5 mars 2017

La plus grosse explosion de l'histoire humaine


L'éruption du volcan Toba, en Indonésie, eut des effets catastrophiques sur toute la surface du globe:

(...) 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.

(...) 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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