The rain of fire

On the morning of October 24, 79 C.E., Mount Vesuvius erupted in one of the deadliest volcanic events in recorded history.

The nearby towns of Pompeii, Herculaneum, Stabiae, and Oplontis had warnings.  There was a series of earthquakes during the lead-up to the eruption, which got a few people to leave the area -- everyone remembered that there'd been a powerful earthquake in February of 62 that had destroyed a number of buildings, and the skittish thought that something similar might be about to happen again -- but by and large, the residents just shrugged their shoulders.  Pliny the Younger, who wrote the only extant eyewitness account of the eruption (he was safely in Misenum, thirty kilometers away across the Bay of Naples, when it happened), said that the earthquakes that preceded the eruption "were not particularly alarming because they are frequent in Campania," and thus the majority of people in the area ignored them and stayed home.

This turned out to be a mistake.

The morning of October 24 dawned clear and bright, but there was already a plume of steam coming from the summit of the mountain that loomed over the four cities.  This, too, was nothing unusual; it's doubtful many people even noticed.  But at around midday, there was a sudden jolt, and the entire peak exploded, sending a column of ash, rock, and superheated steam an estimated thirty kilometers high, blasting out material at a rate of 1.5 million tons per second.  Rocks and ash rained down on the cities, but worse was to come; by evening, the pressure forcing the column upward dropped suddenly and the entire column collapsed, causing a pyroclastic surge with an estimated temperature of six hundred degrees Celsius pouring downhill at about a hundred kilometers an hour.  Anything or anyone left that hadn't been killed by asphyxiation or roofs collapsing died instantly, and the ash flow blanketed the region.  The greatest quantity of ash landed in Herculaneum, which was buried under a layer twenty meters thick.

But all four cities were completely obliterated, to the point that within a hundred years, most people forgot that they'd ever existed.  References to Pompeii, Herculaneum, Stabiae, and Oplontis, four prosperous towns that had been wiped out by the wrath of the gods, were considered fanciful legends -- a little like Plato's mention of the mythical land of Atlantis sinking beneath the waves.

Then, in 1709, a farmer was plowing his field, and the plow hit the edge of a buried wall.  It turned out to be a surviving piece of masonry from Herculaneum.  Something similar happened in Pompeii in 1748.  Archaeologists were called in, and gradually, the work started that is still ongoing -- clearing away meters-thick layers of welded ash to uncover what is left of the four cities.

Today it's a strange, somber place.  Wandering around its cobblestone streets, and looking at the snaggletoothed silhouette of Vesuvius in the distance -- the mountain lost almost half of its original height in the eruption -- was chilling despite the bright warmth of the sun.  We looked at remnants of homes, shops, temples, baths, the central forum, and even a brothel (each room decorated with highly explicit paintings of what services you could expect within).

We got to see some of the casts of the people who died during the eruption, their names long forgotten, their bodies entombed in fused hot ash, then burned and decayed away to leave a cavity that archaeologists filled with plaster to reveal their ghostly forms.

Many of the 1,044 molds of human victims were found with their hands over their faces, futilely trying to shield themselves from the choking, scalding ash.

Today, around three million people live in the shadow of Vesuvius, most of them in the city of Naples and the nearby towns of Pozzuoli, Bagnoli, San Giorgio a Cremano, and Portici.  Our guide said there were two reasons for this, and for the number of people living in other volcanic areas, such as Indonesia, Japan, Costa Rica, Cameroon, and Ecuador -- (1) volcanic soil is wonderfully fertile for agriculture, and (2) people have short memories.  But now that we have a better understanding of plate tectonics and geology, you have to wonder why people are willing to accept the risk.  A man we talked to in Rome had an explanation for that, too.  "Those people down in Naples," he said, shaking his head, "they're crazy."

Today Pompeii is seemingly at peace, its ruins as quiet as the cemetery it in fact is.  Flowers grow in profusion in every grassy spot.

But not far beneath the surface, the magma is still moving.  The processes that destroyed the region in the first century C.E. are haven't stopped, and the tranquil scene up above is very much an illusion.  After seeing the city, we hiked up to the summit of Vesuvius and looked down into the crater, the hole blasted out of the center of the mountain.

