The backyard volcano

Of all of the sciences, geology is the one where deep understanding of the underlying processes eluded us the longest.  Even the two other contenders -- genetics and astronomy -- were at least partially unraveled sooner.  Plate tectonics, the model that provides a framework for comprehending just about every other geological process, wasn't elucidated until Frederick Vine, Drummond Matthews, and Harry Hess came along in the early 1960s.  Until then, geology texts fell back on hand-waving explanations like synclines and anticlines, and pretty much ignored questions like why most of the world's volcanoes and major earthquakes fall along a tracery of curves that encircle the Earth like the stitching on a baseball (the most famous of which is the Pacific Ring of Fire).

Part of the reason it took us so long to figure all this out is because geological processes are, for the most part, slow, so it's easy to look around and conclude that the Earth has pretty much always looked like it does today.  Then... they discovered anomalies like marine fossils in the Himalayas, Kansas, the Rockies, and right here in my own neck of the woods in upstate New York.  It took the brilliant Scottish geologist Charles Lyell to recognize that if rates of sedimentation are fairly constant, then big sedimentary rock layers like the White Cliffs of Dover must have taken tens of millions, rather than thousands, of years to form.  The recognition of how slow most geological phenomena were meant the Earth was a great deal older than the six-thousand-year estimate by Archbishop Ussher -- setting up the first of many clashes between geologists and the church establishment.

But "usually slow" doesn't mean "always slow."  Sometimes major geological processes can occur, literally, overnight.  Take, for example, the appearance in 1943 of a new volcano, dubbed Parícutin after the nearest town, in a Mexican farmer's cornfield.

The locals did at least have a little bit of warning.  For weeks prior to the initial eruption, they had heard sounds "like thunder but with no clouds in the sky," now thought to be the rumblings of magma moving beneath the surface.  There were over twenty small earthquakes over 3.2 on the Richter Scale, and hundreds of smaller ones -- the day before the eruption, there were more than three hundred small earthquakes.

What happened next is best said in the words of Dionisio Pulido, the farmer who witnessed it first-hand:

At 4 p.m., I left my wife to set fire to a pile of branches when I noticed that a crack, which was situated on one of the knolls of my farm, had opened... and I saw that it was a kind of fissure that had a depth of only half a meter.  I set about to ignite the branches again when I felt a thunder, the trees trembled, and I turned to speak to Paula; and it was then I saw how, in the hole, the ground swelled and raised itself two or two and a half meters high, and a kind of smoke or fine dust – grey, like ashes – began to rise up in a portion of the crack that I had not previously seen...  Immediately more smoke began to rise with a hiss or whistle, loud and continuous; and there was a smell of sulfur.

By the next morning, where Pulido's cornfield had been was a scoria cone fifty meters high; a week later, it was double that.  It was continuously erupting volcanic bombs and small pyroclastic flows, and Pulido decided that his home and land were done for, so he got the hell out.  Before leaving, he put up a sign saying "This volcano is owned and operated by Dionisio Pulido" -- indicating that even in dire circumstances, you can still hang on to your sense of humor.

Parícutin in 1943 [Image is in the Public Domain]

The entire eruption cycle went on for two years, and by the end, there was a massive conical mountain, over four hundred meters tall, where before there'd only been a flat valley.  Only three people died during the eruption, and oddly, none of them were from the lava or pyroclastic surges; the three died when they were struck by lightning during an ash eruption.  (The tiny particles of volcanic ash are often electrically charged; lightning strikes in ash columns are common.)

It did, however, render much of the (former) valley uninhabitable.  Here's a photograph of the ruins of the old church of San Juan Parangaricutiro, which was destroyed by lava and ash along with the rest of the village of the same name:

[Image is in the Public Domain]

At the time of the eruption, all that was known was that it added another peak to the Trans-Mexican Volcanic Belt, which runs east-west across the entire country and includes much more famous volcanoes such as Popocatépetl.  Since then, we've learned that the whole range owes its existence to the subduction of the Rivera and Cocos Plates underneath the North American Plate at the Middle America Trench; the waterlogged rock and sediments are pulled down into the upper mantle, heated, and melt, forming the magma that eventually erupts somewhere behind the trench.

