Around 20 super-volcanoes that could potentially cause massive extinction-level events are not as dormant as previously thought, according to new research.
Super-eruptions with global consequences occur, on average, about once every 100,000 years or so.
But it’s now been discovered that super-volcanoes can remain active and hazardous for thousands of years after a super-eruption.
Super-eruptions can have a devastating impact on Earth's climate and ecology, so researchers say there need to be more accurate ways of predicting when one will occur other than looking at the amount of liquid magma.
There are about 20 known super-volcanoes on Earth – including Lake Toba in Indonesia, Lake Taupo in New Zealand, and the somewhat smaller Phlegraean Fields near Naples, Italy.
When a super-volcano erupted 600,000 years ago in Wyoming, in what today is Yellowstone National Park, it ejected more than 1,000 cubic km of ash and lava into the atmosphere – enough to bury a large city to a depth of a few kilometres.
The international team investigated what happened after the Toba super-eruption 75,000 years ago in Indonesia.
They found magma continued to ooze up to 13,000 years after the super-eruption, and the carapace of solidified left-over magma was pushed upward like a "giant turtle shell".
The team used the minerals feldspar and zircon, which contain independent records of time based on the accumulation of gasses argon and helium as time capsules in the volcanic rocks.
Dr Martin Danisik, associate professor at Curtin University in Australia, said: "Gaining an understanding of those lengthy dormant periods will determine what we look for in young active super-volcanoes to help us predict future eruptions.
"Super-eruptions are among the most catastrophic events in Earth's history, venting tremendous amounts of magma almost instantaneously."
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"They can impact global climate to the point of tipping the Earth into a volcanic winter," he added, "which is an abnormally cold period that may result in widespread famine and population disruption.
"Learning how super-volcanoes work is important for understanding the future threat of an inevitable super-eruption, which happen about once every 17,000 years."
He went on: "The findings challenged existing knowledge and studying of eruptions, which normally involves looking for liquid magma under a volcano to assess future hazard."
Dr Danisik warned: "We must now consider that eruptions can occur even if no liquid magma is found underneath a volcano – the concept of what is 'eruptible' needs to be re-evaluated.
"While a super-eruption can be regionally and globally impactful and recovery may take decades or even centuries, our results show the hazard is not over with the super-eruption and the threat of further hazards exists for many thousands of years after.
"Learning when and how eruptible magma accumulates, and in what state the magma is in before and after such eruptions, is critical for understanding super-volcanoes."
The study was published in the journal Nature – Earth and Environmental Sciences.
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