The whole thing was enough to make me feel very small and very powerless.  We flatter ourselves to think we can control the forces of nature, but in reality, we're still at their mercy -- no different from the residents of Pompeii on October 23, who knew the mountain was rumbling but figured there was nothing to worry about.  The rain of fire that was to come only twenty-four hours later was unstoppable.  Although now we can predict volcanic eruptions better than the first-century Romans, we still are at the mercy of a natural world that cares little for our lives.

But there's nothing wrong with being reminded of this periodically.  A bit of humility is good for the mind.

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Out of the ashes

The eruption of Mount Vesuvius in 79 C. E. and its destruction of the cities of Pompeii and Herculaneum make for a story that is as fascinating as it is horrific.

Vesuvius is a stratovolcano, built up from layer after layer of hardened lava (the "strata" of the name).  Stratovolcanoes usually produce felsic lava -- high in silica content -- making the molten rock thick, viscous, and resistant to flowing.  The results are explosive eruptions, not the cascading rivers of lava you see in shield volcanoes such as Kilauea, which produce mafic lava that is low in silica and flows readily.

The eruption of a stratovolcano is catastrophic.  Unlike the Hawaiian shield volcanoes, which certainly can cause significant property damage but seldom loss of life, stratovolcanoes fling chunks of rock around, generate huge amounts of ash, and -- worst of all -- can create pyroclastic flows of superheated air that can move at a hundred kilometers per hour and incinerate everything in their path.  It was a pyroclastic flow from Mount Pelée that killed almost thirty thousand people in only a few minutes on the island of Martinique in 1902; one of three people in the city of Saint Pierre who are known to have survived only did because he was being held in an underground jail cell.

The combination of rock ejection, ash clouds, and pyroclastic flows are sometimes called Plinian eruptions after the Roman author Pliny the Elder, who died during the eruption of Vesuvius.  If you don't mind being a little freaked out by the power of nature, check out this ten-minute video simulation of the 79 C. E. eruption, from the perspective of a person in Pompeii:

The reason the topic comes up is because of a paper that appeared last week in Scientific Reports about some research done by a team led by Gabriele Scorrano of the University of Copenhagen.  Scorrano and his team found two human skeletons, one male and one female, that -- despite being covered by scorching-hot ash and then entombed for almost two thousand years -- contained enough intact DNA to analyze.

The man's, in fact, was complete enough to do a whole-genome analysis, including a Y DNA and mitochondrial DNA study.  The results were interesting, if not surprising; his DNA was similar to that of modern Italians from the region, although both his Y DNA and mtDNA showed markers most commonly found on the island of Sardinia.  

So he likely had ancestry on both sides of his family from Sardinia.  He also, apparently, had tuberculosis.  The woman's skeleton, which contained only fragmentary DNA, showed signs of significant osteoarthritis.  Serena Viva of the University of Salento, who co-authored the study, said, "This could have been the reason for which they waited for it all to finish, maybe in the security of their home, compared to other victims who were fleeing and whose remains were found in open spaces."

The ruins of Pompeii, with Vesuvius in the background [Image licensed under the Creative Commons ElfQrin, Theathres of Pompeii, CC BY-SA 4.0]

Scary stuff, that.  I have to say I'm glad I don't live in Naples; I wouldn't be able to sleep with Vesuvius looming over me, even though it's shown no signs of an imminent catastrophic eruption.  I actually thought the same thing when we were in the Pacific Northwest last week, not only because of nearby stratovolcanoes like Mount Rainier, but because the entire area is at risk of enormous earthquakes because of plate movement along the Cascadia Subduction Zone. 

I know the risk during any given week is extremely low, but it did make me a bit nervous anyhow.  Sometimes a little knowledge can be a lot scary.

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The burning fields

It will come as no surprise to regular readers of Skeptophilia that I have a peculiar fascination for things that are huge and powerful and can kill you.