But at the time, the appearance of a volcano was a source of mystification both to the locals and the scientists.  To be sure, some geological phenomena are sudden; earthquakes, for example, often happen without much in the way of warning (and accurate earthquake prediction is still a dicey affair).  But we're used to things pretty much staying in the shapes and positions they were in before.  It takes a huge earthquake -- the 9.2-magnitude Anchorage megathrust quake comes to mind -- to radically reshape the land, in this case raising a long stretch of coastline by as much as nine meters.  And while big volcanic eruptions, such as the current one from Mount Etna, are spectacular and can be deadly, most of the time they're from volcanoes we already knew about.

Parícutin, though, kind of came out of nowhere, at least by the scientific understanding of the time.  And that's one of the benefits of science, isn't it?  It allows us to understand the processes involved, not just name them after they've happened.  While we're still not at the point where we can predict with much lead time when something like this will happen, at least now we can say with some assurance that we understand why it happened where it did.

Little consolation to Dionisio Pulido, of course.  I'm guessing that "owning and operating" a volcano was nowhere near as lucrative as his cornfield had been.  But that's life in a geologically active area.  However much we understand about the science behind such events, it's good to keep in mind there's always a human cost.

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The pressure cooker

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, Herculaneum, and Stabiae in 79 C.E.  Both Vesuvius and the 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 recent eruption on La Palma in the Canary Islands and the one near Grindavík in Iceland.  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.  The residents of Pozzuoli have had to get used to regular rises and falls of the ground, some by as much as an alarming two meters.  In fact, between 1982 and 1984, there was so much uplift -- followed by magnitude-4 earthquakes and thousands of microquakes -- that the harbor became too shallow for most ships to dock, and the entire population of forty thousand was evacuated until things seemed to simmer down.

In fact, the reason the topic comes up is a study out of Stanford University and the University of Naples that appeared this week in the journal Science Advances, that found this terrifying swell-and-subside isn't due primarily to magmatic movement, as was feared -- it's the bubbling of superheated groundwater.  The study looked at the composition of the "caprock," the rock layer on top of the formation, and found that when mixed with hot water it forms something like a natural fibrous cement.  This then plugs up cracks and prevents groundwater from escaping.

The whole thing is like living on the lid of a giant pressure cooker.

Of course, unlike (I hope) your pressure cooker, the rock doesn't have the tensile strength to manage the pressure fluctuations, so ultimately it breaks somewhere, triggering an earthquake and steam eruptions, after which the caprock settles back down for a while until the cracks all reseal and the pressure starts to rebuild.

This is all pretty scary, but it does point scientists in a direction of how to mitigate its potential for harm.  "I call it a perfect storm of geology -- you have all the ingredients to have the storm: the burner of the system -- the molten magma, the fuel in the geothermal reservoir, and the lid," said Tiziana Vanorio, who co-authored the study.  "We can't act on the burner but we do have the power to manage the fuel.  By restoring water channels, monitoring groundwater, and managing reservoir pressure, we can shift Earth sciences toward a more proactive approach -- like preventive health care -- to detect risks early and prevent unrest before it unfolds.  That's how science serves society."

Which is all very well, but I still wouldn't want to live there.  I visited Italy last year and loved it, but the area around Naples -- that'd be a big nope for me.  When we were in Sicily, itself no stranger to seismic unrest, one of our tour guides said, "We might be taking a risk living here, I suppose.  But those people up in Naples -- they're crazy."

That anyone would build a town on top of an active volcano is explained mostly by the fact that humans 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 join our Sicilian tour guide in saying, "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.

