Mind the gap

In 1869, explorer John Wesley Powell did the first systematic study of the geology of the Grand Canyon.  As impressive as it is, the Grand Canyon's not that complicated geologically; it's made of layers of sedimentary rock, most of them relatively undeformed, one on top of the other from the oldest at the bottom to the newest at the top.  A layer cake of billions of years of Earth history, and a wonderful example of the principle of superposition -- that strata form from the bottom up.

However, Powell also noted something rather peculiar.  It's called the Great Unconformity.  In geologic parlance, an unconformity is a break in the rock record, where the layer below is separated from the layer above by a gap in time when either no rocks were deposited (in that location, at least), or the rocks that were laid down were later removed by some natural process.  At that stage in the science, Powell didn't know when exactly the Great Unconformity occurred, but it was obvious that it was huge.  Something had taken away almost a billion years' worth of rocks -- and, it was later found out, that same chunk of rock was missing not only at the future site of the Grand Canyon, but across most of North America.

It was an open question as to why this happened, but one leading hypothesis was that it was massive glaciation.  Glaciers are extraordinarily good at breaking up rocks and moving them around, as I find out every time I dig in my garden and my shovel runs into the remnants of the late Pleistocene continental glaciation.  At that point, where my house is would have been under about thirty meters of ice; the southern extent is the Elmira moraine, a line of low hills fifty kilometers south of here, left behind when the glaciers, pushing piles of crushed rock and soil ahead of them like a backhoe, began to melt back and left all that debris for us gardeners to contend with ten thousand years later.

There was a time in which the Earth was -- as far as we can tell -- completely covered by ice. The Cryogenian Period, during the late Precambrian, is sometimes nicknamed the "Snowball Earth" -- and the thawing might have been one contributing factor to the development of complex animal life, an event called the "Cambrian explosion," about which I've written before.

The problem was, the better the data got, the more implausible this sounded as the cause of the Great Unconformity.  The rocks missing in the Great Unconformity seem to have preceded the beginning of the Cryogenian Period by a good three hundred million years.  And while there were probably earlier periods of worldwide glaciation -- perhaps several of them -- the fact that the Cryogenian came and went and didn't leave a second unconformity above the first led scientists away from this as an explanation.

However, a paper in Proceedings of the National Academy of Sciences, written by a team led by Francis Macdonald of the University of Colorado - Boulder, has come up with evidence supporting a different explanation.  Using samples of rock from Pike's Peak in Colorado, Macdonald's team used a clever technique called thermochronology to estimate how much rock had been removed.  Thermochronology uses the fact that some radioactive elements release helium-4 as a breakdown product, and helium (being a gas) diffuses out of the rock -- and the warmer it is, the faster it leaves.  So the amount of helium retained in the rock gives you a good idea of the temperature it experienced -- and thus, how deeply buried it was, as the temperature goes up the deeper down you dig.

What this told Macdonald's team is that the Pike's Peak granite, from right below the Great Unconformity, had once been buried under several kilometers of rock that then had been eroded away.  And from the timing of the removal -- on the order of a billion years ago -- it seems like what was responsible wasn't glaciation, but the formation of a supercontinent.

But not Pangaea, which is what most people think of when they hear "supercontinent."  Pangaea formed much later, something like 330 million years ago, and is probably one of the factors that contributed to the massive Permian-Triassic extinction.  This was two supercontinents earlier, specifically one called Rodinia.  What Macdonald's team proposes is that when Rodinia formed from prior separate plates colliding, this caused a huge amount of uplift, not only of the rocks of the continental chunks, but of the seafloor between them.  A similar process is what formed the Himalayas, as the Indian Plate collided with the Eurasian Plate -- and is why you can find marine fossils at the top of Mount Everest.

[Image is in the Public Domain]

When uplift occurs, erosion increases, as water and wind take those uplifted bits, grind them down, and attempt to return them to sea level.  And massive scale uplift results in a lot of rock being eroded.

Thus the missing layers in the Great Unconformity.

"These rocks have been buried and eroded multiple times through their history," study lead author Macdonald said, in an interview with Science Daily.  "These unconformities are forming again and again through tectonic processes.  What's really new is we can now access this much older history...  The basic hypothesis is that this large-scale erosion was driven by the formation and separation of supercontinents.  There are differences, and now we have the ability to perhaps resolve those differences and pull that record out."

