The geologists ofUNIGE – University of Genoa and Peking University studied data from past eruptions to develop a prediction model for eruptions of the Toba volcano. Something that is capable of estimating the size and scope of a possible mega eruption of the Sumatra "giant".
There are 5-10 volcanoes around the world capable of producing a mega eruption that could catastrophically affect the global climate. One of these lies beneath the waters of Lake Toba in Sumatra, and has already caused two super-eruptions in the last million years.
When is the next one? Will there be any warning signs?
To answer this question, geologists from the University of Geneva (UNIGE) and Peking University studied and developed a method. The aim is to determine how long it typically takes Toba volcano to prepare for its super eruptions. The results, published in the journal Proceedings of the National Academy of Sciences (PNAS), I link them to you here, however, they contain bad news. The magma of the super volcano Toba builds up silently, shattering the belief that there will be external signals before a mega eruption.
Toba, a silent killer
As mentioned, the Toba volcano in Sumatra has already hit hard. It caused two of the largest known eruptions on Earth: the first 840.000 years ago, the second 75.000 years ago. Each of the two had an extension of approximately 2800 km3: they would be enough to cover the whole of Switzerland with a 7 cm layer of ash. Two other minor Toba eruptions are dated 1,4 million years ago and 500.000 years ago. There Toba catastrophe theory, referring precisely to the eruption of 75.000 years ago, argues that the volcano precipitated a mass extinction. As? Making an glaciation already underway much more rigid.
Geologists from UNIGE and Peking University are particularly interested in the Toba volcano because there was no historical documentation of the human response to a mega eruption of the size it produced in the past. Such an event would have a catastrophic impact on the global climate and pose numerous problems, particularly in terms of food supply, not to mention population migration.
“The Toba volcano forms a caldera. Previous eruptions created a large depression which is now occupied by meteoric water,” he explains Luca Caricchi, professor at the Department of Earth Sciences of the Faculty of Sciences of UNIGE and co-author of the study. In the center of the lake there is an island raised from the water due to the push of the magma. “This island is gradually increasing in height. And this indicates that the volcano is active and magma is accumulating,” he says Ping-Ping Liu, professor at the Faculty of Earth and Space Sciences at Peking University and lead author of the paper.
Is there really no way to predict a mega eruption?
Zircon is a mineral found in the products of explosive volcanic eruptions. “One of its characteristics is that it 'captures' uranium within its structure,” explains Ping-Ping Liu. Over time, uranium decays into lead. “By measuring the amount of uranium and lead in the zircon with a mass spectrometer, we can determine its age,” says the geologist. By examining zircons found in the remains of ancient eruptions, scientists have deduced when each eruption took place. Younger zircons indicate the date of the most recent eruption, while older ones reveal how long the magma accumulated before previous mega-eruptions.
The results? As mentioned, the first of the two worst eruptions of the Toba Volcano occurred approximately 840.000 years ago after 1,4 million years of accumulation of magma, while in the second, the magma accumulated "only" in 600.000 years, halving the time necessary to produce the eruption”. It is a real '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,” says Luca Caricchi.
In summary: These mega eruptions may become more frequent over time. This is why it is necessary to do everything possible to predict their arrival, especially in volcanoes such as Toba.
The hypotheses of scientists
By estimating the magma accumulation rate, the researchers estimate that about 4km3 of magma accumulates in the Toba basin every thousand years, with a rather stable rate.
This would mean that to reach a catastrophic eruption like those of 840.000 and 75.000 years ago it would take another 600.000 years, but there's no need to worry.
Again according to estimates, there would already be 320km3 of magma. If they came out today with a “minor” eruption, the global environment would still be hit hard. And the main problem remains: extreme events do not occur before such an eruption.
“In the Toba volcano everything is happening silently underground, and the analysis of the zircons now gives us an idea of what will happen,” concludes Luca Caricchi.
It is not enough yet, but it shows an important direction. The development of forecasting models like this (or that of the University of Canterbury, or again that of the University of Illinois) will allow us one day to prepare well and sufficiently in advance.
