The silent build-up to a super-eruption

It is estimated that about 5 to 10 volcanoes worldwide are capable of producing a super-eruption that could catastrophically affect global climate.

One of these volcanoes hides below the waters of Lake Toba in Sumatra and has caused two super-eruptions in the last million years. But when will the next one be? Will there be any warning signs?

To answer these questions, an international team of geologists led from the University of Geneva (UNIGE), Switzerland, and Peking University, China, developed an analysis of the levels of uranium and lead in zircons—a mineral typically found in explosive volcanic eruptions—to determine how long it took the volcano to prepare for its super-eruptions.

Unfortunately, these results, published in the journal Proceedings of the National Academy of Sciences, refute the notion that unusual geological signs would herald an imminent super-eruption. Instead, the magma silently accumulated in the magma reservoir until these massive explosions occurred.

The Toba volcano in Sumatra caused two of the largest eruptions known on the Earth: the first 840,000 years ago, the second 75,000 years ago, each measuring about 2,800 km3, enough to blanket the whole of Switzerland with 7 cm of ash, and representing 70,000 times the amount of magma erupted thus far by the ongoing La Palma eruption.

Two other smaller eruptions took place, one 1.4 million years ago and the other 500,000 years ago.

Geologists from UNIGE and Peking University are interested in the Toba volcano because there is no historical record of human response to a super-eruption of the size that it produced in the past. Such an event would affect the global climate and pose numerous problems, particularly in terms of food supply, not to mention the migration of populations.

“Toba volcano forms a caldera, meaning that previous eruptions have created a large depression that is occupied today by meteoric water,” explains Luca Caricchi, professor at the Department of Earth Sciences at the UNIGE Faculty of Science and co-author of the study. At the center of the lake is an island that raised from the water because of the push of the magma injected in the subvolcanic reservoir.

“We can see that this island is gradually increasing in height, indicating that the volcano is active and that magma is accumulating underneath,” says Ping-Ping Liu, a professor at the Faculty of Earth and Space Sciences of Peking University and leading author of the article. But are we close to the next super-eruption?

Measuring uranium and lead in zircon

Zircon is a mineral that is found in the products of explosive volcanic eruptions. “One of its characteristics is that it takes uranium within its structure,” explains Ping-Ping Liu. Over time, the uranium decays into lead. “So by measuring the amount of uranium and lead in zircon with a mass spectrometer, we can determine its age,” says the geologist.

The scientists determined the age of a large number of zircons extracted from the products of different eruptions: the youngest zircon provides information on the date of the eruption and the older zircons reveal the history of magma accumulation preceding the super-eruptions.

“The first super-eruption occurred around 840,000 years ago after 1.4 million years of magma input, whereas the magma that fed the second super-eruption at 75,000 years accumulated in only 600,000 years,” notes Luca Caricchi. Why was the time of magma accumulation halved even if the two super-eruptions were of the same size? “This is linked to the progressive increase of the temperature of the continental crust in which Toba’s magma reservoir is assembled,” explains Ping-Ping Liu.

The input of magma has gradually heated the surrounding continental crust, which makes the magma cool slower. “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,” she says. The result is that super-eruptions can become more frequent in time.

Estimating the rate of magma accumulation to anticipate the size of the next super-eruption

This technique, based on zircon geochronology, can also be used to estimate the rate of magma input in a magma reservoir. “Today, we estimate that about 320 km3 of magma could be ready to erupt within the reservoir of Toba volcano,” says Luca Caricchi. If such an eruption would occur now, this would be a very catastrophic event that strongly affect not only the highly populated island of Sumatra but also the global environment.

Geologists have estimated that currently about 4 km3 of eruptible magma is accumulating within Toba’s magma reservoir every thousand years and that this rate was rather stable throughout its eruptive history. “The next super-eruption of the size of the last two would therefore take place in about 600,000 years,” he continues. This does not rule out that smaller eruptions could occur in the meantime.

