Mudslide

As part of our ongoing exploration of things that are big and scary and powerful and can kill you, today we have: underwater avalanches.

It's a topic I looked at a while back apropos of the Storegga Slide, which sounds like a bizarre mashup of Swedish folk music and a country line dance but isn't.  This was an undersea avalanche that occurred a bit over eight thousand years ago, a catastrophic slope failure between Iceland and Norway that displaced over three thousand cubic kilometers of debris and triggered a methane clathrate explosion -- resulting in a tsunami estimated at thirty meters in height which went on to inundate large parts of coastal northern and western Europe.

Underwater avalanches are a vastly understudied -- and therefore underestimated -- danger.  The reason it comes up today is a paper this week in Science Advances about a newly-discovered one that was on the same scale as Storegga, but in a different location.  This avalanche occurred an estimated sixty thousand years ago in Agadir Canyon, off the coast of Morocco.

The Agadir Canyon avalanche seems to have started small, possibly triggered by an earthquake.  But like snow avalanches in mountainous regions, once a bit of material starts to move, it causes other parts of the slope to fail, and pretty soon what you have is a monster.  From seafloor analysis of the sediment layers, what appears to have occurred is that the initial slide involved about 1.5 cubic kilometers of debris (itself not an inconsiderable amount), but by the time it peaked, the sediment flow was a hundred times that volume.

"What is so interesting is how the event grew from a relatively small start into a huge and devastating submarine avalanche reaching heights of two hundred meters as it moved at a speed of about 15 m/s, ripping out the sea floor and tearing everything out in its way," said Chris Stevenson, a sedimentary geologist from the University of Liverpool, who co-led the research, in an interview with Cosmos.  "To put it in perspective: that’s an avalanche the size of a skyscraper, moving at more than 64 km/h from Liverpool to London, which digs out a trench thirty meters deep and fifteen kilometers wide, destroying everything in its path.  Then it spreads across an area larger than the UK burying it under about a meter of sand and mud."

Yeah, that puts it in perspective, all right.

The path of the Agadir Canyon avalanche [Image credit: Christoph Bottner, Aarhus University]

The Agadir Canyon avalanche undoubtedly caused a massive tsunami, but given how long ago it occurred, it'd be hard to find evidence at this point.  Let's just say that it would have been a very bad time to live along the west coast of Africa or east coast of the Americas.

"We calculate the growth factor to be at least a hundred, which is much larger compared to snow avalanches or debris flows which only grow by about four to eight times," said Christoph Bottner of Aarhus University in Denmark, who also co-led the team.  "We have also seen this extreme growth in smaller submarine avalanches measured elsewhere, so we think this might be a specific behavior associated with underwater avalanches and is something we plan to investigate further."

The problem is, just about every continent is surrounded by a region of relatively shallow water (the continental shelf) with the abyssal regions just beyond its edge; at the boundary between the two is a very steep region called the continental slope, where the depth increases drastically over a relatively short horizontal distance.  These areas are prone to failure, and while most events are minor -- comparable to a small mudslide on a mountainside -- some of them, like Storegga and Agadir Canyon, can grow to colossal proportions.

And at the present, we don't know which areas are likely to be safe, and which are at significant risk.

So that's our unsettling science story of the day.  This kind of thing is why I always get a grim chuckle out of people who say how benevolent the Earth is, some even going so far as to describe the universe as "fine-tuned for our existence."  This ignores the inconvenient fact of how much of it is actively hostile -- and some of the most hostile bits are right below the seemingly tranquil surface of the ocean.

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A dangerous beauty

The Greek island of Thera -- often known by its Italianized name of Santorini -- is the southernmost of the Cyclades, an island chain in the Aegean Sea southeast of mainland Greece.  Like much of the region, it's a stunningly beautiful place.  In fact, one of Thera's names in antiquity was Καλλίστη -- "the most beautiful one."

[Image licensed under the Creative Commons Pedro Szekely from Los Angeles, USA, Santorini, Greece (38051518795), CC BY-SA 2.0]

The steep, rugged, rocky terrain, though, didn't happen by accident.  Thera and the other Cyclades formed because they sit near the margin of the Hellenic Subduction Zone, where the northern edge of the enormous African Plate is being shoved underneath the much smaller Aegean Sea Plate.  The result is the formation of an island arc, where the material in the subducted plate is pushed downward to a depth were it melts, and the blobs of magma rise toward the surface to create a chain of volcanoes.  (Most of the islands in the Caribbean, the Aleutians, and pretty much the entirety of the nations of Japan and Indonesia were formed this way.)