Not a game I want to play.  Such phenomena make me feel very, very tiny.  I'm very 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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Time to act

I know we really don't need anything else to worry about.  World events have been depressing enough, and here in the United States we've got an election on Tuesday that is making me pop Xanax as if they were Skittles.  But I ran across something in a book I'm reading that was absolutely jaw-dropping, and not in a good way, and I knew I would be seriously remiss in not writing about it here.

I mentioned a few days ago (in a post about some bizarre volcanoes in the East African Rift Zone) that I've been reading Tamsin Mather's wonderful book Adventures in Volcanoland: What Volcanoes Tell Us About the World and Ourselves.  Mather's specialty is monitoring gas production from volcanoes, and using the composition of offgassed material to gather information about magma characteristics and the likelihood of eruptions.  She's traveled all over the world collecting and analyzing samples, comparing hotspot volcanoes (like the ones in Hawaii) to rift volcanoes (like Ol Doinyo Lengai in Tanzania) to trench/subduction volcanoes (like Etna, Vesuvius, Krakatoa, Fujiyama, the Andes, and the North American Cascades).  Her research puts her in position as one of the world's foremost and most knowledgeable experts on volcanic offgassing, and what it means for our understanding of what is going on inside the Earth's mantle.

In her book, she not only references currently-active volcanoes, but prehistoric eruptions -- and one of those she discusses is the astonishingly huge Siberian Traps.  

[Image licensed under the Creative Commons OlgaChuma Ольга Чумаченко, Плато Путорана-3, CC BY-SA 3.0]

This eruption, of a type known as a large igneous province or flood basalt, happened 252 million years ago, at the end of the Permian Period.  Flood basalt eruptions occur when something rifts the crust of the Earth and deep-source, extremely hot basaltic (low silica content) lava flows out.  This lava is incredibly fluid, and fills up valleys like water fills a bowl.  In the case of Siberia, it was a quantity that beggars belief; current estimates stand at around four million cubic kilometers of lava.  The disaster this caused was amplified by the fact that prior to the eruption, the Earth had had a long period of warm, wet climates pretty much worldwide, facilitating the growth of widespread swamps and rainforests.  The age when this occurred is called the Carboniferous Period, so named because all that dead compressed plant matter locked up gigantic quantities of atmospheric carbon, forming enormous seams of coal.

When the Siberian Traps erupted, the lava ripped its way through those massive coal deposits, and the carbon they contained was suddenly returned to the atmosphere as carbon dioxide.  Mather writes:

Estimates of total carbon dioxide emissions over the million-year-scale lifetimes of these basaltic floods are in the region of tens to hundreds of trillion tonnes...  Estimates of varying emission rates over the very long lifetimes of these provinces are harder to make than the totals, but one recent study put the maximum emission rate during the Siberian Traps at around eighteen billion tonnes per year.

The result was widespread disruption of the climate, global marine anoxia, and the largest mass extinction ever -- the Permian-Triassic Extinction, which wiped out on the order of ninety percent of life on Earth.

The kicker comes in the very next paragraph, when Mather tells us that the rate of carbon dioxide production from the most massively devastating volcanic eruption on record, the rock from which covers an area of seven million square kilometers, is half the rate our current fossil fuel use is currently churning out carbon dioxide.

I don't exaggerate when I say I had to read that passage three times before I was convinced I'd understood her correctly.

I've all too frequently heard laypeople give a sneering chuckle at the climatologists, saying stuff like, "What a lot of bullshit.  One volcanic eruption emits more carbon dioxide than all the cars on Earth do."  They rarely cite a source, and when they do it's from something like the fossil-fuel-industry-funded Heartland Institute, but -- because this opinion is a great excuse for continuing to do stuff the same way we always have -- they almost never get challenged on it.

It's astonishing how easy it is to accept a false viewpoint when it gives you a comforting reason not to do anything inconvenient to your lifestyle.

