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Volcanic super-eruptions can build up silently

Scientists estimate that five to ten volcanoes worldwide are capable of producing super-eruptions that would catastrophically affect the global climate. One of these volcanoes lies beneath the waters of Lake Toba in Sumatra and has already caused two super-eruptions in the last one million years. 

By analyzing the levels of uranium and lead in zircon from the Toba volcano, an international team of geologists led by the University of Geneva (UNIGE) and Peking University estimated a super-eruption could take place in about 600,000 years.

The Toba volcano caused two of the largest eruptions on Earth: the first 840,000 and the second 75,000 years ago, both measuring about 2,800 km3 – enough to cover the whole of Switzerland with 7cm of ash. The researchers estimated these dates by measuring the amount of uranium and lead in zircon – a mineral found in the products of explosive volcanic eruptions: the youngest zircons provided information about the date of the eruption and the older ones about the history of magma accumulation preceding the super-eruption.

The scientists found that the time of magma accumulation between the two super-eruptions was halved due to the progressive increase of the temperature of the continental crust in which Toba’s magma reservoir was assembled. 

“This is a ‘vicious circle’ of eruptions: the more the magma heats the crust, the slower the magma cools and the faster the rate of magma accumulation becomes,” explained study lead author Ping-Ping Liu, a professor of Earth and Space Sciences at Peking University. Thus, super-eruptions could become more frequent over time.

 “Today, we estimate that about 320 km3 of magma could be ready to erupt within the reservoir of Toba volcano,” added study co-author Luca Caricchi, a professor of Earth Sciences at UNIGE.  “The next super-eruption of the size of the last two would therefore take place in about 600,000 years.”

The innovative methods used in this study could be applied to any other volcano on the globe and serve to identify those close to a super-eruption. Moreover, the study shows that no extreme events occur before a super-eruption. 

“This suggests that signs of an impending super-eruption such as a significant increase in earthquakes or rapid ground uplift, might not be as obvious as pictured in disaster movies by the film industry. At Toba volcano, everything is happening silently underground, and the analysis of the zircons now gives us an idea of what is to come,” concluded Caricchi.

The study is published in the journal Proceedings of the National Academy of Sciences.

By Andrei Ionescu, Staff Writer

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