separated by years, maybe even decades.
When the volcano reawakens, we may well see the same thing again – smaller ‘starter’ events heralding the main course.
From a mitigation point of view, in such a case, the big problem lies in trying to predict which eruption, if any, will be ‘super’, something that will not actually become apparent until after the event, when the amount of disgorged material can be quantified.
However, whether Yellowstone vomits out 500, 750, or 1,000 cubic kilometres of ash and debris is pretty immaterial – all would be cataclysmic and devastating for the country.
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This is what will happen when the sky falls
Whenever it comes, the next Yellowstone super-eruption will be impossible to miss and – whether you live close by or on the other side of the planet – its consequences will be unavoidable.
The eruption is likely to be focused, initially at least, at a single vent – breaking through where the swelling crust above the magma reservoir is weakest.
As viscous rhyolite magma – packed with gas, and under enormous pressure – breaks the surface, it tears itself apart, the initial detonation deafening anyone unfortunate enough to be in the vicinity.
Blasting upwards faster than the speed of sound, a plume of ash and pumice (the low-density rock we use to abrade hard skin) reaches the edge of space within minutes, spreading laterally to plunge everywhere below into pitch darkness.
A torrent of hot ash and pumice falling across Yellowstone and the surrounding region starts fires, heats the air and makes it almost impossible to breathe. But there is worse to come – much worse.
As part of the eruption column collapses under its own weight, it triggers fast-moving surges of hot ash, incandescent gas, and near-molten pumice fragments – known as pyroclastic flows – that hurtle outwards in all directions.
Travelling at speeds of more than 300km an hour (180mph), overtopping hills and filling valleys, these pyroclastic flows destroy and bury everything within about 100km (60 miles) of the vent, turning every living thing – from lodgepole pine to chipmunk, from moose to human – into charcoal.
Meanwhile, the upper part of the column of ash and pumice expands rapidly, even pushing against prevailing winds, forming an ever-widening, giant ‘umbrella’ that brings darkness and a deluge of ash and pumice as it goes.
Within 24 hours, ash would be falling across much of the United States and parts of Canada, bringing down power lines, shorting out electronics, causing transport chaos, flattening crops in the fields, and contaminating water supplies. Normal life would be at a standstill.
Modelling of the ash cloud generated by a future Yellowstone super-eruption, conducted by USGS scientist Larry Mastin and colleagues, reveals that for most scenarios, ash more than a centimetre deep would cover a land area of anything between a few and several million kilometres.
Places like Miami and New York would get away with just a few millimetres of falling ash, while up to 3cm would fall as far afield as Chicago and San Francisco, and Winnipeg in Canada.
Anywhere closer than 1,500km (930 miles) – like Denver and Salt Lake City – would experience extremely disruptive ash fall, the depth increasing to many metres as Yellowstone is approached.
As ash particles act as nuclei for water in the atmosphere, heavy rains would be triggered to add to the mayhem, turning much of the country into a sea of mud, clogging rivers and bringing widespread flooding.
The ash would also carry with it huge quantities of toxic metals, such as arsenic, cadmium, lead and mercury, bringing the potential for long-term contamination of water, crops and animal feed.
It’s likely that all of this ash won’t be dumped in one go, and that the eruption will happen in stages, perhaps as new vents open up, extending its disruptive impact.
The worst could well come during the climactic phase, when magma is erupted in the form of giant curtains along great arcing fractures. These would open as the central block of crust above the magma reservoir sinks into the evacuated space beneath to form a new caldera.
In total, the whole thing could last for weeks, perhaps as long as a month. But this is just the beginning.
Global sunshade in the aftermath of the super-eruption
While the effects of the heavy and extensive ash-fall would devastate agriculture across much of North America, and bring the US economy to its knees, this isn’t the worst of it.
Any remaining ash in the atmosphere will settle out pretty quickly, but this isn’t the case for the vast quantities of sulphur dioxide gas blasted high into the stratosphere during the eruption, which will spread across the planet within weeks.
When combined with atmospheric water vapour, the gas forms an aerosol of tiny particles that build a global ‘veil’. This shields the planet from incoming sunlight and lowers surface temperatures.
The 1991 eruption of Mount Pinatubo in the Philippines brought about a sudden drop in global temperature of around 0.5°C (1°F) for a couple of years. Although this was the second biggest volcanic blast of the 20th century, it was around one hundred times smaller than Yellowstone’s Lava Creek super-eruption.
Travelling back a couple of centuries, the great 1815 eruption of Indonesia’s Tambora volcano – three to four times bigger than Pinatubo – had a major impact on global weather, leading to the so-called ‘Year Without a Summer’ in Europe.
Widespread harvest failures across the continent and in the eastern United States brought civil unrest, bread riots, and the last major subsistence crisis in the developed world.
What then would be the result of a future Yellowstone explosion that was 25 times bigger?
It would be reasonable to think that scaling up would result in a much bigger climate impact, and computer modelling suggests this is the case.
The global temperature after a Yellowstone super-eruption-sized event is predicted to fall by up to 4°C (7°F) on average, by up to 7°C (13°F) across land, and by more than 10°C (18°F) across central North America.
Temperatures begin to climb again within a few years, but it takes a couple of decades at least for them to return to previous levels. Not surprisingly, the sea ice cover at the poles increases significantly, and there are major changes in global weather patterns.
Needless to say, such severe cooling – which nearly matches a return to Ice Age temperatures – would be catastrophic for global agriculture, leading to widespread harvest failure, and famine on an unimaginable scale, across both the majority world and in developed nations.
All things considered, it would be a surprise if global society and economy survived in any form that we might recognise.
But there is a glimmer of light through the gloom.
A recent NASA study has broken with the consensus to speculate that the temperature fall following Yellowstone’s next super-eruption might end up not being much greater than that following Pinatubo or Tambora, although the researchers admit there are big uncertainties. So, good news? Maybe.
Ultimately, we won’t know just how severe the resulting cooling will be until Yellowstone erupts again. However cold it gets, the direct impact of the eruption on the United States will likely have enormous repercussions across the world, and – in its own right – will severely test the resilience of global society and economy.
Perhaps the only saving grace is that – as the latest research tells us – it doesn’t look like happening anytime soon.
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