Signs of Supereruptions: The Magma Beneath Toba

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AsianScientist (Nov. 2, 2021) – Scientists have pieced together the magmatic story underlying the Toba volcanic system’s supereruptions, devising a novel technique for detecting the signs of impending eruptions. The findings were published in the Proceedings of the National Academy of Sciences.In Sumatra, Indonesia, Toba looks like a peaceful lake on the surface. Beneath, however, hides a massive volcanic system, responsible for two of the largest eruptions ever to unfold on Earth thousands of years ago. Despite ejecting tons of magma in the past, the Toba supervolcano remains active today.To anticipate possible volcanic activity, geologists have identified common warning signs, such as more frequent earthquakes, swelling or deformation of the ground and unusual emissions of fumes. However, predicting supereruptions is extremely complex, given their rarity and the lack of investigations into their origins.Now an international team of scientists from China, Indonesia, Malaysia, Taiwan and Switzerland have developed a new technique for evaluating a volcano’s eruptive potential, reconstructing how Toba’s underlying magma reservoirs prepared for—and led to—the gigantic explosions.By tapping into a mineral called zircon, which crystallizes and stands the test of time, they identified the eruption date and uncovered the volcano’s history of magmatism. While zircon dating is not new, the team complemented the method with computer modeling.They tested how various parameters like magma flow might affect zircon crystallization age, comparing the simulated data with the actual measurements. Strikingly, the results revealed that the typical monitoring signs, like surface deformation and gas emissions, may not change significantly before supereruptions.Moreover, the researchers discovered that the average rate of magma input was constant before and after the supereruptions. Instead of a sudden increase in magma volume, Toba’s supereruptions occurred from the progressive build-up of magma over lengthy timeframes, brewing underground for hundred thousands to millions of years.This progressive maturation and increase in temperature of the overlying crust also led to repeated eruptive events, the researchers found. In a vicious cycle, continued heating of the crust delays magma cooling, which in turn accelerates magma accumulation—ultimately leading to more frequent super-eruptions.According to the team, the current rate of magma accumulation suggests that the next supereruption may not happen until 600,000 years from now, though smaller eruptions are still possible. The technique, they hope, could be used to study other supervolcanoes globally to better anticipate possible eruptive events.“Understanding the thermal state of magma reservoirs before supereruptions is crucial for interpreting the processes leading to such catastrophic events,” the authors wrote. “Our method can be widely applied to other large silicic magmatic systems to evaluate their potential to feed a supereruption.”The article can be found at: Liu et al. (2021) Growth and thermal maturation of the Toba magma reservoir.—Source: Peking University; Photo: Tanya Grypachevskaya/Unsplash.Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.



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