What I find most amazing about this is how the subtle chemistry of rock layers can give us a lens into the conditions on the Earth a billion years ago.  Our capacity for discovery has expanded our view of the universe in ways that would have been unimaginable only thirty years ago.

And now, we have a theory that accounts for one of the great geological mysteries -- what happened to kilometer-thick layers of rock missing from sedimentary strata all over North America.

John Wesley Powell, I think, would have been thrilled.

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Old as the hills

In northwestern Australia, there's an administrative region called Pilbara.

Even though on a map, it looks kind of long and narrow, it's big.  The area of Pilbara is just shy of that of California and Nevada put together.  (I suspect that I'm like many non-Australians in consistently forgetting just how big Australia is.  It's the sixth largest country in the world, and is almost the same size as the continental United States.  Flying from Sydney to Perth is comparable to flying from Atlanta to Los Angeles.)

Pilbara is also extremely hot and dry, and very sparsely populated, with only a bit over sixty thousand residents total, most of whom live in the western third of the region.  The northeastern quadrant is part of the aptly-named Great Sandy Desert, one of the most inhospitable places on Earth.  There are only a few Indigenous tribes that somehow eke out a living there, most notably the Martu, but by and large it's uninhabited.

[Image licensed under the Creative Commons Brian Voon Yee Yap, aka Yewenyi, at en.wikipedia]

What brings up the topic, though, is that Pilbara is interesting for another reason than its hostile climate.

It is the home to some of the oldest rocks on Earth.

The Pilbara Craton -- a craton is a contiguous piece of continental crust -- is estimated to be around three and a half billion years old.  For reference, the Earth's crust only solidified 4.4 billion years ago.  Since that time, plate tectonics took over, and as I've described before, tectonic processes excel at recycling crust.  At collisional margins such as trenches and convergent zones, usually one piece slides under the other and is melted as it sinks.  Even in places where two thick, cold continental plates run into each other -- examples are the Alps and the Himalayas -- the rocks are deformed, buried, or eroded.

The result is we have very few really old rocks left.  The only ones even on the same time scale as Pilbara are the Barberton Greenstone Belt of South Africa and the Canadian Shield (and even the latter has been heavily metamorphosed since its formation).

This makes Pilbara a great place to research if you're interested in the conditions of the Precambrian Earth -- as long as you can tolerate lots of sand, temperatures that often exceed 36 C, and a fun kind of grass called Triodia that has leaf margins made of silica.

Better known as glass.

Frolicking in a field of Triodia is like running through a meadow made of Exacto knives.

Be that as it may, geologists and paleontologists have begun a thorough study of this fascinating if forbidding chunk of rock.  The most recent reconstructions suggest that both Pilbara and the aforementioned Barberton Greenstone were once part of an equatorial supercontinent called Vaalbara (which preceded the supercontinent most people think of -- Pangaea -- by a good three billion years).  And those might be the only chunks of that enormous piece of land left intact.

There are two other reasons Pilbara is remarkable.

It contains numerous fossilized stromatolites, which are layered sedimentary structures formed by cyanobacteria, thought to be the earliest photosynthetic life forms.  There are still stromatolites forming today -- probably not coincidentally, in shallow bays in Western Australia.

[Image licensed under the Creative Commons photographer Paul Harrison (Reading UK), March 2005, Stromatolites growing in Hamelin Pool Marine Nature Reserve, Shark Bay in Western Australia.]

As such, the Pilbara stromatolite fossils are the oldest certain traces of life on Earth, dating to 3.48 billion years ago.

The other reason is that it's also home to a massive impact crater dating to 3.47 billion years ago.  Shortly after those earliest, tentative life forms were living and thriving in the warm shallow ocean waters, a huge meteorite struck near what is now the town of Marble Bar, forming a crater and shatter cone between 16 and 45 kilometers in diameter (because of erosion, it's hard even for the geologists to determine where its edges lie).  The resulting Miralga Impact Structure blew tremendous amounts of molten debris up into the air, and some of it landed on that chunk of Vaalbara that would eventually end up in South Africa -- only to be recovered by geologists almost three and a half billion years later.

So there's a place in Australia that gives new meaning to the phrase "old as the hills."  Given its remoteness and inhospitable climate, I'm unlikely ever to visit there, but there's something appealing about the idea.  Walking on rock that is an intact remnant of a continent from over three billion years ago is kind of awe-inspiring.  Even if all the other rock is still here somewhere -- melted and reformed and eroded multiple times -- the idea that this chunk of the Earth has somehow lasted that long more or less intact is mighty impressive.