I'm not entirely sure where this obsession comes from, but it's what's driven me to write here about such upbeat topics as giant predatory dinosaurs, tornadoes, hurricanes, massive earthquakes, supernovas, gamma-ray bursters, and the cheerful concept of "false vacuum decay" (which wouldn't just destroy the Earth, but the entire universe).  I'm guessing part of it is my generally anxiety-ridden attitude toward everything; after all, just because we don't think there's a Wolf-Rayet star nearby that's ready to explode and fry the Solar System doesn't mean there isn't one.  I know that worrying about all of that stuff isn't going to (1) make it any less likely that it'll happen, or (2) make a damn bit of difference to my survival if it does, but even so I don't seem to be able to just relax and focus on more positive things, such as the fact that with the sea-level rise predicted from climate change, it looks like here in upstate New York I may finally own ocean-front property.

It's also why I keep regular tabs on the known volcanoes on the Earth -- on some level, I'm always waiting for the next major eruption.  One of the potentially most dangerous volcanoes on Earth is in Italy, and I'm not talking about Vesuvius; I'm referring to the Campi Flegrei ("burning fields," from the Greek φλέγω, "to burn"), which isn't far away from the more famous mountain and seems to be powered by the same magma chamber complex that obliterated Pompeii and Herculaneum in 79 C.E.  Both Vesuvius and Campi Flegrei are highly active, and near the top of the list of "world's most dangerous volcanoes."

The problem is, the three million residents of Naples live right smack in between the two, only twenty-odd kilometers away from Vesuvius (to the east) and Campi Flegrei (to the west).  (For reference, Pompeii was nine kilometers from the summit of Vesuvius.)

The Campi Flegrei, looking west from Naples [Image licensed under the Creative Commons Baku, VedutaEremo2, CC BY-SA 4.0]

The problem is that volcanoes like these two don't erupt like the familiar fountains of lava you see from Kilauea on the Big Island of Hawaii, and the current eruption on La Palma in the Canary Islands.  The most typical eruption from volcanoes like Vesuvius and Campi Flegrei are pyroclastic flows -- surely one of the most terrifying phenomena on Earth -- a superheated mass of steam and ash that rush downhill at speeds of up to a hundred kilometers an hour, flash-frying everything in its wake.  That the Campi Flegrei volcanoes are capable of such massive events is witnessed by the surrounding rock formation called the "Neapolitan Yellow Tuff."  A "welded tuff" is a layer of volcanic ash that was so hot when it stopped moving that it was still partially molten, and fused together into a solid porous rock.

A video of a pyroclastic flow from Mount Unzen in Japan in 1991

The Neapolitan Yellow Tuff isn't very recent; it came from an eruption about 39,000 years ago.  But there are signs the Campi Flegrei are heating up again, which is seriously bad news not only for Naples but for the town of Pozzuoli, which was built right inside the main caldera.

That people would build a town on top of an active volcano is explained mostly by the fact that people have short memories.  And also, the richness of volcanic soils is generally good for agriculture.  Once Pompeii was re-discovered in the middle of the eighteenth century, along with extremely eerie casts of the bodies of people and animals who got hit by the pyroclastic flow, you'd think people would say, "no fucking way am I living anywhere near that mountain."  But... no.  If you'll look at a world map, you might come to the conclusion that siting big cities near places prone to various natural disasters was some kind of species-wide game of chicken or something.

In any case, the good news is that a recent study showed that even if Campi Flegrei is (1) heating up, and (2) eventually going to erupt catastrophically, there's no sign it's going to happen any time soon, and it's pretty likely we'd have plenty of warning if an eruption was imminent.  

But still.  Such phenomena make me feel very, very tiny.  And once again, thankful that I live in a relatively peaceful, catastrophe-free part of the world.  Our biggest concern around here is snow, and even that's rarely a big deal; we don't get anything like the killer blizzards that bury the upper Midwest and Rocky Mountain states every year.  Given my generally neurotic outlook on life, I can't imagine what I'd be like if I did live somewhere that had serious natural disasters.

Never leave my underground bunker, is probably pretty close to the mark.

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Some of the most enduring mysteries of linguistics (and archaeology) are written languages for which we have no dictionary -- no knowledge of the symbol-to-phoneme (or symbol-to-syllable, or symbol-to-concept) correspondences.

One of the most famous cases where that seemingly intractable problem was solved was the near-miraculous decipherment of the Linear B script of Crete by Alice Kober and Michael Ventris, but it bears keeping in mind that this wasn't the first time this kind of thing was accomplished.  In the early years of the nineteenth century, this was the situation with the Egyptian hieroglyphics -- until the code was cracked using the famous Rosetta Stone, by the dual efforts of Thomas Young of England and Jean-François Champollion of France.

