Photo of Lake Toba, Sumatra with its island formed by magma from the volcanoes magma reservoir. Credit: UNIGE
Global climate could be affected by super-eruptions. It is believed that between 5-10 volcanoes are capable of producing such a powerful eruption. One of these volcanoes lies below Lake Toba in Sumatra. It has been responsible for two super-eruptions over the past million years. What will be the next eruption? Are there any warning signs?
An international team of geologists from Peking University, China and the University of Geneva (UNIGE) in Switzerland developed a study of the levels of uranium in zirconsa minerals that are commonly found in explosive volcanic eruptions to answer these questions. These results, published in the journal Proceedings of the National Academy of Sciences (PDF), disprove the idea that super-eruptions could be predicted by unusual geological signs. Instead, magma accumulated silently in the magma reservoir and then massive explosions took place.
Sumatra's Toba volcano caused two of the most powerful eruptions on Earth. The first was 840,000 years ago and the second was 75,000 years ago. Each measured approximately 2,800 km3, which is enough to cover the entire of Switzerland with 7cm of ash. This amount of magma represents 70,000 times that of the La Palma eruption. The second eruption occurred 500,000 years ago.
Peking University and UNIGE are both interested in the Toba volcanic eruption because there is no record of humans reacting to a super-eruption that was as large in the past. This event could have a significant impact on the global climate, causing many problems in terms of food supply and migration. Professor Luca Caricchi of the Department of Earth Sciences at UNIGE Faculty of Science, and co-author of this study, explained that the caldera formed by the Toba volcano. The subvolcanic reservoir has injected magma into the lake, causing an island to rise from the water. Ping-Ping Liu is a professor at Peking University's Faculty of Earth and Space Sciences and the lead author of this article. Are we really close to the next super-eruption yet?
Measuring the uranium in zircon and the lead in it
Zircon is an explosive volcanic eruption-product mineral. Ping-Ping Liu explains that one of its features is the fact that it absorbs uranium in its structure. The uranium becomes lead over time. The geologist says that by using a mass spectrometer to measure the amount of lead and uranium in zircon, they can determine the age. Scientists determined the age of many zircons taken from different eruptions. The youngest zircon gives information about the eruption date, while the older zircons show the history of magma accumulating before the super-eruptions.
"The super-eruption that caused the first super-eruption took place around 840,000 years ago, after 1.4 million years magma input. However, the magma which fueled the second super-eruption at 755,000 years accumulated only 600,000. years," says Luca Caricchi. Why did the magma accumulation time decrease by half, even though the super-eruptions were the same size? Ping-Ping Liu explains that this is due to the gradual increase in the temperature of Toba's continental crust, where Toba is located. The magma cooling rate is slower because the magma has slowly warmed the crust. She says, "This is a vicious circle of eruptions: The more magma heats crust, the slower magma cools, and the faster magma accumulates." Super-eruptions can occur more frequently over time.
To predict the size of the next super-erupttion, it is necessary to estimate the rate at which magma accumulates.
Based on zircon geochronology this technique can be used to calculate the rate of magma intake in a magma storage reservoir. Luca Caricchi says that today, it is possible for magma to erupt from the Toba volcano reservoir. This would not only affect Sumatra's highly populated island, but also the entire global environment. According to geologists, approximately 4 km3 of eruptible molten magma is currently accumulating in Toba's magma storage every 1000 years. This rate has been relatively stable over its entire eruptive history. He says that the next super-eruption would be approximately 600,000 years away. However, smaller eruptions may occur during this time.
This method could be used to find the closest volcano to a super-eruption and can be applied to all volcanoes worldwide. Ping-Ping Liu says, "This is a significant advance because there have been very few super-eruptions over the past 2 million years. It is impossible for us to get statistically significant numbers for the frequency and severity of these catastrophic events on a global level." Our study also showed that there are no extreme events before a super-eruption. This suggests that signs of a super-eruption, such as an increase in earthquakes and rapid ground uplift might not be as apparent as what is depicted in disaster movies made by the film industry. Everything is occurring underground at Toba volcano. The analysis of zircons gives us a glimpse of what's to come," says Luca Caricchi.
Continue reading Study uncovers threat of supervolcano eruptions that could be catastrophic
