What triggered the largest volcanic eruption witnessed by mankind?

January 26, 2017 by Börje Dahrén
The researchers analysed quartz crystals from Toba, and found a distinct shift in the isotopic composition towards the outer rim of the crystals. Credit: Troll et al.

Researchers have now found an explanation for what triggered the largest volcanic eruption witnessed by mankind. The volcano's secret was revealed by geochemical clues hidden inside volcanic quartz crystals.

The deadliest volcanoes on earth are called supervolcanoes, capable of producing cataclysmic eruptions that devastate huge regions, and cause global cooling of the climate. The Indonesian supervolcano Toba had one of these eruptions about 73 000 years ago, when 2 800 cubic kilometers of was ejected into the atmosphere and rained down and covered enormous areas in Indonesia and India.

Scientists have long debated how these extraordinary volumes of are generated, and what makes this magma erupt so very explosively. A team of researchers at Uppsala University, together with international colleagues, have now found intriguing clues hidden inside millimeter-sized from the volcanic ash and rock.

'Quartz crystals that grow in the magma register chemical and thermodynamical changes in the magmatic system prior to eruption, similar to how tree rings record climate variations. When the conditions in the magma change, the crystals respond and produce distinct growth zones that record these changes. The problem is that each "tree ring"-analogue is only a few micrometers across, which is why they are extremely challenging to analyse in detail,' says Dr. David Budd at the Department of Earth Sciences, Uppsala University.

The researchers analysed from Toba, and found a distinct shift in the isotopic composition towards the outer rim of the crystals. The crystal rims contain a relatively lower proportion of the heavy isotope 18O compared to the lighter 16O.

'The low ratio of 18O to 16O contents in the crystal rims indicate that something in the magmatic system changed drastically just before the big eruption. The explanation behind these chemical signatures is that the magma melted and assimilated a large volume of a local rock that itself is characterised by a relatively low ratio of 18O to 16O . This rock type also often contains a lot of water, which may be released into the magma, producing steam, and thereby an increased gas pressure inside the magma chamber. This rapidly increased gas pressure eventually allowed the magma to rupture the overlying crust, and send thousands of cubic kilometres of magma into the atmosphere,' explains Dr. Frances Deegan at the Department of Earth Sciences, Uppsala University.

Luckily, these cataclysmic super-eruptions happen very rarely.

'Biologists have previously shown that this particular eruption at Toba pushed humanity close to extinction. It will hopefully take many thousands of years, but the fact is it is only a matter of time before the next super eruption, maybe at Toba, Yellowstone (USA), or somewhere else. Hopefully, we will know more and be better prepared next time!' says Professor Valentin Troll at the Department of Earth Sciences, who led this study of Toba quartzes at Uppsala University.

Explore further: Popcorn-rocks solve the mystery of the magma chambers

More information: David A. Budd et al. Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz, Scientific Reports (2017). DOI: 10.1038/srep40624

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cantdrive85
1.4 / 5 (9) Jan 26, 2017
What triggered the largest volcanic eruption witnessed by mankind?

Solar activity, more than likely.
Guy_Underbridge
2.6 / 5 (5) Jan 26, 2017
..or Thor's might hammer Mjölnir, which primative minds would mistake for Solar activity.
Osiris1
not rated yet Jan 26, 2017
The article posits a very large magma pool. Such a one would have no problem melting stuff above it and 'assimilating' the melt. It takes a LOT of heat to create such a large magma pool and the only place it could get that from is upwellings from below, such as some kind of mantle plume. So what to watch for is three things that make the supervolcano active... 1> mantle plume that had been active for a long time and generated 2> a very large magma chamber that happens to 3>sit below reactive rock strata.

We have satellites that sense a lot of these kinds of data, and can make more sensitive ones literally in step with Moore's Law. Put them to work!
jonesdave
3.7 / 5 (3) Feb 02, 2017
What triggered the largest volcanic eruption witnessed by mankind?

Solar activity, more than likely.


Don't be silly. Please tell me you haven't been taken in by that Ben Davidson loon? On the other hand, if you believe Thornhill's stuff, anything is possible. There was a long running thread about this nonsense on ISF. I proved that my 'having a bacon sandwich for breakfast causes earthquakes' hypothesis was just as accurate as his woo. After months and months, we were never given a possible mechanism. Out and out woo.
http://www.intern...thquakes

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