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News from Afar

I've written here before about the fact that the continents are in motion, something that is only not staggering because we've all known about it since ninth grade Earth Science class.  You can easily see why it took so long to accept.  First, the motion is so slow that it was, for most of human history, beyond the limitations of the technology available at the time to measure directly.  Second, it's just hard to imagine.

Continents?  Moving in solid rock?  What?

But move they do, and it's because if you go down far enough, the rock isn't solid.  Get into the upper mantle, and it's the consistency of taffy, so it flows, pushed by subterranean convection currents.  Those currents create drag forces on the undersides of the tectonic plates, shifting them around.  Although this is an oversimplification, in general, there are three ways that plates can move relative to each other:

• Convergent zones, where plates come together.  When thin, brittle oceanic plates are pushed toward each other, one usually bends and slides under the other at a thrust fault or subduction zone; the subducted plate and the sediment riding on it eventually melt, and the hot, water-rich magma rises to form chains of volcanoes parallel to the fault.  Examples are the Japan Trench and the Sumatra Trench.  When an oceanic plate collides with a thick, cold continental plate, you still get volcanoes boring their way up through the continent -- this is the origin of the Cascade Range.  If it's two continental plates colliding, the rock simply crumples up to form mountains -- such as what is happening in the Alps and Himalayas,
• Divergent zones, where plates move apart.  This is what's happening along the Mid-Atlantic Ridge, and is why the island of Iceland is volcanic -- the eastern and western halves of the island are moving apart, and new basaltic lave bubbling up to fill the gap.

A photograph I took at Meradalir Volcano in Iceland, August 2022

• Strike-slip faults, or transform faults, which occur when plates slide in opposite directions parallel to the fault.  Examples are the San Andreas, Hayward, and Elsinore Faults in California, and the Alpine Fault in New Zealand.

All of these movements can significantly transform the shapes and positions of the continents -- you probably know that 250 million years ago, most of the Earth's land masses were assembled into a giant supercontinent (Pangaea), and the seas into a massive superocean (Panthalassa), with huge consequences to the climate.  Fascinating to realize, though, that Pangaea was only the most recent of the supercontinents; geologists believe that the same lumping-it-all-together occurred at least three or four times before then.

And the reverse can happen, too, when a divergent zone forms underneath a continent, and it tears the land mass in two.  In fact, this is the reason the topic comes up today; a paper last week in Nature Geoscience about the Afar Triple Junction, the point where three faults meet at one point (the Red Sea Rift, the Aden Ridge, and the East African Rift).  Geologists have found that underneath this region, there's a mantle plume -- an upwelling of very hot magma -- that is pulsing like a giant beating heart, driving convection that will eventually tear Africa in two, shearing off a chunk from Ethiopia to Mozambique and driving it east into the Indian Ocean.

[Image licensed under the Creative Commons Val Rime, Tectonic African-Arabian Rift System, CC BY-SA 4.0]

"We have found that the evolution of deep mantle upwellings is intimately tied to the motion of the plates above," said Derek Keir, of the University of Southampton, who co-authored the study.  "This has profound implications for how we interpret surface volcanism, earthquake activity, and the process of continental breakup...  The work shows that deep mantle upwellings can flow beneath the base of tectonic plates and help to focus volcanic activity to where the tectonic plate is thinnest.  Follow on research includes understanding how and at what rate mantle flow occurs beneath plates."

The formation of a new sea -- and the consequent turning of much of east Africa into an island -- isn't exactly what I'd call "imminent;" it's predicted that the Red Sea will breach the Afar Highlands and flood the lowest points of the rift (much of which is already below sea level) in something like five million years.  The region will be highly tectonically active throughout the process, however, and there'll be enough volcanoes and earthquakes in the meantime to keep us interested.

It's a good reminder that although mountains and oceans have been a symbol of something eternal and unchanging, in reality everything is in flux.  It recalls to mind the lines from Percy Shelley's evocative poem "Mont Blanc," which seems a fitting way to end:

Yet not a city, but a flood of ruin
Is there, that from the boundaries of the sky
Rolls its perpetual stream; vast pines are strewing
Its destin’d path, or in the mangled soil
Branchless and shatter’d stand; the rocks, drawn down
From yon remotest waste, have overthrown
The limits of the dead and living world,
Never to be reclaim’d.  The dwelling-place
Of insects, beasts, and birds, becomes its spoil;
Their food and their retreat for ever gone,
So much of life and joy is lost.  The race
Of man flies far in dread; his work and dwelling
Vanish, like smoke before the tempest’s stream,
And their place is not known.  Below, vast caves
Shine in the rushing torrents’ restless gleam,
Which from those secret chasms in tumult welling
Meet in the vale, and one majestic River,
The breath and blood of distant lands, for ever
Rolls its loud waters to the ocean-waves,
Breathes its swift vapours to the circling air.