But here's the straight scoop from Tamsin Mather, who (allow me to reiterate) is a volcanologist who specializes in analysis of volcanic offgassing:

Despite the wide error bars in our estimates of the global rate of volcanic carbon degassing, what we can know is that these natural emissions pale into insignificance compared to what humans produce.  In 2019, human fossil-fuel burning released over 35 billion tonnes of carbon dioxide into our atmosphere.  This is seventy times more than even our most generous current estimates of global magmatic carbon degassing.  In 2022, the aviation industry alone emitted 800 million tonnes of carbon dioxide, eclipsing estimates of that from our planet's background tectonism before even considering other sectors of human industry.  We cannot look to Earth's volcanism today to reassure ourselves that our rate of carbon emission might not be too much of a change in terms of our planet's natural cycles.  Powerful as the forces of tectonics that daily drive the slow creep of plate movement and volcanic activity across the globe are, the human race has currently surpassed them in terms of its carbon dioxide flux to the atmosphere.  It is apposite to reflect upon the level of responsibility that should appropriately come with the level of power attained by our species that, by this carbon metric, overwhelms all Earth's volcanoes.

Despite this, we have a candidate for president here in the United States -- I doubt I need to tell you which one -- who has stated he wants to discontinue investment in renewable energy and withdraw from the Paris Accords, and frequently says "Drill baby drill, and frack frack frack!" to cheering crowds.

Anyhow, I'm sorry to post alarming stuff, but perhaps now isn't such a bad time after all.  We have the chance to make a difference not only by our actions and choices, but in the voting booth.  It put me in mind of a conversation that occurs in my novel In the Midst of Lions, which seems a fitting way to end this post:

Mary Hansard's face registered near panic.  "It's not just here.  It’s everything we know.  Soon it’ll all be gone, and if we don’t find a way out, us with it.  We've got to do something, now.”

Soren glanced at Dr. Quaice.  “Okay, this is scaring the shit out of me.”

Mary tightened her grip on Soren’s sleeve.  “Good.  Good.  You should be scared.  Scared people act.” She hitched a sob.  “Complacent people die.”

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The oddest volcano on Earth

As far as we've progressed in our understanding of science, we still have a long way to go.

This is true in every scientific endeavor, but I was thinking about it apropos of geology while reading volcanologist Tamsin Mather's wonderful recent book Adventures in Volcanoland: What Volcanoes Tell Us About the World and Ourselves.  Mather's fascinating and often lyrical narrative takes us all over the world, describing her studies of volcanoes in Nicaragua, Greece, Hawaii, Iceland, Japan, Indonesia, Wyoming, Sicily, Ethiopia, and Tanzania.  It was this last-mentioned that got me pondering the gaps in our understanding, because she described seeing the bizarre Ol Doinyo Lengai volcano in the northern part of the country.

Ol Doinyo Lengai is strange by any standards.  It sits in the middle of the East African Rift Zone, which extends from Ethiopia to Mozambique, and is one of the Earth's only above-water divergent zones, places where two pieces of crust are moving apart.  The Rift being on land won't last forever, of course; ultimately a crescent-shaped chunk of East Africa will cleave off from the rest of the continent, the ocean will flood in, and afterward the rift will (like most of the others) lie at the bottom of the sea floor.  The separated piece will then creep off to the east, becoming an island -- or, depending on how you define it, a new continent.

The violent geology of the region has created a topography that in a post last year I referred to as "a beautiful hellscape."  The Dallol Depression is already 48 meters below sea level; the only thing keeping the water out is the Afar Highlands to the east acting as a barrier.  It's not only filled with bubbling mud pots and hot springs, but its position near the equator and the surrounding mountains creating a rain shadow make it blisteringly hot -- think Death Valley in midsummer -- so despite the otherworldly beauty of the brilliantly-colored rocks, it's not a place most people would ever think of going.

But even by comparison to the strange landscape that surrounds it, Ol Doinyo Lengai is peculiar.  It is the only active volcano on Earth that produces carbonatite lava, which (as you might surmise) is rich in carbonate minerals like calcite, dolomite, sodalite, apatite, and ancylite.  The magma is cool by volcanic standards, at only around 500-600 C, and yet produces some of the most fluid, low-viscosity lava flows known, moving at around five meters per second -- so about a typical human running speed.