This makes it a dangerous place to live.  It was the site of the Minoan-era city Akrotiri, which became prosperous because of being a central port for the copper trade out of Cyprus (the Latin word for copper, cuprum, actually means "metal from Cyprus").  It was second only to Crete as a center of civilization for the Minoan Empire, and was famed for its art, especially elaborate and beautiful frescoes, pottery, and sculpture.  Many of the houses there had running water carried by bronze pipes, and geothermal heat.

The geothermal heat might have clued its residents in that something was going on underground.  All of the high times came to an end with a colossal eruption of the volcano just offshore in around 1600 B.C.E. 

[Nota bene: this is not what inspired the myth of Atlantis, despite the claims you see all over the place on the interwebz.  Plato made it clear that the legend said Atlantis was "west of the Pillars of Hercules" (the Straits of Gibraltar), somewhere out in the Atlantic (thus the name).  But... allow me to stress this point... Atlantis never existed.  Because it's a myth.]

Anyhow, the eruption of Thera not only destroyed pretty much the entire island, but blew an estimated forty cubic kilometers of dust and ash into the air, triggering atmospheric and climatic effects that were recorded by contemporaneous scholars in Egypt and China and draw comparisons from modern geologists to the Mount Tambora eruption of 1815 that caused "The Year Without A Summer."  The eruption generated a tsunami that devastated coastal cities all over the Mediterranean, including the Minoan city of Knossos on the north shore of Crete.  (The Minoan civilization limped along for another couple of hundred years after this calamity, but was finally finished off by a massive earthquake in 1350 B.C.E. that destroyed Knossos completely.)

Here's the thing, though.

The volcano off the coast of Thera is still active.

A paper last week in Nature Communications looked not at the enormous 1600 B.C.E. eruption, but a much smaller eruption in 1650 C.E.  The leadup to this eruption, however, was about as ominous as you could get.  People noticed the water in the seas off the north coast of Thera boiling and changing color -- and dead fish rising to the surface as well, cooked in situ.  Sulfurous gases wafted over the island.  This was followed by a cinder cone emerging from the sea, which proceeded to fling around molten rocks and ash plumes.

Then... boom.

The new research suggests that what triggered the eruption was a landslide, similar to what kicked off the famous Mount Saint Helens eruption of 1980.  In this case, though, the landslide was underwater, off the northwest flank of the volcano.  This landslide did two things -- it displaced huge amounts of water, generating a twenty-meter-high tsunami, and it took the pressure off the top of the magma chamber, causing it to explode.

The combination killed seventy people and hundreds of domestic animals -- horrible, but nowhere near what the island proved itself capable of 3,600 years ago.  The study found that the magma chamber is refilling at a rate of four million cubic meters per year, meaning with regards to subsequent eruptions -- to invoke the old cliché so often used in connection to active volcanoes and tectonic faults, it's not a matter of "if," it's a matter of "when."

Unsurprisingly, the people in the region seem unaware of the time bomb they're sitting on.  "Local populations, decision-makers, and scientists are currently unprepared for the threats posed by submarine eruptions and slope failures, as has been demonstrated by the recent 2018 sector collapse of Anak Krakatau and the 2022 [Hunga Tonga] eruption," the authors write.  "Therefore, new shore-line crossing monitoring strategies... are required that are capable of being deployed as part of rapid response initiatives during volcanic unrest and which enable real-time observation of slope movement."

It remains to be seen how this could help the almost two thousand people who currently live on the slopes of the island, many of them living in houses sitting on layers of fused ash deposited there during the 1600 B.C.E. eruption.  It's something we've seen here before; people like living in tectonically active regions because (1) the terrain is often dramatic and beautiful, (2) volcanic soils are good for agriculture, and (3) people have short memories.  If the last time things went kablooie was almost three hundred years ago, it's easy for folks to say, "What, me worry?"  (Witness the millions of people living near the terrifying Cascadia Subduction Zone, about which I wrote three years ago.  As well as all the people in the aforementioned countries of Japan and Indonesia.)

Anyhow, that's our rather ominous scientific study of the day.  The Earth is a beautiful and dangerous place, and nowhere does that combination come into sharper focus than the Greek islands.  Makes me glad I live where I do -- despite the cold winters, at least I don't have to worry about the place blowing up.

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A whole lot of shakin'

I didn't realize how complicated it is to calculate the magnitude of an earthquake.

Most of us are probably familiar with the Richter Scale, the one most commonly used in the media.  It was developed in 1935 by seismologist Charles Francis Richter to give a standard scale to measure the power of earthquakes.  The scale is logarithmic; each increase in one on the scale represents a ten-fold increase in intensity.  The scale is based upon the displacement amplitude on a seismograph at a distance of one hundred kilometers from the epicenter, starting with a magnitude 0 earthquake causing the needle to move with an amplitude of one micron.  The scale extends up to an unspecified "greater than 9" -- because at that point, pretty much everything in the vicinity, including the seismograph, gets completely pulverized.