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A perilous beauty

Ever heard of the "Bonneville Slide?"

It sounds like some obscure country line dance, but the real story is more interesting, and it comes with a connection to a curious Native legend that turns out to refer to a real historical event.

The Klickitat People have lived for centuries on both sides of the Columbia River, up into what is now Skamania and Klickitat Counties, Washington, and down into Multnomah and Clackamas Counties, Oregon.  They tell the tale of Pahto and Wy'east, the two sons of the chief of all the gods, Tyhee Saghalie.  The two young men did not get along, and fought over who would rule over which parcel of land.  Their father shot one arrow south and the other north; Pahto was given the lands around where the northern arrow landed, and Wy'east the territory surrounding where the southern arrow fell to the ground.  Tyhee Saghalie then shook the Earth and created a great bridge across the Columbia River so the two could visit each other.

But soon trouble broke out again.  Pahto and Wy'east both fell in love with the same young woman, the beautiful Loowit, and began to fight, burning villages and destroying forests and crops.  Tyhee Saghalie tried to reason with them, but to no avail.  In the end he grew angry himself and shook the Earth again, destroying the bridge; the cataclysm created a flood that washed away whole forests.  He turned all three into mountains -- Wy'east became Mount Hood, Pahto Mount Adams, and the lovely Loowit Mount Saint Helens.  But even in mountain form they never forgot either their anger or their burning love, and all three still rumble and fume to this day.

What is fascinating is that this odd story actually appears to have some basis in fact.

In around 1450 C.E., an earthquake knocked loose about a cubic kilometer of rock, soil, and debris from Table Mountain and Greenleaf Peak.  The resulting landslide -- the Bonneville Slide  -- roared down the Columbia Gorge, creating a dam and what amounted to a natural bridge something like sixty meters high across one of the biggest rivers in the world.  

Greenleaf Peak today [Image licensed under the Creative Commons Eric Prado, Greenleaf Peak, Washington, CC BY-SA 4.0]

The dam couldn't last, however.  The Columbia River has a huge watershed, and the lake that built up behind the dam eventually overtopped the natural "Bridge of the Gods."  The whole thing collapsed -- probably during a second earthquake -- releasing all that pent-up river water in a giant flood.  It left behind geological evidence, both in the form of a layer of flood-damaged strata west of the slide, and the remains of drowned forests to the east, where trees had died as the dammed lake rose to fill the gorge.

Despite the reminder we got in 1980 -- with the eruption of Mount Saint Helens -- it's easy to forget how geologically active the Pacific Northwest is.  Not only is there the terrifying Cascadia Subduction Zone just offshore (about which I wrote two years ago), the other Cascade volcanoes, from Silverthrone Caldera (British Columbia) in the north to Lassen Peak (California) in the south, are still very much active.  Right in the middle is the massive Mount Rainier, visible from Seattle, Tacoma, and Olympia on clear days, which is one of the most potentially destructive volcanoes in the world.  Not only is it capable of producing lava and pyroclastic flows, it's capped by huge glaciers that would melt during an eruption and generate the catastrophic mudflows called lahars.  The remnants of two historical flows from Rainier -- the Osceola and Electron Lahars -- underlie the towns of Kent, Orting, Enumclaw, Puyallup, Auburn, Buckley, and Sumner, and in some places are twenty to thirty meters deep.

The Earth can be a scary, violent place, but somehow, humans manage to survive even catastrophic natural disasters.  And, in the case of the Bridge of the Gods, to incorporate them into our stories and legends.  Our determination to live in geologically-active areas is due to two things; volcanic soils tend to be highly fertile, and we have short memories.  Fortunately, though, we couple what seems like a foolhardy willingness to take risks with a deep resilience -- allowing us to live in places like the Cascades, which are bountiful, and filled with a perilous beauty.