Staying out of the way when Ol Doinyo Lengai erupts is a really good idea.

The lava comes out dark brown or black, but once it freezes and is exposed to the air for a few days, carbonate minerals crystallize on the surface and turn it a frosty white.

[Image licensed under the Creative Commons Thomas Kraft, Kufstein, Lava lengai, CC BY-SA 3.0]

So the entire cone has a snow-covered appearance, but there's no snow there -- it's all mineral deposits.

The weirdest thing is that we don't really understand where all this carbonatite magma is coming from.  My first guess was that somehow the plumbing of the volcano was moving up through a limestone or marble deposit, and picking up the carbonates as it went, but geochemical analysis of the rocks produced from it seems to have ruled that out.  Right now, it's thought to be some kind of weird fractionation -- the source magma deep underground is separating into high-carbon and low-carbon bits, and the high-carbon bits are the ones feeding this particular volcano -- but the fact is, this is a guess, and the word you see most often attached to its mineralogy and chemistry is "peculiar."

So what's happening here in northern Tanzania -- and even more apposite, why it isn't happening anywhere else on Earth -- is a mystery.  The strangeness, though, only increases its fascination, and there are geologists who are devoting a lot of time to figuring out what is going on in this odd and inhospitable place.  Strange, too, that the East African Rift Valley is where humanity got its start; Oluduvai Gorge, where some of the best-preserved hominin fossils were found, is part of the Rift complex. 

Perhaps there's a reason we're drawn to this mysterious spot.  Our roots are here -- in one of the most tectonically-active places on the planet.  That it still leaves us with unanswered questions only makes the draw stronger, bringing us back to the place our distant kin left a hundred thousand years ago, to use the tools of science to finally understand our own ancestral home.

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The disappearing island

Sometimes I don't understand my fellow humans at all.

Take, for example, our habit of drawing imaginary lines all over the place and then pretending those lines should have an impact on what can do.  Over here, you have to follow one set of rules; walk ten meters to the west and cross an invisible line some random person made up, and you have to follow a completely different set of rules.  You want to purchase liquor, own a gun, marry someone of the same sex, gamble, get decent health care or a good education?  Whoa, you first better figure out where the lines are and make sure you're on the right side!  In order to cross some lines (legally, at least) you have to have a specific little booklet and let a grim and humorless person stamp it first.  Try to get across without a booklet and stamp, and boy, are you in trouble.  In fact, some people take these invisible lines so seriously they'll kill anyone who tries to cross.

This kind of behavior may well explain why the aliens take one look at Earth and then warp right the fuck out of the quadrant.

One of the weirdest examples of this phenomenon has to do with an on-again, off-again island in the central Mediterranean, about halfway between Tunisia and the island of Sicily.  You probably know this is a tectonically-active region -- Sicily is the home of Mount Etna -- so there are a number of small volcanic islands and seamounts dotted around the place.  One of these is called (depending on whom you ask) Empedocles Seamount or Graham Island or Île Julia or Isola Ferdinandea.

The reason for the multiple names is that prior to 1831 it had been a submarine volcano, on the order of six meters below sea level at lowest tide.  But then it erupted (as volcanoes are wont to do) and suddenly the peak of the seamount was above sea level.

That's when the fun began.

In August of that year, British sea captain Humphrey Fleming Senhouse saw the newly-formed island (at that point pretty much just a bunch of hot rocks barely poking up out of the water), and in the fine old British tradition of spotting a place and saying "Mine!", claimed it for the British crown.  He named it Graham Island after Sir James Graham, First Lord of the Admiralty.  The problem was, French geologist Constant Prévost was also nearby studying the volcanoes in the region, and when the island appeared he thought King Louis Philippe I of France might fancy having a bunch of rocks, so he claimed it for France (and named it Île Julia, supposedly because it appeared in July).  But it wasn't long before the Sicilians, who after all were nearest to the place, said, "The hell you say" and claimed it for their own, renaming it for a third time Isola Ferdinandea (after King Ferdinand II of the Kingdom of Two Sicilies).

