The geologists ofUNIGE - University of Genoa and Peking University studied data from past eruptions to develop a model for predicting eruptions from the Toba volcano. Something that is able to estimate the size and extent of a possible mega eruption of the "giant" of Sumatra.
There are 5-10 volcanoes around the world capable of producing a mega eruption that could catastrophically affect the global climate. One of these hides under 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 the University of Peking have studied and developed a method. The aim is to determine the time typically required for the Toba volcano to prepare for its super eruptions. The results, published in the Proceedings of 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 about 2800 km3: they would be enough to cover the whole of Switzerland with a layer of 7 cm of ash. Two other minor eruptions of the toba are dated 1,4 million years ago and 500.000 years ago. There Toba catastrophe theory, referring to the eruption of 75.000 years ago, argues that the volcano accelerated a mass extinction. How? Making a glaciation already underway much more rigid.
Geologists at UNIGE and Peking University are particularly interested in the Toba volcano because there was no historical record of the human response to a mega eruption the size it produced in the past. Such an event would catastrophically affect the global climate and pose numerous problems, particularly in terms of food supply, not to mention the migration of populations.
“The Toba volcano forms a caldera. Previous eruptions created a large depression which is now occupied by meteoric water, ”he explains Luca Caricchi, professor in the Department of Earth Sciences of the UNIGE Faculty of Sciences and co-author of the study. In the center of the lake there is an island raised by 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 building up, "he says Ping-Ping Liu, professor at Peking University's Faculty of Earth and Space Sciences 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 the zircons found in the remains of ancient eruptions, scientists deduced when each eruption took place. The younger zircons indicate the date of the most recent eruption, while the older ones reveal how long the magma accumulated before the previous mega eruptions.
The results? As mentioned, the first of the two worst eruptions of the Toba Volcano occurred about 840.000 years ago after 1,4 million years of magma accumulation, while in the second, magma accumulated "only" in 600.000 years, halving the time. necessary to produce the eruption. "It's a real 'vicious circle' of eruptions." The more the magma heats the crust, the slower the magma cools and the faster the magma accumulation rate becomes, "says Luca Caricchi.
In summary: these mega eruptions can become more frequent over time. For this 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 it would take another 840.000 years to reach a catastrophic eruption like those of 75.000 and 600.000 years ago, but there is no need to rest assured.
According to estimates, there are already 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: no extreme events occur before such an eruption.
"In the Toba volcano, everything is silently happening 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.