This innovative method can be applied to any other volcano globally and could serve to identify which volcano is closest to a super-eruption. “This is a great advance, because with few super-eruptions in the last 2 million years, it is not possible for us to obtain statistically significant values for the frequency of these catastrophic events at a global scale,” explains Ping-Ping Liu.

“Our study also 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,” concludes Luca Caricchi.

See more here: phys.org

Header image: WeNatureLists

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Comments (6)

  • Avatar

    Howdy

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    The multiplicity of explanations, of amounts, and times volcanoes reeked havoc is astounding, and yet.
    “But when will the next one be? Will there be any warning signs”
    Sigh.

    Reply

  • Avatar

    Joseph Olson

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    Earth has 259 billion cubic miles of mostly molten rock, containing 800,000 cubic miles of Uranium and 1.2 million cubic miles of Thorium subject to variable fission. Fission of these atoms releases a million (mega) time the energy of a TNT molecule, hence nuclear bombs are measured in megatons. In addition, fission produces an array of “elemental” daughter atoms, which form daughter molecules, like CO2 and Hydrocarbons.

    “From Muscle Power to Carbon Empowerment” at principia-scientific.org

    Reply

    • Avatar

      JaKo

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      Hi Joseph,
      You wrote: “… fission produces an array of “elemental” daughter atoms, which form daughter molecules, like CO2 and Hydrocarbons.” Could you please elaborate on that?
      The dogma of physics explicitly states:
      Everything lighter than Iron can be fused and release some energy. Everything heavier than iron can be fissioned and release some energy.
      (“lighter/heavier” could be understood by atomic “weight”)
      Factoids: H is 1/1, C 6/12, O 8/16 and Fe 26/56 (atomic number/atomic mass)
      I double-checked the decay chains for U & Th, they both end with Pb 82/206 & 208; they can’t decay into anything “lighter” than that.
      Cheers, JaKo

      Reply

    • Avatar

      Jerry Krause

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      Hi JaKo and PSI Readers,,

      JaKo is amazing in what he reads that others have written!!! One cannot believe everything that one reads. Compare what he has just shared with me and other PSI Readers with what Joseph Olson also shared with us. And ponder any differences you see (observe).

      I believe what Jako wrote and I don’t believe what Joseph wrote because of the difference I see.

      Have a good day, Jerry

      Reply

    • Avatar

      Jerry Krause

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      Hi PSI Readers,

      This is an experiment. In the recent comments I read, and I assume you read, that I have made a comment relative to this article. Except I do not find the comment I have made. So I am trying to see what happens with this comment.

      Have a good day, Jerry

      Reply

    • Avatar

      Jerry Krause

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      He PSI Readers,

      Finally my comments have appeared. So now I can make a comment relative to the article’ s photograph. Which I assume is: “One of these volcanoes hides below the waters of Lake Toba in Sumatra and has caused two super-eruptions in the last million years.” This photograph (image) is amazing like that of CraterLake in the State of Oregon USA.

      Hence, I assume that a ‘super-eruption” created Crater Lake sometime in the past. But Mt. Saint Helen (the result of less violent eruptions) blew its top in recent history (a few decades ago) that left a crater. And blew ash into base of the Stratosphere and the circulation of the atmosphere carried the ash about the Earth many times as it spread through out the entire atmosphere and eventually disappeared from the atmosphere.

      Now I have read that the atmosphere is well mixed up to the top of the mesosphere (about 86 km elevation) so that the atmospheric molecules of differing masses do not form layers of molecules, by the continuous action of gravity upon them, with the molecules of greatest mass at the bottom and the molecules of next lesser mass above, etc..

      What I cannot remember reading is what this “mixing action” is which prevents the layered atmosphere to form up to 86 km.

      Now, based upon observed facts, I have an idea what this mixing action is and where it mainly occurs. But I ask any PSI Reader to correct me when I state I have not read about anyone else’s explanation of this mixing action.

      Have a good day, Jerry

      Reply

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