There are 14 supervolcanoes – that we know of. What will happen if one erupts?

In certain spots around the world, sitting quietly for now, lie supervolcanoes. 

These geological giants have the power to wipe out the people living around them for miles, and change the landscape on the Earth as we know it. 

It has only happened once in recent history, when on April 10, 1815, Mount Tambora, in what is now Indonesia, finally erupted after weeks of rumblings.

A towering column of ash soared into the atmosphere. Pyroclastic flows raced down the mountain for days, wiping out villages as they went and triggering tsunamis when they hit the sea.

More than 70,000 people were killed by the eruption, but the death toll extended for many more months. Sulphur ejected by the eruption into the atmosphere cooled the planet so much that 1816 became known as the ‘year with no summer’.

The US faced 20-inch snowdrifts in June. Europe was hit by endless rain. Crops failed and people starved. A typhus epidemic hit the continent, taking hold of the malnourished.

Yet Mount Tambora isn’t technically even a supervolcano.

What is a supervolcano?

Supervolcanoes are actually very hard to identify – they only become ‘super’ after erupting.

There are 14 volcanoes around the world known to have released a supereruption, perhaps most famously the Yellowstone Caldera in Wyoming.

‘Supervolcanoes can produce very rare and very large silicic ‘supereruptions’ – such as those reconstructed at Yellowstone, Taupo and Toba,’ Dr Katie Reeves, a teaching fellow at the University of Warwick, tells Metro.co.uk.

‘The actual number of supervolcanoes on Earth is not fully known as much of our knowledge is based on reconstructing past supereruption events, as we have not witnessed one of these during human history.’

More recently however, Campi Flegrei in Italy has been rumbling away, and some scientists believe this too has the potential to unleash an eruption of devastating proportion, even if not technically ‘super’.

To be deemed super, an eruption must hit eight on the volcanic explosivity index (VEI), meaning it spews more than 1,000 cubic kilometres of material. 

What that really means, non-scientifically, is complete devastation for the region.

What will happen if a supervolcano erupts?

Considering the effects at a local scale, Dr Reeves explains this equates to lots of volcanic material emerging, which can create a volcanic ash plume which, if it collapses, could lead to fast flows of hot volcanic particles and gases, destroying everything in their path.

Taking Campi Flegrei as an example, around half a million residents live in the 80-square mile that forms the volcano’s depression, and another 800,000 people live just outside the depression.

A super-eruption would see heavy ash and pyroclastic flows swallow surrounding towns and villages, and the destruction would continue to rampage through several miles.

The volcano is partially submerged under the sea, meaning the power from the eruption could also lead to a massive tsunami. This could engulf the entire Mediterranean basin and affect countries including France, Spain, Libya, Algeria and Tunisia, along with the coast of the northwestern Italy, the northern coast of Sicily and many islands.

The ash from the volcanic plume may go further afield, falling over an area hundreds of miles wide, which could impact crop fields and agriculture.

Volcanic ash and rainwater would create flows of lahars – mudflow or debris flow, which would destroy homes and infrastructure.

The volcanic ash could cause havoc on human health, causing respiratory illnesses like silicosis, caused by breathingin silica, as well as worsening asthma, bronchitis and COPD.

Reaching around 100 miles into the atmosphere, the volcanic plume itself could travel around the world, with major implications for air travel, and potentially causing global cooling.

‘It is likely that, due to the interconnected nature of the climate and Earth system, the effects following a supereruption would be very widespread,’ says Dr Reeves.

This would also lead to damage costing ‘tens of trillions’ says Dr Mike Cassidy, an associate professor at the University of Birmingham. 

‘We’d see a 1-3C drop in global temperatures within six months, lasting five to ten years. Agriculture would suffer from less sunlight reaching the crops, and extreme weather events like frosts and droughts [would occur]. 

‘Major climate patterns like El Niño and monsoons could be impacted too, affecting hundreds of millions. There would also be serious consequences for water security, as there would be 5-10 % less rainfall, energy, and finance.’ 

But on the plus side, Dr Cassidy says it’s extremely unlikely that humanity would go extinct. Supereruptions have occurred every 17,000 years or so, and humans are very resilient to them.

But in this modern age, there would be implications for air travel. 

‘This has major implications for air travel, as we saw with the much smaller eruption of Eyjafjallajökull in Iceland in 2010,’ says Dr Reeves.

‘These supereruptions may also produce sulphur gases that can also reach the stratosphere due to the height of the plumes – this can react with water vapour in the atmosphere to create sulphuric aerosols that can scatter incoming radiation and temporarily cool the climate, also called a “volcanic winter”. 

The last fully-fledged supereruption was 26,000 years ago, in New Zealand before human societies as we know them began.

However, Dr Cassidy notes that even though not all eruptions from supervolcanoes will count as supereruptions, the chances of a ‘non-super’ global impact eruption are much, happening once every 500 years.

These events could still cause tsunamis, release ash and pumice that block waterways and airspace, as well as releasing hazardous mud and ash flows, destroying infrastructure and killing people within a 60-mile radius.

Dr Cassidy says these large climatic impacts are more common than super eruptions and often happen around every 500 years or so.

Meaning, even if a super-eruption doesn’t happen there is still a 1 in 6 chance of a global impact eruption per century.

‘Myself and colleagues are quite concerned that there is little in the way of preparedness for such events and we are launching a charity in the near future.’

The charity, called Volcano Aid, is supporting schemes that identify dangerous and neglected volcanoes, so local communities can prepare for any effects and ensure there will be a global coordination of volcanic early warning and response.

Hopefully it won’t be needed in our lifetimes, but for now, let’s just keep an eye on them all.

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