INSTANT EXPERT: SUPERVOLCANOES
We know of 27 supervolcanoes, and they’re all worth watching very closely.
Lake Toba, on the island of Sumatra in Indonesia, is an idyllic place. Cross to the island of Samosir and you can sit in front of a rented A-frame traditional ‘jabu’ house and look out at the 100km by 30km lake. You would never guess that under the placid surface lies an underground supervolcano which caused a global cooling event around 75,000 years ago. Over a period of just two to three weeks, the supervolcano sent some 2800km of material into the air – twice the mass of Mount Everest. The quantity of ash alone, an estimated 800km , would have been sufficient to bury everything in Australia under a suffocating layer 10cm deep .
Such eruptions are, thankfully, very rare. It is estimated that supervolcanoes erupt once in 100,000 years on average. But the periodicity is not predictable, and research indicates that one of the world’s most dangerous supervolcanoes is stirring again.
Eruption blacks out the world
Supervolcanoes differ from ordinary ones by being huge craters buried deep in the ground, because supervolcano eruptions are so powerful that when they explode, often only a crater lake is left behind. Such huge underground supervolcanoes exist across the world; we know about 27 of them. The biggest is buried in America’s Yellowstone national park. The last time it erupted was 640,000 years ago.
Volcanoes are classified according to their explosiveness on the VEI scale (Volcanic Explosivity Index). The scale goes from zero to eight, and volcanoes responsible for category seven or eight eruptions are known as supervolcanoes. Scientists are not certain what triggers supervolcano eruptions, but according to current theories the eruptions happen when the ceiling of an underground volcano is sufficiently weakened by pressure or by tremor, so that magma can break through. When a supervolcano does erupt, it pumps at least 1000 cubic kilometres of magma up from the abyss, ejecting gas-filled ash columns 25km up in the air, right into the stratosphere, so that ash particles and the toxic gas sulphur dioxide can spread very far. There is little precipitation at such altitudes, so the volcanic material can remain in the air for long periods of time, and be carried across the world via jet streams.
That is why they are such a potential problem for the climate. The aerosols of the sulphur dioxide – tiny sulphuric acid droplets – can remain in the atmosphere for years, where they function as tiny light refraction mirrors, reflecting sunlight away from Earth’s surface. The result is dramatically reduced temperatures.
Supervolcano eruptions have particularly intensive effects on the global climate when they take place in the tropics. From these regions the volcanic material easily spreads across both hemispheres, thereby intensifying the cooling effect.
Australia’s east coast was once a hotspot of volcanic activity. In 2014 Dr Rhodri Davies and his team from the Australian National University identified the world’s longest known chain of continental volcanoes run
GIOVANNI CHIODIN
VULCANO RESEARCHER, UNIVERSITY OF BOLOGNA, ITALY
The magma of Campi Flegrei could be reaching a state of critical gas pressure. In the end, the process might trigger an eruption.
ning 2000km from the Whitsundays in Queensland to near Melbourne in Victoria. A year later Milo Barham at Curtin University found evidence that their activity 100,000 years ago was violent enough to throw material all the way to the west coast, an eruption similar in scale to Lake Toba.
Lurking disaster below Italy
There is no sign of continued activity in Australia. But in Italy a dormant supervolcano might be priming itself to cause havoc. It is called Campi Flegrei – “burning fields” in Ancient Greek – and is buried deep beneath the Italian city of Naples. The last time this supervolcano erupted was in 1538, but relatively lightly, so that no global temperature catastrophe followed.
Since the 1950s, the Italian supervolcano has shown signs of activity, and in 2005 scientists from Italy’s Institute of Geophysics and Volcanology at the University of Bologna discovered that the pressure had started to intensify in the supervolcano’s magma. If the pressure becomes sufficiently intense, the lid of the underground supervolcano could pop like a champagne cork in an eruption with global consequences.
“The magma of Campi Flegrei could be reaching a state of critical gas pressure, and in the end the process might trigger an eruption,” warned chief volcano researcher Giovanni Chiodini, quoted in Nature in 2016. Scientists disagree as to exactly when a potential eruption might take place – a matter of a few decades, or hundreds of years. All scientists know for sure is that increased monitoring is essential, so not only Italy but all the world could prepare sufficiently well for a potential volcanic winter.