Instead, the lava quietly accumulated in the lava reservoir up until these enormous explosions happen.
The Toba volcano in Sumatra triggered two of the largest eruptions understood on the Earth: the very first 840,000 years ago, the second 75,000 years ago, each determining about 2 800 km3, enough to blanket the whole of Switzerland with 7 cm thick of ash, and representing 70,000 times the quantity of lava appeared to this minute by the continuous La Palma eruption. Two other smaller sized eruptions occurred, one 1.4 million years back and the other 500,000 years ago.
Photo of Lake Toba in Sumatra and its island created by the build-up of lava in the volcanos lava tank. Credit: © UNIGE
Geologists from UNIGE and Peking University are interested in the Toba volcano since there is no historical record of human response to a super-eruption of the size that it produced in the past. At the center of the lake is an island that raised from the water due to the fact that of the push of the magma injected in the subvolcanic tank. “We can see that this island is slowly increasing in height, showing that the volcano is active and that magma is collecting below,” states Ping-Ping Liu, a professor at the Faculty of Earth and Space Sciences of Peking University and leading author of the short article.
Measuring uranium and lead in zircon
Zircon is a mineral that is discovered in the items of explosive volcanic eruptions. “So by measuring the quantity of uranium and lead in zircon with a mass spectrometer, we can determine its age,” states the geologist.
” The very first super-eruption took place around 840,000 years back after 1.4 million years of lava input, whereas lava fed the 2nd super-eruption at 75,000 years built up only in 600,000 years,” keeps in mind Luca Caricchi. Why was the time of magma build-up halved even if the two super-eruptions were of the same size? “This is linked to the progressive increase of the temperature level of the continental crust in which Tobas magma tank is assembled,” describes Ping-Ping Liu. The input of magma has actually gradually heated the surrounding continental crust, which makes the lava cool slower. “This is a vicious cycle of eruptions: the more the lava heats the crust, the slower the magma cools and the much faster the rate of magma build-up ends up being,” she states. The result is that super-eruptions can become more regular in time.
Approximating the rate of lava build-up to prepare for the size of the next super-eruption.
This strategy, based on zircon geochronology, can likewise be used to approximate the rate of magma input in a lava reservoir. “Today, we approximate that about 320 km3 of magma could be ready to emerge within the reservoir of Toba volcano,” states Luca Caricchi. This would be a very disastrous occasion that highly impact not just the highly inhabited island of Sumatra however also the global environment if such an eruption would occur now. Geologists have estimated that presently about 4 km3 of eruptible lava is accumulating within Tobas magma tank every thousand years and that this rate was rather steady throughout its eruptive history. “The next super-eruption of the size of the last two would therefore take location in about 600,000 years,” he continues. This does not rule out that smaller eruptions might happen in the meantime.
“This is a great advance, due to the fact that with couple of super-eruptions in the last 2 million years, it is not possible for us to acquire statistically considerable values for the frequency of these disastrous events at a global scale,” describes Ping-Ping Liu. “Our study also shows that no extreme occasions take place before a super-eruption.
Reference: “Growth and thermal maturation of the Toba magma tank” by Ping-Ping Liu, Luca Caricchi, Sun-Lin Chung, Xian-Hua Li, Qiu-Li Li, Mei-Fu Zhou, Yu-Ming Lai, Azman A. Ghani, Theodora Sihotang, Tom E. Sheldrake, and Guy Simpson, 1 November 2021, Proceedings of the National Academy of Sciences.DOI: 10.1073/ pnas.2101695118.
” The first super-eruption took place around 840,000 years back after 1.4 million years of magma input, whereas lava fed the 2nd super-eruption at 75,000 years accumulated only in 600,000 years,” notes Luca Caricchi. The input of magma has slowly heated up the surrounding continental crust, which makes the lava cool slower. “This is a vicious circle of eruptions: the more the magma heats up the crust, the slower the magma cools and the quicker the rate of magma accumulation becomes,” she says. Geologists have actually estimated that currently about 4 km3 of eruptible magma is building up within Tobas magma tank every thousand years and that this rate was rather stable throughout its eruptive history.
Geologists from the UNIGE and Peking University have actually established a strategy that makes it possible to approximate the maximum size of a future super-eruption of Toba volcano in Sumatra.
One of these volcanoes hides listed below the waters of Lake Toba in Sumatra and has triggered 2 super-eruptions in the last one million year. To address these questions, an international group of geologists led from the University of Geneva (UNIGE), Switzerland, and Peking University, China, established an analysis of the levels of uranium and lead in zircons– a mineral generally found in explosive volcanic eruptions– to determine how long it took the volcano to prepare for its super-eruptions. Instead, the magma calmly built up in the lava reservoir until these huge surges happen.