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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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Building the Rockies

I recently re-read John McPhee's wonderful quartet of books on geology, Basin and Range, Rising from the Plains, In Suspect Terrain, and Assembling California.  His lucid prose and capacity for focusing on the human stories connected with the subject while teaching us some fascinating science brought me back to these books, which I first read perhaps twenty-five years ago.

The first two, in particular, describe something that is quite surprising -- or at least was to me when I first learned about it.  The biggest mountain range in the United States, the Rockies, is actually quite poorly understood, and contains some features that are still yet to be satisfactorily explained.  A good part of the Rocky Mountain range is non-volcanic, and although there are some areas that have igneous rocks the vast majority is made up of sedimentary and metamorphosed sedimentary rock -- sandstone, limestone, shale, slate, quartzite, and marble.  Even some of the igneous rocks only show at the surface because the overlayment of sedimentary rock that once was present has eroded away.

[Image licensed under the Creative Commons Self, Rocky Mountain National Park, CC BY-SA 2.5]

As McPhee describes it, the current thought is that most of what is west of Colorado and Wyoming is probably the result of accretion -- the huge North American Plate overriding smaller plates to the west and gathering up microcontinents and island arcs they carried, cementing them onto the coastline.  It's certain that this is how California formed -- the boundaries between the different "suspect terranes" (the alternate spelling is used when referring to these chunks of land that end up in a very different place from where they were formed) are pretty well established.  Also, the subduction process that brought them to North America is still ongoing, as the small Explorer, Juan de Fuca, and Gorda Plates (in order from north to south) are pulled underneath -- giving rise to the Cascade Volcanoes such as Mount Lassen, Mount Hood, Mount Rainier, and Mount Saint Helens.

We got another piece added to the puzzle with a paper in Nature, out of the University of Alberta, by Yunfeng Chen, Yu Jeffrey Gu, Claire A. Currie, Stephen T. Johnston, Shu-Huei Hung, Andrew J. Schaeffer, and Pascal Audet.  Entitled, "Seismic Evidence for a Mantle Suture and Implications for the Origin of the Canadian Cordillera," the paper describes research that found a sharp boundary in the mantle of the Earth between the "craton" -- the central, oldest piece of the North American continent, encompassing what is now the Midwest -- and a long, narrow microcontinent that slammed into the North American Plate as a primordial sea closed -- moving the coastline hundreds of miles further west.

"This research provides new evidence that the Canadian section of this mountain range was formed by two continents colliding," said Jeffrey Gu, professor in the Department of Physics and co-author on the study, in an interview with Science Daily.  "The proposed mechanism for mountain building may not apply to other parts of the Rocky Mountains due to highly variable boundary geometries and characteristics from north to south."

The cool part is that the research was done by looking deep into the Earth's mantle -- not just by studying the surface features.  And this collision, which is estimated to have occurred a hundred million years ago, has left a scar that is still detectable.  "This study highlights how deep Earth images from geophysical methods can help us to understand the evolution of mountains, one of the most magnificent processes of plate tectonics observed at the Earth's surface," said study co-author Yunfeng Chen.

And this technique could be applied elsewhere, as the Rockies are far from the only mountain range in the world that were created by accretion rather than volcanism.  (The obvious examples are the Alps and the Himalayas -- the latter of which are still rising as the Indian Plate continues to plow into the Eurasian Plate.)  "There are other mountain belts around the world where a similar model may apply," said Claire Currie, associate professor of physics and co-author on the study.  "Our data could be important for understanding mountain belts elsewhere, as well as building our understanding of the evolution of western North America."

So we're piecing together the picture of how the Rockies formed -- ironic, as they seem to have been assembled from pieces themselves.  In the process, we're learning more about the processes that move the tectonic plates, and create the landscape we see around us.  It reminds me of the haunting lines from Alfred, Lord Tennyson, which seem like a fitting way to end:

There rolls the deep where grew the tree.
O Earth, what changes hast thou seen?
There where the long road roars has been
The stillness of the central sea.
The hills are shadows, and they flow
From form to form, and nothing stands,
They melt like mists, the solid lands,
Like clouds, they shape themselves, and go.

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Pacific spike alert

One thing that drives me crazy is the tendency of the woo-woos to take a perfectly legitimate, valid piece of science, and then woo all over it.

