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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Analysis of a cataclysm

Any idea what volcano is responsible for the largest known eruption?

Krakatau?  No.  Vesuvius and the Campi Flegrei?  Not even close.  Tambora or Toba?  Nope.  The Yellowstone Supervolcano?  Closer, but still not right.

The biggest volcanic eruption on record came from an extinct caldera I'd never heard of until a friend and loyal reader of Skeptophilia mentioned it a couple of days ago.  It's the La Garita Caldera in southwestern Colorado, near the little town of Creede, and when it last erupted -- during the Oligocene Epoch, on the order of 28 million years ago -- it did so with an estimated force of 250,000 megatons, which is five thousand times the explosive force of the largest nuclear weapon ever detonated.

The eruption resulted in something called ignimbrite -- a rock layer created from a frozen pyroclastic flow.  When a volcano powered by viscous high-silica (felsic) magma erupts, it's usually explosive, quite unlike the runny, flowing lava from one made of low-silica (mafic) rock.  Instead of creating a liquid flow, the force of the eruption pulverizes the magma and surrounding rock, creating a superheated cloud of ash, dust, and volcanic gas that then rushes downhill, incinerating anything in its path.  This is what did in Pompeii and Herculaneum in 79 C. E., and more recently, occurred during the devastating eruption of Mont Pelée on Martinique in 1902 that killed thirty thousand people in the space of a few minutes.

An ignimbrite forms when the pyroclastic flow loses speed and settles, and the ash, pumice, and glass shards (still plenty hot) fuse together to form a solid layer of rock.  If you've seen pictures of Pompeii (or better yet, been there) you can picture what this looks like, and your mental image is probably of something like a meter's worth of consolidated ash.

The La Garita Caldera eruption produced an ignimbrite an average of a hundred meters thick.

The amount of rock and magma blown to smithereens in the eruption is estimated at around five thousand cubic kilometers -- compare that to the one cubic kilometer blown skyward when Mount Saint Helens erupted in 1980, and you have an idea of the scale.  The resulting rock formation, the Fish Canyon Tuff, covers 28,000 square kilometers.

[Image is in the Public Domain courtesy of photographer G. Thomas]

The most interesting part of this is what caused the eruption.  It's part of the larger San Juan Volcanic Field that was created when the center of the North American continent was stretched and cracked by the Rio Grande Rift.  This is a long, north-south trending fault running from northern Mexico up through New Mexico and into central Colorado, and was responsible for a number of eruptions between forty and eighteen million years ago (although none as big as La Garita).  The reason for this fault, in the middle of the stable continental craton, is still being puzzled over by geologists, but here's one possible explanation.

Starting during the Cretaceous Period, a huge slab of oceanic crust called the Farallon Plate subducted underneath the North American Plate.  This had a couple of major effects -- cementing a number of island arcs onto the west coast of North America (called suspect terranes because they don't have the same geology as the neighboring land they're welded to), and triggering the Laramide Orogeny that created at least parts of the Rocky Mountain Range.

[Nota bene: the geology of the Rocky Mountains is ridiculously complicated, so what I'm presenting here is a vast oversimplification.  If you want a great overview of it, as well as the geology of other parts of North America and the people who study it, a good place to start is the excellent quartet of books by John McPhee, Rising From the Plains, Basin and Range, In Suspect Terrain, and Assembling California.]

In any case, the Farallon Plate was eventually consumed by the subduction zone, leaving only three small pieces still in existence -- the Gorda, Juan de Fuca, and Explorer Plates, which I considered in my post about the Cascadia Fault a month ago.  The rest of Farallon is now underneath western North America.

And, more germane to our topic, the rift zone that powered it eventually got dragged underneath as well.  This meant that the force pushing the Farallon and Pacific Plates apart was now beneath the North American continent.  The result was that the continental crust was stretched, creating a topography called horst-and-graben (or basin-and-range), where extension cracks the rock layers and some of them sink downward, creating an alternating step-up and step-down landscape that you see all over Colorado, Utah, and Nevada.

But along the Rio Grande Rift, the cracks ran so deep that it didn't just cause earthquakes and topographic change.  The fault went down far enough that magma upwelled into the fissure, resulting in a chain of volcanoes -- the aforementioned San Juan Volcanic Field, one of which is the cataclysmic La Garita Caldera.

Eventually -- and fortunately -- the convection current powering the spreading center ran out of steam due to friction with the thick, cold continental crust, and the whole thing simmered down.  The last ignimbrite from the San Juan Volcanic Field is about eighteen million years ago, and the entire area has been geologically quiet since that time.

Whenever I find out about something like this, I'm awed by the power of which the Earth is capable.  We tend to flatter ourselves about our own capacity for controlling nature, but by comparison, we're pretty damn feeble.  Being reminded of this is not, of course, a bad thing -- especially since at the moment our activities stand a good chance of unleashing a backlash from the climate that could be nothing short of catastrophic.

It's best to keep in mind that in a war between nature and humanity, the odds are very much in favor of nature.

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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!]

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!)