This herculean, but ultimately successful, task is the subject of the fascinating book The Writing of the Gods: The Race to Decode the Rosetta Stone, by Edward Dolnick.  Dolnick doesn't just focus on the linguistic details, but tells the engrossing story of the rivalry between Young and Champollion, ending with Champollion beating Young to the solution -- and then dying of a stroke at the age of 41.  It's a story not only of a puzzle, but of two powerful and passionate personalities.  If you're an aficionado of languages, history, or Egypt, you definitely need to put this one on your to-read list.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Brain of glass

Because my other option is to go on a crazed rant about how my country is being run by an amoral sociopath, and about how even given that fact thirty-some-odd percent of Americans still support him and/or idolize him, I decided to look instead at a more cheerful topic: the remains of a young man who got fried by Mount Vesuvius on August 24, 79 C.E.

That eruption gives new meaning to the word "colossal."  It was what geologists call a Plinian eruption -- named, in fact, for author and philosopher Pliny the Elder, who was also killed that day -- one that instead of producing the fountains of lava you see from volcanoes like Kilauea, produces pyroclastic surges composed of ash and superheated air that can reach speeds of one hundred meters per second and temperatures over a thousand degrees Celsius.

In other words, once you see it coming, it's too late to do much besides sticking your head between your legs and kissing your ass goodbye.

(If you want to watch a fantastic -- if terrifying -- ten-minute simulation of what Vesuvius would have looked like from Pompeii on the fateful day, check this out.)

In any case, the eruption in 79 C. E. killed at least twenty thousand people -- probably more -- and released an unimaginable amount of energy in a very short time, estimated to be one hundred thousand times more than the atomic bomb that destroyed Hiroshima.  The city of Pompeii was basically flattened where it stood, and its inhabitants flash-cooked and then encased in ash, which is why researchers have found molds and casts of human bodies (and one dog), still in the positions they were in when they died.

This discovery, though -- the news of which I once again owe my pal Andrew Butters, author and blogger over at Potato Chip Math -- is unique, and is as fascinating as it is gruesome.  A team at University of Naples Federico II discovered the remains of a twenty-five-year-old man in a temple in Herculaneum dedicated to the Emperor Augustus.  He was face down, still lying where he fell.  But when the researchers took a look inside his skull, they got a surprise.

His brain had turned to glass, so quickly that his individual neurons are still visible.  Pier Paolo Petrone, who led the research, said in an interview with CNN, "The brain exposed to the hot volcanic ash must first have liquefied and then immediately turned into a glassy material by the rapid cooling of the volcanic ash deposit."

Here's how the team explains what happened, in their paper, that appeared last week in the journal PLoS-One:

In AD 79 the town of Herculaneum was suddenly hit and overwhelmed by volcanic ash-avalanches that killed all its remaining residents, as also occurred in Pompeii and other settlements as far as 20 kilometers from Vesuvius.  New investigations on the victims' skeletons unearthed from the ash deposit filling 12 waterfront chambers have now revealed widespread preservation of atypical red and black mineral residues encrusting the bones, which also impregnate the ash filling the intracranial cavity and the ash-bed encasing the skeletons.  Here we show the unique detection of large amounts of iron and iron oxides from such residues, as revealed by inductively coupled plasma mass spectrometry and Raman microspectroscopy, thought to be the final products of heme iron upon thermal decomposition.  The extraordinarily rare preservation of significant putative evidence of hemoprotein thermal degradation from the eruption victims strongly suggests the rapid vaporization of body fluids and soft tissues of people at death due to exposure to extreme heat.

Without further ado, here's a microphotograph of the neurons they found:

Vesuvius remains one of the most dangerous volcanoes in the world, and will have another large eruption at some point -- not if, but when.  And this time, it isn't a couple of towns with twenty thousand folks in the bullseye; right downslope from Vesuvius is the city of Naples, which has just shy of a million inhabitants.

The good news in all this is that volcanologists have gotten much better at detecting the danger signals prior to an eruption -- much better than, for example, the seismologists have of predicting when an earthquake might occur.  But as humans have shown time and time again, we really suck at taking the advice of scientists, preferring instead the reassurances of people who honestly don't know what they're talking about, and the time-honored maxim of "everything will be fine, just like it always is."