The latest example of this is one you might have heard about.  Scientists doing isotopic analysis of cored sediments from the Pacific seabed found an unusual spike of an isotope called beryllium-10.  Beryllium-10 is mainly produced by cosmic rays colliding with oxygen and nitrogen atoms in the upper atmosphere; the beryllium atoms then gradually settle, creating what should be a uniform deposition in terrestrial and marine sediment layers.  Beryllium-10 is also radioactive, decaying into boron-10, so the relative concentrations of these two atoms, along with beryllium-10's known 1.4 million year half-life, allows for a convenient way to date sediment layers.

That, of course, presupposes that the formation and deposition rate of beryllium-10 is uniform, and cores from the Pacific seafloor from around ten million years ago show that, for a short time at least, this wasn't true.  These strata, from the mid-Miocene Epoch, showed up with an anomalous spike of beryllium-10.  What caused this isn't certain; two possibilities the researchers suggested were a shift in oceanic currents near Antarctica, causing an alteration in sediment distribution rate, or a nearby supernova producing a higher-than-normal influx of cosmic rays for a time.  In any case, the spike eventually leveled off, and the rest of the core sample was unremarkable, at least in that regard.

Well, "radioactive sediments" and "cosmic rays" and "anomaly" were apparently all it took.  In the past two weeks, since the paper was published, I've seen the following:

• the beryllium-10 spike is the debris from the reactor core of an exploded alien spacecraft, so add this to the list of "evidence for Ancient Astronauts."
• time-traveling government operatives went back to the Miocene to conduct illegal tests of nuclear superweapons so they could get away with it without anyone finding out, except apparently for this wingnut.
• the Sun had a "flare-up" ten million years ago that caused this.  This same phenomenon also caused all of the Earth's major mass extinctions.  It will happen again, and why is NASA covering this up?
• it's all a smokescreen to hide radioactive contamination that's actually from the Fukushima Reactor disaster.
• something something something HAARP something weather modification wake up sheeple something something.

Okay, will all of you lunatics just hang on a moment?

First of all, let's look at the actual spike the paper discusses.

[Image from Koll et al., Nature Communications, 10 February 2025]

See that wee bump at about ten million years?  That's the anomaly.  It's peculiar, sure, and cool that the scientists are trying to find out what caused it.  But it's a slightly higher-than-expected amount of a single isotope, and that's all.  They have even proposed some nifty uses for the discovery -- detecting the spike in sediment layers elsewhere could help to pinpoint how old they are -- but it's not, honestly, all that dramatic otherwise.  It doesn't correlate with a mass extinction (so cross out the Sun-induced extinction events), there are no other anomalous isotopes that show up at the same time (eliminating the superweapons and the ancient spacecraft, unless the aliens constructed their entire ship from beryllium-10), and it dates to ten million years ago (so it has nothing to do with Fukushima).

And HAARP was decommissioned in 2014, so all y'all conspiracy theorists can just shut the hell up about it, already.

I mean, really.  Isn't the actual science cool enough for them?  Why does everything have to fold into these people's favorite weird idea?

I suppose, as I saw a friend post a while ago, "Everything's a conspiracy if you don't understand how anything works."  But in these times when everyone's got a website, and "I read it on the internet" is considered by a lot of people to be the modern equivalent of "I have a Ph.D. from Cambridge in the subject," it's maddening how quickly these ideas spread -- and how little it takes for the wacko interpretations to eclipse the actual science.

So that's our dive into the deep end for today.  Beryllium spikes and ancient astronauts.  Me, I'm gonna stick with the scientific explanations.  Better than worrying about NASA covering up that we're all about to get fried by a "solar flare-up."

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Out of sight

Seismologists and volcanologists are unusual amongst scientists in that for the most part, what they're studying are things that are permanently unavailable for direct observation.

Oh, sure, they can access the results on the Earth's surface; fault lines, lava flows, uplift or subsidence from magma movement, and so on.  But the actual processes -- the stuff down there that is causing it all -- is inaccessible.

The deepest hole ever dug is the Kola Superdeep Borehole, on the Kola Peninsula near the Russian border with Norway, which is an impressive twelve kilometers deep; but when you realize that's only one-thousandth of the diameter of the Earth, it puts things into perspective.  Even so, it was deep enough that the bottom had a measured temperature of 180 C -- hot enough to boil water, but far from hot enough to melt rock.  (It bears mention that a claim circulating last year that they'd gone down fourteen kilometers, hit temperatures of 1000 C, and could hear the screams of the damned -- because, apparently, they'd punctured a hole into hell -- was unfounded.)