As far as I know, the Tunisians decided to leave well enough alone and didn't get involved.

A page out of Constant Prévost's field journal, showing the eruption of whatever-its-name-is [Image is in the Public Domain]

Diplomatic wrangling ensued.  One of of the concerns surrounded whether this was a sign of increasing volcanism, and if it might ultimately link up Sicily with Tunisia, and where would they draw the invisible lines if that happened?  The British were adamant that they wanted it for its strategic location, and drew up plans for building a naval base there.  The French, more luxury-minded, started thinking about a holiday resort.  The Sicilians mostly just said the Italian equivalent of "But... but it's ours," to no particular effect.

It's uncertain what the ultimate outcome of the dispute would have been, because within a few months it became obvious that Graham/Julia/Ferdinandea Island was shrinking.  It turned out that the eruption had mostly produced tephra -- a loose, porous, crumbly rock that doesn't withstand erosion.  Like, at all.  In January 1832 it was reported as barely visible, and by that summer the island had disappeared entirely.  The French, British, and Sicilians all sort of kicked at the dirt and said, "Awww, rats" in an embarrassed sort of way, and then toddled off to look around for other arbitrary and pointless things to fight about.

So at the moment it's back to being Empedocles Seamount, with its peak about eight meters below water level.  Amazingly, though, the dispute is still bugging people.  In November of 2000, some Sicilian divers went down and planted a marble plaque with a Sicilian flag on the top of the seamount, with the idea being if it ever surfaces again the Sicilians will already have laid claim to it.  The plaque has an inscription that reads, "This piece of land, once Ferdinandea, belonged to and shall always belong to the Sicilian people."

Within six months, the combination of waves and tectonic activity fractured the plaque into twelve pieces.  

The whole affair made me think about the quote from Voltaire: "God is a comedian playing to an audience which is afraid to laugh."

But more to the point: is it just me, or is this kind of behavior seriously weird?

I think we accept it just because it's so common, but really, I find myself much more in sympathy with a lot of the Indigenous peoples, who when they first ran into Europeans (whose capacity for invisible line-drawing is second to none) couldn't even understand what the invaders meant when they said "this land is mine now."  The land was here long before you were born, and will still be here long after you're dead.  What does it mean to say it's "yours"?  And it's more bizarre than that when you start factoring in things like mineral rights.  Okay, legally I own 3.5 acres of land.  Do I own what's underneath it?  If so, how far underneath?  Do I own a gradually narrowing conical chunk of material extending all the way to the Earth's center?

What the fuck would that even mean, that I "own" something that I'll never see, never touch, and is in fact physically impossible to reach?

I dunno.  Apparently it makes sense to other people, so maybe I'm the weird one.  All I know is when I think about things like this, and other stuff we argue incessantly about -- like what comprises ninety percent of politics -- I'm hoping the aliens will at least slow down their passage by Earth long enough to pick up a passenger.

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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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Mysterious mountains

It's amazing how far human knowledge has come in only a hundred years.

Consider the following about the year 1924:

• This is the year we would figure out that there are other galaxies beyond the Milky Way; before this, astronomers thought the Milky Way was all there was.  They called the galaxies they knew about (such as Andromeda and the Whirlpool Galaxy) "nebulae" (Latin for "clouds") and thought they were blobs of dust within our own galaxy.  This marks the moment we realized how big the universe actually is.
• In 1924, the quantum nature of reality was still unknown; the first major papers by Heisenberg, Schrödinger, and Born would come out next year.
• It'd be another four years before the first antibiotic -- penicillin -- was discovered.
• It'd be five years before Edwin Hubble announced his discovery of red shift, which showed the universe is expanding and led to the Big Bang model of cosmology.
• We'd have another seventeen years before we'd see the first electron micrograph of a virus; before that, it was known they caused disease, but no one knew what they were or had ever seen one.
• It'd be another twenty years before DNA was shown to be the genetic material, and a good twenty years after that when Franklin, Watson, and Crick figured out its structure and the basics of how it works.
• The first papers outlining the mechanics of plate tectonics were still forty years in the future; at this point, the only one who championed the idea that the continents moved was German geologist and climatologist Alfred Wegener, who was pretty much laughed out of the field because of it (and ultimately died in 1930 on an expedition to Greenland).