Which brings us full circle to Donald Trump and his brazen, idiotic, selfish *Gordon lapses into mumbled obscenities* comment not to be "afraid of COVID" or "let it dominate your life."  Despite the fact that worldwide, a million people have died (i.e. the population of Naples), and twenty percent of those have been in the United States.

Okay, I feel a rant coming on again, so I better stop here. 

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One of my favorite TED talks is by the neurophysiologist David Eagleman, who combines two things that don't always show up together; intelligence and scientific insight, and the ability to explain complex ideas in a way that a layperson can understand and appreciate.

His first book, Incognito, was a wonderful introduction to the workings of the human brain, and in my opinion is one of the best books out there on the subject.  So I was thrilled to see he had a new book out -- and this one is the Skeptophilia book recommendation of the week.

In Livewired: The Inside Story of the Ever-Changing Brain, Eagleman looks at the brain in a new way; not as a static bunch of parts that work together to power your mind and your body, but as a dynamic network that is constantly shifting to maximize its efficiency.  What you probably learned in high school biology -- that your brain never regenerates lost neurons -- is misleading.  It may be true that you don't grow any new neural cells, but you're always adding new connections and new pathways.

Understanding how this happens is the key to figuring out how we learn.

In his usual fascinating fashion, Eagleman lays out the frontiers of neuroscience, giving you a glimpse of what's going on inside your skull as you read his book -- which is not only amusingly self-referential, but is kind of mind-blowing.  I can't recommend his book highly enough.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Pulled from the fires

Note bene: If you haven't read Umberto Eco's brilliant medieval murder mystery The Name of the Rose and are planning to, be aware that the next couple of paragraphs contain spoilers.  If you'd like to read the book and don't want to know the solution, skip down to the stars!

One of the most devastating scenes in The Name of the Rose happens right near the end, when the main characters, the Sherlock-Holmes-like Brother William of Baskerville and his friend and pupil, Brother Adso of Melk, confront the murderous old religious nutter Brother Jorge of Burgos in the place that is the center of all the action -- the labyrinthine Library at the top of the Aedificium of the (unnamed) monastery where the story takes place.  The Library was built not to collect and disperse knowledge but to hide it; Librarian after Librarian voraciously hoarded manuscripts of all sorts but always wanted to be in control of who got to read what, feeling that some books were not fit reading material for anyone but the most holy.

Brother Jorge himself was the Librarian before he had to resign the position because of his failing eyesight, but still kept a tight rein over who got to read what, acting through his proxy (and the nominal Librarian after Jorge retired), Brother Malachi of Hildesheim.  And when Jorge discovered that there was a copy of a particular manuscript in the Library -- the long-lost second volume of Aristotle's Poetics -- that implied that the main purpose of living was not prayer and self-mortification but laughter and joy, he was willing to go to any length to stop people from finding out about it and (in his mind) destroying the solemn foundation of the Church itself.  In the end, he sets fire to the Library, destroying all of the thousands of irreplaceable manuscripts (and himself in the process) rather than let Brother William get his hands on the copy and make others aware of its existence.

All through the book, the Library was built up to mythic proportions.  Eco recreates in us a sense of what it must have been like to witness the burning of the Great Library of Alexandria, an event that it pains me to think about even now.  But now, some scientists have found a way to salvage at least some manuscripts thought lost to fire forever.

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Everyone's familiar with the devastation Mount Vesuvius wrought on the cities of Pompeii and Herculaneum on the 29th of August in the year 79 C.E.  If you haven't already done so, you should watch this amazing, nine-minute-long animation that puts you right in the middle of the eruption -- something that makes me very, very thankful I'm in a tectonically benign part of the world.

The main explosion of the volcano occurred at about one o'clock in the afternoon (we have a good account of the details from the historian Pliny the Younger, who witnessed the cataclysm and survived, and his uncle Pliny the Elder -- who wasn't so lucky).  The blowout vaporized a good chunk of the top of the mountain and triggered a pyroclastic surge that geologists estimate was around 300 C and traveling at over 100 kilometers an hour.  Anyone who had survived the previous rains of ash and rock that morning was flash-fried, and then covered up by 25 meters of volcanic ash deposited in the six hours that followed.