So the fact remains that much of geological science is based upon inference -- not only using surface processes to infer what's happening in Earth's interior, but using data such as earthquake wave traveling speed to figure out what the mantle and core are made of, whether they're liquid or solid or somewhere in between, and how all that stuff in there is moving around.  And being inferential, our understanding of deep geologic processes is constantly subject to revision.

Which brings us to a study out of Utrecht University that appeared in the journal Nature last week, about a discovery showing that deep in the Earth's mantle there are two continent-sized subterranean "islands" at least a half a billion years old -- showing that the stuff down there isn't mixing around quite the way we thought it was.

The upper mantle has been thought of as basically a big recycler.  As pieces of the Earth's crust get forced down into subduction zones (marked by the oceanic trenches that neighbor some of the most tectonically-active regions on Earth), it melts and gets mixed into what's already down there.  Being colder than the surrounding rock, everyone thought the process was slow; other than the bits that get hot enough to melt and then rise to the surface, causing volcanoes like the ones in the North American Cascades, Andes, Caribbean, Italy, Japan, and Indonesia, the rest just has to sit down there till it blends into the material surrounding it.

Apparently some of this will need to be rethought, because these "islands" in the mantle are still holding together despite being so old that they "should have" completely melted away by now.

One of the chunks is under Africa and the other under the Pacific Ocean, and they were located by using the paths and speeds of seismic waves, giving them the moniker of LLSVPs (Large Low Seismic Velocity Provinces).  "Nobody knew what they are, and whether they are only a temporary phenomenon, or if they have been sitting there for millions or perhaps even billions of years," said Arwen Deuss, who co-authored the study.  "These two large islands are surrounded by a graveyard of tectonic plates which have been transported there by subduction, where one tectonic plate dives below another plate and sinks all the way from the Earth’s surface down to a depth of almost three thousand kilometers."

You might be wondering how they figured out that they are a half a billion years old, given that they're way out of reach of direct study.  That, in fact, is the most fascinating part of the study, and has to do with the fact that rocks which cool quickly (such as obsidian and basalt) have much smaller crystals than ones that cool more slowly (like granite and gabbro).  The molecular reassembly that results in crystal formation takes time, especially in thick, viscous liquids like magma, so if lava is rapidly cooled on the surface it doesn't have time to form crystals.

"Grain size is much more important," Deuss said.  "Subducting tectonic plates that end up in the slab graveyard consist of small grains because they recrystallize on their journey deep into the Earth.  A small grain size means a larger number of grains and therefore also a larger number of boundaries between the grains.  Due to the large number of grain boundaries between the grains in the slab graveyard, we find more damping, because waves lose energy at each boundary they cross.  The fact that the LLSVPs show very little damping, means that they must consist of much larger grains."

Large grain size = a long time spent underground.  Mineralogist Laura Cobden, who specializes in mineral crystallization rates in igneous rock, estimated that based on the inferred crystal size in the two "islands," they've been down there, relatively undisturbed, for around five hundred million years.

[Image from Deuss et al.]

So that's our cool science news from the geologists for today.  Two islands in the mantle that are stubbornly resisting melting away.  Why these structures have been so persistent is beyond the scope of this study; but as with all science, finding out something's there is the first step.  After that, the theorists can figure out how to explain it all.

Even if they never have a chance to see it.

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The cliff's edge

The universe is a dangerous place.

Much of what we've created -- the whole superstructure of civilized life, really -- is built to give us a sense of security.  And it works, or well enough.  During much of human history, we were one bad harvest, one natural disaster, one epidemic from starvation, disease, and death.  Our ancestors were constantly aware that they had no real security -- probably one of the main drivers of the development of religion.

The world is a capricious, dangerous place, but maybe the gods will help me if only I pray hard enough.

When the Enlightenment rolled around in the eighteenth century, science seemed to step in to provide a similar function.  Maybe the world could be tamed if we only understood it better.  Once again, it succeeded -- at least partially.  Industrial agriculture and modern medicine certainly saved millions of lives, and have allowed us to live longer, healthier lives than ever before.  Further reassuring us that it was possible to make the universe a secure, harm-free place for such creatures as us.

And we still have that sense, don't we?  When there's a natural disaster, many people respond, "Why did this happen?"  There's an almost indignant reaction of "the world should be safe, dammit."