When you start looking more closely, though, the problems with the scale start to become obvious.  First of all, if the measurement is being made one hundred kilometers from the epicenter, the terrain in between is a significant factor.  Tremors passing through material with a high amount of shear (such as sand or mud) will lose intensity fast, as compared to ones going through a material that is rigid (such as solid rock).  Second, the origin of the earthquake usually isn't at the epicenter, which is the point on the surface nearest the source; the origin is the hypocenter, directly underneath -- but which can be at any depth from right near the surface down to hundreds of kilometers down.  (The deepest earthquake ever recorded was a minor tremor off the island of Vanuatu in 2004, which had a hypofocus 736 kilometers deep.)  Then there's the fact that earthquakes can be of different durations -- a less powerful earthquake that lasts longer can do as much damage as a more powerful, but shorter, tremor.

Another problem is that earthquakes can result in differences in the oscillation of the waves relative to the direction they're moving.  This is largely due to the fact that there are three basic sorts of faults.  There are thrust faults or convergent faults, where two tectonic plates are moving toward each other; what happens then can be one plate being pushed underneath the other (subduction), which is what causes the quakes (and the volcanoes) in Indonesia and Japan, or the two plates kind of smashing together into a jumble, which is the process that created the Himalayas.  There are extension faults or divergent faults, where the two plates are moving apart; this usually creates smaller but more frequent quakes, and lots of volcanism as magma bubbles up from the underlying mantle.  This is happening in Iceland, and is also the cause of the Great Rift Valley in Africa, which will eventually peel off the Horn of Africa (Somalia and parts of Ethiopia, Kenya, and Tanzania) and open up a new ocean.  Last, there are strike-slip faults or transform faults, where the plates are moving in opposite directions on each side of the fault, such as the famous San Andreas Fault in California.

Map of the (known) tectonic plates [Image is in the Public Domain courtesy of NASA/JPL]

The problems with the Richter Scale have led to the development of several other scales of intensity, such as the Surface-wave Magnitude Scale (which is pretty much just what it sounds like, and doesn't take into account source depth), the Moment Magnitude Scale (which is based on the amount of energy released as measured by the amount and distance of rock moved), the Duration Magnitude Scale (which figures in how long the tremor lasts), and so on.  But these all use different numerical benchmarks, and given that the Richter Scale is more widely known, a lot of people have continued to use that one despite its downsides.

The reason all this comes up is a new study from the University of Southampton that has identified evidence of what appears to be the biggest earthquake known; an almost unimaginable 9.5 on the Richter Scale quake that happened in Chile 3,800 years ago.  Trying to find the epicenter brings up yet another problem with measuring quake intensity, because the evidence is that this particular quake originated from the rupture of a part of the thrust fault between the Nazca Plate and the South American Plate off the coast of the Atacama Desert -- a rupture that was one thousand kilometers long.

The result was a tsunami that deposited marine sediments and fossils of oceanic animals several kilometers inland, and then traveled across the Pacific Ocean and slammed into New Zealand, tossing boulders the size of cars over distances of hundreds of meters.  That region of the Atacama Desert had been inhabited prior to the quake -- astonishing considering how dry and inhospitable the place is -- but it was (understandably) abandoned by the survivors for a long while afterward.

"The local population there were left with nothing," said geologist James Goff, who co-authored the study.  "Our archaeological work found that a huge social upheaval followed as communities moved inland beyond the reach of tsunamis.  It was over a thousand years before people returned to live at the coast again, which is an amazing length of time given that they relied on the sea for food.  It is likely that traditions handed down from generation to generation bolstered this resilient behavior, although we will never know for sure.  This is the oldest example we have found in the Southern Hemisphere where an earthquake and tsunami had such a catastrophic impact on people’s lives.  There is much to learn from this."

The obvious next question is, "Could this happen again?"  The answer is not just that it could, but it will.  Probably not in the same spot, but somewhere along the many tectonic boundaries in the world.  Nor do we know when.  Earthquake prediction is very far from an exact science.  We have instruments like strain gauges to estimate the tension rock is experiencing, but that doesn't tell you what's going on deeper in the ground, nor when the rock will fracture and release that energy as an earthquake.  Predicting volcanic eruptions is much easier; vulcanologists have gotten pretty good at detecting magma movement underground, and recognizing when a volcano is likely to blow.  (This is why the ongoing hoopla about the Yellowstone Supervolcano is all hype; sure, it'll probably erupt again, but some time in the next hundred thousand years or so, and it's showing no signs of an imminent eruption.)

The Earth is a dynamic planet, and the plates on the surface are in constant motion, jostling, coming together, moving apart, a bit like ice sheets on a river when they begin to break up in the spring.  You can't help but be fascinated by the amount of power it's capable of -- a catastrophic release of energy so large that the scales we've developed to measure such things are all but incapable of expressing.