Some artifacts survived.  Buildings (although damaged by the pyroclastic flow and the concomitant earthquakes) were found preserved when excavations began in earnest in the eighteenth century.  Tiles and paintings were remarkably unscathed, and there are pieces of art from the ruined city that look like they were created yesterday.  Rather horrifyingly, there are casts and molds of a good many of the victims, who were cooked by the blast, encased in ash, and then once their bodies decayed, the cavity was filled with minerals seeping in, leaving bizarre human shapes still in the contorted positions where they fell.

Anything else made of organic matter, though, was pretty well incinerated.  Any bits of charred wood that survived rotted away within a few years after the eruption.  Even less likely to survive were parchments -- written records -- although the carbonized remains of almost two thousand scrolls were found when the city of Herculaneum was excavated.

Tantalizing to think there still could be readable information there, to wonder what lost treasures of literature and history those blackened cylinders might be.  But there was no way to see if anything was still there other than ash, nor a way to unroll them and find out without having them crumble to powder...

... until now.

Brent Seales of the University of Kentucky, working with a team made up of Jens Dopke, Francoise Berard, Christy Chapman, Robert Atwood, and Thomas Connolley, has pioneered a technique that hinges on the fact that a lot of the inks used by the ancients had traces of lead and other heavy metals which are still present in the tracery of script on the burned fragments.  By taking the scrolls -- without unwrapping them and causing further damage -- and using a targeted beam of x-rays, scientists can see inside them and possibly piece together what the text actually said.

One of the scrolls charred by Vesuvius and recovered from Herculaneum

"A new historical work by Seneca the Elder was discovered among the unidentified Herculaneum papyri only last year, thus showing what uncontemplated rarities remain to be discovered there," said Dirk Obbink of the University of Oxford, who has worked with the team to train the algorithm to read the burned scrolls using parchments that have already been (at least partially) deciphered.  "It's my hope that the scrolls might even contain lost works, such as poems by Sappho or the treatise Mark Antony wrote on his own drunkenness.  I would very much like to be able to read that one."

As would a lot of us.  The idea that something thought lost forever might be restored is thrilling, and the work Seales's team is doing is groundbreaking.  Until we develop time travel and go back to save the manuscripts from the Library of Alexandria, it's our best chance to find new primary sources from the ancients -- something that historians, and bibliophiles like myself, have dreamed about for years.

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I am not someone who generally buys things impulsively after seeing online ads, so the targeted ad software that seems sometimes to be listening to our conversations is mostly lost on me.  But when I saw an ad for the new book by physicist James Trefil and astronomer Michael Summers, Imagined Life, it took me about five seconds to hit "purchase."

The book is about exobiology -- the possibility of life outside of Earth.  Trefil and Summers look at the conditions and events that led to life here on the home planet (after all, the only test case we have), then extrapolate to consider what life elsewhere might be like.  They look not only at "Goldilocks" worlds like our own -- so-called because they're "juuuuust right" in terms of temperature -- but ice worlds, gas giants, water worlds, and even "rogue planets" that are roaming around in the darkness of space without orbiting a star.  As far as the possible life forms, they imagine "life like us," "life not like us," and "life that's really not like us," always being careful to stay within the known laws of physics and chemistry to keep our imaginations in check and retain a touchstone for what's possible.

It's brilliant reading, designed for anyone with an interest in science, science fiction, or simply looking up at the night sky with astonishment.  It doesn't require any particular background in science, so don't worry about getting lost in the technical details.  Their lucid and entertaining prose will keep you reading -- and puzzling over what strange creatures might be out there looking at us from their own home worlds and wondering if there's any life down there on that little green-and-blue planet orbiting the Sun.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

An avalanche of fire

One of the most utterly terrifying phenomena on Earth is called a pyroclastic flow.

Pyroclastic flows are explosive eruptions of volcanoes that release not molten rock, but finely pulverized debris and hot gases that then flow downhill at an astonishing rate -- in some cases, forming a cloud at a temperature of 1000 C moving at an almost unimaginable 700 kilometers per hour.  Pompeii and Herculaneum were destroyed by pyroclastic flows from Mount Vesuvius on August 24, 79 C.E., which killed everyone in their path and buried the cities under layers of ash, where they remained for centuries until being unearthed by archaeologists.

