SCIENTISTS studying an ancient supervolcano in Indonesia have found that such volcanoes remain active and hazardous for thousands of years after erupting, challenging a long-held theory.

The likes of Yellowstone volcano have long left the public worrying that they could one day blow, despite experts at the United States Geological Survey (USGS) saying there is no reason to believe it will again. It is just one of around 12 supervolcanoes across Earth – each one at least seven times larger than Mount Tambora, which had the biggest eruption in recorded history. And an international research team say that there may need to be a rethink of how their potentially catastrophic supereruptions are predicted.

Professor Martin Danisik, from the John de Laeter Centre based at Curtin University, said supervolcanoes often erupted several times with intervals of tens of thousands of years between the big eruptions but it was not known what happened during the dormant periods.

He said: “Gaining an understanding of those lengthy dormant periods will determine what we look for in young active supervolcanoes 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.

“They can impact global climate to the point of tipping the Earth into a ‘volcanic winter,’ which is an abnormally cold period that may result in widespread famine and population disruption.

“Learning how supervolcanoes work is important for understanding the future threat of an inevitable super-eruption, which happen about once every 17,000 years.”

The team investigated magma left behind after the Toba supereruption 75,000 years ago that showed the volcano was active long after the event.

Prof Danisik added: “Using these geochronological data, statistical inference and thermal modelling, we showed that magma continued to ooze out within the caldera, or deep depression created by the eruption of magma, for 5,000 to 13,000 years after the super-eruption, and then the carapace of solidified left-over magma was pushed upward like a giant turtle shell.

“The findings challenged existing knowledge and studying of eruptions, which normally involves looking for liquid magma under a volcano to assess future hazard.

“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 supereruption 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 supervolcanoes.”

The paper, “Resurgence initiation and subsolidus eruption of cold carapace of warm magma at Toba Caldera, Sumatra,” was published in journal Nature—Earth and Environmental Sciences.