It's the last one that's germane to our topic today, which is a largely-unexplained (and massive) feature of North Africa that goes to show that however far we've come, there are still plenty of things left for the scientists to explain.  It's called the Tibesti Massif, and largely lies in the far north of the country of Chad, with a bit spilling over the southern border of Libya.

It's a strange, remote, and forbidding landscape:

[Image is in the Public Domain courtesy of photographer Michael Kerling]

What's peculiar about it -- besides the fact that it looks like the "desert planet" set from Lost in Space -- is that its terrain was largely created by volcanism, despite the fact that it lies smack in the center of one of those "stable continental cratons" I talked about in my previous post.  It's got a very peculiar geology -- the basement rock is Precambrian granite, over which there's a layer of Paleozoic sandstone, but above that is a layer of basalt which is in some places three hundred meters thick.  Basalt is one of those mafic rocks I mentioned; iron-rich, silica-poor, and ordinarily associated with seafloor rift zones like Iceland and deep-mantle hotspots like Hawaii.  But over that are felsic rocks like dacite, rhyolite, and ignimbrite, which are usually found in explosive, subduction zone volcanoes like the ones in the Caribbean, Japan, and Indonesia.

What's odd about all this is that there's no mechanism known that would generate all these kinds of rocks from the same system.  The current guess is that there was a mantle hotspot that started in the late Oligocene Epoch, on the order of twenty-five million years ago, that has gradually weakened and incorporated lower-density continental rocks as the upwelling slowed, but the truth is, nobody really knows.

It's still active, too.  The Tibesti Massif is home to hot springs, mud pools, and fumaroles, some of which contain water at 80 C or above.

So we've got a volcanic region in the southern Sahara where, by conventional wisdom, there shouldn't be one, with a geology that thus far has defied explanation.  Some geologists have tried to connect it to the Cameroon Line or the East African Rift Zone, but the truth is, Africa is a much bigger place than most people think it is, and it's a very long way away from either one.  (It's about three thousand kilometers from the northernmost active volcanoes in both Cameroon and Ethiopia to the southern edge of the Tibesti Massif; that's roughly the distance between New York City and Denver, Colorado.  So connecting Tibesti to either the Cameroon Line or the East African Rift is a bit like trying to explain the geology of Long Island using processes happening in the Rocky Mountains.)

And the problem is, figuring out this geological conundrum isn't going to be easy.  It's one of the most remote and difficult-to-access places on Earth, hampered not only by the fact that there are virtually no roads but the one-two punch of extreme poverty and political instability in the country of Chad.  So even getting a scientific team in to take a look at the place is damn near impossible.  The geologists studying the region have resorted to -- I swear I'm not making this up -- using comparisons to research on the geology of volcanoes on Mars, because even that is easier than getting a team into northern Chad.

The idea that we have a spot on the Earth still so deeply mysterious, despite everything we've learned, is both astonishing and thrilling.  Here we sit, in 2024, as arrogantly confident we have a bead on the totality of knowledge as the people did back in 1924, despite the fact that history has always shown such confidence in our understanding is unfounded.  The reality is humbling, and far more exciting.  As Carl Sagan put it, "Somewhere, something amazing is waiting to be known."

I wonder what the next hundred years will bring, and if the people in 2124 will look back at us with that same sense of "how could they not have known that?"

Onward -- into the great unknown!

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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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