Volcanic Eruptions

All civilization has from time to time become a thin crust over a volcano of revolution - Havelock Ellis

Volcanic Eruptions

image by: Olikristinn

Volcanoes are notoriously deadly, but there’s no more frightening a way to meet your own personalized doom than via a pyroclastic flow. These fast-moving ferocious fires look more like summoned demons from a videogame than anything natural – but what exactly happens when one hits you?

Pyroclastic flows are the signature fireworks of the most explosive kinds of volcanic eruptions. These mixtures of ash, lava blebs and broiling gas exceed temperatures of 1,000°C (1,832°F) and move at speeds of up to 700 kilometers per hour (about 450 miles per hour).

They tend to rush down the slopes of stratovolcanoes, the mountainous types responsible for the most explosive eruptions. Sometimes, when the ratio of gas to ash is higher, they are referred to as “pyroclastic surges.” These currents are so dense that have been known to actually go up hill and across water, not just downslope. In short, if you see one coming towards you, there’s no escape unless you have an extremely agile helicopter.

Assuming you’re on the ground, you’ll first encounter the intense heat riding at the front of the flow. If it’s a surge, you will instantly combust; your skin will rupture and becoming blackened by the severe heat of the gas before most of the ash even touches you microseconds later.

Even hiding inside a building won’t save you. When a surge passes by, the temperature of the air in the environment around it will be about 300°C (570°F), enough to destroy anything living within mere moments. Any fabric you have on will quickly burn away, and if you’re wearing any metal, it’ll sear itself into your skin for as long as it is still intact. A flow isn’t much better, as you’ll be sautéed as soon as the ash front hits you. In both cases, your muscles will suddenly contract, and you’ll curl up into something resembling a pugilistic pose. The ash and gas will rush into your airways and, if you had time to live after the extreme heat boiled off your internal organs, you’d quickly asphyxiate.

Some of the famous Vesuvian victims in Pompeii and Herculaneum were found with their skulls blown apart. It appears that the heat of the surge was so extreme that their brains boiled, releasing trapped gases so quickly that it blew apart their heads.

Either way, all that would be left of you would be a charred skeleton – if you’re lucky. Generally speaking, there are two types of pyroclastic flows.

The first forms when an ash column emerging from an eruption catastrophically falls back to Earth. Perhaps the gas content of the magma has dropped and the explosive, decompressive thrust at the volcano's vent runs out of power. Maybe the turbulent ash column mixes in too much cold air, or the lava in the column has cooled down too much. Either way, when the ash plume suddenly becomes denser than the surrounding air, it collapses and falls back onto itself, producing pyroclastic flows.

For the second, rarer type, we need to go back to Mount St Helens as it was back in May 1980. This volcano didn’t just erupt out of its vent at the summit; a huge internal pressure build up had nowhere to go but sideways, and the volcano obliterated itself by forcing its contents out of its side in a devastating lateral blast.

Plenty of hikers, journalists, volcanologists and indeed civilians have met their ends at the hands of a pyroclastic flow. They are indiscriminate killers, wiping out anything and anyone in their path – well, unless your name was Ludger Sylbaris.

Sylbaris was living on the French-Caribbean island of Martinique in 1902. Although accounts differ as to why, he was imprisoned for a serious offence in the city of St. Pierre on the night of May 7. He was thrown into solitary confinement; his cell was both windowless and underground. It was even reinforced with bombproof walls in order to make sure he couldn’t escape.

Then, at breakfast time the very next day, Martinique's Mt. Pelée erupted and blackened the sky with a terrifying, apocalyptic ash cloud. When this collapsed, pyroclastic flows formed and rushed down into the city, completely flattening it and killing all 40,000 people living there.

Everyone was turned into dust – everyone, of course, except for the man in the bombproof cell. Although he was badly burned, he survived, and was rescued from the rubble four days later. He was pardoned of his crimes, and joined Barnum & Bailey’s travelling circus, where he was known as the man who lived through Doomsday.

Source: Robin Andrews, This Is How A Volcano's Pyroclastic Flow Will Kill You, Forbes, January 8, 2017.

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Last Updated : Wednesday, November 29, 2017