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Oarfish, earthquakes, and shadow people

I'm perpetually astonished at how little it takes to get the woo-woos going.

I suppose, though, that's the definition of confirmation bias -- taking thin evidence (or skimpy anecdote) as incontrovertible support for what you already believed.  Me, I try to approach stuff with more caution -- I'm not perfect, but I do my best when confronted with a strange or intriguing story to stop and think, "Wait a moment, how do I know this is true... and means what people are saying it means?"

I ran into two particularly good examples of that yesterday.  In the first, we have people saying that the appearance of three dead oarfish in coastal Japan is indicative that they're in for a major undersea earthquake and tsunami.  Now, there's no doubt that seeing an oarfish would make you sit up and take notice; they live in deep waters and are usually only seen when they're dead or dying, and can get up to eleven meters long.  (Yes, I double-checked that statistic, and it's correct.)

American servicemen displaying a dead oarfish they found off the coast of California in 1996 [Image is in the Public Domain]

So I suppose it's no wonder that people stop and say, "Okay, that's weird," when they see one.  But oarfish are not uncommon, despite seldom being seen; and there are lots of cases of dead oarfish washing up on shore that were not followed by geological catastrophes.   "I have around twenty specimens of this fish in my collection so it’s not a very rare species, but I believe these fish tend to rise to the surface when their physical condition is poor, rising on water currents, which is why they are so often dead when they are found," said Hiroyuki Motomura, professor of ichthyology at Kagoshima University.  "The link to reports of seismic activity goes back many, many years, but there is no scientific evidence of a connection so I don’t think people need to worry."

Which, of course, will have precisely zero effect on the woo-woos.  What the hell does some silly scientist know about, um, science?  There will be an earthquake, you'll see!  (Of course, it helps that the oarfish were found on the coast of Japan, because Japan is -- stick with me, here -- a freakin' earthquake zone.)

The other story comes from a perusal of some twelve million documents that were declassified two years ago by the CIA.  This started all the conspiracy theorists sifting through them, because of course if the CIA wanted to keep an evil conspiracy secret, the first thing they'd do is declassify all the files surrounding it.  But even the wooiest woo-woo takes a while to go through twelve million files, so it was only a couple of weeks ago that we found out that in the files were photographs of...

... "shadow people."

We're told about how spooky and eerie these photographs are, and how they could be aliens or ghosts, or connected to MKUltra or the Illuminati or god alone knows what else.  "The silhouettes are composed of visual noise, almost like television static," we're told, "and have empty voids where their faces should be."  There were two of them, we find out, and each silhouette has a number on it -- 1569 on one, 1572 on the other.

I thought, "Okay, that does sound pretty creepy."  And naturally, I wanted to see the images myself.  So I clicked the link, and here's what I saw:

And I said -- this is a direct quote -- "You have got to be fucking kidding me right now."

This isn't a photograph, it's a drawing.  And not even a very good one.  (In the interest of rigorous research, I looked at the other one, which is identical except for saying "1572" and facing the other direction.)  It is mildly curious that these would be in CIA files, although I wouldn't be surprised if it turns out that the CIA people stuck 'em in there when they declassified the files in order to watch the woo-woos leap about and make excited little squeaking noises.

Which is exactly what happened.

The universe is a wonderful, complex, intriguing, mysterious place.  There is plenty to investigate, plenty to be amazed at, without making shit up or stretching pieces of observable evidence to the snapping point.  So let's all calm down a little, okay?  I'm sure Japan will eventually have another major earthquake (cf. my previous comment about earthquake zones), and I'm also sure there'll be weird random things in the CIA files, whether or not my surmise about people sticking them in deliberately to stir the pot turns out to be true.  But grabbing those little pieces of data and running off the cliff with them is not advisable.

Confirmation bias, unfortunately, makes a terrible parachute.

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A particularly disturbing field in biology is parasitology, because parasites are (let's face it) icky.  But it's not just the critters that get into you and try to eat you for dinner that are awful; because some parasites have evolved even more sinister tricks.

There's the jewel wasp, that turns parasitized cockroaches into zombies while their larvae eat the roach from the inside out.  There's the fungus that makes caterpillars go to the highest branch of a tree and then explode, showering their friends and relatives with spores.   Mice whose brains are parasitized by Toxoplasma gondii become completely unafraid, and actually attracted to the scent of cat pee -- making them more likely to be eaten and pass the microbe on to a feline host.

Not dinnertime reading, but fascinating nonetheless, is Matt Simon's investigation of such phenomena in his book Plight of the Living Dead.  It may make you reluctant to leave your house, but trust me, you will not be able to put it down.