What happens if a super volcano goes off

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But in the context of Campi Flegrei's past, it would be minor. The volcano's most notorious supereruption was the Campanian Ignimbrite eruption, which occurred some 39, years ago.

It punched an estimated cubic kilometres of molten rock 70km up into the stratosphere, along with an estimated , tons of sulphur dioxide.

The ash cloud was carried as far as central Russia, some 2,km away. The eruption occurred at a time when much of Europe was already going through a lengthy glacial period, and the consequences are thought to have devastated much of the continent for centuries.

Entire swathes of land, including Italy, the Mediterranean coast and the entirety of eastern Europe, were left covered in up to 20cm of ash. This would have destroyed vegetation and created a vast desert. Much of Russia was immersed in 5cm of ash, enough to disrupt plant life for decades or more. In addition, the huge quantity of sulphur dioxide released would have created a volcanic winter.

Sulphur dioxide backscatters the Sun's radiation in the upper atmosphere, preventing it from reaching the ground. The Mount Pinatubo eruption, one of the biggest of the 20th Century, did exactly this, temporarily lowering the global temperature by around 0.

But the Campanian Ignimbrite eruption may have had a far greater impact, with some scientists estimating that it decreased temperatures in Europe by as much as 4C , drastically altering the climate for many years. The timing of this huge eruption is suspicious, because many archaeologists believe that 39, years ago is roughly when our cousins the Neanderthals died out in Europe. It has long been speculated that the eruption triggered extreme environmental conditions across Europe, contributing to the extinction of the Neanderthals, at least in some regions.

However, while the impact on the Neanderthals was surely significant, many scientists now believe it is unlikely that this single event was cataclysmic enough to wipe them out. Archaeological evidence suggests that Neanderthals persisted in parts of western Europe for some 10, years after the Campanian Ignimbrite eruption. This may be because of the way the ash dispersed. Much of eastern Europe was covered in a layer of ash from the eruptions Credit: iStock.

There is even an argument that the eruption could have benefited the Neanderthals, by delaying the arrival in Europe of modern humans, who would have competed with them for resources. For now, it is unclear how much damage Campi Flegrei's last major eruption did. But it is far from the only supervolcano on the planet. Earth's geological history is a catalogue of apocalyptic-looking volcanic events. In south-west Colorado, there is a vast canyon approximately km wide and one kilometre deep.

It serves as the legacy of one of the most explosive single events in the planet's history. La Garita Caldera was formed by an eruption nearly 28 million years ago, which expelled 5, cubic kilometres of molten rock.

Fortunately the chance of this occurring is very low. Yellowstone houses a supervolcano, making it thousands of times more powerful than a normal-sized volcano.

There is little indication another super-eruption is due anytime soon - and it is even possible Yellowstone might never have an eruption on a similar scale again. USGS researchers have calculated how such an enormous eruption would affect nearby regions in the short-term, meaning years to decades. The overwhelming majority of those eruptions in Yellowstone have been smaller lava flows — with the last occurring at Pitchstone Plateau some 70, years ago.

Now, in the unlikely event of a much bigger super-eruption, the warning signs would be much bigger. It could take weeks or months for those earthquakes to break up the rocks above the magma before an eruption.

And what if we did get a super-eruption — an event that was 1, times more powerful than a regular volcanic eruption, ejected at least cubic miles of material, and lasted weeks or months? The lava flows themselves would be contained within a relatively small radius within the park — say, 40 miles or so. In fact, only about one-third of the material would actually make it up into the atmosphere. The main damage would come from volcanic ash — a combination of splintered rock and glass — that was ejected miles into the air and scattered around the country.

In their new paper , Lowenstern and his colleagues looked at both historical ash deposits and advanced modeling to conclude that an eruption would create an umbrella cloud, expanding even in all directions. This was actually a surprising finding. A super-eruption could conceivably bury the northern Rockies in three feet of ash — devastating large swaths of Wyoming, Idaho, Colorado, Montana, and Utah. Meanwhile, the Midwest would get a few inches of ash, while both coasts would see even smaller amounts.

The exact distribution would depend on the time of year and weather patterns:. Mastin et al Any of those scenarios would be terrible news.

That much volcanic ash is capable of killing people, plants, and animals and crushing buildings. Even a few inches of ash which is what much of the country can get can destroy farms, clog roadways, cause serious respiratory problems, block sewer lines, and even short out transformers. Air travel would have to shut down across much of North America. An eruption that big would also cool the planet temporarily.

A volcanic eruption that big would also have major effects on the global climate. Volcanoes can emit sulfur aerosols that reflect sunlight back into the atmosphere cool the climate.

These particles are short-lived in the atmosphere, so the effect is only temporary, but it can still be dramatic. The Tambora eruption in cooled the planet enough to damage crops around the world — possibly leading to famines in some areas.

And those were relatively tiny eruptions compared to what a supervolcano is, in theory, capable of. Right now, there's no sign of a pending eruption. Yellowstone park does continue to get earthquakes, and the ground continues to rise and fall, but that's nothing out of the ordinary.

The USGS also notes that, if you simply took the past three eruptions, the odds of Yellowstone erupting in any given year are 0. But even that's not a good estimate, since it's not at all certain that Yellowstone erupts on a regular cycle or that it's "overdue" for another eruption.

In fact, there might never be a big eruption in Yellowstone again. That's not a sure thing," says Lowenstern. It may not even see a fourth eruption.