Largest Known Volcanic Eruption in History Explained
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Those who worry about a supervolcano eruption in Yellowstone Park often point to a supereruption 75,000 years ago in Indonesia as a harbinger of what could happen. Many blame that supervolcano for a global winter that lasted at least 6 years, a global cooling that lasted 1,000 years and the near-extinction of the human race. The cause of this volcano’s massive explosion has been a mystery … until now.

A team of researchers from Uppsala University in Sweden think they found the answer in quartz crystals in and around present-day Lake Toba in Sumatra, Indonesia – the caldera of the deadly Toba supervolcano. Why were they studying quartz crystals?

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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.

Good answer from team member Dr. David Budd. Fortunately, there’s still plenty of quartz crystals left from the 2,800 cubic kilometers of volcanic ash that that was blasted over Indonesia and India. According to their study, published last week in the journal Scientific Reports, the layers of the crystals show a rapid change in oxygen isotopes in the magma, indicating something drastic related to the oxygen level had happened to increase the force of the eruption.

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Comparison of amount of volcanic ash tossed by the Toba event compared to other famous eruptions

That ‘something drastic’ was the melting of a particular kind of rock around the magma, said Dr. Frances Deegan, co-author of the study.

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 and eventually allowed the magma to rupture the overlying crust, and send thousands of cubic kilometres of magma into the atmosphere.

That eruption, now referred to as the ‘Toba event’, had an estimated volcanic explosivity index of 8 (the maximum) and was 100 times greater than that of the largest volcanic eruption in recent history, the 1815 eruption of Mount Tambora, also in Indonesia, which was responsible for a one-year global winter in the Northern Hemisphere called the “Year Without a Summer.” While scientists disagree on the effect of the Toba event on the total human population at the time, they agree it caused 6-10 years of severe global climate change.

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Comparison of Toba event magma volume to past Yellowstone events

Should anyone within 500 miles of Yellowstone be worried? Study member Professor Valentin Troll has the answer:

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!

Better prepared next time? Get back to studying those crystals!