If you're not too prone to freak-out over such things, I strongly recommend this ten-minute animation that recreates the destruction of Pompeii:

More recently, a 1902 eruption of Mount Pelée on the island of Martinique triggered a pyroclastic flow that obliterated the city of Saint Pierre, killing 30,000 people in an estimated five minutes.  There were only three survivors -- Louis-Auguste Cyparis, who was lucky enough to be in an underground dungeon; Léon Compère-Léandre, who lived on the edge of town and still suffered severe burns; and Havivra Da Ifrile, who was on the beach when the eruption started and had the presence of mind to jump in a rowboat, where she was later found, unconscious and adrift, three kilometers offshore.

Saint Pierre before the eruption...

... and after:

[Images are in the Public Domain]

What has long been a mystery to volcanologists is how pyroclastic flows achieve the speeds they do, which, after all, is the key to their deadliness.  Lava flows, while they can do tremendous damage to houses and land, rarely cause loss of life because they can almost always be outrun (or in some cases, outwalked).  The fastest pyroclastic flows, on the other hand, are moving so rapidly that even if you had warning, you couldn't move quickly enough to escape.

But a paper last week in Nature describes how a team from three universities in New Zealand (Massey University, the University of Auckland, and the University of Otago) and one in the United States (the University of Oregon) created a model of pyroclastic flows, and found that the reason they travel so quickly is basically the principle of air hockey -- the cloud is suspended on a cushion of superheated air, reducing the friction to nearly zero.

In "Generation of Air Lubrication Within Pyroclastic Density Currents," by Gert Lube, Eric C. P. Breard, Jim Jones, Luke Fullard, Josef Dufek, Shane J. Cronin, and Ting Wang, we find out about a series of experiments that are not only cool but must have been extremely fun to carry out.  They built a twelve-meter-long chute, mined some volcanic particles (deposited in the 232 C.E. eruption of New Zealand's Mount Taupo), heated it up to 130 C, and sent 1000 kilograms of it at a time barreling down the chute, all the while filming it with an ultrafast camera.

As Michelle Starr, writing for Science Alert, describes the results:

[W]ithin the flow there were extremely high shear rates - the rate at which layers in a fluid flow past each other.  When shear increases, so does air pressure; and when shear rates are at their highest, that pressure produces a cushion of air just above the ground, pushing particles away from each other, with denser volcanic dust layers sliding over the top of it.

The result is that the flow keeps moving downhill at higher and higher rates until it hits an obstacle, dissipates, or cools enough that the effect diminishes and the particles slow down.

This makes me glad I live in such a benign part of the world.  Here in upstate New York, the worst we have to worry about is the occasional snowstorm, and the fact that the summers are distressingly short.  (This year, summer is scheduled for the second Thursday in July.)  But compared to living near an active volcano, or a hurricane zone, or Tornado Alley, or near a seismic fault line -- I'd say we're pretty damn fortunate.

But of all the natural disasters the Earth is capable of creating, I don't think there's anything quite as terrifying as these avalanches of fire -- unpredictable, lightning-fast, and capable of destroying everything in their path.  Compared to that, I'd choose our long, cold winters in half a heartbeat.

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This week's Skeptophilia book recommendation is a fun one; Atlas Obscura by Joshua Foer, Dylan Thuras, and Ella Morton.  The book is based upon a website of the same name that looks at curious, beautiful, bizarre, frightening, or fascinating places in the world -- the sorts of off-the-beaten-path destinations that you might pass by without ever knowing they exist.  (Recent entries are an astronomical observatory in Zweibrücken, Germany that has been painted to look like R2-D2; the town of Story, Indiana that is for sale for a cool $3.8 million; and the Michelin-rated kitchen run by Lewis Georgiades -- at the British Antarctic Survey’s Rothera Research Station, which only gets a food delivery once a year.)

This book collects the best of the Atlas Obscura sites, organizes them by continent, and tells you about their history.  It's a must-read for anyone who likes to travel -- preferably before you plan your next vacation.

(If you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!)