[Image licensed under the Creative Commons svantassel, Danger Keep Away Sign, CC BY-SA 3.0]

This is why in 2012 a judge in Italy sentenced six geologists to six years in prison and a hefty fines for failing to predict the deadly 2009 L'Aquila earthquake.  There was the sense that if the best experts on the geology of Italy didn't see it coming... well, they should have, shouldn't they?  

That in the present state of our scientific knowledge, it's not possible to predict earthquakes, didn't seem to sway the judge's mind.  "The world is chaotic, dangerous, and incompletely understood" was simply too hard to swallow.  If something happened, and people died, there had to be someone to blame.  (Fortunately, eventually wiser heads prevailed, the charges were thrown out on appeal, and the geologists were released.)

In fact, I started thinking about this because of a study out of the University of California - Riverside that is investigating a technique for predicting earthquake severity based on the direction of propagation of the shock wave front.  This can make a huge difference -- for example, an earthquake on the San Andreas Fault that begins with failure near the Salton Sea and propagates northward will direct more energy toward Los Angeles than one that begins closer in but spreads in the opposite direction.

The scientists are using telltale scratch marks -- scoring left as the rocks slide across each other -- to determine the direction of motion of the quake's shock wave.  "The scratches indicate the direction and origin of a past earthquake, potentially giving us clues about where a future quake might start and where it will go," said Nic Barth, the paper's lead author. " This is key for California, where anticipating the direction of a quake on faults like San Andreas or San Jacinto could mean a more accurate forecast of its impact...  We can now take the techniques and expertise we have developed on the Alpine Fault [in New Zealand] to examine faults in the rest of the world.  Because there is a high probability of a large earthquake occurring in Southern California in the near-term, looking for these curved marks on the San Andreas fault is an obvious goal."

The thing is, this is still short of the ultimate goal of predicting fault failure accurately, and with enough time to warn people to evacuate.  Knowing the timing of earthquakes is something that is still out of reach.

Then there's the study out of the Max Planck Institute for Solar System Research that found that the Sun and other stars like it are prone to violent flare-ups -- on the average, once every century.  These "superflares" can release an octillion joules of energy in only a few hours.

The once-every-hundred-years estimate was based on a survey of over fifty-six thousand Sun-like stars, and the upshot is that so far, we've lucked out.  The last serious solar storm was the Carrington Event of 1859, and that was the weakest of the known Miyake Events, coronal mass ejections so big that they left traces in tree rings.  (One about fourteen thousand years ago was so powerful that if it occurred today, it would completely fry everything from communications satellites to electrical grids to home computers.)

The problem, once again, is that we still can't predict them; like earthquakes, we can know likelihood but not exactitude.  In the case of a coronal mass ejection, we'd probably have a few hours' notice -- enough time to unplug stuff in our houses, but not enough to protect the satellites and grids and networks.  (If that's even possible.  "An octillion joules" is what is known in scientific circles as "a metric shit tonne of energy.")

"The new data are a stark reminder that even the most extreme solar events are part of the Sun's natural repertoire," said study co-author Natalie Krivova.  "During the Carrington event of 1859, one of the most violent solar storms of the past two hundred years, the telegraph network collapsed in large parts of northern Europe and North America.  According to estimates, the associated flare released only a hundredth of the energy of a superflare.  Today, in addition to the infrastructure on the Earth's surface, especially satellites would be at risk."

All of this, by the way, is not meant to scare you.  In my opinion, the point is to emphasize the fragility of life and of our world, and to encourage you to work toward mitigating what we can.  No matter what we do, we'll still be subject to the vagaries of geology, meteorology, and astrophysics, but right now we are needless adding to our risk by ignoring climate change and pollution, and encouraging the ignorant and ill-founded claims of the anti-vaxxers.  (Just yesterday I saw that RFK Jr., who has been nominated as Secretary of the Department of Health and Human Services, is pursuing the de-authorization of the polio vaccine -- an extremely low-risk preventative that has saved millions of lives.)

Life's risky enough without adding to it by listening to reckless short-term profit hogs and dubiously sane conspiracy theorists.

My point here is that the chaotic nature of the universe shouldn't freeze us into despairing immobility; it should galvanize us to protect what we have.  The unpredictable dangers are a fact of life, and for most of our evolutionary history we were unable to do much about any of them.  Now, for the first time, we have figured out how to protect ourselves from many of the risks that our ancestors faced every day.  How foolish do we as a species have to be to add to those risks needlessly, heedlessly, rushing toward the edge of the cliff when we have the capacity simply to stop?

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