This Is What Caused The Most Powerful Eruption In Human History


Robin Andrews

Science & Policy Writer

clockJan 31 2017, 19:52 UTC

The Toba eruption (obviously not pictured here) changed the world. Wead/Shutterstock

Secretly, some madcap volcanologists want to see a supervolcano erupt, just to observe its world-changing effects in real time. Most of us, however, don’t want to see this inevitable event take place – a terrifying act of nature that we are powerless to stop.


It’s a good thing then that researchers are hard at work, digging through the ruins of ancient eruptions, to work out how these bad boys explode in the first place.

Take the eruption of Indonesia’s Toba supervolcano around 73,000 years ago. This was by far the most powerful eruption in human history, one that plunged the world into darkness and caused a six-year-long volcanic winter, but a lot about precisely why it erupted has remained a mystery.

Now, scientists at Uppsala University have used an ingenious method to work out exactly why this eruption was so catastrophic.

By looking at the unusual compositional layering of ancient magmatic crystals, the team were able to work out that Toba’s magma source was so violent and hot that it essentially melted a lot of the subterranean rocky environment it wormed its way into.


Essentially, the emplaced magma melted much of its own magma chamber. That’s like a shaken-up fizzy drink inside a plastic bottle eating away at most of the bottle itself before spurting out everywhere.

By assimilating so much of this water-rich rock into the original magma, the molten mass gained a lot of extra gas. All this trapped, highly pressurized gas desperately wanted to escape to the surface, so when the roof of Toba collapsed, the resulting decompression was profoundly energetic and incredibly destructive.

When this cauldron-like volcano exploded, in full view of a very primitive humanity, it produced a crater 100 kilometers (about 62 miles) long and produced at least 2,800 cubic kilometers (672 cubic miles) of volcanic debris. Within days, all of South Asia was smothered by an ash layer 15 centimeters (6 inches) deep.


Image in text: A couple of ancient crystals from within Toba that show some unusual and revealing layering. Uppsala University

Writing in the journal Scientific Reports, the team of scientists from Sweden were able to see into the past and work all this out by carefully picking apart the layers of the crystals formed within the magma chamber that was beneath Toba all those thousands of years ago.

You see, when crystals form within magma, they move around a lot, through different parts of the chamber and across a range of temperatures, pressures, and chemical compositions. As they cool, different layers form around their edges that record the conditions of the magma they were swimming through at the time.


“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,” lead researcher David Budd, a geophysicist at Uppsala University, said in a statement

The crystals within Toba appear to indicate that, just before the eruption took place, a new source of magma – one full of water – was injected and absorbed into the primary source of molten doom.

The surrounding rocks fit the bill, and the researchers concluded that the magma must have been able to annihilate and subsume much of the rocky magma chamber just prior to the volcanic fireworks that took place.



A NASA Landsat image of Lake Toba today, the rough outline of the crate left behind by the 73,000 event. NASA

Toba’s cataclysm registered as an 8 on the Volcanic Explosivity Index (VEI), the maximum value on the scale. This type of eruption is extremely rare - as far as volcanologists can tell, there have only been 42 in the last 36 million years.

We are “due” for another, though. All eyes are on Campi Flegrei beneath Naples, or the infamous Yellowstone caldera.

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